R18 Sexual selection Flashcards
How has sexual and asexual reproduction evolved ?
They have deviated on ce but has been lost many times
Sexual is very costly
What is the “two-fold” cost of sex?
the production of males don’t have reproductive qualities like having a female clone itself, if it was asexual.
What is sexual selection?
a sub-set of natural selection used to describe the processes underlying the evolution of differences in attributes of males and females
Sexual selection occurs only when parental investment is unequal
How does the gametes and limiting rate of reproduction vary between males and females?
Females: few, larger and more costly gametes, they are limited by the amount of resources they can obtain
Males: many, small and cheap gametes, they are limited by the number of mates (operational sex ratio)
What is differential parental investment ?
the different sizes of gametes allow more to be made, maximising the reproduction of the male
- Increasing the chance of beneficial alleles making it to the next generation
What is selected for during sexual selection?
- Physical traits: size and weaponry
- Physiological traits: sperm production
- Behaviour
How does competition affect an individuals fitness?
more competitive = more fit
How does pre-copulation selection work ?
the female choice that hinders a male’s affinity to reproduce
How does post-copulation selection work ?
continues after mating, sperm competition, mate guarding (can be pre or post) mate manipulation (physical guarding, extending copulation, using copulatory plugs, increase oviposition (lay eggs), reduce females remating, get rid of sperm of other males), infanticide (killing of offspring by their mum)
What is promiscuous competition?
having among the largest relative testes size of any mammal
What is sperm competition?
- Sperm competition ( when a female mates with multiple males) allows for the weaker male to be drowned out
What is an example of intra-sexual selection?
Antler size
What are some intra-sexual selections ?
- Epigamic characters: behaviour, ornamentation
- Direct benefit: provide a direct benefit to the other sex; food, protection, parental care
- Honest signal : individuals are chosen because their phenotype signals indirect tangible benefits (beneficial genes)
- Fisher’s runaway sexual selection:
o Step 1: a mutation exaggerates a males appearance and conders greater fitness, good genes are displayed
o Step 2: that mutation or a second mutation causes females to prefer that trait, now the females prefer the original males offspring
o Step 3: runaway selection, females mate with males with exaggerated trait, produce sexy sons, males exaggerate more and the cycle continues - Sensory bias: females may only be able to hear certain males, birds use the quality of variety of different songs
What may hermaphrodites fight for ?
Sperm are cheaper so they fight to inject sperm into each other, they fight for the cheaper role (the male).
Why are there still small testes if sexual selection acts against them ?
Small testes are still present as there are physiological limits to having larger testes so males with small testes will eventually get a chance to pass on their genes
