Sexual Selection Flashcards
(34 cards)
what is the problem with a peacocks plumage?
it challenges natural selection - doesn’t provide survival benefits, costly displays use lots of energy
what is sexual selection?
gives a benefit over others solely in respect to reproduction - need to pass on genes
what are primary sexual characteristics?
ovaries and testes
directly related to sperm and egg
what are secondary sexual characteristics?
- Shape and size (sexual dimorphism)
- Colour (sexual dichromatism)
- Behaviour (sex specific behaviours)
how did male and female sexes evolve?
- ancestor, single gamete size
- some bigger and did better
- get more at one end of the spectrum
- another strategy was to produce low quality but lots of them
- get disruptive selection
- disadvantageous for sperm to go with sperm so have to have one of each
why might secondary characteristics have evolved?
- identifying own species?
- male-male competition - evolved to fight for females
use elephant seals as an example.
- competition between males can drive dimorphism
- elephant seals have huge males
- females grouped at breeding grounds so a defendable resource
- males fight each other, leads to bigger male sizes
what is female choice based on?
- good providers
- sensory bias
- compatible genes
why is a good provider a female choice?
- male will provide care and benefits
- important for the female to choose a good provider
- happens a lot in fish
use fish as an example of a good provider.
- orange pigmentation: from carotenoids in insects - shows better care
- ones that prefer orange produce more offspirng
- orange spreads
- orange pigmentations an honest signal
- males could cheat by producing orange without carotenoids
why is sensory bias a female choice?
due to pre - existing bias of a sign of a better provider
eg if females prefer larger males
how can males evolve to exploit sensory bias?
- appear larger without paying the costs
eg a sword tail makes fish look larger than it is
how can sensory bias be shown in humans?
- Low voices are associated with attractiveness in humans
- Females voted low pitch with a face more attractive
- theory: deep rooted bias due to large bodied predators
shouldn’t the female be evolving to not be fooled?
- eg males losing sword tails as females lose preference
- many cases the preferences persists
what is the sexy self hypothesis?
For instance a big sword tail is attractive - sons will have swordtails - makes them attractive to other females
- get a feedback loop
- no further suvrival benefits but attractiveness
how are the females unnder selection in sensory bias?
sensory processing evolution
what is Fishers runaway selection?
good gene
- signals become honest again
what is zalavis handicap principle?
- Not just a runaway loop
- Means they are fit - good quality genes
what would happen if the individuals evolved to the most extreme trait possible?
low genetic variation
what is Zuks parasite hypothesis?
- handicap principle only works if you take in parasites
- constant co - evolutionary arms race
- host defense v parasite
- trade off investment in immune defense and sexual signalling
- strong signal –> not riddled with parasites
why are compatible genes are female choice?
- females have different preferences
- advantageous to heterozygostiy
- certain alleles may complement each other
- a deleterious allele will be lethal
use MHC as an example of compatibility?
- individuals vary in preferences maintaining diversity
- MHC genes are important in determing resistance to pathogens
- MHC genes are very variable and good for male choice
what is pre - copulatory sexual selection?
only 1 mate then investment would be in becoming the mate
what happens if you are below the threshold in pre and post copulatory?
for the male there is a risk no mating happens at all
