Sexual Selection

Question 1

What is sexual selection, and how does it differ from natural selection?

Answer 1

Sexual selection is a form of natural selection that favors the evolution of elaborate traits in one sex and preferences for those traits in the opposite sex. Unlike natural selection, which focuses on traits related to survival, sexual selection involves traits linked to mating success, such as courtship behaviors or morphological features.

Question 2

What are the primary results of sexual selection?

Answer 2

Morphological differences between sexes and differences in reproductive behavior, such as males engaging in courtship displays and females evaluating male performance.

Question 3

What are intersexual and intrasexual selection?

Answer 3

Intersexual selection (mate choice): One sex has preferences for specific traits in the opposite sex.

Intrasexual selection (mate competition): Members of the same sex compete for access to mates.

Question 4

What traits are influenced by sexual selection?

Answer 4

Traits related to mating success, such as primary and secondary sexual characteristics. These traits are heritable and affect allele frequencies in populations over time.

Question 5

What is the fundamental asymmetry of sex?

Answer 5

Males produce abundant, small sperm, while females produce fewer, energetically costly, and larger eggs. This leads to males competing for rarer eggs and females investing more in reproduction.

Question 6

Provide an example illustrating the fundamental asymmetry of sex in wrens

Answer 6

Male fairy wrens produce billions of sperm, while a female’s single egg can constitute 20% of her body mass, demonstrating the disparity in reproductive investment.

Question 7

Why do sex differences in reproductive behavior evolve?

Answer 7

Differences in gamete size (anisogamy) result in females investing more in reproduction, leading to choosiness, while males, having lower parental investment, engage in more mating and competition.

Question 8

What is reproductive variance, and how does it differ between sexes?

Answer 8

Reproductive variance refers to differences in reproductive success. Males typically have greater variance due to high competition, while females tend to have more consistent reproductive success.

Question 9

What are the two types of fitness benefits females consider in mate choice?

Answer 9

Direct benefits: Increase the female’s survival or reproductive success through resources, parental care, or protection.

Indirect benefits: Enhance the genetic quality of offspring, leading to higher fitness.

Question 10

Provide an example of a direct benefit in mate choice in hangflies

Answer 10

Male hangflies provide females with nuptial prey. The larger the prey, the longer the copulation, resulting in higher reproductive success.

Question 11

How do carotenoid-based colorations signal male quality?

Answer 11

Bright coloration, derived from carotenoids, indicates a diet rich in nutrients that enhance immune function, signaling a male’s foraging efficiency and health

Question 12

What is the good genes hypothesis in sexual selection?

Answer 12

Females prefer males with traits or displays that signal genetic quality, ensuring their offspring inherit beneficial genes.

Question 13

How do satin bowerbirds demonstrate the good genes hypothesis?

Answer 13

Female satin bowerbirds prefer males with well-constructed, highly decorated bowers. Bower quality correlates with male health, plumage brightness, and resistance to parasites.

Question 14

What is sensory bias in sexual selection?

Answer 14

Males evolve traits that exploit pre-existing sensory preferences in females, often unrelated to mating but initially evolved for other reasons, like foraging.

Question 15

Provide an example of sensory bias in guppies.

Answer 15

Female guppies prefer males with bright orange spots, which mimic their attraction to orange carotenoid-rich food sources. This preference benefits both foraging and mating.

Question 16

What is the runaway model of sexual selection?

Answer 16

It describes a feedback loop where a male trait and female preference for that trait co-evolve, becoming increasingly exaggerated over generations until limited by natural selection.

Question 17

What stops the runaway process?

Answer 17

Genetic variability exhaustion or high trait production costs, which are countered by natural selection for survival.

Question 18

What are common traits and behaviors seen in intrasexual selection?

Answer 18

Males may develop armaments (e.g., antlers) and use threat displays to avoid costly battles. Size and weaponry often signal dominance and fitness.

Question 19

How do males use honest signals to deter rivals?

Answer 19

Honest signals like vocalizations or physical displays reflect a male’s size or condition. For example, barking geckos use low-frequency calls correlated with larger body size.

Question 20

What is mate guarding, and why is it beneficial?

Answer 20

Mate guarding prevents a partner from seeking additional mates, ensuring paternity. For example, in birds, males guard females to reduce the likelihood of extra-pair copulations.

Question 21

How do scientists test the effects of sexual selection?

Answer 21

Experiments manipulate variables like male traits or female preferences to measure their effects. For example, in blue tits, cross-fostering experiments correlated bright male plumage with parental care.

Question 22

What predictions does the runaway selection model make?

Answer 22

Families should exhibit linkage disequilibrium, where female preferences match male traits, as seen in stickleback fish with red male coloration and female preference for red.

Question 23

What is reproductive skew?

Answer 23

It refers to the unequal partitioning of reproductive success, often higher in males due to competitive advantages.

Question 24

What role does frequency-dependent selection play in sexual selection?

Answer 24

The strength of selection on a trait depends on its frequency in the population, influencing the dynamics of traits and preferences over generations.