Terms to know: sexual selection, male-male competition, female choice, runaway sexual selection, honest advertisement, sensory bias (exploitation), good genes

Questions:

1. In many species of insect, male insects produce complex chemicals called pheromones which have (at least to other insects) a strong odor.  Females in these species do not produce pheromones (but they can smell them).  Predators that eat the insects can also smell these pheromones, so the pheromones decrease male survival by attracting predators.   (a) Since these pheromones decrease survival, how can they have evolved? (b) Why would you expect that males but not females have pheromones? (c) Suppose that females choose males based on their pheromones.  Give three hypotheses that could explain how female choice for pheromones might have evolved.
2. House finches are small red and brown birds. G.E. Hill has shown that females will mate with the reddest males they can find, AND males will mate with the reddest females they can find.  Male house finches typically have bright red breasts, but female house finches are typically brown with only a slight wash of red on the sides. (a) Explain why female choice of males would be expected to result in evolution of bright red males, but male choice of females would not have this result (NOTE: explain this based on sexual selection, assume that natural selection on redness does not differ between the sexes). (b) Hill has found that the red coloration in males depends on diet: the more red pigments males eat, the redder they get. Males bring food to females incubating eggs; brighter red males feed at higher rates than do duller males. With which of the three main hypotheses of the evolution of female preference are these observations most clearly consistent?
3. Jacanas are birds in which one female typically mates with several males. A female will lay eggs in the nests of each of several males, all of whom build these nests on the female's territory.  The males do all the "work" of incubating and raising the young.  In jacanas, females are larger and more brightly colored than males.  Give a likely explanation for why females are larger and more brightly colored based on sexual selection.  Why is it unusual for females to be larger and more brightly colored than males?  What are the two major kinds of interaction between individuals in jacanas that could have resulted in sexual selection in jacanas?
4. Male widowbirds have long tails.  Females mate preferentially with males with longer tails.  Give three hypotheses that could explain the evolution of long tails in male widowbirds, one based on "honest advertisement", one based on "runaway selection" and one based on "sensory exploitation."
5. In a species of poison-dart frog that lives in tropical rainforests in Panama, after the female lays eggs and the male fertilizes the eggs, the male stays with the eggs and cares for them by keeping them free of mold.  Once the eggs hatch into tadpoles, the male carries tadpoles on his back up trees to find pools of waters held in plants that grow on these trees; he deposits each of his tadpoles in a different pool of water.  In contrast, a female who has laid her eggs takes no further part in parental care; she goes and finds other males with whom to mate, and lays more eggs.  (a) In these frogs, which sex would you expect, based on sexual selection theory, to be larger and more brightly colored?  Why? (b) Actually, it turns out that both sexes are extremely brightly colored, but the reason has nothing to do with sexual selection.  Can you give a plausible explanation for why these frogs are brightly colored (HINT: consider what kind of frog they are)
6. In a species of frog, it has been shown that the "chuck" vocalization occurs at a frequency (pitch of sound) to which females ears are particularly sensitive.  Females tend to mate with males who give the most "chuck" vocalizations.  With which of the three main hypotheses for the evolution of female choice are these observations most consistent?
7. Male-male competition can occur in a variety of ways.  Based on Freeman and Herron (2001) Chapter 9, explain how each of the following is a form of male-male competition, and give an example in which this form of male-male competition has been demonstrated.
1. combat between males
2. sperm competition
3. infanticide by males
8. Use the study of stalk-eyed flies (Freeman and Herron (2001) Chapter 9) to explain how to demonstrate the features that must exist for runaway sexual selection to occur.