Chapter 10: Studying Adaptation: Evolutionary Analysis of Form and Function

trade-off

A situation in which evolution of increased fitness of one trait causes reduced fitness in another trait

adaptation

A trait that increases the ability of an individual to survive or reproduce compared with individuals without the trait.

phenotypic plasticity

An influence on phenotype by the environment

Which of the following is not a guideline for good experimental design? A. Use randomization to equalize other miscellaneous effects across groups. B. To avoid scatter in the data, repeat the test on no more than ten individuals. C. Phrase your question as precisely as possible. D. Treat all groups in exactly the same way. E. Test as many competing, realistic hypotheses as you can think of.

B

Which of the following statements are correct? A. Differences between populations may be assumed to be adaptations to their different environments. B.Adaptations that are intuitively obvious need not be tested experimentally. C. Not every trait is an adaptation. D. Adaptations are usually perfect.

C

According to Delph and Lively's studies, why do fuchsia flowers turn red when they are no longer receptive to pollen rather than simply falling off? A. It would be extremely maladaptive for fuchsias to drop their flowers before pollen tubes deliver pollen to the ovules -- which takes several days after pollination. B. Fuchsias receive a selective advantage from advertising to pollinators that individual flowers are no longer receptive to pollen. C. Fuchsias are constrained by their total energy budget to limit the number of flowers that can be blooming at one time. D. The first two choices are correct.

D

adaptive

Describes a trait that increases the fitness of an individual relative to that of individuals lacking the trait.

genotype-by-environment interaction

Differences in the effect of the environment on the phenotype displayed by different genotypes; for example, among people living in the same location some change their skin color with the seasons and others do not.

genotype-by-environment interaction

Genetic variation for phenotypic plasticity; a phenomenon in which some genotypes show higher phenotypic plasticitiy than others, in response to changes in environment

Cleaner wrasses are a type of small coral reef fish that performs a wriggling dance at a certain location in the reef. Larger fish come to these locations, or stations, apparently attracted by the wriggling dance, and stay motionless while the cleaner wrasses move over them, apparently feeding off of the larger fish's body. The larger fish even permit the cleaner wrasses to swim into their mouths and feed there. Like oxpeckers, cleaner wrasses have long been assumed to be providing a beneficial cleaning service to their hosts, removing parasites and dead or diseased skin. How could you test this hypothesis?

Many answers are possible. Good observations are usually the first step: Do cleaner wrasses create wounds? Are they seen feeding on wounds? Do larger fish exiting from cleaner wrasse stations have fewer parasites than those who have not visited cleaner wrasses? Do larger fish make deliberate choices about visiting cleaner wrasse stations? Once observations have revealed the general pattern of fish behavior, we could design experiments to test the beneficial value of cleaner wrasses - for example, capturing all cleaner wrasses from a reef and seeing if other fishes' parasite loads increase. Several such studies have now been done, and it appears that most cleaner wrasses do provide good cleaning services to their hosts. Some species of other fish are "aggressive mimics", appearing like cleaner wrasses and circulating at cleaner wrasse stations, but biting larger fish instead of cleaning them. The larger fish, in turn, are "choosy", visiting only those wrasse stations where they get good service - for example, parrotfish return preferentially to those wrasse stations where they previously received both prompt service and good cleaning. In another twist on the story, some of the mimics exhibit phenotypic plasticity, only acquiring wrasse-like coloring when there are wrasse stations nearby.

Describe how Huey et al. tested the hypothesis that garter snakes behaviorally thermoregulate by identifying (1) what important feature(s) of the environment they monitored; (2) what specific prediction they made about the snakes' behavior; and (3) how they demonstrated that the snakes' behavior was not random.

Note that the essential logic of hypothesis testing (observation, generating hypotheses, making predictions, testing predictions) is the same for experimental and observational studies. Similarly, both types of studies involve the use of controls and replication. Neither is inherently superior to the other; the best one to use depends on the question being asked.

In bats, what is the evidence that brain size is negatively correlated with testis size? Is this true for all bats? What methods were used in data analysis? Does the evolution of larger testes cause the evolution of smaller brains?

Pitnick's study of 57 bat species showed that those species that have evolved large testis size have also tended to evolve smaller brain size. This was a comparative study that used phylogenetically independent contrasts to control for effects of relatedness among different species. This type of study is powerful at revealing interesting correlations, but (like most non-experimental studies) it cannot demonstrate the "direction of causation" - i.e. it cannot show which factor (smaller brains or larger testes) caused the other to occur, or whether both were caused by a third factor. Pitnick et al. suspect that it is difficult for a species to maintain large testes and large brains simply because both are metabolically expensive - particularly for a flying species in which presumably every ounce matters. Interestingly, the correlation does not hold for fruit bats, which are heavier and not as nimble at flight as the insect-eating bats.

reaction norm

The normal range of possible phenotypes that a given genotype may produce under different environmental conditions

reaction norms

The pattern of phenotypic plasticity exhibited by a genotype.

phylogenetically independent contrasts

The set of pairwise divergences that occurred within a clade as lineages arose from the nodes.

adaptation

Trait that increases the fitness of its possessor

monoecious

Typically used for plants, to describe either: (1) a species in which male and female reproductive functions occur in the same individual; or (2) a species in which separate male and female flowers are present on the same individual.

Why was it important that Weeks ran the oxpecker experiment three times, with different assortments of cattle? Why was it important for Weeks to do the experiment at all? Are you satisfied with his results?

Weeks ran the oxpecker experiment several times to rule out the possibility that the result of the first trial might have been due to a random fluke or to an unusual set of cattle. For this reason, it is always important to replicate experiments whenever possible. It was important to do the experiment in the first place for the simple reason that all assumptions should be tested - the assumptions that oxpeckers are beneficial to cattle had never been well-tested.

In comparative studies, it is important to be aware of relationships among species because ___________________.

data points should be independent, and two related species might have derived their trait from a shared ancestor, rather than each having evolved it independently

A trait may be assumed to be an adaptation if ____________________.

it is shown, in a well-designed study, to have a function and to increase fitness

Felsenstein's method of independent phylogenetic contrasts is a method _________________.

of controlling for phylogenetic relatedness in comparative studies

In general, the hypothesis that a particular trait represents a trade-off implies that

the trait is the result of "conflicting" selection pressures.