Sexual selection

Question 1

what is the difference between isogamy and anisogamy?

Answer 1

isogamy
= sexual reproduction involving gametes of similar form
e.g. differ only in mating type region (+ or -)

anisogamy
= sexual reproduction involving gametes that differ in form or function

Question 2

What do anisogamous eukaryotes have 2 types of?

Explain what this means

Answer 2

phenotype
sex gametes

male phenotype
- produces small mobile gametes

female phenotype produces large immobile gametes

Question 3

what is the 2-fold cost of sex?

Answer 3

an asexual individual passes on 2x as many genes as a sexual individual

asexual offspring are 100% related to mother

mother loses 50% of her contribution in each generation of sexual reproduction

Question 4

what is the red queen hypothesis?

Answer 4

metaphor for evolutionary arms race
= must keep adapting to maintain (NOT increase) fitness
- need to able to change with the conditions

Question 5

how is evolutionary arms race related to resistance to parasites?

Answer 5

sexual reproduction is advantageous

-> genetic recombination creates new gene combinations which are resistant to parasites

Question 6

what are the genetic advantages of sexual reproduction?

Answer 6

sexual populations have more genetic variation

recombination prevents accumulation of deleterious mutations (Muller’s ratchet)

recombination enables selection for advantageous mutations near deleterious (Ruby in the rubbish)

Question 7

define sexual conflict

Answer 7

a conflict between the 2 evolutionary interests of individuals of the 2 sexes

divergent phenotypic + behavioural traits

Question 8

Bateman’s principle

Answer 8

male reproductive success (RS) increases with the no. of mates
-> interested in mating with many females

female RS doesn’t increase with no. of mates
-> interested in mating with high quality males

leads to conflict of interest between sexes over mating

Question 9

why does neither sex win or lose?

Answer 9

the fitness of males and females is tied together

both sexes would have male and female offspring

Question 10

give an example of a behavioural consequence of sexual conflict

Answer 10

Infanticide:
female’s interest
= raise current offspring

male’s interest
= speed up female reproduction

Males taking over females with dependent young will kill the offspring

Question 11

what are the evolutionary consequences of sexual conflict?

Answer 11

one sex will have higher investment and thus lower levels of sexual activity

can lead to a biased operational sex ratio

Question 12

which types of species can undergo sex role reversal?

Answer 12

polygamous species
- females may have to compete for males e.g. in seahorses

(monogamous species exhibit conventional sex roles)

Question 13

which species can exhibit flexible sex roles?

Answer 13

Katydids
females compete for males when resources are scarce

-> males provide a nutritious spermatophore

Question 14

what were the 2 selection processes Darwin recognised?

Answer 14

natural selection
= selecting traits that enhance survival

sexual selection
= selecting traits that enhance reproductive success

Question 15

define sexually selected traits

Answer 15

traits selected due to sexual selection BUT would be disadvantageous in the absence of sex

e.g. antlers, peacock’s tail

Question 16

how are sexual selected traits maintained in a population?

Answer 16

mating benefits (reproductive success) outweigh the survival cost

Question 17

what are the 2 types of sexual selection?

Answer 17

intersexual
= mate choice

intrasexual
= competition within a sex

Question 18

give pre and post-mating examples of intrasexual selection

Answer 18

pre:
male-male fights
weapons
territory defence

post:
mate guarding
sperm competition 
sperm displacement 
copulatory plugs

Question 19

give pre and post-mating examples of intersexual selection

Answer 19

pre:
female mate choice
male ornaments
courtship behaviours

post:
cryptic female choice
(sperm selection/dumping)
egg-sperm binding proteins

Question 20

give an example of male-male competition

Answer 20

Elephant seals

fights can be costly

male size»»> female size

1 male can defend large harem of 100s of females

v few males father offspring
-> highly skewed male RS

Question 21

give an example of sperm displacement

Answer 21

Drosophila

males remove rival’s sperm from female reproductive tract

Question 22

give an example of copulatory plugs

Answer 22

Mice

males cement the female’s genitalia after copulation
via proteins in the sperm

Question 23

give an example of sperm competition

Answer 23

Polygynous birds

males produce large quantities of sperm that out-compete rival males’ sperm in the female reproductive tract

Question 24

give an example of female mate choice

- Sedge warblers

Answer 24

greater song repertoire
-> female pairs earlier with male
(correlation not causal, as male may just have had good territory)

Question 25

give an example of female mate choice

- Barn swallows

Answer 25

males with elongated tails paired up sooner than control or shortened tails

Question 26

what are the direct benefits of females choosing?

Answer 26

resources:
nuptial gifts,
safe site to deposit eggs,
breeding territory with abundant food

Question 27

explain the direct benefits of females choosing larger American bullfrogs

Answer 27

male bullfrogs compete for good territories

embryo mortality is lower in territories of large males

Question 28

what is the indirect benefits of female choosing?

Answer 28

good genes

-> viable young

Question 29

what are the versions of the ‘good genes’ hypothesis?

Answer 29

Handicap principle
= reliable signals of male quality must be ‘costly’
- if they can survive then they must have good genes

Resistance to parasites
= sexual displays are indicators of genetic resistance to disease + parasites

e.g. barn swallows with longer tails have fewer parasites

Question 30

what is the Fisherian runaway hypothesis?

Answer 30

females prefer elaborate courtship and ornaments

• > mate with them
• > males in the next generation are more likely to possess these traits + females are more likely to prefer these traits

Question 31

what is the sexy son hypothesis?

Answer 31

females choose mates whose genes will produce male offspring with the best chance of reproductive success

Question 32

give examples of alternative mating strategies

Answer 32

Horned scarab beetle

• some males have big horns
• those without big horns have big testes = produce more sperm

Scorpionfly
1. defend dead insect = nuptial gift 
2. secrete saliva = nuptial gift 
3. forced copulation 
(different strategies based on size of male)