Sexual Selection

Question 1

sexual dimorphism

Answer 1

males and females of the same species differ in phenotype

Question 2

how does sexual dimorphism affect survival rate?

Answer 2

sexual dimorphism may decrease survival rate

Question 3

how does sexual dimorphism affect reproduction?

Answer 3

sexual dimorphism vastly increases reproduction

Question 4

sexually dimorphic males

Answer 4

1. Brighter colors
2. Various adornments
3. Bigger bodies
4. More competitive

Question 5

sexual selection

Answer 5

operates on characteristics that act to increase reproduction

Question 6

sexually dimorphic females

Answer 6

among smaller organisms, the female usually has the larger size

Question 7

mate choice

Answer 7

usually the female will select a mate

Question 8

How does mate choice influence the lek?

Answer 8

males gather to compete for the attention of a female

Question 9

male-male comepetition: inter- or intra- species?

Answer 9

intra-species competition

Question 10

Traits and Preferences Co-Evolve

Answer 10

1. Females choose males with exaggerated traits
2. Male offspring will have this exaggerated trait, and female offspring will have the same preference for this exaggerated trait

Question 11

Post-mating competition

Answer 11

prevents other males from fertilizing already-fertilized female

Question 12

sex roles

Answer 12

come directly from sexual selection

Question 13

How did differences between males and females evolve?

Answer 13

differences in reproductive biology

Question 14

What are the relevant differences in male and female reproductive biology, with regard to sex roles?

Answer 14

Females have a much greater investment (eggs, gestation, care)

Males have greater reproductive potential (sperm, lots of sperm)

Question 15

Harem

Answer 15

one dominant, polygynous male mates and defends a group of females

Question 16

Why is there less sexual dimorphism in monogamous animals?

Answer 16

Mating system correlates with sexual dimorphism.

Question 17

Role reversal

Answer 17

Roughly 30 species of bird have females that mate with multiple males

Question 18

Why did the sight of a peacock’s tail make Darwin feel sick?

Answer 18

How can a long showy tail be beneficial to a species survival? Takes a lot of metabolic energy to create and the colors make the bird more attractive to predators.

Question 19

Correlation between levels of aggression between males vs. disparity in number of mates:

Answer 19

the greater the disparity among males in terms of number of mates, the greater the level of aggression

Question 20

Causes of sex role reversals for migratory shorebirds

Answer 20

per long migrations, expensive egg production, building nest, raising chicks is ALL too much for females. Females are stressed and “at their end of their physiological rope”. Moms need to eat! If female is malnourished then low egg production, low egg quality, weak chicks. Increased chick mortality means fewer genes passed on to next generation. Solution = “stay-at-home” males that build nests and raise chicks

Question 21

Cause of sex role reversals for “polyandrous” females

Answer 21

Owing to their “polyandrous” behavior (one female mates with many males), female phalaropes must compete with other females for males…… So females have brighter colors than male stay-at-home-dads.

Question 22

How does sexual selection perpetuate sexual dimorphism?

Answer 22

1. Both the trait and the preference for it co-evolve
2. Females choose males with distinctive trait
3. Offspring inherit exaggerated trait (males) and preference for that trait (females)
4. Selection reinforces both trait and preference