Lecture 7- Sexual selection

Question 1

example of a sexually selected trait being actively harmful for survival

Answer 1

cricket- has a song which attracted females, but parasitoids recognise it and can use it to identify and kill them

Question 2

what is anisogamy

Answer 2

mating involving differential investment in gamete size- sperm are smaller/cheaper to produce compared to eggs (disassortative functions)

Question 3

bateman gradient

Answer 3

for males, partner number correlates with number of successful offspring, for females, mate number doesn’t impact mating success much- different aims

Question 4

explanation for bateman gradient

Answer 4

males are limited by the number of females, whereas females are limited by their environment

Question 5

issues with bateman principles

Answer 5

mating success was inferred from offspring numbers so didn’t consider other matings, which can over-estimate sexual selection on males

Question 6

evidence for bateman principles

Answer 6

big analysis bt Janike et al- suggests that there does tend to be more variance in male reproductive success, but there can be exceptions

Question 7

intrasexual selection

Answer 7

competition among individuals of the same sex for members of the opposite sex

Question 8

intersexual selection

Answer 8

selection of reproductive partners by one sex among members of the other

Question 9

female mate choice study

Answer 9

andersson 1982- elongating tails in long-tailed birds made them more reproductively successful measured by nest building- females clearly responded to changes in male phenotype

Question 10

nature of female bias

Answer 10

sensory bias based on natural selection, rather than being adaptive to specific females

Question 11

fisherian runaway

Answer 11

evolution of ornaments due to linkage disequilibrium between female preference for an ornament and its evolution

Question 12

handicap principle

Answer 12

sexually selected traits are costly, and can be maintained by ‘better’ individuals, so these reflect quality or ‘condition’ of a potential partner

Question 13

example of the good genes idea

Answer 13

eyespan in some male insects is a sexually selected trait, when fed a poor diet, it gets smaller
immunocompetence- higher testosterone means you can cope with the repressed immunity, which suggests better immunity

Question 14

what are the drivers of polyandry

Answer 14

often male driven and maladaptive to females
convenience to avoid cost of resisting
resources, e.g. paternal care
fertility insurance
genetic benefits through increased diversity

Question 15

what trade-offs are there with polyandry (for males)

Answer 15

post-copulatory selection becomes important, not actually a guarantee of paternity all of the time

Question 16

what are p and m

Answer 16

p- share of paternity in a set of ova
m- number of females mated

Question 17

example of alternative mating tactics

Answer 17

having different ‘types’ of males, leads to density-dependence type processes, e.g. if there are a lot of less aggressive and territorial males, the more aggressive type becomes dominant etc