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Biol 1309 - Adaptations

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Adaptation – what does it mean?

• Like the word fitness, the word adaptation can be confusing:

• evolutionary biologists use it differently from non-biologists. For example, someone gets laid off and talks about “adapting” to the situation by tightening financial belt. Although this means less money, it does NOT affect the genes or the evolutionary fitness

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The Adaptation word is confusing!

• in evolutionary biology, the term adaptation is used in two different ways:

1. can be a process: the change that occurs in a population over time as natural selection influences which organisms survive and reproduce in a particular environment

2. can refer to the result of the process: the traits that confer reproductive success

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Adaptation – our working definition

• An adaptation is any trait that allows an organism to be successful (to survive and reproduce) in a given environment

• Traits might include:physical manifestations (Thick fur, large flowers,

enhanced eyesightOR behavioral traits (hunting or evasion techniques)OR physiological traits (for example, ability to break down lactose)

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Adaptations are Inherited Traits

• Adaptations are traits that organisms inherit from their parents - NOTcharacteristics that are acquired after birth

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Adaptations – more info…

• Traits are NOT a matter of choice

– either has the genes for specific traits or not

• Even though a trait may not be visible in the young, it may be expressed later in life

– Different adaptations may be required at different points of an organism’s life

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Adaptation Trait – example of age

• fawns have spots that help to camouflage them, but they lose them as adults…

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Adaptations & Natural Selection

• Adaptations are the result of natural selection

• When natural selection acts on a trait that is correlated with increased reproductive success, then natural selection causes adaptive evolution– Individuals with that trait

are more likely to survive and reproduce at a higher rate than individuals without that trait.

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Examples of Adaptations

• Halophytes are plants that live in salty conditions

• These plants have several adaptations for the high salt environment:

– ability to conserve water

– either do not absorb salt through their roots or they excrete excess salt on their leaves

Spartina alterniflora (Cordgrass)

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Examples of Adaptations

– Salicornia sp. is able to survive if roots are covered with water for extended periods

– Can send out long runners over the sand to anchor in shifting sand and quickly produce new offshoots to survive if original plant is buried in sand

Salicornia europaea

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Drug Resistance Adaptation Example

• A lot of genetic variation in bacteria

• The antibiotic penicillin was discovered in the 1930s and mass produced in the 1940s during World War II– Used extensively and

was very effective in treating bacterial infections

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Drug Resistance Adaptation Example

• Within ten years of the end of the war, penicillin no longer killed some bacteria

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Drug Resistance Adaptation Example

• bacteria resistant to penicillin lived and reproduced, assing on the trait.

• Due to overuse, the number of bacteria that were resistant to penicillin increased with each new generation

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Examples of Adaptation – The Lion!

• African lions are large predators that can weigh up to 500 lbs

• Adaptions that make them successful predators include:– coloring to blend into

surroundings– lion's roar is used to

communicate with other group members and warn intruders of territorial boundaries

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Example of Adaptation – The Lion (cont.)

• Long, retractable claws to grab and hold prey

• A rough tongue helps peel the skin of prey animals away from flesh and flesh away from bone

• Loose belly skin allows the African lion to be kicked by prey with little chance of injury

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Example of Adaptation – The Lion (cont.)

• Lion manes are sexually selected traits that proclaim a male's fighting ability and nutritional status

• Both opponents and mates take advantage of this information to assess a lion's overall fitness, but the long, black mane that females desire and males respect has a serious drawback in the form of heat stress

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Example of Adaptation – The Lion (cont.)

• The consequence of this heat-related coloring is severe enough that lions in the hottest climates have little or no mane at all

• Raises the possibility that increased global temperatures may cause lions with dark, luxurious manes to be things of the past

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Innovation in Our Own Time

• Adaptations don’t evolve all at once

• Usually come about as a result of a series of mutations

– Mutation is an accidental, random, permanent change in a gene

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Innovation in Our Own Time E.coli!

• Lenski’s work with E. coli use of citrate

– Took a couple of thousand generations of growing on citrate

– Eventually came to be dominant

– Ability to feed on citrate came about as a result of a series of mutations

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Innovation in Our Own Time –more bacteria

• Evolution of soil bacterium, Sphingobium, into PCP eaters (Pentachlorophenol)

• kills the fungus that causes wood to rot

• Leached into soil

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Innovation in Our Own Time – pcp (cont…)

• Soil microbes couldn’t break down PCP

• Copley compared genes for PCP-degrading proteins with the other genes, discovered the enzymes Sphingobium uses to break down PCP are related to enzymes the bacterium already uses… Sphingobiumevolved 5 different enzymes to breakdown PCP

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Innovation in Our Own Time promiscuous proteins

• Proteins often do more than one job

• One of the proteins that Sphingobium uses to break down PCP is PcpC

• PcpC is a promiscuous protein can evolve new functions)

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Promiscuous Proteins (enzymes)

• Promiscuous enzymes usually do one job REALLY well and other jobs less well

• There is a constraint to the evolution of new protein enzyme functions, thus an organism might benefit from a protein doing something new

• The protein might carry out one process faster than it carries out the second

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Innovation in Our Own Time –multiple genes

• A multitasking gene may be accidentally copied

– This results in 2 genes that can make the same protein• One copy of the gene can evolve to make the slower

reaction even faster

• The other copy can continue to run original reaction at the same rate

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Innovation in Our Own Time –horizontal gene transfer

• Another way around this problem is called horizontal gene transfer

• Horizontal gene transfer occurs when a bacterium gets new genes and copies of genes they already have from another bacterium (imported genes)

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Innovation in Our Own Time –new rxns

• These imported genes can join in existing pathways

– Help the bacterium carry out new reactions

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Borrowing a Gene

• Gene recruitment and gene duplication -important for evoluting new adaptations

• Gene recruitment - an evolutionary transition where a gene is expressed in another organism, or another pathway

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Gene Duplication

• Gene duplication - a mutation that produces an extra copy of a gene

• New adaptations occur when existing adaptation, that might have a completely different function, is modified

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Differentiation?

• Egg and sperm fuse to produce a zygote

• The zygote develops into an embryo

• As the embryo develops, cells in different pats of the body begin to do different things -differentiate

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Differentiation (cont…)

• Some cells differentiate into:

– Bone

– Neurons

– Cardiac tissue

– Epithelium

• All the cells are using the same set of genes

• A source of the differences for these cells is a protein known as a transcription factor, a protein that binds to specific DNA sequences and influences how nearby genes are expressed

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Transcription Factors

• Some transcription factors can turn genes on, others turn genes off…

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Transcription Factors

• Genes for transcription factors can mutate and provide opportunity for patterns of new development

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The Genetic Tool Kit

• Transcription factors are essential for making the right proteins in the right places

– shape an organism’s entire anatomy

• different animals use the same genetic “tool kit” during development

• Networks of genes control the development of animal embryos – for example:

– Hox genes help determine what different segments in a fly embryo will become in the adult

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The Genetic Tool Kit

• The genes are arranged in the same order as they are expressed in the embryo

• Some expressed genes shut down other developmental genes start up.

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The Genetic Tool Kit

• For example, fly larvae cells express a gene called Distalless, or DII

• Genes produced at the back of the larva (Ubx, abdA, and AbdB) repress the DII gene

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Genetic Expressions are Different…

• Another gene, homothorax (hth), is repressed all the Hox genes (produced only in the fly’s head…)

• As a result, different segments make different combinations of proteins

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Gene Combinations and Body part Development

• Those combinations determine which body parts grow where:

– DII and hth genes together trigger the growth of antennae

– DII alone triggers the growth of legs or mouthparts

– No DII or hth means no appendages are produced at all

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Finch Beaks and Protein Levels

• Different species of finches grow dramatically different beaks

• Much of the variation is due to different levels of two proteins

– Calmodulin

– BMP4

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Recycled Feathers…

• Read about Recycled Feathers, pages 167-169 in The Tangled Bank

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Genetic Control of Body Plan

• Common ancestry of genes that control the overall body plan

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Fly vs Human!

• A fly:

– Segmented exoskeleton

– Soft interior

– Main nerve runs along the bottom of its abdomen

– Digestive system runs along its back

– Segmented legs

– Wings

– Hexagonal compound eyes

• Human:

– Endoskeleton

– Surrounded by muscle and tissue

– Spinal cord runs down the back

– Digestive system runs along abdomen

– Four limbs

– Eyes like little cameras

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Comparing Fly vs Mammal (mouse)

• Anatomically huge differences, genetically, not so much

• Basic body plans were built with the same basic genetic tool kit

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The Genetic Tool Kit

• Head-to-tail of a mouse is marked off by a set of genes called Hox genes

– Hox genes are a set of genes that regulates the development of animals

– Define the head-to-tail axis of bilateral animals

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The Genetic Tool Kit• Mice and most vertebrates

have 4 sets of Hox genes

• Each set is arranged along a chromosome in the order it is expressed from head to tail in the body

• Flies have a related set of Hox genes that do the same thing

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Interchangeable Genes?

• Hox genes in mice and flies are so similar they are literally interchangeable -replace or shut down Hox gene in a fly and insert the corresponding Hox gene from a mouse, the fly will develop normally

• Read Evolving Eyes, pages 172-180, in The Tangled Bank

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Constraining Evolution

• Why are there no 9-toed tetrapods?

• Why are dragonflies no longer as big a hawks?

• Constraints on evolution

– Limits

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Constraining Evolution

• Why are dragonflies so small?

• Environmental factors

– Chemistry of the planet changed

• Insects get oxygen through small tubes in their exoskeletons

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Constraining Evolution – insect size

• As insects got bigger, they needed more oxygen to support their larger bodies

– Needed more and more tubes to get enough oxygen to support the bigger bodies

– Tubes are an inefficient way to get oxygen into a big animal

• In bigger insects, the tubes would occupy a bigger proportion of the body

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Constraining Evolution – limited resources

• The higher level (pulse) or initial oxygen may have temporarily lifted constraints on insect size

• When the oxygen levels leveled out, big insects no longer supported

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Genes Constraining Evolution

• Genes can constrain evolution

• Make it difficult for certain developmental programs to evolve

• May be why there are no 9-toed tetrapods

– Pleiotrophy: influence of a single gene on several phenotypic traits

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History Constraining Evolution

• History can constrain evolution

• New adaptations do not come about from nothing

– Must have something to work with

– Modification of already existing structures, pathways, etc

• Evolution of two lineages into similar forms is called convergent evolution

– Similar adaptations

– Use different routes

– Dolphins have a tapered body and a fluke at the end of its tail

• Generates force like a bird’s wing

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Convergent Evolution

• Sharks and tuna have similar body plans

• Allows them to move efficiently through the water

• Dolphin’s fish-like body evolved through the loss of their hind legs

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Convergent Evolution

• Leaves us with the question: Are these the same species?

• Depends on what level you look at to answer the question

Smilodon, N& S America, related to catsThylacosmilus, SA, related to kangaroos