Sexual selection Flashcards
what is the difference between isogamy and anisogamy?
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
What do anisogamous eukaryotes have 2 types of?
Explain what this means
phenotype
sex gametes
male phenotype
- produces small mobile gametes
female phenotype produces large immobile gametes
what is the 2-fold cost of sex?
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
what is the red queen hypothesis?
metaphor for evolutionary arms race
= must keep adapting to maintain (NOT increase) fitness
- need to able to change with the conditions
how is evolutionary arms race related to resistance to parasites?
sexual reproduction is advantageous
-> genetic recombination creates new gene combinations which are resistant to parasites
what are the genetic advantages of sexual reproduction?
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)
define sexual conflict
a conflict between the 2 evolutionary interests of individuals of the 2 sexes
divergent phenotypic + behavioural traits
Bateman’s principle
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
why does neither sex win or lose?
the fitness of males and females is tied together
both sexes would have male and female offspring
give an example of a behavioural consequence of sexual conflict
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
what are the evolutionary consequences of sexual conflict?
one sex will have higher investment and thus lower levels of sexual activity
can lead to a biased operational sex ratio
which types of species can undergo sex role reversal?
polygamous species
- females may have to compete for males e.g. in seahorses
(monogamous species exhibit conventional sex roles)
which species can exhibit flexible sex roles?
Katydids
females compete for males when resources are scarce
-> males provide a nutritious spermatophore
what were the 2 selection processes Darwin recognised?
natural selection
= selecting traits that enhance survival
sexual selection
= selecting traits that enhance reproductive success
define sexually selected traits
traits selected due to sexual selection BUT would be disadvantageous in the absence of sex
e.g. antlers, peacock’s tail
how are sexual selected traits maintained in a population?
mating benefits (reproductive success) outweigh the survival cost
what are the 2 types of sexual selection?
intersexual
= mate choice
intrasexual
= competition within a sex
give pre and post-mating examples of intrasexual selection
pre:
male-male fights
weapons
territory defence
post: mate guarding sperm competition sperm displacement copulatory plugs
give pre and post-mating examples of intersexual selection
pre:
female mate choice
male ornaments
courtship behaviours
post:
cryptic female choice
(sperm selection/dumping)
egg-sperm binding proteins
give an example of male-male competition
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
give an example of sperm displacement
Drosophila
males remove rival’s sperm from female reproductive tract
give an example of copulatory plugs
Mice
males cement the female’s genitalia after copulation
via proteins in the sperm
give an example of sperm competition
Polygynous birds
males produce large quantities of sperm that out-compete rival males’ sperm in the female reproductive tract
give an example of female mate choice
- Sedge warblers
greater song repertoire
-> female pairs earlier with male
(correlation not causal, as male may just have had good territory)
give an example of female mate choice
- Barn swallows
males with elongated tails paired up sooner than control or shortened tails
what are the direct benefits of females choosing?
resources:
nuptial gifts,
safe site to deposit eggs,
breeding territory with abundant food
explain the direct benefits of females choosing larger American bullfrogs
male bullfrogs compete for good territories
embryo mortality is lower in territories of large males
what is the indirect benefits of female choosing?
good genes
-> viable young
what are the versions of the ‘good genes’ hypothesis?
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
what is the Fisherian runaway hypothesis?
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
what is the sexy son hypothesis?
females choose mates whose genes will produce male offspring with the best chance of reproductive success
give examples of alternative mating strategies
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)
