Adaptation

• What is an adaptation?

• It is a genetically based trait, or integrated suite of traits, that increases the fitness of its possessor.

What is adaptation.

• Adaptations come about in response to a problem. That is, it is achieved through the process of natural selection.

• It is through the adaptations brought about by natural selection that organisms appear to be well designed.

Identifying Adaptive Traits

• Not all traits are adaptive– Learned traits– Traits that were originally adaptive for one

problem, now used to fix another.– Traits that have no current benefit toward

fitness i.e. molecular genetic drift

• Traits must be rigorously tested to determine whether they are adaptive

All hypothesis must be tested

• Hypothesis are tested by 1. using the hypothesis to make predictions

2. Next, the predictions are tested by either - experimentation,

- observation,

- Or comparative studies

3. Then the test are analyzed to determine if the predictions are correct.

The Giraffe’s Neck

The Awkwardness of Giraffes

• Why are Giraffes so tall?

• Is it an adaptation?

• What is it an adaptation for?

Giraffe’s Neck Reconsidered• Simmons and Scheepers

conducted studies to observe whether the giraffe’s long neck was used to gain an advantage in forging.

• They found that giraffes most often feed on foliage that is at shoulder height.

• In times of drought when foliage is scarce they feed on low brush

• Giraffe adaptation

• The giraffe neck was actually adapted as a means of defeating other males in a battle over females.

• Bull giraffes employ their heads and necks as clubs and occasionally even kill each other.

If the giraffe neck was actually selected for as a means of defeating other males in a battle over females. The neck is now coopted for use in feeding higher in the trees than other organisms can.

• Is this adaptation?– Adaptation: a trait or integrated suite of traits that

has evolved in response to selection for the function that it currently performs and that increases the fitness of its possessor. (fighting)

• The giraffe’s neck is an exaptation when it is used to eat leaves off tall trees.

Exaptation

• The term exaptation refers to situations in which traits perform a certain function now but either arose for some other function or originally had no function at all.

• A type of exaptation in which there was no original function is called spandrel

Example

• In male giraffes long necks were originally adapted for fighting then their current advantage for feeding would be an exaptationexaptation (arose for a different adaptive reason)

• but in females long necks would be a spandrelspandrel since they originally arose with no adaptive value for females but now may impart a feeding advantage.

Points to Consider

• Should differences among populations or species always be considered adaptive?

• Exaptive?– Spot patterns on

giraffes

Masai giraffe Reticulated giraffe

How do We determine whether a trait is an adaptation?

• Three major approaches to determining adaptive significance of traits – Experiments– Observational studies– Comparative studies

Experimental exampleZonosemata (snowberry) flies and jumping

spiders

• What is being investigated?

Zebra Jumping spiders stalk their prey.

Warn others of their species off with leg waving behavior

A prey of the jumping spider, the snowberry fly, exhibits a curious behavior that resembles the leg-waving of the jumping spider.

QUESTION: Why do the flies wave their striped wings?

Experimental exampleZonosemata flies

• What are 3 hypotheses that might explain this behavior?

Experimental exampleZonosemata flies

• What were some of the controls used in the experiment and why was each important?

•What was the experimental set-up

Experimental exampleZonosemata flies

• What predictions were made?

Experimental exampleZonosemata flies

• What were the experimental results?

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RESULTS

Observational Studies

• When are these type of studies done?

• When experiments are impractical or inappropriate, observations can yield sufficient information to evaluate a hypothesis– Experimental study: Why giraffes have long necks?

Observational Studies

• Observational studies must employ the following criteria:

1. Hypothesis must lead to observed predictions.

2. Observed occurrence of the trait must be shown to be non random in the population.

3. The observed trait is adaptive

Example – Garter Snake study

Show they are choosing a particular temperature more often than would happen by random movements

• Watched snakes, where they spent their time and what their body temps were

• Found that they maintain their body temperatures between 28 and 32 degrees Celsius.

• Discovered options for thermoregulation

sun/shade

under rocks ( thin,medium, thick)

moving up or down in burrows

Found that of the 3, all could be used to effectively maintain desired daytime temps but only rocks could provide enough warmth at night

• Studied thin, medium and thick rocks.

• Predicted only medium rocks work for the right temps both night and day.

• Most snakes found under rocks.

Now have to show that being under

medium rocks is not random behavior

• Compared availability of thin, medium and thick rocks in the habitat to the frequency that each was used by garter snakes

• All rocks are equally represented in the habitat so if random events, the snakes should be found equally under each type of rock.

• Results ….

Comparative Studies

• Compares traits across different species lines

• Proper application of comparative methods requires knowledge of the evolutionary relationships among the species under study.

Example of comparative studyBats

• Question– Why do some bats have bigger testes than

others?

• Hypothesis: – David Hosken hypothesized that large testes

are an adaptation for sperm competition

• Prediction– If you compared different species of bats,

those that form larger social groups will have larger testes because there is more competition for passing on their genes?

Studies initial showed correlation between social group size and testes

size.

However a closer look indicates that the data could be skewed by evolutionary relationships.

• Perhaps the larger testes groups are simply from one common ancestor and the smaller from another.– Example

If we replace the individual points for A, B and C and for D,E and F with a single point representing their most recent common ancestor we get….

But two data points is not very reliable for making extended conclusions.

A better question: when species diverge form a common ancestor does the species that evolves larger group sizes also evolve larger testes?

Plot sister species independently

Drag point closest to the vertical axis to the origin

Erase lines

Felsenstein method

Felsenstein’s method

• Each data point represents the divergence that arose between a pair of sister species as they evolved away from their common ancestor.

Bat results: show that when a bat species evolved larger group sizes than its sister species, it also tended to evolve larger testes for its body size.

Phenotypic Plasticity

Section 9.5

Phenotypic Variation

• Phenotypes are influenced by the environment • Total variation is called the phenotypic variation

and it has two components: VG and VE.

– contributions come from both the environment and the genetic makeup

• Phenotypes may respond in different degrees to different environmental situations

Phenotypic Plasticity

• When an individuals phenotype is influence by its environment it is said to be plastic.

• When phenotypes are plastic, individuals with identical genotypes may have different phenotypes, provided they live in different environments.

Can plasticity be adaptive?

1. Show that the plastic trait is positively selected for

2. show that individuals that are plastic for the trait are more fit than those who are not plastic

Daphnia magna: The water flea

• Tiny crustacean that lives in freshwater lakes.

• Daphnia reproduce asexually (clones).

• Thus researchers are able to grow genetically identical fleas in different environments

The Water flea Experiment

• Researchers studied 10 clones (genotypes) from each of three different lakes.

• They were grown in 2 different environments – One where fish predators had lived and one where

fish had not lived.

• checked phototactic (to light) response in the two different environments

Water Flea Results

• The Daphnia from Blandaart lake, where fish are present, were much more plastic in their ability to respond to light than Daphnia from lakes that had no fish

• Showed that selection for phenotypic plasticity has been selected for in a lake where fish are present.

Phenotypic Plasticity

• The Phenotypic plasticity is the result of differences in phenotypic expression (for a given genotype) based on the interaction of specific individuals with the environment in which each lives.

• Phenotypic plasticity may evolve.• Phenotypic plasticity may or may not be

adaptive.

Tradeoffs and constraintsTradeoffs and constraints

Factors that limit adaptive evolution

Trade-offsTrade-offs

• Two evolutionary forces may work on the same part from different directions and the resources devoted to one body part or function may be stolen resources from another part or function

• Giraffe’s long neck may allow to fight off competition but it sure makes getting a drink inconvenient, difficult and maybe even dangerous.

A trade-offtrade-off example The Begonia

• In Begonias there is a trade-off between the size of female flowers and the size of the inflorescence. Even though larger female flowers attract more pollinators, the female flowers remain smaller than optimal for pollination because bees also visit larger inflorescences and larger inflorescences can not contain individual flowers as large as the optimal flower size alone would dictate

• trade-off between the number of female flowers and individual flower size may be dictated by two things. 1) more flowers, more seeds and 2) perhaps more bees will be attracted to larger inflorescences

ConstraintsConstraints

• Constraints are factors that tend to slow the rate of adaptive evolution. – They prevent a population from evolving a

particular trait to its optimal value.

Two types of constraintsconstraints

• DevelopmentalDevelopmental – based on how an organism develops in embryo or how an organisms structure is related to function.

• PhylogeneticPhylogenetic – (Historical constraint) based on inheriting the needed genetic variation from its ancestors

ConstraintsConstraints

• Fuchsia excorticata– Is pollinated by birds– Flowers turn from

green to red– Researchers realized

the color changed to red after polination.

ConstraintsConstraints (developmental example)

• Why does the Fuchsia retain its flowers and turn them red for 5 days AFTER pollination?– Pollinators are no longer visiting, the flowers

are of no more use but are still tapping needed resources.

• Investigations showed that it was a cue for pollinators.– telling pollinators which flowers not to visit.

ConstraintsConstraints (developmental example)

• The pollen tubes need to grow through the area of the abscission layer.– When the petals drop an

Abscission zone develops and blocks the pollen tubes.

• If petals are dropped too soon the pollen tube never makes it to the ovules.

Genetic variation

• ConstraintConstraint may also occur due to a lack of the genetic variation needed to allow the adaptation that appears to make so much sense yet never occurs.

Question?Question?

• What adaptive compromises has taken place with regards to sickle cell and Malaria

Adaptations work with what is available

Many structures are far from optimally designed

Every Adaptive Trait Evolves from something else

• Because of Phylogenetic constraints every adaptive trait evolves from something that was already present.

• The fact that everything evolves from something else is just one reason why an organism’s traits, even when clearly adaptive, are often imperfect

ContrivancesContrivances

• ContrivancesContrivances - less than optimally designed structures (if interested visit http://www.talkorigins.org/faqs/jury-rigged.html

• Stephen Gould gives many examplesThe Panda’s thumbEye Development see the link at

http://www.pbs.org/wgbh/evolution/library/01/1/quicktime/l_011_01.html

• In order to show that a particular structure has developed from similar ancestral structures, one must be able to …

1. Establish the ancestral condition 2. Understand the transformational sequence, how and why the characters changed through time

• Mammalian Ear development is well documented in this way in the fossil record

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The Human Ear

• External ear: Hearing; terminates at eardrum• Middle ear: Hearing; contains auditory ossicles• Inner ear: Hearing and balance; interconnecting fluid-

filled tunnels and chambers

• Karl Reichert: – The Parts of the

ears of mammals are the same thing as parts of the jaws of reptiles. (1837)

Ear evolution steps and rationale

Ancestral history Crossopterygians (Fish) had none of the ear bones

Large rod that connects the upper jaw to the braincase

Ear evolution

Acanthostega (an air-breathing swamp dweller) has a stapes which connects a hole over the inner ear with a notch in the skull called the spiracle.

The hyomandibula functioned as

an exaptation (preadaptation) for hearing.

Mammal-like Reptiles

• At the end of the Permian fossils of mammal like reptiles were abundant.

• The most reptilian of the mammal-like reptiles had only a single bone in its middle ear.

• The successively more mammalian mammal-like reptiles the bones of the reptilian jaw got smaller and smaller.

Embryonic Development of the Middle Ear

Gives rise to the Stapes

Gives rise to the Malleus and Incus

• From a developmental stand point, the stapes bone develops from the Hyoid arch, while the incus and malleus develop from the Meckel’s cartilage.

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Inner Ear• Labyrinth

– Bony• Cochlea: Hearing

• Vestibule: Balance

• Semicircular canals: Balance

– Membranous

• -Lymphs– Endolymph

• In membranous labyrinth

– Perilymph• Space between

membranous and bony labyrinth

Inner ear working right and not

Inner Ear Hair Cells

http://www.dana.org/uploadedImages/Images/Content_Images/SenBodyFunc1_PR2007_cont.jpg

http://www.aecom.yu.edu/aif/gallery/haircells/haircell.gif

Inner Ear Hairs

• The hairs are covered with gel• When the gel moves, the hairs bend.• As they bend, they send messages to the brain.• The brain interprets messages as location and/or sound.

http://openlearn.open.ac.uk/file.php/3373/SD329_1_017i.jpg

Neuromasts• Fish have similar structures in their skin.• It works the same way.• They sense pressure changes in the water.

http://www.bio.miami.edu/~cmallery/150/neuro/c7.49.12.lateral.line.jpg

Constraints

• Evolution did not develop new bones for the middle ear. The bones were already there; they were repurposed to a different function.