Sexual selection

Question 1

What is the Fisher-Muller hypothesis?

Answer 1

The idea that beneficial mutations may exist in different individuals, sex can bring them together and without sex they would only end up in the same genome if evolution proceeds sequentially.

Question 2

What is the evidence for the Fisher-Muller hypothesis? (adaptive evolution)

Answer 2

When yeast were exposed to a harsh environment they adapted in sexual species but not in asexual species. There was no prior difference in fitness of the yeast.

Question 3

What is the Muller’s Ratchet process?

Answer 3

The idea that asexual lineages accumulate deleterious mutations through time - if the asexual lineage is hit by a mutation there is no way to get rid of it and the fitness of the lineages will decline as the mutations accumulate.

Question 4

What is the Red Queen hypothesis?

Answer 4

The idea that species are constantly facing changing environments that they must adapt to in order to survive.

Question 5

What is an example of the Red Queen hypothesis?

Answer 5

Parasites evolve rapidly to adapt to common genotypes. Genotypes that currently resist the infection will increase in frequency and become targets for parasites and they will evolve to exploit this resource. Sex generates novel genotypes to escape the parasites.

Question 6

Why are asexual lineages lost?

Answer 6

Mutation accumulation (Muller’s Ratchet), inability to escape parasites and an inability to adapt and/or outcompete sexuals.

Question 7

List the 4 types of mating system.

Answer 7

Monogamy, polygyny, polyandry and polygynandry.

Question 8

List the differences between the 4 types of mating system.

Answer 8

Monogamy involves one male and one female, polygyny involves many females and one male, polyandry involves many males and one female and polygynandry involves many males and many females.

Question 9

Why do mating systems matter?

Answer 9

As males and females have the same average fitness, but mating systems determine the variance in mating success for each sex.

Question 10

Why does the variance matter?

Answer 10

It provides the opportunity for variation in mating success to cause selection - opportunity for traits that determine mating success to be under selection and evolve.

Question 11

What are the different pressures on males and females?

Answer 11

Females typically invest more in each gamete/offspring (small number of larger, costly eggs) whereas males invest very little per gamete/offspring (large numbers of tiny sperm). It’s expected that females should be choosy when choosing mates.

Question 12

What is sexual selection?

Answer 12

Selection on traits caused by variation in mating success. It is sometimes viewed as a form of natural selection, and sometimes viewed as a separate process.

Question 13

What is intersexual selection?

Answer 13

Mate choice - one sex imposing selection on the other sex by choosing who to mate with based on traits.

Question 14

What is intrasexual selection?

Answer 14

Mate competition - competition between individuals of the same sex for access to mates.

Question 15

Why would individuals choose particular mates?

Answer 15

May gain direct benefits (food gifts in insects e.g. hanging flies, safety from predators) or may choose mates that will produce high quality offspring

Question 16

What is the Hamilton-Zuk hypothesis?

Answer 16

The idea that costly traits such as bright colouration may reflect a males overall health and can act as an indicator trait that is an honest signal.

Question 17

What is runaway sexual selection?

Answer 17

The idea that females may select for large male traits (ornaments) that will result in a runaway process that can lead to these ornaments being so large that they are detrimental to the males house.

Question 18

What is an example of the runaway process?

Answer 18

Long-tailed widowbirds.

Question 19

How is the runaway process often stopped?

Answer 19

Natural selection can select for the less-extreme males, despite these extremes being preferred by females.

Question 20

How can intrasexual selection also lead to runaway traits?

Answer 20

Elaborate weapons may be formed that may only act as signals, rather than being used to physically fight.

Question 21

What is post-copulatory sexual selection?

Answer 21

When competition between males occurs after mating - sperm competition.

Question 22

What is sexual conflict?

Answer 22

When the best interests of males and females are opposing, such as mate guarding in water striders where males guard females after copulation to prevent her remating, whereas females may benefit from multiple mating.

Question 23

What is an example of sexual conflict in deers?

Answer 23

Males are bigger and have large antlers that increase reproductive success but no parental care is provided by males. Females lack weapons and invest heavily in parental care, but males with high reproductive success will sire daughters with low reproductive success.

Question 24

How has sexual conflict from sperm competition arose?

Answer 24

Sperm competition has led to the evolution of a large number of seminal fluid proteins that mediate competition between males for fertilisation, such as in Drosophila some sperm can reduce female willingness to remate, create a plug to prevent remating or increase egg laying by females.

Question 25

Why can selection be more complicated than it seems?

Answer 25

There may be mutual mate choice, such as in monogamous species or ecological factors can differentially affect males and females.