Chapter 22 Descent With Modification

Classification of Species, a history

• Aristotle (384-322B.C.E.)

– Species fixed, unchanging, eternal world, absolute

– Scala natura

• Life forms arranged in linear order of perfection

• Carolus Linnaeus (1707 - 1778)

– Binomial nomenclature

• Homo sapiens

– Nested classification based on similarities

• Birds/bats

• Systema Natura book

Carl von Linné

Fossils

• Remains or traces of organisms from the past

• >10,000 years old

• Organism dies sediment compression rock strata

• Paleontology = study of fossils

Fossils buried in strata

• Charles Lyell, geologist (1797- 1875)

– Uniformitarianism, Earth changes slowly and continually

– Change NOT due mainly to catastrophes

– Examples of slow processes

– Wind, erosion, water flow

• Lamarck (1744-1829)

– Evolution explains change in fossils over time

• Theory of use and disuse

• Theory of inheritance of acquired characteristics

– Both not correct

This is a big tree dwarfed by many years of cuttingWhat size plant will seeds from this Bonsai produce?

Charles Darwin (1809-1882)Descent with modification (evolution)

Alfred Russel Wallace came to same conclusion just before Darwin published

The Origin of Species

Voyage of the Beagle

Observed plants, animals

Darwin’s observations and inferences

• 1. Adaptations

– Characteristic of organisms enhance survival

– Adaptations could lead to new species

• Galapagos finches

Each on a different island

• 2. organisms descend from a common ancestor

– Unity of life

– Can be represented as a tree

– Millions of years

Species grouped by evolutionary relatedness!

Mechanism of Natural Selection

A. Members of a population vary in traits

Genetic diversity

B. Traits are inherited from parent to offspring

C. More offspring produced than environment can support

D. Those with beneficial traits survive AND reproduce successfully

(survival of the fittest)

E. Populations change over time

F. Can lead to speciation

Note:

• Individuals do not evolve, populations do

• Only heritable traits are passed on

• Environmental factors vary!

Evidence for Evolution

I. FOSSILS

document change in living organisms over time

Example

Whales have a terrestrial , 4 legged, ancestor

Bones suggest a cow- like animal

50 mya

II. HOMOLOGOUS STRUCTURES

Reflect a common ancestry

Shared features

1. Skeletal structures

common mammalian ancestor

Function/name?

Homologous structures (cont.)

2. embryology- shared developmental plan

Homologous structures (cont.)

3. Vestigial structures

served function in ancestor, function lost, but structure remains

Snakes retain vestige of pelvis

Ancestor to snakes had legs

Homology (cont.)

4. Genetic homology

universal genetic code

supports evidence for relatedness of species

Beta globin amino acid sequence

DEVGGEALGRLLVVYPWTQRYFDSFGDLSSASAI Mus musculus

DEVGGEALGRLLVVYPWTQRYFDSFGDLSSASAI Rattus norvegicus

DEVGGEALGRLLVVYPWTQRFFESFGDLSTADAV Bos taurus

• Convergent evolution

– Sometimes distantly related species have similar structures

– Evolved separately (arose more than once)

– Example: mammals

marsupial

Rodent (placental)

III. BIOGEOGRAPHY

Geographic distribution of species

Affected by continental drift

slow movement of continents over time

250 mya Pangaea

As continents move, species disperse, environmental changes

Example: endemic species found in one location BUT, have relatives nearby

Island species colonized by mainland species

IV. Direct documentation of evolution

Peacock sexual selection

http://www.youtube.com/watch?v=T7ftXEQvnyU

Direct documentation

– Predators influence natural selection

– Prey adaptations to avoid predation

• Male guppies

• Color genes expressed in males only

• Predators attracted to color

• Sexual selection

– Females attracted to colors

Observations

Pool 1 with few predators: brightly colored males

Pool 2 with many predators drab males

Add brightly colored males to pool 2 over 15 generations, males more drab

Why?

Rosemary and Peter Grant, Princeton University

• In 1981 an unusually large male finch from Santa Cruz arrived on Daphne Major.

• The biologists tagged the bird number 5110, and followed him and his offspring through seven generations total.

• In the fourth generation drought killed off all descendants except one male and one female.

• These offspring can only breed with each other because they have strange bird song. Finches learn their songs from their father, and the Grants suggest that 5110 sang the songs from his birth home of Santa Cruz then modified his mating song by roughly copying the Daphne Major birds’.

• This imperfect copying has, over time acted as a barrier to breeding with other finches . So the immigrant bird’s descendants have bred only with each other for three generations.

• New species?

The Grants won the Kyoto prize for their life work

Theory

• Unifies many observations

• Supported by all evidence

• Predictions stand up

Chapter 23 The Evolution of Populations

0rganisms do not evolve

• Microevolution

– Change in allele frequencies in population over time

– Affected by

• Natural selection

• Genetic drift

• Gene flow

23.1 Genetic Variation

A. Genetic Variation: Variation within a population

Discrete characters

one gene

Quantitative characters

vary along continuum

two or more genes

• Gene variability in a populationaverage heterozygosity f (Aa)information about genetics of a population

• High heterozygosity = high genetic variability• Can range from 0 to 1

Fruit fly has ~ 13, 700 genesOn average 1,920 are heterozygous (14%)

• Very low heterozygosity in cheetahs indicate severe effects of small population sizes

Originated about 4 million years ago and was common in Europe, North America, Asia , Africa. They disappeared about 10,000 years ago from North America when major climatic changes took place. Also disappeared from Europe and most in Asia and Africa vanished. Present populations derived from inbreeding by very few surviving and closely related animals. Every one is nearly identical.

B. Genetic Variation: Variation between Populations

• Geographic variation, ex. Mus musculus

Islands of Madeira – mice brought 15th century

several populations have evolved in isolation

Portugal

Populations descended from single ancestral population, changes in chromosomes (not genes)

Geographic cline

Graded change along geographical axis

Mummichog fish cline in cold adaptive allele

Mutation

Ultimate source of new alleles

Relevant only if in sperm/egg

Mutation: Point mutations

one base pair change in DNA

possible effects:

-none – does not change amino acid sequence of protein

-harmful – protein function compromised

-beneficial - rare

Mutations that alter gene number or sequence

• Gene duplication

– May expand the genome with no negative effects

– Mammal ancestor had 1 odor gene duplication

• Humans have 1,000 olfactory receptor genes– 60% inactivated in later mutations

• Mice have 1,300

Jianzhi Zhang and colleagues (Univ. Michigan)

• Paper (handout)

• Homework – article analysis

Sexual reproduction

• Leads to genetic diversity

– .crossing over during meiosis

– . Random segregation of alleles into gametes

– . Independent assortment

– (and mutation)

Hardy Weinberg Principle

• A population that is NOT evolving :

(hypothetical population)– No mutations

– Random mating

– No natural selection

– Extremely large population

– No gene flow

• Change in any one of these change in allele frequencies evolution

23.3 Allele Frequencies (cont.)

• Affected by:

1. Natural Selection

• Differential success in survival and reproduction

• Allele frequencies different in each generation

• Adaptive evolution

– Some alleles favored over others

– These increase in frequency with time

Adaptation (at population level)

DDT is a pesticide used beginning 1940s banned in 1972

• Example: Drosophila

• 1930s wild strain – no DDT resistance gene

– zero tolerance to DDT

Figure: increase in frequency of pesticide resistance in mosquitos after spraying with DDT. A sample of mosquitos was captured at each time indicated and the number that were killed by a standard dose of DDT (4 % DDT for 1 hour) in the laboratory was measured. From Curtis et al. (1978).

Adaptive evolution

2. Genetic Drift

• Chance events can cause allele frequencies to vary

The founder effect

A. A few individuals become isolated from population

B. The new population has different allele frequencies than the main population

• Founder effect examples:

• Few individuals wind up on island during storm

• A few individuals are cut off by an earthquake

Founder effect

Bottleneck effect

– Sudden drastic population reduction

– Lessens genetic diversity

– Example: greater prairie chicken

• 1800s – millions in Illinois

• 1993 - 50 birds in 2 populations

– Low genetic diversity

– 50% of eggs hatch

Genetic Drift, summary

• Significant factor in small populations

• Allele frequencies can change wildly with generations

• Genetic variation is lost

• Harmful alleles may become fixed in population

23.4 Natural Selection is a mechanism that causes adaptive evolution

• A blend of chance and sorting as natural selection favors certain alleles.

• Relative fitness

– Relative contribution individual makes to gene pool of next generation

• Note: the organism is subject to natural selection, populations evolve

• Directional selection– extreme phenotype

most fit

– f(alleles) in population shifts in a direction

• Example: deer mice– Dark favored, live

among dark rocks

– Why is this a beneficial trait?

Disruptive selection– Individuals of both

extremes most fit

• Some mice colonized white rocks, some dark

• What happened to the intermediate color mice?

• Stabilizing selection

– Intermediate phenotypes favored

Example: birth weight in humans

Examples of adaptations

• Cuttlefish

• Adaptation?

Snake adaptation

• Sexual selection

– Individuals with certain inherited characteristics more likely to obtain mates

• Can lead to sexual dimorphism

– Differences between males and females

• Intrasexual selection

– Individuals of same sex compete for mate

• Intersexual selection

– Mate choice

– Showy tail in peacocks advertises fitness to female

– Showiness may be risky

• Ex. guppies

Preservation of genetic variation

• Diploidy

– Allows recessive alleles to be maintained in population in heterozygotes

– Maintains genetic diversity

The heterozygote advantage

– Sometimes a heterozygote has greater fitness!

– Beta globin gene encodes subunit of hemoglobin

Genotype Phenotype

SS =

Ss =

ss =

Heterozygote advantage

• Frequency of s allele highest in areas with malaria

Why natural selection cannot fashion perfect organisms

1. Selection can only act on existing variation

2. Evolution builds on what is present in organism alreadyEx. terrestrial lineage of whales, bats

3. Adapations are compromisesEx. shoulder joint (human)

4. Evolution based on interaction between chance, environment

Ex. wind storm kills many insects, including most fit

Chapter 24 Origin of Species

Speciation

• Process by which one species splits into two or more

• Unity of life – species evolutionarily related

• Microevolution

– Change in allele frequencies in populations

• Macroevolution

– Change over geological time speciation

Biological species concept

• Species is a group whose members can interbreed (and produce fertile offspring)

• Share a gene pool

• Reproductive isolation

• Pre-zygotic barrier

– Sperm from one cannot fertilize egg from another

– Why?

• Habitat isolation, temporal isolation, behavioral isolation, mechanical isolation

Mates late winter Mates late summer Misalignment of genital openings

Different sperm proteins

• Post-zygotic barrier

– Hybrids are infertile

– Example: mule

May not survive

Mechanisms of speciation

• Allopatric speciation

– A population is divided geographically

– Each group continues to evolve, but separately

salamanders

• Natural selection

– Selects for different traits depending on environment

• Genetic drift

• Speciation occurs - When populations are reintroduced – do not interbreed (reproductive isolation)

Sympatric speciation

• Gene flow reduced between members of same population/same geographical area

• Ex. Polyploidy

– Extra set(s) of chromosomes

– Not uncommon in plants

Sympatric speciation (cont.)

• Can be driven by habitat

– North American maggot fly lived in hawthorn tree, then, some colonized apple trees. These flies developed faster, now, temporally isolated (mating on

apple tree flies is 3 wks earlier)

Rhagoletis pomonella.

Hybrid zones

Both frogs found in the hybrid zoneHybrids have high embryonic mortality and anatomical abnormalities

• Hybrid zone outcomes:

1. Reproductive barriers strengthened

• Limits hybridization

2. Barriers weakened

• Species fuse into single species

3. Stable hybrid zone

Genetics of speciation

• Identify genes that control traits involved in reproductive isolation

• Ex. Japanese snail, Euhadra

– Single gene controls shell spiral direction

Chapter 25

• History of Life on Earth

The Fossil Record

• Record of life on earth over time

• Incomplete record/limited

• Radiometric dating of strata

– Decay of radioactive isotopes

– Half life = time for 50% of isotope to decay

C-14 half life = 5,730 years

C-14

C-14 dating not effective > ~75,000 years

Measure C-12/C-14 ratio

• For older fossils in rocks

– Use K-40 (1.3 billion year half life)

Key Events in Life’s History

Geological eras of life

1. Paleozoic

2. Metazoic

3. Cenozoic

The first single celled organisms 3.5 bya

Stromatolites

Microbes bind thin layers of sediment

Large amount of biomass/communities

Algal biscuits fossils

May have contained cyanobacteria, algae, eukaryotic cells……

Oscillatoria

• The first eukaryotes 2.1 bya (older?)

– Single celled

– Nucleus

• Multicellular animals > 535 mya

– Soft bodied, small

– <1 meter

The Cambrian explosion

• 535 mya

• Cnidaria, Porifera, Mollusca fossils

Cambrian explosion lasted ~40 my

• Larger animals

• Hard shells

• Predator/prey evolution

500 mya trilobite

The colonization of land by animals

• 500 mya

• Adaptations to prevent dehydration

• Tetrapods ~ 365 mya

Mass Extinctions (5)

• >50% of animals extinct in “short” period of time

1. Permian extinction

– 250 mya

– 95% of marine species extinct

– Most terrestrial species

Cause: Oxygen deficit?

– Neil Tyson DeGrasse

2. Cretaceous extinction 65 mya

Most marine and terrestrial species including dinosaurs

Cause: asteroid

hot vapor, debris

blocked sunlight? 10 km

Consequences of mass extinctions

• Once a species is extinct, it does not return!

Adaptive radiation

• Periods of evolutionary change in which new species adapt to fill different ecological roles

• Occurred after each mass extinction

• Example: Cretaceous mass extinction 65mya

– Mammal radiation

Evolution is not goal oriented

Chapter 52 Ecology and the Biosphere

Ecology

• Study of the interactions between organisms (biotic factors) and the environment (abiotic)

• Environmentalism

– Advocating for the protection of nature

• Red kangaroo (Macropus rufus)

– Abundant in interior Australia – dry climate

– Not found along coast – wet

– Hypothesis? Abiotic factor? Biotic?

• Moisture, predator, temperature, food, competition, disease

• “ The ‘control of nature’ is a phrase conceived in arrogance, born of the Neanderthal age of biology and philosophy, when is was supposed that nature exists for the convenience of man”

• Efforts led to a ban on DDT

• Silent Spring (1962)

Rachel Carson

Factors affecting species distribution

1. Dispersal and distribution

A. Range expansion

Movement of individuals away from area of origin

B. Transplants

– Intentional or accidental

Kudzu, a Japanese invasive vine growing in Georgia, US

Brown tree snake (from Australia)has eaten all Guam Flycatcher, Rufus Fantail, Bridled White-Eye and Micronesian Honeyeater eggs, now eating the Mariana Crow, the Guam Micronesian Kingfisher, the Island Swiftlet and the Mariana Fruit Bat.

• 2. Habitat selection and behavior

A. Behavior

An individual may avoid a certain habitat even though it is suitable

Corn borer moth prefers to lay eggs on corn even though larvae can feed on other plants

B. Biotic factors that affect species distribution

– Parasitism, competition, pollinators, predators, food source…

• C. Abiotic factors

– Temperature, water, salinity, sunlight, soil

– Vary spatially and temporally

• Temperature

– Cells rupture <OoC

– Proteins denature>45oC

– Metabolic rate may be affected by T

• Water

– Dehydration

• Salinity

– Osmosis

– Example: freshwater fish gains water -it is adapted to excrete water.

• Sunlight

– Photosynthesis

• Rocks, soil

– pH, minerals, substrate

Chapter 54

Community Ecology

1. Competition

• Interspecific competition

– Individuals of different species compete for a resource

– Limits growth and survival

• Canadian lynx and fox compete for snowshoe hare

Outcomes of competition

• Competitive exclusion

– Paramecium experiment (G.F. Gause, 1934)

P. aurelia + P. caudatum

Competition for food source

P. caudatum dies

Even a slight advantage will lead to

disappearance of less fit species

P. aurelia P. caudatum

• Niche development– Niche = species use of both abiotic and biotic resources (habitat is

“address” niche is “profession”)

– Example: Anolis lizards in DR

Niche (continued)

2 similar species can coexist in same community if niches are different

Resource partitioning in Anolis lizardsA. distichus prefers sunny twigs A. insolitus prefers shady branches

Hypothesis: competition in the past selected for individuals using different sets of resources

The fundamental niche of distichus may be sun and shade, but its realized niche is sun – how could this be tested?

Anolis lizards, resource partitioning

Fundamental and realized niches in barnacle species (Joseph Connell, Scotland, 1961)

Balanus cannot survive on high rocks, it dries out during low tide – compare fundamental and realized nice

• Character displacement– Observed in sympatric populations (overlapping ranges)

– Divergence of body structure and resource use

Twig anole Trunk anole Trunk ground anoleBahamas and Cuba

2. Predation• Predator adaptations

smell, sight, claws, stingers, teeth, aggressive mimicry

• Prey adaptations

hiding, herds, alarm calls, cryptic coloration aposematiccoloration, Batesian mimicry, Mullerian mimicry

Zebra Vervet monkey

Aposematic and cryptic coloration

Golden poison frog A warning coloration to indicate a toxic defense(alkaloid toxin –batrachotoxin in skin - one frog could kill 20 humans)

• Batesian mimicry

– A harmless species mimics a harmful one

Hereroplanes ornatus (hawk moth larvae)

• Mullerian mimicry

– Two or more unpalatable species resemble each other

– Each species gains additional protection

Both untasty

• Aggressive mimicry

– Predator shares feature with harmless model to attract prey

“flower“ lantern tongue “worm”

3. Herbivory• Interaction in which organism eats plant or

algae

• Adaptations – smell, teeth, digestion

• Plant defenses

– Chemicals – peppermint, strychnine, nicotine

– Spines, thorns

4.Symbiosis

• Two that live in direct contact

• May be harmful, neutral, or helpful

• Parasitism

– One organism (parasite) derives nourishment from another (host)

– Endoparasite lives within host

– Ectoparasite – lives on host

plant root

• Parasites affect:

– Survival

– Reproduction

– Population density

– Behavior

• Lake Superior Island • 70,000 ticks per moose hair damage,

blood loss increase chance of cold stress, wolf predation

• Mutualism

– Benefit both species in a relationship. Ex. acacia and ant

Central America, ant hollows out large thorns of the acacia plant for nests, feed on secretions from four nectariesat the base of each petiole and on the protein rich tips of the leaves, which together provide an almost complete diet for the ant.

The ants protect trees from invertebrate as well as vertebrate herbivores. With movement of the branch, the ants emerge releasing a nasty odor and physically attack the herbivore.

• Commensalism

– One species benefits, the other is not, but is not harmed

Cattle Egret often seen in the company of grazing animals. The grazers stir up insects, which the egret eats. There is no apparent benefit to the cattle.

The birds will also follow mowers……

The clownfish slowly accustoms the anemone to the chemical makeup of the fish's skin; this gradual acclimatization prevents the anemone from stinging the clownfish. The fish gets a safe habitate and some food; the anemone gets cleaned clownfish chasing away fish that would harm the anemone, may attract prey. Some scientists do not see any benefit for the anemone and classify this as a commensalism.

?

Costa Rica. Tree sloth has algae growing in its fur. Algae help to camouflage the sloth against the lichen-covered tree (note brown fur of baby, not covered with algae).

A moth lives only in the sloth's fur and consumes the algae. What is the relationship between the moth and the sloth?Xenarthra

Each sloth can host 100 moths and 1000 beetles. The entire life cycle of beetle and moth is connected with the sloth, each spending its larval period in sloth dung, and their adult period eating the algae.

Effect of Interaction On:

Type of Interaction Species 1 Species 2

Competition (-) (-)

Predation Predator ( ) Prey ( )

Parasitism Parasite ( ) Host ( )

Herbivory Herbivore ( ) Plant ( )

Commensalism ( ) ( )

Mutualism ( ) ( )

Species in communities

• Species richness = the number of different species in a community

• Relative abundance = number of each

Community 1: 25A, 25B, 25C, 25D = 4 species of same relative abundance

Community 2: 80A, 5B, 5C, 10 D……..?

• Trophic structure

– Feeding relationships between organisms

Food chain

Primary producers primary consumers secondary consumers decomposers

Food web

Linking food chains

• Food web links food chains

• A species may be in web at different trophic levels

Species with a large impact

• Dominant species

– Most numerous

– More biomass

In temperate bogs the dominant vegetation is usually species of Sphagnum moss

Foundation species

primary producer

Kelp in kelp forest , CA

• Keystone species

Beaver are well-known for building dams. These dams create relatively large areas of still water where there once was a small stream. For organisms that live in such still waters the beaver is a wonderful keystone mutualist; for animals that like flowing water it's not such a good deal.

• The American Alligator, left, excavates depressions in its habitat that fill with water. During dry times, these gator holes may be the only places with water. Thus, to all the organisms whose survival depends on the water in those holes the alligator is a keystone mutualist. Of course, the gator might eat a few of those things that come to live in its wallow.

Community Ecology is useful for understanding pathogen life cycles and controlling disease

• Pathogens can alter community interactions

• Coral reef communities

– White band disease kills corals

• Zoonotic disease

– Transferred from animals to humans

– Direct contact or vector

– Parasite life cycle

– River blindness and black flies

– Avian flu tracking