Sexual Selection II

Question 1

What are two situations in which female ornamentation would be selected for? (Not examples, just scenarios)

Answer 1

1. Males make a large parental investment
2. Both males and females invest a similar amount in parenting

Note: Who is the limiting sex?

Question 2

What are two examples of female ornaments and why do they appear?

Answer 2

1. Great crested grebes (head ornaments) - both sexes needed to care for young
2. Chacma baboons (swelling)- females compete for access to the dominant male

Question 3

What causes sex role reversal? What is an example?

Answer 3

1. OSR and ecology favor female comp. for males
2. Pipefish - male is pregnant for several weeks = limiting sex

Question 4

What is periodic sex role reversal? What is an example?

Answer 4

1. Sex roles can change based on food availability (because there are changes in costs for each sex with differing amount of food).
2. Katydids - males make spermatophore for females

Scarce food = females compete over access to males (higher cost for males to make spermatophore)

Abundant food = males compete for females that reject low quality males (more males available so they can be choosy)

Question 5

Define the term “sex differences in competition”. What is an example?

Answer 5

1. Sexes may both compete, but compete for different things.
2. Eclectus parrot - Females = nest hollows (more colorful bc they live inside hollow). Males = females with best nest sites (more cryptic bc they find food)

Question 6

What is sperm competition? What is cryptic female choice? What is an example? What does this set up the context for?

Answer 6

1. Sperm competition = competition between male sperm inside the female
2. Cryptic female choice = Females chose which sperm gets let in her eggs INSIDE her body
3. Dung fly females mate with more than one male so sperm competition and cryptic female choice occur.
4. Multiple mating by females

Question 7

What are three hypothesis for females multiply mating?

Answer 7

1. Cost of resistance vs acquiescence
2. Material benefits
3. Genetic benefits

Question 8

Female Multiple Mating:
What does it mean for cost of resistance to exceed cost of acquiescence? What is an example?

Answer 8

1. The cost of a female to resist an extra mating is larger than the benefit of resisting (male’s choice not the female’s)
2. Dung flies - males fight for access to females (could result in female drowning)

Question 9

Female Multiple Mating:
What are three material benefits a female may get from multiply mating? What are two quick examples of these?

Answer 9

1. Increased sperm (increased chance of mating success), resources (territory, nutrients, oviposition site), and cooperation in rearing offspring
2. Damselflies (resources: oviposition site), and galapagos hawks (cooperation)

Question 10

Female Multiple Mating:
What are genetic/indirect benefits of multiple mating? Why do males not force copulations? What can a monogamous male do to limit extra pair copulations? What is an example?

Answer 10

1. Genetics only offered normally through extra pair copulations
2. Males don’t force because they need female cooperation (so pairing is her choice)
3. Mate guarding
4. Blue birds (35% of pairs had affairs)

Question 11

How do extra pair copulation rates affect sexual selection? What does this suggest about plumage?

Answer 11

1. Dimorphism is greater in systems with high levels of affairs.
2. Suggests plumage is about attracting affairs as it is mates

Question 12

Female Multiple Mating:
What are the social benefits to multiple mating? What is an example? What was the effect of visiting the same nest box together before the breeding season? Which pairs had the strongest level of winter associations?

Answer 12

1. Social network ties skew tendency to choose extra pair partners
2. Blue tits: Birds that ass. in winter were close neighbors during breeding and were more likely to have extra pair young
3. More likely to extra pair
4. Social pairs and extra-pair partners