What is adaptation? What is adaptation?

AdaptationAdaptation

Comes from ad (to or toward) and aptus (a fit)

Evolutionary context –◦ genetically-basedgenetically-based change in response to a

problem◦achieved through the process of natural

selection. ◦A period of timeperiod of time passes before adjustment

occurs

Adaptation is both a Adaptation is both a processprocess and a and a state of beingstate of being (a phenotypic trait or (a phenotypic trait or character)character)We identify traits as adaptations only when

they are evolved for the solution of a specific problem (selected function or purpose).

Adaptation - a working definition:a genetically based genetically based 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

Just because a trait has a specific effect does not mean that the trait is adaptive for that purpose.

Evolution is blind!Evolution is blind!

Selection acts only on what is before it and not with an end goal in mind.

Selection may lead to adaptations that …

are either a further modification of traits already present (by changing their use) or…

selection may act to eliminate traits

All of the trends in selection that cause traits to change over time are adaptive but the changes are not done with some pre-determined end goal in mind

Identifying adaptations can be Identifying adaptations can be difficult and care must be takendifficult and care must be taken

Many traits evolved under one selective regime but are now being used under a very different selective regime.

The current function may not reflect the context in which the trait was originally evolved

Need to distinguish current utility from historical origin

What is the What is the significance of significance of these slides as they these slides as they relate to relate to adaptation?adaptation?

GiraffesGiraffes

What kind of story do the slides tell usWhat was the original explanation for the

adaptive value of the Giraffe neck? What other possibilities have now been

investigated? Does the giraffe neck give any feeding

advantage to those who possess it?

If the giraffe neck was actually selected for If the giraffe neck was actually selected for as a means of defeating other males in a as a means of defeating other males in a battle over females, then battle over females, then

the neck is now coopted for use in feeding higher in the trees than other organisms can.

Sometimes the term pre-adaptation is used for such co-opted traits But pre-adaptation is a bad label to use here.

The term exaptation has been suggested by Stephen Gould

refer to situations in which traits perform a certain function now but either arose originally for some other function or had no function at all originally

Gould has also proposed the use of the term Gould has also proposed the use of the term spandrel spandrel for an adaptation that originally for an adaptation that originally arose with no adaptive purpose at all but arose with no adaptive purpose at all but now has adaptive valuenow has adaptive value

In male giraffes if long necks were originally adapted for fighting then their current advantage for feeding would be an exaptationexaptation (originally 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.

Examples of exaptations:bone tissue skull sutures

Adaptationist program Adaptationist program Seeks to find adaptive explanation for

every trait in organismsMuch difference of opinion on this

approachEverything is not adaptive. Some things

are actually maladaptive or non-adaptive. Some traits or variations in traits are actually selectively neutral

Adaptations are not always perfectNeed to keep in mind that Adaptation is

also constrained by compromisescompromises, trade-offstrade-offs and correlationscorrelations with other with other traitstraits

We will discuss each of these ideas later

Various types of studies are involved in the Various types of studies are involved in the attempt to explain what is happening in an attempt to explain what is happening in an evolutionary contextevolutionary context

To determine that a trait is actually an adaptation we need to….

determine what the trait is for and then ….

show that individuals that have that trait actually contribute more genes to the next generation than the individuals that don’t have the trait

The obvious answer is not always the right one

Giraffe story in the textGiraffe story in the text

What are the two current hypotheses?

The case of the giraffe demonstrates the importance of being able to look at things with fresh eyes and come up with alternative hypotheses.

Examine the picture to the left does it suggest a third possible hypothesis for long necks?

Three major approaches to Three major approaches to determining adaptive significance determining adaptive significance of traitsof traits

ExperimentsObservational studiesComparative studies

ExperimentationExperimentation

Experimental exampleExperimental exampleZonosemata (snowberry) Zonosemata (snowberry) flies and flies and jumping spidersjumping spidersWhat 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 exampleExperimental exampleZonosemata Zonosemata fliesflies

What are 3 hypotheses that might explain this behavior?

Experimental exampleExperimental exampleZonosemata Zonosemata fliesflies

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

•What was the experimental set-up

Experimental exampleExperimental exampleZonosemata Zonosemata fliesflies

What predictions were made?

Experimental exampleExperimental exampleZonosemata Zonosemata fliesflies

What were the experimental results?

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RESULTS

What important points of What important points of experimental design are experimental design are

demonstrated in the demonstrated in the Snowberry Fly example?Snowberry Fly example?

Effective ControlsEffective Controls

What were the control groups in this experiment?

Why were they important?Allow us to work towards eliminating

competing hyotheses.

Handling all treatments exactly Handling all treatments exactly alikealike

What were some of the things considered here?◦Same arena◦Method of presentation of flies◦Timing of presentation◦Others?

RadomizationRadomization

What needed to be randomized and why?◦Order the flies were presented in◦Others?

RepetitionRepetition

Sample size needs to be large enough for statistical analysesstatistical analyses.

Replicated experiments reduce the amount of distortion because sample size is larger which lowers the amount of lowers the amount of biasbias.

Allow the measurement of variationvariation in data points.

Observational StudiesObservational StudiesWith Garter Snakes

Observational StudiesObservational Studies

When are these type of studies done? In this method we need to show two

things: 1. Occurrence of trait is non random in the population2. The observed trait is adaptive

Example – Garter Snake studyHow did this study show that snake movements is an adaptation to control body temperature?

Show they are choosing a Show they are choosing a particular temperature more often particular temperature more often than would happen by random than would happen by random movementsmovementsWatched snakes, where they spent their time

and what their body temps wereFound that they maintain their body

temperatures between 28 and 32 degrees Celsius.

Discovered options for thermoregulationsun/shade, under rocks (thin, medium, thick), or moving up or down in burrows.

Found that of the 3, all could be used Found that of the 3, all could be used to effectively maintain desired to effectively maintain desired daytime temps but only rocks could daytime temps but only rocks could provide enough warmth at nightprovide 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 Now have to show that being under medium rocks is not under medium rocks is not random behaviorrandom behaviorCompared 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 ….

Table 10.1

Comparative StudiesComparative Studies

Comparative StudiesComparative Studies

Tests for patterns across speciesProper application of comparative

methods requires knowledge of the evolutionary relationships among the species under study.

Example bat studies

Example of comparative studyExample of comparative study

Bats: Is the larger size of testes in some bats adaptive due to sperm competition?

Do bats from larger social groups have larger testes because there is more competition for passing on their genes?

Showed initial correlation Showed initial correlation between social group size and between social group size and testes size.testes size.

But the data could be skewed by But the data could be skewed by evolutionary relationships.evolutionary relationships. The testes size could still be related to

who evolved from whom. Perhaps the larger testes groups are

simply from one common ancestor and the smaller from another.

Need to do a correction for this 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.

Felsenstein’s method of Felsenstein’s method of

phylogenetically independent contrastsphylogenetically independent contrasts. .

When species diverge from 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

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 PlasticityPhenotypic Plasticity

De Meester’s first study with Daphnia

No stocking Heavy Stocking Reduced stocking

De Meester’s second experiment

Every Adaptive Trait Evolves from Every Adaptive Trait Evolves from something elsesomething else

In order to show that one thing has evolved from similar structures in ancestors must be able to …1. Establish the ancestral condition 2. Understand the transformational sequence, how and why the characters changed through time

Video demonstrating Video demonstrating transitional adaptationstransitional adaptations

Whale evolutionYou may review this video at

http://www.pbs.org/wgbh/evolution/library/03/4/quicktime/l_034_05.html

Adaptations work with Adaptations work with what is availablewhat is available

Many structures are far from optimally designed

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

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

The Panda’s thumbEye Development see the link at

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

TradeoffsTradeoffs

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 A trade-offtrade-off example example The Begonia 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

Two types of Two types of constraintsconstraints

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

PhylogeneticPhylogenetic – based on inheriting the needed genetic variation from its ancestors

Constraints Constraints ((developmental example)developmental example)A behavior or trait that would be adaptive is

physiologically or mechanically impossible.Why does the Fuchsia retain its flowers and

turn them red for 5 days AFTER pollination, when pollinators are no longer visiting, the flowers are of no more use but are still tapping needed resources.

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

Turns out that pollen tubes need to grow through the area of the abscission layer for the petals and if petals are dropped too soon the pollen tube never makes it to the ovules. So the petals need to remain for at least 4 days after pollination for fertilization to take place.

ConstraintConstraint - phylogentic - phylogentic

Pigs can’t flyAnimals can’t do photosynthesisBeetle example on page 388-389

◦Need to be able to detoxify the chemicals in individual host plants they may prey upon.

◦Showed genetic variation which allows beetles to attack different host plants, and detoxify the new hosts unique chemical defenses depends on which phylogenetic group the beetles belong to.

Constraints in ArthropodsConstraints in Arthropods

Molting: Molting is more hazardous for larger animals. Exoskeleton strength: The exoskeleton may not be strong enough to support larger animals. Respiration: Many arthropods can only get enough oxygen to support small bodies.

Arthropods inherited both an exoskeleton and jointed legs. These traits have opened up many opportunities in arthropod evolution, but they have also blocked other possibilities. Can you think of any constraints on the size that arthropods will reach?

Adaptive CompromiseAdaptive Compromise

Sickle cell and Malaria

End Day One AdaptationEnd Day One Adaptation

DefinitionsDefinitions

Some DefinitionsSome Definitions Preadaptation(exaptation):Preadaptation(exaptation): A character

that was adaptive under a prior set of conditions and later provides the initial stage for evolution of a new adaptation under a different set of conditions.

Examples: 1. A bird’s flight feathers (from feathery

scales on certain dinosaurs, where they served the function of insulation);

2. The vertebrate eye (from a series of light-sensitive organs).

DefinitionDefinition

Vestigial structureVestigial structure: an anatomical structure found in all or most normal individuals of an extant species; typically very small in size, and with apparently little or no important function now.

Such parts typically would be found in ancestors of this species, but as larger and clearly functional structures.

An example would be the human ear-wagging muscles.

DefinitionDefinitionAtavism (Atavistic structure)Atavism (Atavistic structure): a vestigial

structure found in only a small fraction of the normal members of an extant species

ExampleThe rudimentary thigh bone found in

about 5% of individual whales.

DefinitionDefinitionContrivance:Contrivance: A structure modified and

used for a function which is different from the original (or previous) function for that structure in an ancestor.

ExampleThe vertebrate eye

The design of the vertebrate retina is “inside-out.”

The retina is behind the nerves that form the optic nerve.

Where the optic nerve leaves the eye, there is a hole, which results in a blind spot.

DefinitionDefinitionImperfection:Imperfection: A “contrivance” which still

retains some of the features of its ancestral source structure, to a greater or lesser degree; clearly not fully or perfectly “adapted” to its new function, but serving adequately.

ExampleThe panda’s “thumb” is an example here,

as are the many contrivances found in orchid flowers.

This term could also be applied to vestigial or atavistic structures.

Exercise on examples of some Exercise on examples of some adaptations and imperfectionsadaptations and imperfections

The EndThe End