Sexual Selection

Question 1

Sexual Dimorphism

Answer 1

differences in morphology between male and female members of a species

• can include physical traits as well as behavioral traits (i.e. birdsongs)

Question 2

Sexual Dimorphism (male characteristics)

Answer 2

• more brightly colored
• sport various adornments
• larger body size

Question 3

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

Answer 3

• how can a long showy tail be beneficial for the survival of a species?!
• it takes A LOT of metabolic energy to create and the colors make them more attractive to predators

Question 4

What is sexual selection?

Answer 4

differential success in reproduction

• if the female likes the male with the more colorful feathers, the male produces more offspring and the trait is passed down

Question 5

Examples of Sexual Selection Processes

Answer 5

1. ) Mate Choices

2. ) Intra-Sexual Selection

Question 6

Mate Choices

Answer 6

“power to charm females”

• i.e. peacocks and their feathers

Question 7

Intra-Sexual Selection

Answer 7

“power to conquer other males in battle”

• i.e. elephant seals, deer (bucks)

Question 8

How does sexual selection perpetuate sexual dimorphism?

Answer 8

• both traits and the preference for it co-evolve
• females choose the males with distinctive traits
• offspring inherit exaggerated trait (males) or the preference for that trait (females)
• selection reinforces both trait and preference

Question 9

Examples of post-mating competition

Answer 9

males hang around after mating and guard against other male suitors

• fruit flies and their “penis scoop” that can scoop out the sperm of competitors
• dragon flies who attach themselves to the female after sex
• some snakes and rodents have sperm that temporarily block reproductive tract after mating

Question 10

Factors involved in evolution of typical sex roles (male vs. female)

Answer 10

1. ) relative investment in reproduction

2. ) Reproductive potential

Question 11

Relative Investment in Reproduction

Answer 11

usually greater in females (therefore women are more choosey)

Question 12

Reproductive Potential

Answer 12

usually greater for males (therefore males must be more competitive and aggressive)

Question 13

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

Answer 13

Monogamy vs. Polygamy

• the greater the disparity among males in terms of number of mates results in a greater level of aggression

Question 14

Causes of sex role reversals (migratory shorebirds and polyandrous females)

Answer 14

migratory shorebird females experience high levels of stress;

• if the female is malnourished then she has low egg production and the eggs she produces will be low in quality resulting in weak chicks
• solution? male birds stay at home to prevent weak offspring end result!