Sexual Selection Study Guide

 

Chapter 11  Most questions for chapter 11 will be taken directly (i.e. close to verbatim) from this study guide, except where the item is just telling you to "know something". Section 11.5 will not be covered.

            Online quiz questions 1-5,12, 14, 15,17-18.

  1. Know and understand answers to homework questions.
  2. What is sexual selection? How is it related to natural selection?
  3. In mammals, do females or males usually invest more resources in each individual offspring?
  4. Explain what relative investment in offspring predicts about whether access to resources or access to mates limits reproductive success.
  5. What is the difference between intersexual selection and intrasexual selection? What kinds of traits do they each tend to produce? Give two examples of each.
  6. Under what conditions do we expect intersexual selection to be important ?
  7. Describe the experimental (yellow dung flies) and comparative evidence (bats) that sperm competition causes evolution of larger testes size.
  8. Describe the alternative male mating strategies in fence lizards (the rock paper scissors example). How are they related to frequency dependent selection?
  9. Describe the alternative male mating strategy in salmon. How is it related to frequency dependent selection?
  10. Describe in detail how female choice was demonstrated for barn swallows, gray tree frogs, and sticklebacks (from Reusch paper).
  11. What are the four main hypotheses for what females gain by being choosy?
  12. What is the evidence that suggests that female barn swallows are choosing males for their good genes? Do female grey tree frogs choose genetically superior males? How do we know (describe the experiment).
  13. What is the evidence that female barn swallows are selecting for genes that confer disease resistance.
  14. What is "runaway sexual selection"?
  15. Consider the fact that female grey tree frogs choose males based on call, and female barn swallows choose males based on plumage appearance/tail length, but that both appear to be getting genetically superior males. What does this suggest about the relationship between good genes and the characters females choose?
  16. Do female sticklebacks choose males based on MHC allele number or based on choosing an MHC genotype dissimilar from their own? Explain  the importance of the results.
  17. The scatterplot in Fig. 11.43 (p. 442) shows the relationship between the importance of attractiveness in mate choice (as reported by subjects responding to a questionnaire) and the prevalence of six species of parasites (including leprosy, malaria, etc.) in 29 cultures). What is the pattern in the graph? How might this relate to the good genes hypothesis and to the Hamilton-Zuk hypothesis? (Note, there is heritable resistance to these parasites).

Chapter 10.4

What is the comparative method?
Why is it important to account for phylogenetic relatedness when employing the comparative method?
What is the rationale for using the comparative method to infer the action of natural selection?

Sample exam questions:

9. The following data shows variation in lifetime reproductive success for men and women among the Kipsigis people of Kenya.

9a. 4pts. Which sex has greater variation in reproductive success? Is this pattern general across species?

9b. 4pts. What prediction(s) is/are generated by the theory of sexual selection based on these data?

 

 

 

 

3.         The graph below illustrates the relationship between relative testes size and social group size in 17 species of megachiroptera. These bats roost in groups that differ in size.

 

3a. 4pts. The correlation between group size and testes mass is highly significant.  However, having read about the comparative method and seen several examples (including this one), you are skeptical of the result for a technical reason. Explain what the technical issue is and how (in general terms) this can be corrected.

 

3b. 10pts.  Once the statistical issues with this analysis were resolved, there was still a very strong correlation between testes mass and group size. Interpret these results in two parts. In part 1, explain why this is considered strong evidence of adaptive evolution.  In part 2, explain the relevance of these specific results to the theory of sexual selection.


  1.  
  2. The following is considered a potential explanation for why females choose males with brighter or exaggerated plumage.
    1. Males invest relatively little in each offspring, and are mate-limited
    2. Bright males have greater disease resistance, which is passed to offspring
    3. Bright plumage is an honest advertisement of male quality
    4. The brightest males hold the best territories.
    5. Females have a pre-existing sensory bias for brighter, larger things.

The graph at right (fig. 11.9) shows the proportion of Galapagos marine iguanas in different size classes, for males and females.  The asterisks denote maximum size at which iguanas were able to maintain their weights, for two different years (i.e. an iguana above this size was unable to eat enough to stay that big.) Very large individuals of both sexes are also known to have higher mortality rates. Based on this information and what you know about this example, discuss the conflicting evolutionary forces affecting body size in these iguanas.

7. Regarding sexual selection, which of the following examples likely explained by female choice, male-male competition, or neither? (write one of these three below each).

A.     Male redwing blackbirds compete for territories nearest to the open water

B.     Some male redwings do not acquire territories, but do "float" around the marsh looking for copulatory opportunities

C.     The female hanging fly copulates longer with males who present her with larger prey items.

D.     The male damselfly uses the barbed horns on his penis to remove sperm left by the female's previous mate.

E.      Unrelated male grouse form leks in which they compete for female attention by "drumming" and displaying tail feathers and neck ruffs.

 

Female European barn swallows choose to mate with males that have longer tails. The graphs (SEE SEPARATE SHEET) show some results from two experiments. Summarize the results (6pts)  and explain their importance to specific aspects of the good genes model for female choice.

 

GRAPHS FOR LAST QUESTION:

Upper Left: Change in male tail length between years vs.manipulation of his mite load.

Upper Right and lower graphs: Results of cross-fostering experiment. Clutches were divided in two, with some going back in the nest of the biological father and others to the nest of a foster father.