Evolutionary Analysis: Global Edition

Jon C. Herron, Scott Freeman, Jason Hodin

Chapter 10

Studying Adaptation: Evolutionary Analysis of Form and Function - all with Video Answers

Educators

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Chapter Questions

Problem 1

Describe in your own words the difference between an experimental study, an observational study, and a comparative study. What sorts of questions are they each suited for (i.e., why don't researchers always use the experimental method)? Give an example of each type of study from this chapter.

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 2

What were Futuyma and colleagues' two hypotheses to explain why leaf beetles have not colonized all possible species of host plants? What did the researchers do to test the hypotheses? How do their results illuminate the general question of whether all traits in all organisms are adaptive?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 3

In social insects like ants, considerable morphological variations occur among individuals, leading to allometric variation. During the course of their development, pathways are determined which lead to such size and functional plasticity. Moreover, the ratio of such morphologically variant individuals changes from generation to generation.
a. What is the significance of this phenotypic plasticity for such insects?
b. How does it add to the fitness of the colony?
c. Do you think this plasticity is an overinvestment by a colony and can be abandoned in order to survive?

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Jeremy Spiro-Winn

Numerade Educator

Problem 4

What is an evolutionary trade-off? Why do they occur? Give two examples. How does the occurrence of tradeoffs illuminate the general question of whether all traits are adaptive?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 5

What is an evolutionary constraint? Why do they occur? Give two examples. How does their occurrence illuminate the general question of whether all traits are adaptive?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 6

How does Apert syndrome explain why some traits occur that may be maladaptive?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 7

Traits that are maladaptive for an organism may still be driven to fixation. Which level of selection would have to be stronger for this? What would happen if another level of selection were stronger?

Hailey Tomashek

Hailey Tomashek

Numerade Educator

Problem 8

a. Why was it important that Greene and colleagues tested tephritid flies whose wings had been cut off and then glued back on?
b. Why did they do the wing-cutting experiments at all? For example, why didn't they just compare intact tephritid flies to houseflies?
c. Why was it important that the five types of flies were presented to each spider in random order?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 10

Geckos are unusual lizards in that they are active at night. Describe the difficulties a gecko would face in trying to use behavior to regulate its temperature at night. Would you predict that geckos have an optimal temperature for sprinting that is the same, higher, or lower than that of a typical diurnal lizard? Huey et al. $(1989 \mathrm{a})$ found that the geckos they studied had optimal temperatures that are the same as those of typical diurnal lizards (a finding in conflict with the researchers' own hypothesis). Can you think of an explanation?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 11

Populations sometimes lack the genetic variation that would provide raw material to evolve particular adaptations. How would you elaborate on this statement, taking the example of the host shifts in the beetle genus Ophraella, studied by Futuyma et al. Also explain the host shifts that take place.

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Syed Anas

Numerade Educator

Problem 12

Throughout this chapter, we have stressed this fundamental question: How can we test whether a given trait is adaptive or not? As a further exercise, think about the costs and benefits of being a certain body size. For example, a mouse can easily survive a 30 -foot fall. A human falling 30 feet would probably be injured, and an elephant falling 30 feet would probably be killed. Finally, a recent study of the bone strength of Tyrannosaurus rex revealed that if a fast-running $T .$ rex ever tripped, it would probably die (Farlow, Smith, and Robinson 1995). Given these costs, why has large body size ever evolved? Can you think of some costs of small body size? How would you test your ideas?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 13

Natural selection operates at the level of individuals within populations. At this level, it is the birth, reproductive success, and death of individual organisms that determines which alleles become common and which would disappear. If an allele influences phenotype such that the average individual carrying it has greater than average reproductive success, then the allele's frequency will rise; otherwise, its frequency will fall. Generally this paradox is towards favorable traits so that beneficial ones are selected over harmful ones. However it has been recently worked out that selection operating at the level of cells, organelles, or sequences may oppose selection at the level of whole organisms. If a trait has to be adaptive, at what level is it more likely to be selected and why?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 14

Consider skin color in humans. Does this trait show genetic variation? Phenotypic plasticity? Genotype-byenvironment interaction? Give examples documenting each phenomenon. Could phenotypic plasticity for skin color evolve in human populations? How?

Kendrick Buford

Kendrick Buford

Numerade Educator

Problem 15

The example on begonias (Section 10.6 ) illustrated that organisms are frequently caught between opposing agents of selection. Each of the following examples also illustrates a tug-of-war between several agents of natural selection. For each example, hypothesize about what selective patterns may maintain the trait described and what selective patterns may oppose it.
a. $A$ male moose grows new antlers, made of bone, each year.
b. Douglas fir trees often grow to more than 60 feet tall.
c. $A$ termite's gut is full of cellulose-digesting microorganisms.
d. Maple trees lose all of their leaves in the autumn.
e. $A$ male moth has huge antennae, which can detect female pheromones.
f. $A$ barnacle attaches itself permanently to a rock when it matures.

JS

Jeremy Spiro-Winn

Numerade Educator

Problem 16

Schemske and Ágren (1995) used artificial flowers instead of real flowers in their experiment (Section 10.6 ). What were the advantages of using artificial flowers? (There are at least two important ones.) What were the disadvantages?

Charles Kirschbaum

Charles Kirschbaum

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Problem 17

$\mathrm{P} 1$ is a virus that infects bacteria. It often resides for long periods as a plasmid inside a bacterial cell, replicating and being transmitted to descendants of the original cell. Among the genes in $\mathrm{P} 1$ 's genome are two loci that form what is called an addiction module. One of the genes (called doc, which stands for "death on cure") encodes a small protein that is both highly poisonous to bacterial cells and chemically stable. The other gene (called phd, which stands for "prevent host death") encodes a protein that serves as an antidote to the poison. This antidote is chemically unstable because it is degraded by a bacterial protease. If a bacterial cell containing the P1 plasmid divides and produces a daughter cell that does not contain the plasmid, that daughter cell's protoplasm still contains the poison and the antidote. The antidote breaks down quickly, and the poison persists. The daughter cell then dies. Explain why it might be selectively advantageous for the $\mathrm{P} 1$ virus to carry an addiction module. How does selection at the level of the virus and its genes affect selection at the level of the bacteria that harbor them? (For more information on this example, see Lehnherr et al. 1993; Lehnherr and Yarmolinsky 1995.)

James Kiss

Numerade Educator

Problem 18

An exercise used in some graduate programs is to have students list 20 questions they would like to answer. Groups of students discuss the questions and help each other sort out which would be most interesting to pursue. There are many criteria for deciding that a question is interesting. Is it new? Does it address a large or otherwise important issue? Would pursuing it lead to other questions? Is it feasible, or would development of a new technique make it feasible? Try this exercise yourself.

Brandon Fox

Numerade Educator

Problem 19

An important aspect of evaluating scientific papers is to consider other explanations for the data that the authors might have overlooked. See if you can think of alternate explanations for the data presented in the following papers: Finally, see the following review of Soler and Moller's work for an example of how scientific criticism can result in better science by all involved:

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Jeremy Spiro-Winn

Numerade Educator

Problem 20

Male sticklebacks sometimes steal eggs from other males' nests to rear as their own. Sievert Rohwer suggested that egg stealing is a courtship strategy. Males often eat eggs out of their own nests, in effect robbing the reproductive investment made by their mates and using the proceeds to fund their own reproductive activities. Females, in consequence, should prefer to lay eggs in nests already containing the eggs of other females, thereby reducing the risk to their own. A female preference for nests already containing eggs would mean that males without eggs in their nests could increase their attractiveness by stealing eggs from other males. See:

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Jeremy Spiro-Winn

Numerade Educator

Problem 21

For a dramatic example of phenotypic plasticity in which an herbivorous insect uses the chemical defenses of its host as a cue for the development of defenses against its predators, see:

JS

Jeremy Spiro-Winn

Numerade Educator

Problem 22

Among the challenges faced by parasites is moving from one host to another. This challenge is a particularly potent agent of selection for parasites in which every individual must spend different parts of its life cycle in different hosts. What adaptations might you expect to find in parasites to facilitate dispersal from host to host? For dramatic examples in which parasites manipulate their hosts' behavior or appearance, see:

Sara Ross

Numerade Educator

Problem 23

Brown-headed cowbirds (Molothrus ater) lay their eggs in other birds' nests, a behavior called nest parasitism. When this strategy succeeds, the host birds accept the cowbird egg as one of their own and rear the cowbird chick. When it fails, the host birds recognize the cowbird egg as an imposter and eject it from the nest. Why do any host species accept cowbird eggs in their nests? Given the obvious cost of rearing a chick of another species, acceptance seems maladaptive. Evolutionary biologists have proposed two competing hypotheses to explain why some host species accept cowbird eggs. The evolutionary lag hypothesis posits that species that accept cowbird eggs simply have not yet evolved ejection behavior. Either the host species lack genetic variation that would allow them to evolve ejection behavior, or the host species have been exposed to cowbird nest parasitism only recently and therefore have not had sufficient time for such behavior to evolve. The evolutionary equilibrium hypothesis posits that host species that accept cowbird eggs do so because they face a fundamental mechanical constraint: Their bills are too small to allow them to grasp a cowbird egg, and if they tried to puncture the cowbird egg they would destroy too many of their own eggs in the process. Given this constraint, host species have evolved a strategy that makes the best of a bad situation. Think about how you would test each of the competing hypotheses. Then see: Given that some host species eject cowbird eggs by first puncturing the egg, then lifting it out of the nest, what adaptations would you expect to find in cowbird eggs? Would these adaptations carry any costs? See:

Leah Lampen

Numerade Educator

Problem 24

For additional examples in which evolutionary biologists used a comparative approach employing independent contrasts to address interesting questions,
see:

JS

Jeremy Spiro-Winn

Numerade Educator

Problem 25

For an experiment addressing why humans, who have much-reduced body hair compared to our closest relatives, have not lost our body hair entirely, see:

JS

Jeremy Spiro-Winn

Numerade Educator