10/ sexual selection Flashcards
true or false there is a direct relationship between amount of resource captured and fitness
true
2 ways sexual selection acts
- intrasexual. between members of the same sex. few winners and many losers
- intersexual. competition between dif sexes
monogamy features
- little sexual selection and no sexual dimorphism
4 mating systems
- monogamy
- polygamy - both m and f have multiple partners
- polyandry - female has multiple partners
- polygyny - male has multiple partners
extra pair paternity, dunnocks
- surprisingly high rates in supposed monogamous species - offspring from male female hasn’t bonded w
- eg dunnocks have very variable mating systems. frequently polyandrous despite appearing monogamous
- females frequently mate w unpaired males
extra pair paternity in birds
chaffinch, blue tit, dunnock, tree swallow, superb fairy wren
intrasexual competition examples
- fighting male male: stag beetles
- mate guarding, stop females mating w other males before or after copulation: gamerus sp, scatophaga stercoraria
- sperm competition - females likely to have many males sperm
- lek competition: gathering of males compete w each other, females chose best males, lekking costly for males: paper wasp, fruit fly etc
what do females gain by choosing a male
- access to resources
- good genes - high level of survival to offspring like resistance to parasites
- good genes - attractiveness
runaway sexual selection - experiment
- 1982 anderson altered tail length of widowbird
- longer tail = increased mating success, even w unnaturally long tails
how does runaway sexual selection work
- females evolve preference for eg longer tails
- selection for long tailed males
- offspring have longer tails and genes for longer tails preference
poecilla reticulata fish natural vs sexual selection
- initial: course gravel in 1, fine gravel in 2, predator present
- few gens later: 1 = big spots for camouflage, 2 = small spots
- but sexual selection favours spots that contrast background when there’s no predator present
what is runaway sexual selection
selection on survival and reproduction in opposite directions
how to identify whether sexual selection is occuring
look at patterns across multiple species to see whether traits vary as we’d predict
how are sexual selection and dimorphism related
more sexual dimorphism = more sexual selection
the lek paradox
- if females are selecting for certain traits, you’d expect those to increase in the pop
- however there’s still loads of variation of the sexually selected traits - high variability and additive variance
how to predict sexual vs natural selection
- if there’s stronger natural selection, sexual selection should be weaker
- eg ground nesting birds (higher predator risk) have lower sexual dimorphism and sexual selection
