ADAPTATION

THE MEANING OF ADAPTATION

The inheritable characteristics that enable an organism to survive in a given environment are called adaptations.

Organisms that contribute to the gene pool by leaving offspring are considered more fit than those that do not leave offspring.

Not only the number of offspring is considered but the number of descendants.

Fitness of an individual is measured by the proportionate contribution it makes to future generations.

Fitness depends on natural selection.

Adaptation is any behavioral, morphological or physiological trait that increases the fitness of an organism under a given set of environmental conditions

TOLERANCE

Law of tolerance: Organisms live within an upper and lower limit in a range of environmental conditions.

Law of minimum: the availability of a substance limits the growth and survival of organisms regardless of how abundant are other resources.

Law of limiting factors: not only the minimum amount of a substance limits growth and survival but also an excess of a resource will limit.

These laws emphasize environmental conditions.

The range of tolerance is not fixed. An organism can acclimate to seasons and changes in conditions.

The short-term response of an individual toe exposures to different or changing natural environments is acclimatization.

HOMEOSTASIS AND FEEDBACK SYSTEMS

Homeostasis is the maintenance of a relatively stable internal environment in a varying external environment.

Negative feedback: a change causes a reversal or halting of the process, and the return to a set point.

Positive feedback: the movement away from a set point is enhanced and continuous.

Organisms live within a maximum and minimum values by using negative feedback to regulate activity above a set point.

Physiological and behavioral mechanisms contribute to maintaining homeostasis.

Characteristics that allow an organism to survive and reproduce under a set of conditions inhibit reproduction and survival under a different set.

AUTOTROPHS AND HETEROTROPHS

Life on earth is composed on carbon-based compounds.

Autotrophs: CO2 is the primary source of carbon (primary producers). Heterotrophs: the source of carbon is other organisms or their by-products (secondary

producers). Consumers: feed on organisms living or dead. Decomposers: feed on dead organic matter or waste products.

PLANT ADAPTATIONS TO THE ENVIRONMENT II: THERMAL, MOISTURE, AND NUTRIENT ENVIRONMENTS.

PLANTS AND THE THERMAL ENVIRONMENT

Plants are constantly absorbing short-wave and long-wave radiation from the surrounding environment.

THERMAL ENERGY BALANCE

Plants maintain a thermal balance through evaporation and convection.

Leaf size, shape and the stomatal opening/closing control influence these processes.

The energy absorbed by plants per unit of time is referred to as the plant’s net radiation balance, Rn.

Plants absorb and reflect solar radiation, and absorb short-wave radiation and emit long-wave radiation. The difference between the two is the net radiation balance.

Rn = M + S + (C + λE)

Less than 5% of the absorbed radiation is used in photosynthesis and stored in chemical bonds, M.

Energy is also used in heating the plant tissues and raising the temperature of the boundary layer, S.

Convection (C) and evaporation (E) dissipate energy into the environment; evaporation includes transpiration and direct evaporation.

λ = latent heat of vaporization; energy required to transform one unit of liquid water to vapor.

Transpiration and evaporation occur in plants: evapotranspiration.

Evaporation occurs from the surface of leaves.

Heat is dissipated by evaporation and transpiration.

Air temperature directly affects evaporation and transpiration.

Transpiration is the result of stomatal conductance and vapor pressure deficit.

Convection depends on the temperature difference between the plant and the surrounding air.

Factors influencing heat loss by convection:

Difference between leaf and air temperatures. Conductance of the boundary layer.

Wind removes the warm air of the boundary layer and increases the difference between the leaf and the atmosphere; the boundary layer conductance increases with the movement of air.

The size and shape of the leaf affects the conductance of the boundary layer.

The ratio of surface to volume affects heat convection.

Small, lobed leaves are more effective at heat exchange than are larger, less lobed leaves.

Plants must replace the water lost in evapotranspiration.

Air temperature and wind velocity impose limits on the ability of plants to dissipate excess heat energy.

Water lost must be replaced; therefore, precipitation patterns have a direct effect on the plant’s energy balance.

THERMAL EFFECTS ON PHOTOSYNTHESIS AND RESPIRATION

Photosynthesis and photorespiration are sensitive to temperature changes, and respond directly to variations in temperature.

High temperatures favor oxygenation over carboxylation.

Carboxylation occurs during the dark phase, Calvin cycle, of photosynthesis and is the direct result of the activity of rubisco.

Rubisco activase is an enzyme required to change rubisco from the inactive to the active form in order to carry out carboxylation.

Rubisco activity is sensitive to temperature:

The net photosynthetic rate is the difference between the rate of carbon uptake in photosynthesis and the rate of carbon lost in respiration.

The net photosynthetic rate varies in plants depending on the environment in which the plant lives.

Plants living in cooler climate have a lower maximum (Tmax) and minimum temperature (Tmim) in which photosynthesis approaches zero. Their temperature optimum is lower, Topt

Biochemical and physiological adaptations allow the plant to shift its optimum uptake of carbon through photosynthesis toward the prevailing temperature of the environment. This process can also be observed during the seasonal shifts of temperature: acclimation.

PEP carboxylase is found in CAM and C4 plants, and is absent in C3 plants.

C3 and C4 show consistent differences in their photosynthetic response to temperature.

There is no photorespiration during the initial carbon fixation by PEP carboxylase in C4 plants.

The Topt of PEP carboxylase is higher than rubisco and high temperatures have little effect on C4 plants.

The Topt for the C3 pathway approaches that of rubisco. The Topt for C4 corresponds to the range of temperatures in which the activity of both enzymes, rubisco and PEP carboxylase, is relatively high.

TEMPERATURE AND PLANT GROWTH

Plants require certain amount of photosynthetic activity accumulated over time to reach certain point of development: maximum growth, flowering, ripening of seeds, etc.

Plants require a number of degree-days of growth (photosynthetic activity) to reach maturity or bloom. The rates of photosynthesis vary with the time of the day and the season. It stops above and below certain temperatures, Tmax and Tmin. The optimum temperature occurs between these two values.

The index of degree-days is used to relate growth to variations of temperature in a single season.

The index of degree-days is the sum of the departures in temperatures above some minimum or base temperature.

The minimum temperature is selected as the temperature at which photosynthesis approaches zero.

The mean daily temperature reflects growth and carbon accumulation.

EXTREME TEMPERATURES AND PLANT SURVIVAL

Freezing temperatures can result in the formation of intra- and extracellular ice as well as phase change in membrane lipids.

Factors associated with the ability of cells to withstand freezing temperatures:

Increased solute concentrations. Unsaturated lipids (soluble fats) increase. Lipid concentration increases. Amino acids are removed from proteins: depolimerization. Cell membrane becomes more permeable. Small cell size Abscisic acid.

Abscisic acid accumulates in the leaves with dehydration. Through its effects on second messengers such calcium ions, potassium ion channels open in the guard cells causing a massive lost of potassium. This loss of ions from the guard cells, causes water to leave the cells and the subsequent loss of turgor of the guard cells closes the stomata.

Critical minimum temperature: 0° to 10°C and -15° to -40°C.

In region where the temperature falls between -15° to -40°C, the dominant vegetation consists of broad-leaf deciduous plants.

These plants lower their freezing point by supercooling, the lowering of the freezing point by increasing solute concentration.

Cells can lower the freezing point by no more than 3°C by increasing solute concentrations.

30 genes were found in Larix kaempferi that increase the supercooling capability to -60ºC. Water in the cell wall and middle lamella freezes first with dropping temperature and releases heat (heat of fusion or specific heat of melting), which is absorbed by the adjacent cells and helps them to remain liquid. Then, water moves out of the cells attracted to the ice crystals.

Tolerance to freezing is not uniformly distributed through a plant.

Roots, bulbs and rhizomes are the most sensitive to freezing (-10 to -30°C). Terminal buds are less resistant than lateral buds. Woody stems are more resistant than buds and leaves.

Changes in the ultrastructure of the cells have been observed: multiple small vacuoles, increase in the number of vesicles, etc.

Hairs insulate by trapping air and heat.

The growth habit also helps in surviving freezing temperatures: the interior temperature of cushion and rosette plants may be 20°C higher than the surrounding air.

A high temperature of 45°C disrupts metabolic processes.

Heat shock proteins are involved but their role is not well understood.

Cacti can maintain protein synthesis as fast as proteins breakdown and, in this way, avoid ammonia poisoning.

Morphological and nactic movements allow plants to adjust to high temperatures, e.g. folding of leaves, spines, narrow leaves, photosynthesis carried out in the stem, changing the orientation of leaves to a parallel position to sun rays.

PROCESSES OTHER THAN SURVIVAL AND GROWTH

Temperature affects germination, reproduction, flower formation, flower unfolding, and ripening of fruits.

Temperatures between –3 and +13°C are needed by certain annuals and biennials to flower normally in the spring.

PLANT RESPONSE TO WATER

Open stomata allow CO2 into the leaves for photosynthesis, but also allow the water to escape, transpiration.

WATER UPTAKE AND THE SOIL-PLANT-ATMOSPHERE CONTINUUM

A water potential gradient exists between the soil, and the tissues of the roots, the stem and branches, the leaves, and the atmosphere.

This water potential gradient is responsible for the movement of water from the soil through the plant into the atmosphere.

The units used to describe the water potential are megapascals, MPas.

Water flows from areas of high water potential (ψ) to areas of low water potential. This is called osmotic potential.

The soil has the highest water potential and the atmosphere the lowest.

Ψatmosphere < ψleaf < ψstem < ψroots < ψsoil

The movement of water across a membrane is called osmosis.

The osmotic potential of the cells (concentration of solutes in the cytoplasm), the matric potential or tendency of water molecules to adhere to soil particles, and the pull of gravity or gravitational potential, all influence the total water potential in the body of the plant.

As plants lose water through transpiration, the solute in the cells becomes more concentrated, the water pressure drops in the cells, and water moves in from the areas of higher concentration.

As water moves from the soil into the roots, the water potential of the soil drops and becomes more negative.

The tendency of water to adhere to surfaces is called matric potential.

As the water content of the soil drops, the remaining water adheres more tightly to soil particles and the matric potential drops.

Cohesion between the water molecules also plays a role increasing surface tension in the soil pores between the clay particles and creating menisci (sing. meniscus). Adhesion to clay particles and the formation of menisci can increase the matric potential significantly and make it unavailable to plant roots.

The texture of the soil affects the matric potential. Clay provides more surface than do sand and maintains a more negative matric potential.

As the soil water potential drops, it becomes more difficult for the plant to maintain its water potential and eventually it cannot absorb more water.

At this point, the stomata close to prevent the loss of water through transpiration but this also prevents the entry of CO2 into the leaves and disrupts photosynthesis.

The value of the leaf water potential at which the stomata close varies with the species, and depends on the biochemistry, physiology and morphology of the species.

Water must overcome the pull of gravity in order to move up the vascular tissue of the plant.

The gravitational potential is a factor of the height of the plant from a reference point. It is positive above the reference point and negative below. It is important in the movement of water in tall trees.

The gravitational potential, ψg, increases by 0.01 MPa m-1 above the ground.

RESPONSE TO SHORT-TERM MOISTURE STRESS

The closing of the stomata prevents the loss of heat by transpiration but the plant continues to intercept radiation and its internal temperature rises.

An increase in internal temperature results in heat stress that interferes with protein synthesis and if prolonged, with chlorophyll synthesis.

The plant may respond by curling its leaves, wilting, and dropping the leaves prematurely. The oldest leaves are shed first. If the drought continues, the tender twigs and branches die back.

Some plants under water-stress reduce their osmotic potential by accumulating ions of Ca2+, Mg2+, K+ and Na2+, and amino acids, sugars and sugar alcohols. The lower water potential of the leaves maintains the potential gradient from plant to soil.

Conifers and evergreens may experience a browning and a dieback during the winter months due to water stress. If the temperature is high enough for water in the vascular tissue to liquefy, the trees lose their water by transpiration but the water cannot be replaced because the ground is frozen. Dehydration of the foliage occurs.

PLANT RESPONSES TO LONG-TERM VARIATIONS IN WATER AVAILABILITY

Individual plants growing under dry conditions have thicker leaves than members of the same species growing under moist conditions.

The leaves are thicker because more layers of mesophyll are produced. There is more mesophyll per unit of area.

More mesophyll layers increase photosynthesis but reduce the surface area that absorbs radiation and loses water through transpiration.

Root production increases under dry conditions by shifting the allocation of carbon from leaves to roots.

Individuals growing under contrasting environmental condition show responses that compensate for the shortage of an essential resource.

INTERPSECIFIC VARIATION IN ADAPTATIONS TO MESIC AND XERIC ENVIRONMENTS.

Xerophytes have greater water use efficiency than mesophytes, that is, a greater rate of carbon uptake per unit of water transpired.

Water use efficiency: rate of carbon uptake per unit of water transpired. Photosynthesis/transpiration

C4 have higher water use efficiency than C3 plants.

C4 plants maintain a very low concentration of CO2 within the mesophyll of the cells by having a great rate of carboxylation. This causes a steep gradient of CO2 concentration between the inside of the leaf and the outside air.

The steeper CO2 gradient allows C4 to maintain a higher rate of photosynthesis than C3 plants for a given stomatal conductance.

The ratio of root mass (g) to leaf is (cm2) increase with decreasing water availability.

Species adapted to high and low resource availability show responses that compensate for the shortage of an essential resource:

Under xeric condition, there is a lower stomatal conductance and lower rate of net photosynthesis than those species living in mesic environments.

Lower stomatal conductance, however, results in greater water use efficiency.

Lower allocation of carbon to production of leaves results in greater root production that increases the plant’s access to soil water.

Reduced leaf surface area and reduced photosynthesis results in less carbon uptake and reduced growth.

There is a trade off between higher rates of photosynthesis and growth when water is available and survival, growth and reproduction when water is consistently in short supply.

LINK BETWEEN PLANT WATER AND ENERGY BALANCE

Plants dissipate heat through the loss of water by transpiration.

If the water potential in the soil declines, the ability to absorb water also declines.

Under mesic conditions, transpiration is the preferred means for heat dissipation.

Plants also dissipate heat by convection.

In xeric environments, plants dissipate most its heat by convection.

Leaf size decreases gradually as conditions change from mesic to xeric.

PLANTS RESPONSE TO FLOODING

Too much water around the roots causes the death of root tips due to lack of oxygen.

Root death follows due to poor absorption. Detritus is added to the vascular tissue and the xylem clogs.

High water table causes plants to develop horizontal root systems that grow along the oxygenated soil zone.

PLANT ADAPTATIONS TO FLOODING

Aerenchyma is a specialized tissue that contains air spaces that facilitate gas exchange and transport of air from shoots to roots.

The porosity of plants adapted to flooding could be as great as 60%. Plants living in mesic or xeric environments usually have a porosity of 2-7% space by volume.

Pneumatophores are adaptations to permanently flooded environments. They probably help in providing oxygen to roots.

Aerenchyma formation: Without oxygen...

Roots shift for aerobic to anaerobic respiration. Uptake of ions is inhibited The concentration oxygen, potassium, nitrogen, and phosphorus decreases. Ethylene is produced and accumulates. Ethylene is insoluble and does not diffuse out of the roots and oxygen uptake is prevented. Ethylene causes cells next to the cortex to break and separate to form interconnected gas-

filled chambers, aerenchyma tissue.

Stem and lenticel hypertrophy

Hypertrophy is the enlargement of an organ without an increase in the number of constituent cells. An example of this is buttressing or butt swell which is an increase in the diameter at the base of the stem.

The role of this seems to be to increase air space which allows for increased movement of gases.

Besides that, the wide base provides extra support for shallow rooted structures on a soggy substrate.

PLANT ADAPTATIONS TO SALINITY

Salts originate from the weathering of rocks, irrigation and floods, human and animal additions and fertilizers.

As salinity increases, plants have more difficulty in extracting water from the soil.

In salty environments either soil or water, the water potential is lower than that of the cells or water tends to leave the cells. Eventually the cells dehydrate and plasmolyze.

High concentration of organic ions may be toxic, e.g. high Al3+ is suspected to interfere with Mg2+ uptake.

Halophytes are plants adapted to salty environments.

Soils with more than 0.2% salt content are considered salty. These soils are common in desert regions.

1. The endodermis is the first effective barrier to too much salt in the environments of halophytes. Their cortex contains a large amount of salt but their leaves have much less salt.

2. Some plants have specialized organs to dispose of excess salt. These plants do not have very effective barrier to salt absorption and the excess salt must be eliminated by other means.

Salt-excreting glands selectively remove slat from the vascular tissue of the leaves.

Other plants accumulate salt in the leaf tissues and then shed the leaves.

A few halophytes are obligate and require salt in their environment to grow best, e.g. mangroves grow best in low salinity; Salicornia grows best in moderate salinity and growth decreases in low and high salinity.

Some non-halophytes are resistant to salt spray but others are particularly sensitive.

Fleshy leaves are often found in halophytes: storage of water, e. g. Salicornia or pickelweed.

PLANTS AND NUTRIENTS

All plants require at least 16 nutrients for growth. Some plants require additional elements.

Macronutrients are those elements that are needed in large amounts.

There are 9 macronutrients: C, H, O, K, P, S, N, Ca, and Mg.

C, H, and O form the bulk of the body of the plant and they are derived mostly from H2O and CO2.

Nutrients are released in to the soil by weathering processes and absorbed by plant roots and incorporated into their tissues.

There is a nutrient cycle from the soil to the plant and back to the soil.

NUTRIENT UPTAKE AND PLANT PROCESSES

Availability of nutrients and demand affects the nutrient uptake by plants.

Nutrient uptake is mediated by enzymes.

As the concentration of nutrients increase, the absorption rate increases. Eventually the plant reaches a maximum uptake rate and any further increase in concentration does not affect the uptake rate.

The Michaelis-Menten equation relates these to factors:

V = (Vmax X Cext)/Km + Cext)

V = rate of nutrient uptakeVmax = saturation uptake rate; all enzyme molecules are bound to substrate.Cext = external concentrationKm = value of Cext at which V is half of Vmax; 50% of the active sites are bound to substrate.

Nutrients are the substrate. At low concentrations of nutrients, the enzyme exists in an equilibrium between both the free form of the enzyme and the enzyme–substrate complex; the nutrient substrate is the limiting factor; increasing nutrient concentration also increases enzyme substrate complex at the expense of the free enzyme, shifting the binding equilibrium to the right. Since the rate of the reaction depends on the concentration enzyme-substrate complex, the rate is sensitive to small changes in nutrient concentration. However, at very high nutrient concentration, the enzyme is entirely saturated with substrate (nutrient), and exists only in the enzyme-substrate complex form. Under these conditions, the rate is insensitive to small changes in nutrient concentration.

The nutrient concentrations of plant tissues have a direct relationship to key processes related to plant growth, survival and reproduction.

Example: over 50% of the total nitrogen in leaf tissues affects photosynthesis, including the synthesis of rubisco and chlorophyll.

PLANT ADAPTATIONS TO VARIATIONS IN NUTRIENT AVAILABILITY

1. Root growth versus shoot growth

There is an increase allocation of carbon to root production with declining nutrient availability.

The allocation of carbon to roots varies between species living in nutrient rich or nutrient poor habitats.

Species living in nutrient rich habitats continue to increase its growth rate as nutrient availability increases.

Species living in nutrient poor habitats declines after a short increase in growth as the nutrient concentration increases.

Species living in a moderated nutrient environment increase its growth up to a point and reaches a plateau.

Growth response was measured as the accumulation of dry weight over the period of the experiment.

2. Leaf longevity

Experiments have shown that species with short-lived leaves tend to have higher leaf nitrogen concentrations than those species having longer-lived leaves.

Species with short-lived leaves tend to have a higher rate of photosynthesis than those with longer-lived leaves: an inverse relationship between leaf life span and photosynthetic rate.

There is a cost in producing a leaf in carbon and essential nutrients.

Long-lived leaves are found in nutrient poor habitats, so when a leaf is produced it lasts long because there is slow nutrient uptake due to the low availability of nutrients. If leaves are shed often in a low nutrient environment, the plant will lose more nutrients than it can take from the soil resulting in a net loss and eventually in death.

3. Influence on nutrient availability

Roots take up nutrients in soil solution as water is absorbed.

Active transport of nutrient also occurs.

As nutrients are taken from the soil, a zone of nutrient depletion is formed around the roots. Nutrients flow into this zone of nutrient depletion from the surrounding areas as a result of the diffusion gradient established by the root uptake.

As leaves become old, senescent, nutrients are removed and transported to perennial part of the plant to be reused. This process is called nutrient retranslocation.

Mutualistic relationships between plants and mycorrhizae and nitrogen-fixing bacteria increase nutrient availability to plants.

Rhizobium bacteria are the nitrogen-fixing bacteria associated with the roots of plants. Rhizobium depends on the carbon provided by the plant as a source of energy, and in turn they provide the plant with nitrogen.

Cyanobacteria, blue-green algae, are the nitrogen-fixing organisms found in aquatic environments.

These mutualistic associations are most beneficial in environments with low-nutrient availability. In environment with high nutrient availability it represents a cost since the plant must provide photosynthates to support the bacteria and mycorrhizal fungi with little benefit.

CALCICOLES AND CALCIFUGES

Soil acidity affect nutrient uptake because acidity affects the solubility of minerals.

Calcicole plants are those that prefer a basic or alkaline soil; soils rich in calcium slats. Calcifuge plants are those that prefer an acid soil. Calcifuge means lime-hating; low in calcium

salts. Neutrophilus plants are those that tolerate either condition.

Low pH is associated to calcium deficiency.

Highly acidic soils contain high amounts of aluminum and iron, which are toxic to many plants.

Free aluminum accumulates on the surface of the root and in the root cortex. it interacts with phosphorus to form highly insoluble compounds.

PLANTS OF SERPENTINE AND TOXIC SOILS.

Serpentine is a magnesium-iron silicate, (Mg, Fe)2SiO4. It also contains Ca, Al, Na and Ti. It may contain chromite, FeCr2O4 and garnierite, (Mg, Ni)SiO3 • nH2O Si, Mg and Fe are the major constituents; Al is low. Concentration of Ca and heavy metals is low but plays an important role in the soil.

Heavy metals such as iron, nickel, chromium, cesium, zinc and cobalt are toxic to plants, causing chlorosis and stunted growth.

They interfere with nutrient uptake and root growth and penetration.

High concentrations of heavy metals (Ni, Cr, Co), and Mg, a low Ca/Mg ratio and low fertility characterize serpentine soils; they are low in Ca, P, Na, and Al.

Serpentine soils contain a flora tolerant of these conditions.

Serpentine soils have a high proportion of endemic and ecotype species.

Endemics are species restricted to a particular habitat or geographical region. Ecotypes are ecological races well adapted to a local set of conditions

These types tolerate Ni and Cr in their tissues at levels highly toxic to other plants.

Some plants have developed mechanisms that exclude heavy metals from the plant.

A few species grow only in the presence of certain heavy metals and are indicators of the presence of those metals in the soil.

The selective influence of heavy metals...

Favors tolerant seedlings from the surrounding area. Continue selection against susceptible genotypes despite gene flow from the surrounding

population. Selection for the ability to survive in physically harsh, largely xeric, nutrient-poor environment.

ANIMAL ADAPTATIONS TO THE ENVIRONMENT

ANIMALS AND NUTRIENT ACQUISITION

Plants are the source for animals of organic compounds.

The diversity of plants presents a wide range of potential energy source for animals. A wide variety of physiological, morphological and behavioral characteristics enable animals to exploit these plant energy sources.

Plants and animals have different chemical composition:

Plants are high in carbohydrates and low in proteins. Animals are high fat and proteins and low in carbohydrates.

Cellulose and lignin make up most plant carbohydrates.

Proteins contain a large amount of nitrogen

The ratio of carbon to nitrogen in plants is 40 to 1. The ratio of carbon to nitrogen in animals is 14 to 1.

Herbivores are the animals responsible for converting plant protein into animal protein and fat.

MEANS OF ACQUIRING NUTRIENTS

Species interactions are called coactions. Coactions are reciprocal.

The relationship of one species to another is the interface between population ecology and community ecology.

In trophic interactions one species uses another as food.

The relationship between the eaten and eater are strong evolutionary forces for both: an arms race.

TROPHIC INTERACTIONS.

It is the basis of energy transfer through the community. There is a variety of strategies used to find food and to avoid to be eaten. It affects the population numbers of eaters and preys. It has an evolutionary effect through selection.

Herbivores: eat plant materialCarnivores: eat meat and other animals.Omnivores: eat both plant and animal matter.Detritivores: eat dead plant and animal.

HERBIVORY

Herbivory means feeding on plants (syn. phytophagous).

Herbivory includes defoliation and consumption of fruits and seeds. Defoliation is the destruction of leaves, bark, wood, roots and sap. It includes protozoans and animals that feed on bacteria and algae.

Herbivory affects plant growth and reproduction. It decreases the ability to survive even though it may not be killed outright.

Herbivory includes...

Eating fruits, nectar and pollen. Leaf mining, e.g. insect larvae Boring into stems, roots, seeds, buds and fruits, e.g. beetles. Root eating, e.g. pigs, gophers. Sap sucking, e.g. aphids. Gall formation, e.g. certain flies and wasps.

Types of herbivory

Many behavioral, morphological, and physiological adaptations are associated with herbivory.

Grazers feed on grass and herbs. Browsers feed on twigs and leaves of woody plants. Frugivores feed on fleshy fruits. Granivores feed on seeds.

Grazing stimulates production of new tissues in grasses by removing older tissues functioning at a lower rate of photosynthesis.

The relationship between frugivores and plants is usually mutualistic.

Most grazers and browsers live on a high diet of cellulose. These are some of the dietary problems:

High in carbon but low in protein. Most hydrocarbons are locked in the form of the indigestible cellulose. Grazers and browsers lack the enzymes needed to digest cellulose. These animals depend on specialized bacteria and protozoans living in their gut where they carry

anaerobic fermentation.

Bacteria and protozoans digest cellulose and proteins, and synthesize fatty acids, amino acids, vitamins and proteins.

Some species of wood-eating wasps and beetles depend on fungi for the digestion of cellulose and plant protein.

Ruminants include cows, deer, antelopes, giraffes, buffaloes, sheep and goats. These animals posses complex digestive systems.

Herbivore digestive system is inefficient and their fecal matter contains a large amount of partially digested food rich in energy.

Coprophagy: Some animals ingest fecal matter to extract the energy that remains in the undigested food.

Some coprophagous animals are dung beetles, young elephants to obtain bacteria from their mother’s feces, lagomorphs like rabbits, hares have a simple digestive system and produce two kinds of pellets;

the soft pellets are consumed and pass through the system twice, several species of monkeys.

FRUGIVORY

Frugivory is the feeding on fleshy fruits.

The relationship between frugivores and plants is usually mutualistic.

Frugivory as a year round activity is important in the tropics.

50 - 90% of the trees and shrubs produce fleshy fruits. There are always some species in bloom.

Frugivory is important in temperate regions during the summer and autumn months.

Trees and shrubs tend to produce fleshy fruits in the late summer and autumn. The time when many animals are migrating.

SEED PREDATION

Seed predation removes individuals from the population.

Some plant species depend on seed predators to disperse their seeds. These species produce large number of seeds to insure that some will survive and germinate.

Seed production varies from year to year due...

Response to favorable climatic conditions. Bumper crops use much energy and energy reserves have to be rebuilt.

By synchronizing years with abundant seed production alternating with years of poor seed production, seed predators are discouraged from increasing and remaining in the area.

The great abundance of seeds satiates the herbivore and allows some seeds to escape and germinate.

Years of abundant seed production coinciding with low predator population will overwhelm the predator population and many seeds will escape predation.

If all seeds mature at the same time and are released, the seed-predator will not be able to eat all of them.

Weather events synchronize seed production.

CARNIVORY

First level carnivores feed on herbivores.

Second level carnivores feed on first level carnivores.

In some communities there are higher levels of carnivory.

Carnivores do not have the difficulty of herbivores digesting food. There is a greater similarity in the chemical composition of the food and the flesh of the carnivore

Carnivores have a shorter intestine than herbivores because they do not have to digest large amounts of cellulose.

OMNIVORY

Omnivores feed at several trophic levels: herbivory, carnivory, etc.

The food habits of many omnivores vary with the season.

DETRITIVORES

Detritivores feed on dead organic matter: dead leaves, fallen twigs, etc.

Detritivores depend on mutualistic relationships with microorganisms to help in the breakdown of cellulose and lignin.

They are mostly invertebrates.

NUTRITIONAL NEEDS

Nitrogen is an essential component of proteins.

The highest quality of food is rich proteins.

Animals require 20 amino acids to make their proteins; 14 of these amino acids are essential in the diet. They have to come from food. The animals do not make them.

Insects have the same dietary requirements as vertebrates, although the need more potassium, phosphorus, and magnesium and less calcium, sodium, and chlorine.

The highest quality food is high in nitrogen in the form of protein.

Plants are ultimate source of these nutrients.

The highest amount of nitrogen is concentrated in the young shoots and leaves, the new growth.

Bacteria in the rumen of ruminants synthesize vitamin B1 and some amino acids from simple nitrogenous compounds.

Carnivores rarely have a dietary problem because they consume animals that have resynthesized and stored protein and other nutrients from plants in their tissues.

Mineral deficiency seems to be responsible in part for the distribution of several species.

Sodium, magnesium and calcium influence the distribution and fitness of grazing herbivores.

Large herbivores seek mineral licks, where they eat soil rich in minerals.

Spring vegetation is high in K relative to Ca and Mg. High K in the diet stimulates the production of aldosterone, This stimulates the excretion of K and Mg. Herbivores then experience a deficiency of Mg and seek animal licks.

Quantity more than quality seems to be more limiting to carnivores.

LINK BETWEEN FOOD SOURCE, SPECIES MORPHOLOGY AND BEHAVIOR.

Consumers utilize a wide variety of food sources.

Each type of food presents a constraint related to the ability of the organisms to acquire and assimilate the food item.

These constraints directly influence the evolution of characteristics relating to the physiology, morphology and behavior of the species.

The morphology of each species allows it to exploit a specific food source.

Species live in different habitats according to their ability to exploit the food sources.

ANIMAL ADAPTATIONS TO THE THERMAL ENVIRONMENT

In order to maintain the body temperature within a tolerable range, the animal must maintain a balance between the heat gained and the heat lost.

The rate of metabolic heat production is equal to the gain/loss of heat through convection, conduction, radiation, evaporation and the rate of heat storage in body through metabolic processes.

The thermal balance in the core of the animal is influenced by heat produced by metabolism, heat stored, heat flow to skin and affected by the thickness and conductivity of fat, fur, hair, feathers, and

scales, heat flow to the ground heat lost by evaporation.

A general formula for the heat balance in animals is...

M = Ko(Tb - Ta)

M = net metabolic heat production. Tb = body core temperature. Ta = atmospheric temperature.

Ko = constant for a given set of conditions variable among species; it is a function affected by surface area, conduction, convection, and radiation.

The terms homeotherm, poikilotherm and heterotherm emphasizes the nature of the variation of the body temperature.

1. Homeotherm – body temperature held constant across range of environmental temperatures, e. g. birds and mammals.

2. Poikilotherm – body temperature fluctuates with environment, e. g. fish, amphibians, reptiles and invertebrates.

3. Heterotherm – animals that are facultative endothermic homeotherms, but don’t consistently maintain body temperatures, e. g. bees, bats.

The terms endotherm and ectotherm emphasizes the mechanism by which body temperature is determined.

1. Endotherm – any animal deriving majority of body heat from internal metabolism.a. energetically expensiveb. generally capable of high levels of aerobic activity – e.g. distance running, flying, etc.c. involves adaptations for conserving body heat – e.g. fur, feathers

2. Ectotherm – animals that routinely derive majority of body heat from their environmenta. energetically less expensive – more energy goes to growth and reproductionb. slower at cold temperaturesc. involves adaptations for maintaining physiological functions despite body temperature fluctuations – e.g. different enzymes that function at different temperatures, changes in lipid composition of cell membranes to maintain fluidity

POIKILOTHERMS

Poikilotherms have a high thermal conductance between the body and the environment and a low metabolic rate.

Their rate of metabolism at rest increases exponentially with an increase of ambient temperature.

For every 10oC rise in temperature, oxygen consumption and thus metabolic rate doubles.

Hoff's rule describe these relationship: Q10 =Rt/Rt-10

Q10 = temperature coefficient.Rt = rate at any given body temperature T.Rt-10 = rate of body temperature at T - 10oC.

The Q10, temperature coefficient, for most poikilotherms is around 2.

The range of body temperatures over which poikilotherms carry out their daily activities is called the active temperature range, ACT.

Many animals show little sensitivity to drastic temperature changes within their active temperature range.

Disadvantages: Activity is limited to periods of the day when the temperature is high enough, ACT range. Active in temperate zones during spring, summer and early fall. When energy consumption is high, they depend on the anaerobic breakdown of glycogen for energy,

which causes the accumulation of lactic acid in tissues.

Advantages: Poikilotherms reduce metabolic activity during periods of temperature extremes and of food or water

shortage. Low energy demands enable them to colonize areas of limited food and water, such as deserts.

They are not limited to a minimum size and definite shape, e.g. paramecia, millipedes, snakes; they can exploit habitats that are unavailable to homeotherms.

Adaptations to high temperature

The rate of heating decreases in poikilotherms as size increases.

Large poikilotherms (over 10 kg) such very large lizards and tortoises, heat slowly and need a much higher temperature than smaller ones to reach the active Tb. They are found in habitats with little temperature fluctuations.

Aquatic poikilotherms (fish and aquatic invertebrates) live in a generally more stable environment and have less behavioral and physiological thermoregulatory capabilities than terrestrial forms. Their body temperature matches that of the surrounding water.

Fish can become acclimatized within the limits of thermal tolerance. The upper and lower limits of their thermal tolerance varies with the temperature at which the fish has become acclimatized.

If the fish lives at a the higher end of the tolerance range, it acclimatizes so that both the lethal high and lethal low temperatures are higher than if it were living within the cooler end of the range.

Aquatic poikilotherms can adjust slowly to seasonal temperatures.

Amphibians seek preferred temperatures within their habitat.

Semiterrestrial salamanders vary their body temperature with the season and have little behavioral thermoregulation. They live in moist, shaded places.

Semiterrestrial frogs use heliothermism to increase their body temperature. Because of evaporation these animals live near water.

Reptiles show little relation between their core temperature and the ambient temperature.

They cool their body by panting and by evaporation through the skin. Critical thermal maximum (CTM) is the temperature at which the movement of the animal is so

reduced that it cannot escape from the thermal conditions that will lead to is death. They use heliothermism and other behavioral means of controlling their body temperature.

Adaptations to lower temperatures.

Supercooling occurs when the body temperature falls below freezing without freezing body fluids.

Solutes in the cytosol of the cells allow supercooling to occur. Some of the substances involved are glycerol, sorbitol, and mannitol.

Some intertidal invertebrates in high latitudes and some aquatic insects survive the cold by freezing and then thawing.

Up to 90% of the body fluids freeze; the remaining fluids contain highly concentrated solutes, polypeptides and glycopeptides.

Ice is formed outside the cells by moving water out of the tissues into body spaces. The organs become distorted temporarily.

Increase is glycerol lowers the freezing point of cells.

Insects enter a resting state called diapause.

Diapause - neurohormonally mediated dynamic state of low metabolic activity. Occurs in genetically determined stages species specific in response to token stimuli. Once diapause is initiated it does not terminate with immediate return of favorable conditions.

HOMEOTHERMS

Birds and mammals are endotherms. The maintain their thermal optimum by oxidizing glucose and other energy-rich molecules.

Homeotherms remain active regardless of the environmental temperature but at a high-energy cost.

They regulate their body temperature by...

1. seasonal changes in insulation, 2. evaporative cooling: vasodilation, vasoconstriction, 3. increasing or decreasing production of metabolic heat: shivering

There is a relationship between body size and basal metabolic rate at rest. Basal metabolic rate is measured as oxygen consumption.

As body mass increases, basal metabolism decreases; as body mass decreases, basal metabolism increases.

For each species there is a range of environmental temperatures within which the metabolic rates are minimal, the thermoneutral zone. The animal does not have to regulate its temperature within this range.

Outside this zone, metabolism increases. When core body temperature crosses the upper threshold of this zone, sweating occurs; when it drops below the lower threshold, shivering results.

Critical temperatures mark the thermoneutral zone.

Animals lose heat to the environment in proportion to the surface area exposed relative to volume of body mass. The greater the surface-to-volume ratio of a part of the body, the faster it can transfer heat to its surroundings.

Regulation of heat exchange

Countercurrent heat exchange is a specialized parallel arrangement of incoming arteries and outgoing veins that transfer heat from warm arterial blood to cold venous blood, forming a heat exchanger that conserves heat in the body core.

The arteries and vein are often divided into a large number of small, parallel intermingling vessel that form a discrete vascular bundle or net known as rete.

Within the rete the blood flows in two directions and a heat exchange takes place.

If the ambient temperature is higher than the core temperature, heat will flow into the body and cause heat stress.

Sweating, panting and gular fluttering are forms of evaporative cooling.

Changes in the insulating layer of the body help to maintain optimal body temperature.

Shivering in the uncoordinated, involuntary, high frequency contraction of skeletal muscles that converts chemical energy to thermal energy.

In mammals, certain hormones can cause mitochondria to increase their metabolic activity and produce heat instead of ATP. This is called nonshivering thermogenesis, NST.

Most endotherms have a specialized heat-producing tissue called brown adipose tissue.

This tissue has many mitochondria and large amount of stored fats. When fats are oxidized no ATP is produced but much heat is released. Brown adipose tissue releases about 10 times more heat than other body tissues. It is an adaptation of small endotherms to achieve the required body temperature.

HETEROTHERMS

Heterotherm – animals that are facultative endothermic homeotherms, but don’t consistently maintain body temperatures.

At different times of the day or season, they take characteristics of endotherms or ectotherms.

a.) Regional heterotherms – animals that allow some body parts to stay at lower temperature than others.

1.) examples – birds in winter, humans in cold room.2.) generally involves alteration of circulation and/or counter current heat exchange between blood vessels.

b.) Temporal heterotherms – animals that expend a greater amount of energy maintaining their body temperatures during some periods of the day or year as compared to others.

1) Torpor – periods during the day when traditionally endothermic animals let their body temperatures fall.

i.) conserves energyii.) generally restricted to periods when animal would be inactive – e.g. night for birds, day for some mammals; hummingbirds, poorwills, bats, pocket mice, kangaroo mice.iii.) generally smaller animals – high SA/Vol ratios result in rapid heat loss/high energy expenditure to maintain body temp.

2.) Hibernation – seasons during the year when traditionally endothermic animals let their body temperatures fall.

i.) saves energyii.) body temperature must fall to qualify as true hibernation – e.g. bears are not hibernators because body temperature rarely falls much below normal, ground squirrels are hibernators because Tb drops significantly

3.) Other examples when traditionally ectothermic animals generate body heat for specific activities

i.) Insect flight. a) flight temperature range for insects is between 30oC and 44oC.b) many insects can fly at low environmental temperatures (0 o C or less) – e.g. night/winter flying moths, bumblebees.c) contract flight muscles isometrically to generate heat – e.g. shivering of moths.d) often rely on countercurrent exchange to maintain higher temperature of some body regions but not others – e.g. aorta passes near the

thorax flight muscles and cooled in the abdomen thermal window.e) often have adaptations for conserving heat – e.g. hair/fur of moths and bees.

ii.) Large, active fishesa.) most fish lose heat generated by muscles to surrounding water, especially when blood circulates in countercurrent fashion to water flow through gills.b.) large fish (e.g. tuna, sharks) generate significant amounts of heat through muscle activity when swimming.c.) unique pattern of blood flow keeps cold blood from the gills near the body surface.d.) counter current heat exchanger warms blood flowing to body coree.) enhances capacity for activity.

iii.) Egg-brooding snakes – female pythons contract muscles isometrically to elevate body temperature 5-7ºC above environment to speed egg development.

Torpor is a dormant state in which the activity of the animal is low and metabolism decreases.

Torpor occurs when conditions become unfavorable and/or food is not available. Some small mammals and birds exhibit daily torpor that seems to be adapted to their

feeding patterns, e. g. bats and shrews during the day, chickadees and hummingbirds at night.

Hibernation is long-term torpor that evolved as an adaptation to winter cold and food scarcity.

Hibernation is a state of regulated hypothermia, lasting several days or weeks that allows animals to conserve energy during the winter. During hibernation animals slow their metabolism to very low levels, with body temperature and breathing rates lowered, gradually using the body fat reserves that were stored during the active warmer months. Some hibernating animals stir as often as once a week; other animals sleep through the entire season.

Both land-dwelling and aquatic mammals hibernate. Animals that hibernate include mice, bats, ground squirrels, terrapins, snakes, frogs, and newts. http://en.wikipedia.org/wiki/Hibernation

Body temperature may be reduced to as low as 1°C - 2°C.

Estivation is summer torpor that enables animals to survive high temperatures and low water supply.

ANIMAL ADAPTATIONS TO THE MOISTURE ENVIRONMNET

Osmoregulation is the management of water content in the body and solute composition.

When two solutions separated by a selectively permeable membrane have the same osmolarity are said to be isoosmotic. The terms hyperosmotic and hypoosmotic are also used.

Osmoconformers are isoosmotic to their surroundings.

Osmoregulators are animals that must control their internal osmolarity.

Marine invertebrates and hagfishes are osmotic conformers. Their body fluids vary with changes in the seawater.

Marine bony fish must replace lost fluid.

They lose water osmotically through their skin and gills. Drink large amounts of water and take in salt. Excrete excess salt through their gills through active transport. Excrete little urine in order to conserve water.

Chondricthyes accumulate and tolerate urea and their tissues are hypertonic to seawater.

Water diffuses into their body. They maintain a high concentration of urea and trimethylamine oxide (TMAO), which protects

proteins from damage by urea. Concentration of body salts, urea, TMAO and other compounds is greater than 1,000 mosm/L

and therefore slightly hyperosmotic to seawater. This decreases the water loss through the skin.

Water slowly enters the body of sharks and relatives. Kidneys excrete large volume of urine. Excess salt is excreted by the kidney and in some by the rectal gland.

In freshwater fish...

Freshwater is hypotonic to the cell. Ions tend to move out of the cell into the surrounding water. Electrolytes lost must be replace by eating and by active transport from the surrounding

water. The gill cells are hypertonic relative to the surrounding water, therefore, the cells gain water

through osmosis. Cells and tissues that are gaining water are under osmotic stress. Osmotic stress means that the concentration of solutes in the cells and tissues is abnormal. The ability to achieve electrolyte balance is called osmoregulation. Freshwater fish excrete large amounts of water in the urine and do not drink water. Some protists have contractile vacuoles that pump out excess water.

Some animals that live in temporary ponds or films of water around soil particles can lose almost all their body water and survive. This ability is called anhydrobiosis.

Tardigrades (water bears) contain 85% water in their body; in a dehydrated state they have less than 2% water in their bodies.

These animals can live in this desiccated state for years. The mechanism is not understood.

Land animals...

Land animals constantly lose water to the environment through evaporation. Gas exchange occurs through the wet surfaces of the lung epithelium. Sweating and panting in order to keep their body cool also loses water.

Vertebrates depend on the kidneys to maintain water balance.

The concentration of urine depends on the length of the loop of Henle. The longer the loop, the more concentrated the urine.

Marine mammals that have drunk seawater possess large kidney with long loops that eliminate salt in highly concentrated urine.

Adaptations to deserts:

1. Many desert mammals obtain water from their own metabolic process. The oxidation of fats and carbohydrates produces water. They have very long loops of Henle and produce highly concentrate urine.

2. Some desert animals can tolerate some degree of dehydration Desert rabbits can stand up to 50% loss of their body weight. Camels up to 27% of their body weight.

3. No sweat glands.

4. Dry feces.

5. Hyperthermia:

Hyperthermia is an acute condition resulting from excessive exposure to heat, it is also known as heat stroke. The homeothermal regulatory mechanisms become overwhelmed and unable to effectively deal with the heat, and body temperature climbs uncontrollably. Wikipedia

"...adult Arabian oryx (Oryx leucoryx) during 2 years in the arid desert of west-central Saudi Arabia. We report the first case of heterothermy in a free-living ruminant in a desert environment: Tb varied by 4.1±1.7°C day–1 during summer (June to September) and by 1.5±0.6°C day –1 during winter (November to March). Over both seasons, mean Tb was 38.4±1.3°C.... Without heat storage in summer, we estimated that oryx would have to increase their water intake by 19%, a requirement that would be difficult to meet in their desert environment. If heat storage was calculated based on the daily change in Tb rather than on heat storage above mean Tb then we estimated that oryx saved 0.538 litres H2O day–1 animal–1 during summer."Stéphane Ostrowski, Joseph B. Williams and Khairi IsmaelThe Journal of Experimental Biology 206, 1471-1478 (2003)http://jeb.biologists.org/cgi/content/full/206/9/1471

If Tb rises above ambient temperature, this drives the force Tb – Ta reducing the dependence on evaporative heat loss; it also reduces the intake of heat, thus conserving water.

RESPONSE TO DROUGHT AND FLOODING

Seasonal and periodic droughts can have pronounce effects on animal populations.

Rainfall influences the quantity and quality of forage, which in turn influences mortality and may affect density.

Drought stress promotes outbreaks of leaf-eating insects by influencing thermal and nutritional conditions that favor insect growth.

The increased contents of nitrogen, minerals and sugars in the leaves of drought-stressed plants provide a rich food for leaf-eating insects.

High temperatures raise the rate and efficiency of enzymatic reactions in insects, and enhance their detoxification systems.

There is an optimum humidity at which the nymphs of some insects develop the fastest.

Excessive moisture encourages the growth of pathogens, especially fungi, among insect populations.

ANIMAL ADAPTATIONS TO THE LIGHT ENVIRONMENT

Daily and seasonal changes in the light environment trigger daily and seasonal responses in the activities of animals.

Chronobiology examines the animal cycles caused by daily and seasonal cycles.

CIRCADIAN RHYTHMS

The circadian rhythm is a name given to the "internal body clock" that regulates roughly regulates 24-hour cycle of biological processes in animals and plants.

The term circadian comes from the Latin circa, meaning "around" and dies, "day", meaning literally, "around the day."

The period of the circadian rhythm, the number of hours from the beginning of a period of activity one day to the beginning of activity on the next, is called the free-running cycle.

Circadian rhythms are physiological and behavioral rhythms and include:

– sleep/wakefulness cycle– body temperature– patterns of hormone secretion– blood pressure– digestive secretions– levels of alertness– reaction times

Circadian rhythms are genetically controlled. They are...

Affected little by temperature Insensitive to a great variety of chemical inhibitors Are not learned Are not imprinted on the organism by the environment.

Animals and plants are influenced by two daily periodicities:

an external rhythm of 24 hours the internal circadian rhythm of approximately 24 hours.

For the two rhythms to be in phase, some time-setter must adjust the internal and external periods.

Light brings the circadian rhythm of organisms into phase with their external environment.

THE BIOLOGICAL CLOCK

The biological clock is the time-keeper of biological and physiological activities in organisms.

The biological clock maintains the circadian rhythm.

The persistence of rhythms in the absence of a dark-light cycle or other exogenous time signal clearly seems to indicate the existence of some kind of internal timekeeping mechanism, or biological clock.

In unicellular organisms and plants, the clock appears to be located in individual cells.

In multicellular organisms it is located in the brain.

In most insects studied appears to be located in the optic lobe or in the tissue between the optic lobe and the brain.

In birds the clock is located in the pineal gland.

In mammals, it is located in a part of the hypothalamus just above the optic chiasm, thesuprachiasmatic nuclei (SCN), where the two optic nerves intersect; the pineal body also plays a role. The SCN is in the hypothalamus. It is a tiny cluster of about 10 thousand nerve cells.

Disruption of the clock or its synchronization occurs during jet-lag, shift workand old-age.

Disruption of the clock detrimentally affects our well-being and mental andphysical performance.

The biological clock is reset every day by dawn and dusk.

The operation of the clock in mammals involves a special hormone, melatonin, produced by the pineal gland that serves to measure time.

More melatonin is produce in the dark than in the day. The amount produced is a measure of changing daylength.

Biological Clock and Melatonin Alan Hedge, Cornell University, 11/1999. Biological Rhythms

The circadian clock controls longer term cycles:– seasonal rhythms in reproduction– seasonal rhythms metabolism and appetite

The pineal hormone melatonin, (a hormone that induces sleep) mediates this seasonality.

Melatonin is synthesized from tryptophan.

The SCN clock ensures that melatonin is secreted only at night. Melatonin secretion lastlonger on the longer winter nights.

The duration of the circadian melatonin is used by the brain to orchestrate seasonal rhythms.

MODELS OF BIOLOGICAL CLOCKS

It appears that the biological clock is organized as a hierarchy of clocks.

The various overt rhythms influencing physiological and behavioral process are controlled by subservient or slave clocks coupled to a master clock.

When the master clock is reset by a light signal, it in turn resets the other clocks.

A slave clock may take longer to reset thus causing temporary disturbance.

Biological clocks let the organism anticipate environmental cues.

Transition from night to day go along with changes in humidity and temperature.

CRITICAL DAYLENGTHS

In the higher latitudes the daily periods of light and dark lengthen and shorten with the seasons.

The activities of plants and animals are geared to the changing seasonal rhythms or night and day.

Most animals of temperate regions have reproductive periods that closely follow changing daylengths of seasons.

For most birds the height of the breeding season is the lengthening days of spring. For deer the mating season is the shortening days of fall.

The signal for these responses is critical daylength.

Many organisms have short-day and long-day responses.

One critical daylength is reached as long days move into short, and other as short day move into long.

The direction from which the critical daylength is approached distinguishes the possible critical daylengths.

Some examples of physiological and behavioral activities controlled by light:

Diapause is usually controlled by photoperiod. Gonadal development in birds. Spring migration in birds. Food storage in mammals. Reproduction in mammals. Antler growth in deer.

Diapause is a period in which development is suspended and physiological activity diminishes.

TIDAL AND LUNAR CYCLES

Animals that live in the intertidal zone of the sea show rhythms in their behavior that coincide with the cycles of high and low tides.

Their rhythms mimic the ebb and flow of tides every 12.4 hours, which is one-half of the lunar day of 24.8 lunar hours, the interval between successive moonrises.

Research suggests that intertidal organisms have one independent clock to synchronize daily activities and two strongly coupled circalunidian clocks to synchronize tidal activity.

Each lunar day clock drives its own tidal peak. In one clock quits ticking in the absence of environmental cues, the other continues running.

Day-night cycles reset solar-day rhythms, and tidal changes reset tidal rhythms.

NATURAL SELECTION AND ADAPTATION

An adaptation is a characteristic that enhances the survival or reproduction of organisms that have it. This characteristic has evolved by natural selection.

The members of the population become better suited to some feature of their environment through change in a characteristic that affects their survival or reproduction.

Natural selection is the only mechanism known to cause the evolution of adaptations.

ADAPTATIONS IN ACTION: SOME EXAMPLES

1. The skull bones of most terrestrial vertebrates are rigidly attached to one another, but in snakes, they are loosely joined. They swallow their prey by drawing it into a gullet with recurved teeth mounted on a number of freely moving bones that act as levers and fulcrums, operated by complex muscles.

2. Pseudocopulatory pollination in orchids. Several species of orchids have modified flower parts to look somewhat like a female insect, and the flower emits a scent that mimics the attractive sex pheromone of a female, bee, fly or thynnine wasp depending on the orchid species. The flower is pollinated in the process of copulation; the insect does not derive any benefit from this activity.

3. Australian arboreal weaver ants construct nests of living leaves by the intricately coordinated action of numerous workers, groups of which draw together the edges of leaves by grasping one leaf in their mandible while clinging to one anther.

4. Not in your book. Philodendron and other aroids produce two kinds of leaves adapted to different environments: small leaves for the dark forest floor and growth toward the dark looking for a tree trunk to climb, and large leaves with long petioles to catch sunlight in the upper regions of the forest canopy.

THE NATURE OF NATURAL SELECTION

Design and mechanism.

Most adaptations are complex and appear to have a design, to be constructed to perform a certain function, e.g. growth, feeding, pollination, etc.

The process of natural selection is random and mindless.

Those with variations that enhance survival and reproduction replace those less suited who reproduce to a lesser extent.

Adaptive biological processes appear to have goals but there is no conscious anticipation of the future in cells.

Teleological statements express goals as the leading reason for an action in the physical world, e.g. “… in order to…”

The future cannot cause material events in the present.

This apparent purpose is caused by the interaction of environmental conditions and the operation of a program coded or prearranged information residing in DNA sequences, that controls a process.

Definitions of natural selection.

Natural selection is not evolution. These two words are not synonyms.

Evolution can occur by natural selection, artificial selection or by genetic drift.

Survival is a prerequisite for reproduction.

Fitness is often defined as reproductive success. It is the average per capita rate of increase in numbers.

The components of fitness are:

1. Probability of survival to reproductive age.2. Average number of offspring produced via female function.3. Average number of offspring produced via male function.

Sexual selection is based on the competition for mates. It can be considered a form of natural selection.

The probability of survival and the average number of offspring enter into the definition of fitness, and these concepts apply only to groups of events; all the individuals in a population with a particular genotype.

Natural selection exists if there is an average difference in reproductive success.

Differences in survival and reproduction exist among individual organisms, among genes and among populations and species.

Different kinds of biological entities may vary in fitness, resulting in different levels of selection.

The difference among traits that affect fitness.

Natural selection may occur among genes, individual organisms, and groups such as populations or species.

Selection has an evolutionary effect only if there is inheritance.

Natural selection is a name for consistent statistical differences in reproductive success among genes, organisms, or populations.

Natural selection and chance

Neutral alleles are not affected by natural selection because they do not affect reproductive success.

Fitness differences are average differences, biases, differences in probability of reproductive success.

This does not mean that every superior genotype reproduces prolifically, and every inferior genotype does not reproduce and perishes.

Natural selection is a consistent difference in fitness among phenotypically different biological entities, and is the antithesis of chance.

It is not possible to tell if difference in reproductive success between two individuals is due to fitness or to chance.

Selection OF and selection FOR.

Natural selection may select for a certain body size, mating behavior or other feature. There may incidental selection of other features that are correlated with those features.

In speaking of a function of a feature, it is implied that there has been natural selection of organisms with that feature and of genes that program it, but for the feature itself.

A feature may have other effects or consequences that were not its function and for which there was not selection.

EXAMPLES OF NATURAL SELECTION

Look over these examples on pages 285 to 290.

Bacterial populations; Inversion polymorphism in Drosophila; Male reproductive success; Population size in flour beetles; Kin discrimination in cannibalistic salamanders; Selfish genetic elements.

LEVELS OF SELECTION

We can consider higher-level units and included units: species/populations; populations/individuals, etc.

There are two measures of fitness: 1. Reproductive success of its constituent members, e.g. individuals that produce offspring.2. Reproductive success of the higher level units, e.g. population that produces other populations.

Selection of organisms and groups

Sociobiology is the biological basis of social behavior in animals.

E.g. flocking, parental care, territoriality, courtship, dominance, cooperation, etc.

Altruism is doing well for others.

E.g. sharing food, warning of danger, adopting orphans, etc.

There is always cost to altruistic behavior.

It raises the genetic fitness of another individual while lowering its own.

How can altruistic traits be maintained in a population when the altruistic gene is selected against?

Altruistic trait cannot evolve by individual selection.

An altruistic genotype amid other genotypes that were not altruistic would necessarily decline in frequency, simply because it would leave fewer offspring per capita than the others.

If a population were to consist of altruistic genotypes, a selfish mutant – a cheater – would increase to fixation.

Statements about organisms acting against their own good for "the good of the species" are wrong.

Traits that benefit the population at the cost of the individual might have evolved by group selection.

Populations with higher rates of “selfish genotypes” may have a higher chance of extinction than populations with “altruistic genotypes.”

Group selection has been criticized by George Williams in his book Adaptation and Natural Selection, 1966.

Here is his reasoning: Individual organisms are more numerous than the populations into which they are aggregated. Individuals are born and die much faster than populations. Selection requires differences in rates of birth and death at both levels, individuals and

populations. The rate of replacement of less fit by more fit individuals is potentially much greater than the rate

of replacement of less fit by more fit populations. Therefore, individual selection will prevail over group selection.

Most biologists are of the opinion that very few characteristics have evolved because they benefit the population or the species.

Kin selection has been proposed as a mechanism for the evolution of altruistic behavior.

Proposed by William Hamilton in 1964.

Kin selection is selection at the level of the gene.

Either the individual or its immediate relatives leave behind many offspring.

The altruist’s relatives are more likely to carry copies of the altruistic allele than are members of the population at random.

When the altruist’s enhances the fitness of its relative, even at some cost to its own fitness, it can increase the frequency of the allele.

Genes reach the next generation via relatives.

As far as evolution is concerned, it makes no difference what animals passed the "good" genes to the next generation, the actor or its siblings.

Kin selection also explains eusociality.

Division of labor. The sterile castes give up fitness entirely and devout their efforts to the good of the colony.

Cooperative caring of the young. Overlap of at least two generations of life stages able to contribute to the colony's wellbeing. The

colony is in fact a family made mostly of the queen and her offspring. It is found in bees, wasps and termites, and one mammal, the naked mole rat of Africa.

Most features are unlikely to have evolved by group selection, the one form of selection that could in theory promote the evolution of features that benefit the species even though they are disadvantageous to the individual organism.

Species selection

Species selection is the process responsible for the proliferation of species that have lower extinction and higher speciation rates.

It refers to a differential rate of extinction and speciation due to some characteristic of the species such as geographic isolation or allele frequency.

Differential speciation: Some lineages have higher speciation rate than other related lineages.

For example: orchids, family Orchidaceae with about 19,500 species, have highly modified flowers to attract specialized pollinators and have produced more species over time than its close relative, the iris family, Iridaceae, which consists of about 1,750 species.

There has been differential speciation in this case caused by the flower type and the attraction of pollinators.

Differential extinction also occurs. Some lineages have long survival time, e.g. asexual forms have a higher rate of extinction than sexual forms.

See Fig. 11.16.

Many groups of plants and animals have given rise to asexually reproducing lineages, but also all such lineages are very young as indicated by their very close genetic similarity to sexual forms.

Asexual forms that arose long time ago have not persisted.

THE NATURE OF ADAPTATIONS

Definitions of adaptation

1. Adaptations can be defined from the point of view of its present effect in increasing the fitness of an individual.

“An adaptation is a phenotypic variant that results in the highest fitness among a specified set of variants in a given environment.” Kern Reeve and Paul Sherman (1993)

“A characteristic body part, shape or behavior that helps a plant or animal survive in its environment.”www.reefed.edu.au/glossary/a.html

2. Adaptation can also be defined from the historical perspective of it phylogenetic origin:

“For a character to be regarded as an adaptation, it must be a derived character that evolved in response to a specific selective agent.” Paul Harvey and Mark Pagel (1991)

“A biological adaptation is an anatomical structure, physiological process or behavioral trait of an organism that has evolved over a period of time by the process of natural selection such that it increases the expected long-term reproductive success of the organism.”

en.wikipedia.org/wiki/Adaptation_(biology)

The presence of a particular feature versus another may be due to adaptation or phylogenetic history.

Preadaptation is a feature that by chance serves another function: the swim bladder of rhipidistian fish became the lung of early amphibians.

An exaptation is an adaptation that performs a new function, different from the original function performed when the adaptation arose through natural selection. The concept involves the idea of modification for the new function.

Wings of penguins and alcids are used for swimming rather than flying.

The term “preadaptation” supposes forethought and it is being eliminated from biological vocabulary and replaced with exaptation or cooptation.

Recognizing adaptations

Not all traits of organisms are adaptations.

A trait…

1. May be the consequence of physics or chemistry, e.g. the red color of the blood.

2. May have arisen through genetic drift rather natural selection.

3. May have evolved not because of particular advantage but because it is correlated to another feature that was advantageous, e.g. pleiotropy, genetic hitchhiking.

4. A character state may be a consequence of its phylogenetic history, an ancestral character state that acquired a new function.

Several methods may be used to infer if a feature is an adaptation:

1. Complexity cannot evolve except by natural selection.

2. Design of a feature corresponds to its function.

Functional morphology and ecological physiology study how the design of features allows organism to survive and function in an ecological setting.

The relation of morphological variation and functional morphology to environmental change.

“Ecological physiologists identify the physiological adaptations of organisms and organ systems, investigate the molecular, cellular and physiological mechanisms underlying these adaptations, and determine how these adaptations affect growth, reproduction, movement, survival and other basic biological characteristics of organisms and their ecological role in communities.” UC Santa Barbara, Santa Barbara CA 93106http://www.lifesci.ucsb.edu/eemb/research/ecological_physiology/ecological_physiology.html

3. Experiments may show that a feature enhances survival or reproduction in a way the increases fitness relative to individuals in which the feature is modified or absent.

4. The comparative method consists of comparing sets of species to pose or test hypotheses on adaptation and other evolutionary phenomena.

Convergent evolution: A feature that evolves independently in many lineages because of a similar selection pressure.

o E. g. the similar beak of birds that feed on nectar appeared in six different lineages.o E.g. Human digestion of milk and its occurrence in areas where milk and dairy products

are an important part of the diet. Phylogenetic information may be necessary in some cases for the proper use of the comparative

method.

The number of independent convergent evolutionary events by which a character state evolved in the presence of one selective factor versus another should be considered.

WHAT NO TO EXPECT OF NATURAL SELECTION AND ADAPTATION

Natural selection does not necessarily produce anything that can be called evolutionary progress.

Necessity of adaptation

Not all environmental changes reduce population size.

An environmental change that does not threaten extinction may set up selection for change in some characteristics.

New adaptations may evolve in an unchanging environment if new mutations arise that are superior to the previously existing one.

Perfection

Selection may fix only those genetic variants with a higher fitness than other genetic variants in that population at that time.

Selection cannot fix the best of all conceivable variants if they do not arise; the best possible variants may fall short of perfection because of various kinds of constraints.

Progress

Evolution does not have goals

Measurement of “improvement” or “efficiency” must be relevant to each species’ special niche or task.

Harmony and the balance of nature

Selection at the level of genes and individual organisms is inherently selfish: the gene or genotype with the highest rate of increase increases at the expense of other individuals.

Cooperative behavior can be explained by kin selection.

Kin selection does not work across species boundaries: natural selection cannot produce any modification in a species exclusively for the good of another species.

Mutualistic relationships between species consist of mutual exploitation.

The equilibrium observed in ecological communities does not reflect any striving for harmony.

Morality and ethics

Natural selection is the name for differences among organisms or genes in reproductive success.

Natural selection cannot be described as moral or immoral, just or unjust, kind or cruel.

Hence, it cannot be used as a justification or model for human morality or ethics.

Neither the evolutionary theory nor any other field of science can speak of or find evidence of morality or immorality.

Science describes what it is, not what ought to be.

The naturalistic fallacy, the supposition that what is natural is necessarily good, has not legitimate philosophical foundation.

ANIMAL FORM AND FUNCTION

One definition of adaptation.

An adaptation is a trait that allows individuals to produce more offspring in a particular environment than individuals without the trait.

Adaptations are the result of natural selection.

The environment does the selecting.

The genetic characteristics of the population changes with time; the genetic characteristics of the individual do not change with time.

Sometimes the phenotype of an individual changes with the environment. This is called acclimation.

E.g. North America wood frogs produce molecules that protect their cells from being damaged by the formation of ice crystals. The ability to produce these molecules is an adaptation; the actual production of the molecules is an acclimation.

Organisms are adapted to their environment. All are successful. Human physiology is not better than clam physiology. There is no better physiology.

NATURE OF ADAPTATION

Not every structure and feature is adaptive. There are features that were present in ancestral population but are not currently adaptive.

Vestigial structures e. g. tailbone, goose bumps, appendix in humans. Pelvic bones in whales, vestigial eyes in cave fish. Some structures appear early in the development and remain in the adult, e.g. human males

have rudimentary mammary glands.

Genetic constraints.

Genetic correlation: selection on alleles for one trait (increased beak depth), caused a correlated and non-optimal increase in another trait (increase beak width).

Adaptations are constrained by genetic correlation with other traits, lack of genetic variations, historical constrains and historical constraints.

Historical constraints

Traits have evolved from previously existing traits., e. g. the ear bones evolved from part of the jaw and brain case in early mammals.

Natural selection act on structures that have a function and evolve them into structures with different functions.

Trade-offs

In reproduction, females make a trade off between the number of eggs and the size of the eggs they produce. If the number of offspring is large, the mother can provide less food.

It is not possible for an organism to be perfectly adapted to all aspects of the environment all the time, e.g. sweating to cool off may cause dehydration.

Adaptations are compromises limited by genetic and historical constraints.

TISSUES, ORGANS AND SYSTEMS

The form and function of body structures are correlated.

A tissue is made of a group of closely associated, similar cells adapted to carry out specific functions.

1. Epithelial tissue (epithelium) consists of fitted tightly together to form a continuous layer or sheet.

It covers body surfaces and lines cavities.

It functions in protection, absorption, secretion and sensation.

The outer surface of this tissue is typically exposed because it lines cavities.

The cell layer is attached to the underlying tissue by a non-cellular membrane, the basement membrane, made polysaccharides and fibers

Epithelial cells may be organized or differentiated into epidermis (skin), membranes, glands and sensory receptors.

Epithelial cells are cuboidal, columnar or squamous.

2. Connective tissue joins other tissues of the body, supports the body and its organs, and protects underlying organs.

It consists of relatively few cells, separated by an intercellular substance.

Typically the intercellular substance consists of fibers made of proteins, scattered through a matrix, a thin gel made of polysaccharides.

Different kinds of connective tissue will have different kinds of fibers and matrices.

The nature and function of each kind of connective tissue is determined in part by the structure and properties of the intercellular substance.

Intercellular substance contains...

1. Collagen fibers made of the protein collagen, the most abundant protein in the body.

Collagen fibers are wavy, flexible and resistant to stretching.

2. Elastic fibers are made of the protein elastin and branch and fuse to form a network.

They return to their original form after the stretching force is removed.

3. Reticular fibers are very small-branched fibers that form delicate networks.

They are made of collagen and glycoprotein.

Types of connective tissues

1. Loose (areolar) connective tissue is found everywhere in the body. It supports organs and is a reservoir of salts and fluid. Together with adipose tissue, it forms the subcutaneous layer that attaches the skin to muscles and other structures beneath. The matrix is gel-like and contains all three fiber types, mast cells, fibroblasts and macrophages.

2. Dense connective tissue is found in the tendons, ligaments and dermis of the skin. It supports and transmits mechanical forces. Dense connective tissue may be regular or irregular depending on the arrangement of the collagen fibers. The matrix is made primarily of collagen fibers and a few elastin fibers. Fibroblasts are the major cellular component.

3. Elastic connective tissue is found in structures that must expand like lungs and large arteries. It consists of bundles of parallel elastic fibers. Fibroblasts present.

4. Adipose tissue is found in the subcutaneous layer and in patches around some internal organs. It stores food, insulates the body and provides additional support to organs like kidneys and mammary glands. Adipocytes store fat.

5. Cartilage makes the skeleton of chondrichthyes; it is found at the end of bones of other vertebrates, and provides flexible support to organs like the trachea, ears and nose. It resists compression.

Chondrocytes (mature cells) found in lacunae. This tissue lacks nerves, lymph and blood vessels. Chondrocytes are nourished by diffusion through the matrix. Chondrocytes remain alive and lie in lacunae.

6. Bone makes the skeleton most vertebrates. It supports and protects internal organs, acts as a reservoir of calcium, and place for muscle attachment.

Osteocytes (mature cells) are found in lacunae. In compact bone, the lacunae are arranged in concentric circles around the

Haversian canal, through which capillaries and nerves pass. Compact bone consists of units called osteons. This tissue is rich in blood vessels.

7. Blood is found within the heart and blood vessels. In its liquid matrix transports cells (RBC, WBC, platelets) wastes, nutrients, and other materials.

3. Muscle tissue is specialized to contract.

Each cell is an elongated fiber containing many myofibrils.

Myofibrils are made of the protein actin and myosin.

Skeletal muscles are striated and under voluntary control. Striations or bands reflect the alignment of the filaments responsible for contraction of the muscle cells. The cells are multinucleated.

Smooth muscles contract involuntarily, lack striations and cells are uninucleate.

Cardiac muscles are striated and act involuntarily. Cardiac muscle cells branch and the fibers are joined end to end at the intercalated disc. They are found only in the heart.

4. Nervous tissue is composed of neurons, which are cells specialized for conducting nerve impulses, and glial cells, which are supporting cells.

A typical neuron consists of a cell body, dendrites and an axon.

Neurons communicate at junctions called synapses.

A nerve consists of many neurons bound together by connective tissue.

The nervous tissue also contains various types of supporting cells that insulate and protect the delicate neurons.

ORGANS AND SYSTEMS

An organ consists of a group of tissues associated into a differentiated structure to perform a specific function or functions in the body.

Organs are associated together into organ systems. Organ systems perform together a specialized and vital function in the body.

Organs and organ systems work together to maintain appropriate conditions in the body, a constant internal environment called homeostasis.

Homeostatic mechanisms that maintain homeostasis may involve several organ systems that work together.

BODY SIZE AND SCALING

As cells become larger, the volume increases at a greater rate than the surface area.

Above a critical size, the number of molecules needed by the cell could not be transported into the cell fast enough to sustain its needs.

Once inside the cell molecules must be transported to their place of utilization.

Cells divide in order to maintain an optimal ratio of surface to volume.

Sizes and shape of cells are relate to the functions they perform.

The micrometer is the unit normally used to measure cells.

1m = 1 millionth of a meter (10-6) or 1 thousandths of a millimeter (0.001 ml). The nanometer is used to measure cellular organelles. 1nm = 1 billionth of a meter (10-9) or 1 thousandths of a m. Starting with the meter, the ml, m and nm are 0.001 of the previous unit.

Metabolic rate is the overall rate of energy consumption by an individual.

Because energy production in animals depends on aerobic respiration, metabolic rate is often measured in terms of oxygen consumption; the units used are ml O2 consumed per hour.

Basal metabolic rate (BMR) is the rate at which oxygen is consumed at rest, with an empty stomach, in the absence of temperature or water stress.

Mass-specific metabolic rate is the rate per gram of tissue.

It is expressed in ml O2/gram of tissue/hour.

Large animal have low metabolic rate because they have relatively small surface area for exchanging the oxygen and nutrients required to support metabolism.

The large surface area of small animals means that they lose heat very fast.

Adaptations that increase the surface area

Flattened, folded and branched structures have very high surface relative to its volume.

Flattened surfaces: gills of fish. Folded surfaces: microvilli increase the surface area of the cell. Branched structures: capillary network increase diffusion.

Allometry

Allometry is the differential growth of body parts. It means that body size and some anatomical or physiological feature do not change in the same proportion.

e. g. large animals have larger bones than small animals, but their bones are not only large but also disproportionately larger.

Allometry is an adaptation to certain environment or lifestyle. E. g. Dogs have larger hearts than cats of the same size. Dogs run down their prey while cats jump or sprint to hunt. Stamina requires a larger heart to pump blood to the muscles during long-distance chase.

HOMEOSTASIS

Homeostasis is the constant physical and chemical conditions in cells, tissues and the body in general.

There are many mechanisms for achieving homeostasis.

Animals have an optimal value or preferred point for functioning well.

Blood pH, nutrient availability, body temperature, etc. are some of the parameters that have to be maintained within certain range around the optimal point in order to maintain homeostasis.

Epithelial tissue is located at the interface between the external and internal environment.

Epithelial cell membranes have many embedded proteins that control the flow in and out of the cells.

Homeostasis is important to maintain the ideal conditions for enzyme function.

Temperature, pH, and other physical and chemical conditions have dramatic effects on protein structure. Enzymes work within a narrow range of conditions.

Gaining and losing heat

There are two general categories based on how animal obtain heat:

Endotherms produce heat in their own tissues and have higher basal metabolic rate.

Ectotherms obtain heat mostly from the environment and have low basal metabolic rate.

Some ectotherms can generate heat to keep warm certain organs of their body.

Many ectotherms and most endotherms have specialized heat-producing tissue called brown adipose tissue.

This tissue has many mitochondria and large amount of stored fats. When fats are oxidized no ATP is produced but much heat is released. Brown adipose tissue releases about 10 times more heat than other body tissues. It is an adaptation of small endotherms to achieve the required body temperature.

Exchanging heat with the environment

Heat flows from areas of higher temperature to areas of lower temperature.

All organisms exchange heat with the environment.

There are four ways to exchange heat with the environment:

Conduction: the direct transfer of heat between two objects that are in direct physical contact.e.g. you sitting directly on a metal stand during a football game in winter.

Convection: when air or water moves over the body, heat is removed from the body. The air or water in contact with the body is constantly replaced and not allowed to warm up.

Radiation: the transfer of heat between two bodies that are not in direct contact.

Evaporation: when a liquid is converted into a gas, e.g. when you sweat, the evaporation of the sweat removes heat from your skin.

Air is a poor conductor of heat and, therefore, it is a good insulator.

Animals have developed methods of trapping air to conserve heat, e. g. birds have feathers and mammals have fur.

In water there is no heat lost due to evaporation; radiation is poorly conducted in water.

To conserve heat,

otters have water repellent fur that traps air next to the skin. whales, seals and other marine mammals have a thick layer of fat.

Countercurrent heat exchanger is found in several groups of aquatic animals and mammals and birds that live in cold habitats.

The veins and arteries are next to each other in the limbs or tongue. Arteries carry warm blood from inside the body to the extremities. The heat flows from the arteries to the veins and is returned to the body instead of being lost to

the surroundings.

To regulate body temperature, the body has a sensor that monitors some aspect of the environment.

An integrator is part of the nervous system that evaluates the incoming sensory information and decides if a response is necessary.

An effector is any structure that helps to restore the desired internal condition.

Endotherms maintain enzyme activities at all times. Mammals and birds remain active in winter and at night. They sustain high levels of aerobic activity like running and flying. This is done at a cost of energy. Endotherms need high levels of energy-rich food.

Ectotherms thrive with much less food. They can use a greater proportion of their total energy intake to support reproduction. They generally live in warm habitats.

VARIATION

Mutations and recombinations give rise to variation among organisms.

This genetic variation is the foundation of evolution.

Phenotype refers to the external appearance of the organism, e.g. Seed shape: round or wrinkled; it also includes internal anatomy, physiology and behavior.

Genotype refers to the genetic makeup of the organism.

Individuals with the same appearance (phenotype) may differ in their genetic makeup (genotype).

Locus: a site on a chromosome or the gene that occupies that site.

Allele refers to genes that govern variations of the same feature, e.g. yellow seed and green seed are determined by two alleles of the same gene.

Haplotype is one of the sequences of a gene or DNA segment that can be distinguished from homologous sequences by molecular methods such as DNS sequencing.

Gene copy refers to the number of representatives of a gene. It does not distinguish between alleles.

In a diploid population, each individual carries two copies of a gene, e.g. 100 individuals = 200 gene copies.

Allele copy distinguishes between alleles.

A heterozygous individual has two copies of the gene, e.g. allele A1 and allele A2.

SOURCES OF PHENOTYPIC VARIATION

Individuals may differ in their phenotypes because of genetic differences, environmental differences or both.

Environmental variance: Environmentally induced variation. The environment directly affects the development or expression of many features.

Temperature determines the sex in many turtles and crocodiles. Crowding on wing development in insects. See fig. 9.2 on page 217.

Maternal effects: effects of a mother on her offspring that are due not genes inherited from her, but rather to nongenetic influences, such as the amount or composition of yolk in her eggs, the amount and kind of maternal care or physiological condition while carrying the eggs or embryos.

Genes may cause congenital differences among individuals, by nongenetic maternal effects or by environmental factors that act on the embryo before birth or hatching.

Alcohol, smoking and drugs by pregnant women may cause birth defects in babies. These defects do not have a genetic basis.

Some variation seems to arise from random events at the molecular level. This is called Developmental noise.

In some organisms, e.g. fruit flies, there are measurable differences between the left and the right side of the body, which have the same genes and the same environment. These differences occur at random on either side. This is called fluctuating asymmetry.

Epigenetic inheritance occurs when the genome is modified without affecting the nucleotide sequence. This results in different functions of the genes.

These changes may remain throughout the life of the cell and may be passed on to daughter cells during mitosis.

DNA sequence remains unaltered. The expression of the gene is modified by non-genetic factors. Examples:

Histone modifications that affect transcription. DNA methylation X chromosome silencing

Genomic imprinting: Genomic imprinting is an epigenetic process that involves DNA methylation and histone modifications in order to achieve monoallelic gene expression without altering the genetic sequence. These epigenetic marks are established in the germline and are maintained throughout all somatic cells of an organism. http://en.wikipedia.org/wiki/Genomic_imprinting

Imprinted alleles are silenced and only non-imprinted alleles are expressed. The expressed genes are inherited only either by the mother or by the father. Genes are imprinted during gamete formation, either the egg or the sperm.

The parent who provided them to the offspring determines the expression of imprinted genes.

See: http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/I/Imprinting.html

To determine whether variation among individuals is genetic, environmental or both several methods can be used:

Testing for Mendelian inheritance by using the backcross method. Correlation between the average phenotype of offspring and that of their parents, or greater

resemblance among siblings than among unrelated individuals. Suggests that genetic variation contributes to phenotypic variation.

Rearing offspring from different parents in a common environment for a few generations help to distinguish differences due to genotype from maternal or environmental effects.

FUNDAMENTAL PRINCIPLES OF GENETIC VARIATION IN POPULATIONS

At any given locus, a population may contain two or more alleles that have arisen over time by mutations.

An allele may be more common that others and is often called the wild type. Some times two or more of the alleles are very common. The relative commonness or rarity of an allele –its proportion of all gene copies in the population–

is called the allele frequency. In sexual reproduction, alleles may combine forming a homozygous or heterozygous genotype. Genotype frequency is the proportion of a population that has a certain genotype. Genotypes may be homozygous or heterozygous in all its loci.

Any alteration in genotype frequencies in one generation will alter the frequencies of the alleles carried by the population’s gametes when reproduction occurs. The genotype frequencies of the next generation will be altered as well.

Such alteration from generation to generation is the central process of evolutionary change.

The factors that can cause the frequencies to change are the causes of evolution.

FREQUENCIES OF ALLELES AND GENOTYPES: THE HARDY-WINBERG PRINCIPLE

The principles states that a population at genetic equilibrium, allele and genotype frequencies do not change from generation to generation.

The principle shows that the process of inheritance by itself does not cause changes in allele frequency.

It also explains why dominant alleles are not necessarily more common that recessive ones.

Punnett Square of the Hardy-Weinberg Equilibrium A a

A AA p2 Aa pqa Aa pq aa q2

Example: p2 + 2pq + q2 = 1 where p is the frequency of the dominant allele B and q the frequency of the recessive allele b.

p2 is the frequency of AA. 2pq is the frequency of Aa. q2 is the frequency of aa. 1 is the total population.

The allele frequencies do not change from one generation to the next.

The genotype frequencies will remain unchanged.

Departure from genetic equilibrium (Hardy-Weinberg principle) indicates the amount of evolutionary change.

Change from generation to generation is sometimes called microevolution.

THE SIGNIFICANCE OF THE HARDY-WEINBERG PRINCIPLE: FACTORS IN EVOLUTION.

The following conditions have to be met for a population to remain in genetic equilibrium.

1. Random mating. Each individual of the population has equal chance of mating. Panmictic: random interbreeding population.

2. No net mutations. The frequencies of genes must not change due to mutations.

3. Large population size in order to avoid frequency changes due to random fluctuations.

4. No migration. There can be no exchange of genes with other populations that might have different allele frequencies.

Mating among individuals from different populations is called gene flow or migration.

5. No natural selection in order to avoid that some genotypes be favored over others.

The required conditions for the Hardy-Weinberg principle to work probably do not occur in the real world.

Obviously, the Hardy-Weinberg equilibrium cannot exist in real life. Some or all of these types of forces all act on living populations at various times and evolution at some level occurs in all living organisms. The Hardy-Weinberg formulas allow us to detect some allele frequencies that change from generation to generation, thus allowing a simplified method of determining that evolution is occurring.http://www.k-state.edu/parasitology/biology198/hardwein.html

Inasmuch as nonrandom mating, chance gene flow, mutation, and selection can alter the frequencies of alleles and genotypes, these are the major factors that cause evolutionary change within populations.

FREQUENCIES OF ALLELES, GENOTYPES, AND PHENOTYPES

1. At Hardy-Weinberg equilibrium, the frequency of heterozygotes is greatest when the alleles have equal frequencies.

2. When a rare allele is very rare, almost all its carriers are heterozygotes, and difficult to detect.

This is called concealed genetic variation

3. A dominant allele may be less common than a recessive one.

INBREEDING

Inbreeding is a form of nonrandom mating.

Gene copies are identical by descent if the have descended, by replication, from a common ancestor.

Inbreeding, coefficient of: A measure of how close two people are genetically to each another. The coefficient of inbreeding, symbolized by the letter F, is the probability that a person with two identical genes received both genes from one ancestor.http://www.medterms.com/script/main/art.asp?articlekey=3953©1996-2007 MedicineNet, Inc.

If the genes are identical by descent, the individual is said to be autozygous.

In self-fertilization or selfing, all loci are affected equally.

Inbreeding increases the proportion of homozygotes and decreases the proportion of heterozygotes.

For a good explanation of inbreeding coefficient see: http://www.netpets.com/dogs/healthspa/demyst.html

GENETIC VARIATION IN NATURAL POPULATIONS.

Morphology and viability

Genetic polymorphism is the presence in a population of two or more variants, alleles or haplotypes.

Multiples alleles: human blood groups.

The term includes genetically determined phenotypes and variations at the molecular level.

Experiments with fruit flies have shown that homozygous chromosomes often caused either death of the fly, caused sterility or reduced survival.

Studies on fruit flies and the mortality of children from marriages between relatives have shown that organisms carry several lethal recessive genes.

The average person carries 3-5 lethal alleles acting between late fetal and adult stages (Morton et al., 1956)

These genes are lethal only in the homozygous condition.

Natural populations carry an enormous amount of concealed genetic variation.

Inbreeding Depression

Inbreeding increases the proportion of homozygotes. Deleterious recessive genes will be expressed more often.

Populations with a high rate of inbreeding often show a decline in components of fitness like fecundity and survival. This decline is called inbreeding depression.

Inbreeding may increase the risk of extinction of small populations in the wild.

Inbreeding is a problem in captive populations and is highly controlled in zoo populations.

Genetic Variation at the Molecular Level

To know how much genetic variation is present in a population, it is necessary to find out what fraction of the loci are polymorphic, how many alleles are present in each locus, and what their frequencies are.

You should know what is electrophoresis and it works!

Enzyme electrophoresis is used to find the polymorphic loci.

Variant forms of an enzyme are called allozymes. They are coded by different alleles in the same locus.

Allozymes move at different rates depending on the amino acids that have been substituted.

Not all amino acid substitutions alter electrophoretic mobility; this causes an underestimation of the genetic variation present.

Results of a study conducted by Lewontin and Hubby on 18 loci of populations of Drosophila pseudoobscura.

In every population of Drosophila pseudoobscura about one third of the loci were polymorphic. This is equivalent to say that the average individual is heterozygous at 12% of all its loci. In one study, 28% of 71 loci were polymorphic in a human population.

The estimated number of polymorphic loci in humans is 3000.

Even with two alleles each, 3000 polymorphic loci could generate 33000 = 101431 genotypes.

Almost every human in a sexually reproducing species is genetically unique.

Populations are more genetically diverse than almost anyone had previously imagined.

Variation At The DNA Level

DNA sequencing distinguishes the extent of synonymous and non-synonymous nucleotide substitutions in the amino acid coding region of the DNA.

It is also possible to compare changes in the coding and non-coding regions of the DNA.

Chromosomal and mitochondrial DNA and RNA sequences have been used.

Considerable sequence variation, especially synonymous variation, has been found in most of the gene and organisms that have been studied.

GENETIC VARIATION IN MULTIPLE LOCI

Populations of most species contain a great deal of genetic variation.

The origin of all genetic variation is mutation but a lot of the genetic variation in the short term is due to through recombination.

In sexually reproducing eukaryotes, genetic variation results from:

Union of genetically different gametes. Independent assortment of non-homologous chromosomes Crossing over between homologous chromosomes.

Genes are transmitted to the next generation but genotypes are not transmitted.

Favorable gene combination may arise in an individual but if this individual mates with a member of the population, this combination will be lost immediately by the same process of sexual reproduction.

Recombination can either help or slow adaptation.

Genes that are found on the same chromosome are said to be linked.

Linkage refers only to a physical association and not to a functional association.

Linked genes tend to be inherited together.

Genes linked to a gene that is favorably selected for a particular reason, will also increase its frequency due its linkage to the favored gene. This is called genetic hitchhiking.

Recombination of alleles occurs during crossing over or non-homologous end joining.

Recombination is a common method of reappearing damaged DNA in bacteria and eukaryotes.

Also, non-random association of alleles can occur even when they are not linked on the same chromosome. It is a deviation from the expected random assortment of genes.

“Linkage disequilibrium is a term used in the study of population genetics for the non-random association of alleles at two or more loci, not necessarily on the same chromosome. It is not the same as linkage, which describes the association of two or more loci on a chromosome with limited recombination between them. Linkage disequilibrium describes a situation in which some combinations of alleles or genetic markers occur more or less frequently in a population than would be expected from a random formation of haplotypes from alleles based on their frequencies. Non-random associations between genes at different loci are measured by the degree of linkage disequilibrium (D).” http://en.wikipedia.org/wiki/Linkage_disequilibrium If there is no association of the alleles, the loci are in linkage equilibrium.

“Two loci are in linkage equilibrium if genotype frequencies at one locus are independent of genotype frequencies at the second locus; otherwise the two loci are in linkage disequilibrium.” http://evotutor.org/EvoGen/EG4A.html

“What causes linkage disequilibrium? Recombination breaks down non-random genetic associations, and yet in some cases non-random associations exist.

Causes of linkage disequilibrium:

1. Natural selection. If selection favors individuals with particular combinations of alleles, then it produces linkage disequilibrium.

2. The linkage equilibrium has not yet been reached because recombination is slow. It takes a number of generations for recombination to do its randomizing work and, particularly for tightly linked genes; linkage disequilibrium can persist for some time. Chromosome inversions and parthenogenesis have this effect.

3. Mixture of two populations: A population may have been formed recently by union of two populations with different allele frequencies and LD has not yet decayed.

4. Non-random mating. If individuals with gene A1 tend to mate with B1 types rather than B2 types, A1B1 haplotypes will have excess frequency over that for random mating.”

5. Genetic drift.

6. Mutations. A new allele created by mutation can cause associations with other alleles that did not exist before the mutation.

7. Founder effect. The genes of the founders are disproportionately more frequent in the new population.

8. Recombination may be very slow due to chromosome inversions and parthenogenesis.

Helpful websites:http://www.blackwellpublishing.com/ridley/tutorials/Multi-locus_population_genetics9.asphttp://hihg.med.miami.edu/code/http/modules/education/Design/Print.asp?CourseNum=5&LessonNum=2

VARIATION IN QUANTITATIVE TRAITS

Continuous (metric, quantitative, polygenic, continuous) variation of a character is the result of several genes located in different loci working to produce a given phenotype, e.g. nose shape and skin color in human.

These phenotypes vary along a continuous gradient.

These variations are said to be polygenic because they depend on the interaction of several genes among themselves and with the environment.

Many phenotypic traits, including morphological, physiological and behavioral features, exhibit polygenic variation.

Quantitative or continuous variation often approximated the normal curve, bell-shaped curve.

Heritability

Heritability is the variation of phenotypes due to genetic variation, genetic factors, in the population.

In general, physical characters are highly heritable, e.g. finger length, height.

The description and analysis of quantitative variation are based on statistical measures because the loci that contribute to quantitative variation generally cannot be singled out for study.

The amount of genetic variation in a character depends on the number of variable loci, the genotype frequencies at each locus, and the phenotypic difference among genotypes.

Variance quantifies the spread of individual values around the mean value. It measures how far the observations differ from the average, the mean.

A sample mean is an estimate of the true mean of the population being studied. The true mean can only be obtained by measuring every individual of the population.

The proportion of the phenotypic variance that is due to genetic variation, genetic variance, is the heritability of the trait.

Environmental variance is cause by the direct influence of the environmental factors on different organisms.

The variance in a phenotypic character (VP) is the sum of genetic variance and environmental variance.

VP = VG + VE

Each genotype in a population has an average phenotypic value.

Individuals with that genotype vary in their phenotypes because of environmental influences.

The amount of variation among the averages of the different genotypes is the genetic variance, VG.

The average amount of variation among individuals with the same genotype is the environmental variance, VE.

“By performing specific experiments quantitative geneticists can estimate the proportion of the total variance that is attributable to the total genetic variance and the environmental genetic variance. If geneticists are trying to improve a specific quantitative trait (such as crop yield or weight gain of an animal), estimates of the proportion of these variances to the total variance provide direction to their research. If a large portion of the variance is genetic, then gains can be made from selecting individuals with the metric value you wish to obtain. On the other hand if the genetic variance is low, which implies that the environmental variance is high, more success would be obtained if the environmental conditions under which the individual will be grown are optimized.” Heritability (h2) measures the part of phenotypic variability that is due to genetic variation, VG.

h2 = VG/(VG + VE) or h2 = VG/VP

Studies have shown that in many species the heritability of variation in a character is about 0.9 or 90%.

Responses to artificial selection

A character can be altered by selection only if it is genetically variable.

Artificial selection can be used to detect genetic variation in a character.

Under artificial selection, the reproductive success of individuals is determined largely by a single characteristic chosen by the investigator, rather than by their overall capacity for survival and reproduction.

Most of our domestic animals and plants are the result of artificial selection.

Evolutionary geneticist have concluded from experiments using artificial selection that…

Species contain genetic variation that could serve as the foundation for the evolution of almost all of their characteristics.

Many or most characters should be able to evolve rapidly.

VARIATION AMONG POPULATIONS

In a panmictic population all individuals have the potential to mate with all other individuals; there are no mating restrictions.

Few species consist of a single panmictic population, e. g. Devil’s Hole pupfish, the eel Anguilla rostrata.

Most species consist of separate population, with most mating taking place between members of the same population.

Populations of a single species in different geographic areas often differ genetically. This is called geographic variation.

A subspecies or geographic race in zoological taxonomy means a recognizable distinct population or group of populations that occupies a different geographic area from other populations of the same species.

In botanical taxonomy, subspecies names are sometimes given to sympatric, interbreeding forms.

Populations with overlapping range in which individuals frequently encounter each other are called sympatric, e. g. eastern subspecies of the Northern flicker. See example on pages 241 and 242.

Populations with adjacent non-overlapping ranges that come into contact are called parapatric, e. g. the hybrid zone of the Northern flicker in which hybrid forms of the eastern and western subspecies interbreed.

Populations with separated distributions are allopatric e. g. the eastern and western subspecies of the Northern flicker.

Hybrid zones are formed where the range of two subspecies overlap.

A gradual change in a character or in allele frequencies over geographic distance is called a cline.

There is direct relationship between latitude and body size in mammals and birds; this cline has been called Bergmann’s rule.

Larger body size reduces the surface area relative to body mass reducing heat loss: an adaptive geographic variation.

Cline refers to a gradual change in a character or allele frequency over a geographic distance. Clines in allele frequencies also occur. See fig 9.28 about AdhF allele frequency.

An ecotype is a population of a species adapted to a particular environment and having distinct characteristics different from other populations in other environments.

The distinct characters are the result of natural selection taking place in a specific environment.

See the study by Clausen, Keck ad Hiesey on ecotypes of Potentilla glandulosa, the sticky cinquefoil.

“Populations of a species usually exhibit at least some degree of genetic differentiation among geographic localities. This geographic structuring has several causes, such as social structure, mating system, dispersal capability, cohesion of parents with their offspring and habitat fragmentation. These processes lead to certain patterns of gene flow, genetic recombination, natural selection and random drift, which in turn have an impact on the structure (Avise 1994).”http://herkules.oulu.fi/isbn9514255364/html/x706.html

Gene flow

The exchange of genes between two populations is called gene flow or gene migration.

Gene flow is a common occurrence.

Gene flow is due to the movement of individuals or gametes, e.g. pollen ad spores.

Migrants that do not reproduce do not contribute to gene flow.

In a continuous distributed population, the probability of mating with individuals a greater distances decreases. This is called isolation by distance.

Gene flow tends to homogenize the allele frequencies unless is counterbalanced by genetic drift or natural selection.

Gene flow may introduce or reintroduce genes that had disappeared or become rare due to genetic drift.

Gene flow may reduce the chance of speciation. Gene flow causes populations to converge in allele frequencies.

The rate of gene flow measures the change allele frequencies per generation due to migration into the population.

If a population becomes extinct and the area is recolonized by individuals from several populations, the allele frequencies are a mixture of those among the source populations.

Different populations will be genetically similar if they had been recently founded by migrants from a single population.

Gene flow is greatest among mobile organisms, e.g. marine invertebrates with planktonic larva.

Animals that move little are generally divided into small, genetically distinct populations.

Gene flow by both pollen and seed dispersal is very restricted in many species of plants.

Allele frequency differences among populations

Populations that are found at the extreme distances of their range are seldom exchange genes. They are isolated by distance.

Isolation by distance produces populations with greater divergence in allele frequency than adjacent populations that exchange genes.

Nei’s Index of Genetic Distance is a measure of the genetic difference between two populations. It measures how likely it is that gene copies taken from two populations will be different alleles, given data on allele frequencies.

It measures how dissimilar two species or two populations of the same species are. “The genetic distance of Chimpanzees and Human beings is only 1.6% (they are about 98.4%

identical), suggests that Human beings and Chimpanzees last had a common ancestor about 5 million years ago, and that Chimpanzees are more closely related to Humans than they are to Gorillas (about 9 million years ago) and Orangutan (about 12 million years ago).” http://en.wikipedia.org/wiki/Genetic_distance

This index is used to construct phenograms.

Phenograms are diagrams that show the similarity and differences between populations. See fig. 9.32B.

Most genetic differences in a species occur between populations in different geographic regions than within the region. See the mtDNA study of McGillivray’s warbler on page 247.

DNA sequencing may be used to show the similarities between population by producing clusters of populations.

GEOGRAPHIC VARIATION AMONG HUMANS

Human races

Homo sapiens is a single biological species.

The number of human races is arbitrary. Between 3 and 60 races have been described.

Genetic differences among human populations consist of allele frequency differences only.

One early study of allozymes variation showed that about 85 % of the genetic variation in the human species is among individuals within populations, and only about 8% is among the major “races”.

Based on the slight allele frequency difference among populations, five major geographic clusters could be distinguished: sub-Saharan Africa, Europe-Central Asia, East Asia, Oceania and native America. No native Australians were included in the study.

In spite of these similarities, some loci show strong patterns of geographic variation: the sickle-cell hemoglobin allele is most frequent in parts of Africa, and cystic fibrosis mutations are most prevalent in northern Europe.

VARIATION IN COGNITIVE ABILITIES

General cognitive ability (IQ) appears to be substantially heritable, and the heritability increases with age from childhood to adolescence to adulthood and old age.

Despite that substantial heritability of IQ, there is abundant evidence that education and an enriched environment can substantially increase IQ scores.