Chapters 12 and 13

Question 1

Which of the following is a case of altruism?

Answer 1

A prairie dog gives up a foraging opportunity to keep watch for predators

Question 2

Individual amoebae of the slime mold Dictyostelium discoideumaggregate to form a spore-producing fruiting body. Cheaters make spores, but do not contribute to the stalk. Since many more spores with cheating genotypes are dispersed, they have higher fitness. Why does directional selection not lead to fixation of the cheater genotype?

Answer 2

This is actually a case of frequency-dependent selection. With too many cheaters in a population, the fruiting body’s stalk is not built well, and all individuals have lower fitness

Question 3

Which statement is the least likely explanation for the evolution of behaviors in which subordinate male animals assist dominant males defending mating territories or in mating displays?

Answer 3

The subordinate males mistake the dominant males for females

Question 4

In which situation would you expect the interacting parties not to cooperate?

Answer 4

Individuals are unlikely to encounter each other again in the future

Question 5

Suppose five boats are adrift at sea, each one containing a number of your relatives, and you have the power to save one boat from a dire fate. According to kin selection theory, it would be in the best interest of your genome to save a boat that contains

Answer 5

One sister, one half-brother, and three cousins

Question 6

A woman has a son with her first partner, and that son has a son of his own—the grandchild of the original woman. The original woman also has a son with a second partner, who also grows up to have another son; a second grandchild. What is the relatedness, r, of the two grandchildren?

Answer 6

0.0625

Question 7

In birds and mammals, parental care tends to be provided by females, while in fishes and frogs, it tends to be provided by males. Which statement about this difference is consistent with evolutionary theory?

Answer 7

Selection favors defection more strongly in the sex for which parental care is more costly

Question 8

Pre-eclampsia is a pregnancy complication that is often explained as resulting from parent-offspring conflict. What underlies this conflict?

Answer 8

The fetus demands more resources from the mother than would be optimal for her

Question 9

Eusociality occurs in multiple species of insects. What is the characteristic of wasps, bees, and ants that facilitates the presence of sterile workers?

Answer 9

Haplodiploidy

Question 10

Which factor favors evolutionarily stable mutualisms?

Answer 10

Restricted opportunities to switch partners, genetic self-interest linked to the partner’s fitness, repeated or lifelong associations of partners, vertical transmission of endosymbionts, i.e., symbionts are transmitted directly from parents to offspring.

Question 11

The relationship between a plant and an herbivore is most closely analogous to the relationship between

Answer 11

A host and its parasites

Question 12

What behavior is most likely to disrupt the mutualistic interaction as described?

Answer 12

When parasites are scarce, mutualistic cleaner wrasse will cheat and instead bite the scales off of larger fish at a cleaning station

Question 13

Which major evolutionary transitions in the history of life might be explained by group selection?

Answer 13

Transition from individual genes into a chromosome, transition from individual cells into a multicellular organism, transition from separate molecules into a gene, transition from multicellular organisms into a social group

Question 14

Vampire bats (Desmodus rotundus) form long-term social bonds and regurgitate blood to unrelated members of their group who did not successfully secure a blood meal that night. By providing sustenance to these members, they prevent starvation from occurring. What is this interaction an example of?

Answer 14

Indirect reciprocity

Question 15

Many species of animals make “alarm calls,” which warn others in their group that a predator is approaching. Alarm calls also attract the attention of the predator, making it more likely that the individual making the call will be eaten. Why might natural selection cause a species evolve to make alarm calls? How might you test that hypothesis?

Answer 15

Natural selection may have caused a species to evolve to make alarm calls because it gives the population of the species a chance at escaping the predator at the expense of the individual making the alarm call. Through altruism, the individual making the call is able to ensure higher inclusive fitness through sacrificing them self for others in their group indirectly.

The hypothesis can be tested by placing an animal that makes alarm calls in between two other clear cages of its predator and its species’ population. The animal making the alarm call would see the predator on one side of the cage and its species population on the other side. It can therefore be assumed that if the animal makes an alarm call, it is warning to its species of danger in the vicinity allowing them the chance to escape even though the individual making the call is physically closer the predator than the rest of the species population. Various sounds from different sources including the predator can be used to determine whether the call being made by the individual is in fact an alarm call.

Question 16

Darwin argued that natural selection would never cause a species to evolve a trait that benefits another species at a fitness expense to its own species. A study of egrets in Florida found that parents eject their own chicks from their nests, and this behavior feeds alligators living in the swamp below the nests. This steady supply of food improves the health and condition of the alligators. In view of Darwin’s logic, what are two hypotheses that might explain why the egrets perform behaviors that benefit alligators?

Answer 16

Two hypotheses that might explain why egrets perform behaviors that benefit alligators is David Lack’s hypothesis such that selection will favor the clutch size that produces the most surviving offspring and that by providing alligators with food, it may be less likely the alligators will predate on the egret chicks. Parental investment and scarcity in resources would be a plausible reason to why egrets would eject some of their chicks in order for the species to achieve the highest fitness. Additionally, by doing so, the egrets can mutually benefit alligators (possibly a predator) such that the alligators will not attack the nest of unejected chicks consuming more than the parents had gotten rid of.

Question 17

What differences do you expect to see in how females behave toward their brothers in haplodiploid species (such as ants) compared with diploid species (such as beetles)?

Answer 17

In haplodiploid species, females would prefer to help out their sisters since due to the haplodiploid determination, they would get higher direct fitness benefit from their sisters (0.75) rather than from their brothers (0.25). Diploid species would prefer to help out their brothers and sisters equally since they would get approximately the same amount of direct fitness benefit from either sibling due to the nature of the diploid condition with two sets of chromosome from the same parents.