Lecture 18: Sexual Selection

Question 1

What were “Darwin’s puzzles” regarding sexual selection?

Answer 1

• Sexual dimorphism

- “Disadvantageous” secondary sexual characteristics

Question 2

Define anisogamy

Answer 2

sexual reproduction by the fusion of dissimilar gametes

Question 3

What is the relationship between parental investment and sexual selection?

Answer 3

• Parental invest (P.I.) proportional to benefit/cost ratio of ‘child rearing’
• Sexual selection due to a correlation between gender and parental investment
• Females tend to have higher P.I. than males

Question 4

Understand Bateman’s experiments

Answer 4

• Sex differences in reproduction success
• males have higher variance in reproductive success (mates)
• females have lower variance in reproductive success

Question 5

For what sex is sexual selection strongest?

Answer 5

Sexual selection is strongest for the sex with high variance in reproductive success (due to more variation)

Question 6

What is the relationship between behavior and sexual selection?

Answer 6

• Males (sex with strong sexual selection) should be competitive, fight for additional mates
• Females (sex subject to weak sexual selection) should be “choosy”, allocate their expensive resources efficiently

Question 7

Define Intra-sexual selection

Answer 7

Contests between individuals of one for access to mates

Question 8

Define Inter-sexual selextion

Answer 8

High investment sex chooses individuals of low-investment sex

Question 9

What is male-male competition?

Answer 9

A form of intra-sexual selection in which males compete with other males by using either direct combat or forms of sperm competition

Question 10

What is female choice?

Answer 10

A form of inter-sexual selection in which females choose based on “quality” of males, can lead to the evolution of elaborate structures

Question 11

Understand the relationship between female choice and nuptial gifts.

Answer 11

Gift presented to females (who choose), size of “gift” related to duration of copulation and sperm transfer, selection leads to larger gifts

Question 12

What is runaway sexual selection?

Answer 12

There are males traits attractive to females, females preferentially choose males with exaggerated traits.
There is a correlation between 
1) inheritance of male trait and 
2) female preference for the trait
LD

Question 13

Understand the balance between natural and sexual selection

Answer 13

Sexual selection can increase trait, natural selection limits trait, equilibrium trait size

Question 14

What is Zahavi’s handicap principle?

Answer 14

Exaggerated traits are costly to males, but are signals of good genes. If thinking in terms of the handicap model, with out without the trait –> alive or death