Lecture 8

Question 1

Pros of Sexual Reproduction – Mutation Benefits

Answer 1

Sexual reproduction allows the combination of two new, currently beneficial mutations, increasing adaptability.

Question 2

Cons of Sexual Reproduction – Cost of Sex

Answer 2

Sexual reproduction has a two-fold cost: only half of an individual’s genes are passed on, reducing the number of direct descendants compared to asexual reproduction.

Question 3

Pros of Sexual Reproduction – Recombined Chromosomes

Answer 3

Offspring inherit alleles from both grandparents, leading to increased genetic diversity and adaptability.

Question 4

Cons of Sexual Reproduction – Finding a Mate

Answer 4

Finding a high-quality mate can be challenging and requires effort, including considerations of sperm availability or childcare.

Question 5

Pros of Sexual Reproduction – Evolutionary Advantage

Answer 5

Genetically variable offspring evolve faster, increasing survival in changing environments.

Question 6

Cons of Sexual Reproduction – Reduced Relatedness

Answer 6

Offspring are less related to a perfectly adapted parent, which may reduce short-term fitness advantages.

Question 7

Pros of Sexual Reproduction – Avoiding Muller’s Ratchet

Answer 7

Asexual populations accumulate harmful mutations over time, whereas sexual reproduction helps eliminate them through recombination.

Question 8

Cons of Sexual Reproduction – Disease Risk

Answer 8

Sexually transmitted diseases are a risk, but choosing a healthy, attractive mate (e.g., one with bright plumage) can help mitigate this.

Question 9

what is Anisogamy

Answer 9

differences in the sizes of gametes between sexes

Question 10

what does Anisogamy result in?

Answer 10

differential investment in reproduction
females: tend to invest more in offspring care
males: are more likely to invest in competing for mates

Question 11

Why is male parental care rare in many species?

Answer 11

Males often have uncertain paternity, meaning they risk investing in offspring that may not be their own.

Question 12

Why do females typically invest more in offspring than males?

Answer 12

Females have certain parentage, ensuring their investment directly benefits their own genetic offspring.

Question 13

What is the operational sex ratio (OSR)?

Answer 13

The OSR is the ratio of males to females available for mating at a given time, influencing the intensity of sexual competition.

Question 14

How do investment differences between sexes affect OSR?

Answer 14

The sex that invests more in offspring (typically females) is in shorter supply, often leading to a male-biased OSR.

Question 15

What causes a male-biased OSR?

Answer 15

A slower female reproductive rate (e.g., pregnancy, lactation) reduces the number of available females, leading to more males competing for mates.

Question 16

when is the highest OSR ratio seen

Answer 16

when the female is pregnant or lactates for long periods of time and male does not assist with offspring care

Question 17

How does OSR relate to sexual selection?

Answer 17

The more abundant sex (usually males) competes more intensely, while the less abundant sex (usually females) becomes choosier in mate selection.

Question 18

What is Bateman’s 1947 hypothesis?

Answer 18

Bateman proposed that sexual selection is stronger on males because male reproductive success depends on the number of mates, whereas female success depends on resources.

Question 19

what were the 2 predictions from Bateman’s original hypothesis now recognized as partially incorrect

Answer 19

1. males should compete among themselves for opportunities to mate and be promiscuous
2. females should be choosy about males they copulate with

Question 20

what is sexual selection

Answer 20

Sexual selection is a form of natural selection where traits evolve due to competition for mates, influencing reproductive success.

Question 21

What is intrasexual selection?

Answer 21

Competition within the same sex, usually males, for access to mates or fertilizable eggs (e.g., fighting, dominance displays).

Question 22

What is intersexual selection?

Answer 22

Selection based on mate choice, where one sex (usually females) selects mates based on traits like resources or displays.

Question 23

How do males typically maximize fitness?

Answer 23

By mating with multiple females, increasing the number of offspring they produce.

Question 24

Which individuals experience the strongest intrasexual selection?

Answer 24

The sex with the lowest reproductive investment and highest variance in reproductive success (typically males) experiences the strongest selection.

Question 25

What are common outcomes of intense intrasexual competition?

Answer 25

1. Physical combat (e.g., fighting to the death for mates) 2. Sperm competition (e.g., producing more or better sperm) 3. Infanticide (e.g., males killing offspring of previous males to induce female fertility sooner)

Question 26

How is intrasexual selection similar to natural selection?

Answer 26

1. Traits vary within a population 2. Traits are heritable 3. Certain traits increase reproductive success

Question 27

How does intrasexual selection differ from natural selection?

Answer 27

1. It influences mating success, not survival directly. 2. Competition occurs within the same sex, rather than against all individuals. 3. Some traits lower survival (e.g., large antlers, bright coloration that attracts predators).

Question 28

What is infanticide?

Answer 28

Infanticide is the killing of dependent offspring, often by adult males, to increase their own reproductive success.

Question 29

Why do males commit infanticide?

Answer 29

In species where females do not ovulate while nursing, killing infants from previous males causes females to return to estrus sooner, allowing the new male to mate.

Question 30

How does mating system affect testes size in primates?

Answer 30

Males in multi-male mating systems have larger testes due to sperm competition, while dominant male guarding systems have smaller testes due to low competition.

Question 31

Why might a female’s mate stop helping if she mates with others?

Answer 31

In some species, males reduce parental care if they suspect the offspring are not theirs. - red-winged birds

Question 32

How can mating with multiple males physically harm a female?

Answer 32

In some wasps, excessive sperm can clog the reproductive tract, making egg-laying difficult.

Question 33

Why might foraging be a better use of time than seeking multiple mates?

Answer 33

Instead of mating repeatedly, females can focus on gathering food to produce more eggs, increasing reproductive success.