Sexual Selection Flashcards
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
what happens if you are above the threshold in pre and post copulatory?
intesnity of sperm competition increases
what would you invest in pre copulatory?
searching, weapons, ornaments
what is post copulatory?
sperm competition, make sure your sperm gets used and noone else gets to mate
what would you invest in post copulatory?
testes size, ejaculation, volume
how do damselfly ensure their sperm will get there first?
has primary and secondary genitalia. penis evolved to clear out any other sperm in the females genital tract
what is cryptic female choice?
happens once sperm are inside. females deliberatly mate with multiple males to let the sperm fight it out
what could sperm competition success mean?
- healthy male
- good sperm competition
- or btoh
what are female storage organs?
complex and rapidly co - evolve with sperm traits - restores female control
describe how sexual selection can drive speciation
drives mate recognition traits
important in reproductive isolation
leads to speciation
where would rate of change in sexual selection change and speciation be accelerated?
- isolate populations
- different preferences
- leads of isolation and speciation
