adap 2 - sexual selection Flashcards
REVIEW UP TO SLIDE 13
Fundamental asymmetry of sex
Males prod abundant small sperm but females produce few large eggs
small sperm outnumber fewer larger eggs therefore competition among males to fertilize rare eggs
Do males and females do the same things to up fitness?
NO males and females must use diff strats to increase their own individual fitness
Flow of female fitness etc.
large gamete size
higher parental investment
low levels of sexual activity
gen . less sexually active fems
selection among mates
the better the males quality, higher the individuals fitness
flow of male fitness etc.
small gamete size but many
lower parental investment
high levels of sexual activity (bc not investing in parental care or gametes)
high ratio of sex. act. males than females
COMPETITION for mates
the more mates, the higher the individual’s fitness
Biased operational sex ratio
Within the population, less sexually active females than males
MISSED MANY LOL
honest signalling
traits that honetsy signal male quality facilitate female choice, allowing them to make accurate decisions about potential mates
types of fitness benefits
Direct benefits - increase fitness of females directly
Indirect benefits - increase fitness of offspring
Direct benefits
females choose males that give them resources that increase their own survival and reproduction
predicts that males that offer more resources are given a better chance to mate
examples of honest signalling
Carotenoid based colouration - diet rich in carotenoid pigments enhances an individuals immune system, also increases colouration/brightness of feathers
honest signal of an individual’s quality and signals foraging efficiency and availability of carotenoid rich prey
sensory bias
males evolve bright shiny “bling” to take advantage of biases in gemale sensory systems that evolved previously for other reasons (e.g. ecology)
runaway model for sexual selection
a secondary sexual trait expressed in one sex becomes genetically correlated with a preference for the trait in the other sex
frequency dependent selection
strength of selection on an allele depends on the frequency of the allele
Runaway model of sexual selection
positive feedback loops of coevolution btwn the trait and preference for the trait
causes linkage disequilibrium where allele causing trait, and pref for trait found tgth more commonly
as runaway selection proceeds, gen by gen:
- linkage diseq gets stronger
- average preference of females increases
- male trait increases in freq
How could you see if runaway selection has occurred?
Within families, tends to be female preferences that match male traits
steps of runaway sexual selection
- variability in male trait and female pref. Non-choosy females are agonistic
- agnostic females mate indiscriminately, choosy females mate more with males with specific trait therefore raise its freq and gen linkage disequilibrium
- with each generation, linkage disequ ^, average pref of females ^, male trait freq ^
what could stop runaway sexual selection?
if trait begins to impede survival, natural selection takes over
intrasexual selection
male - male competition
winners mate more than losers
Results of intrasexual selection
Sexual selection for fighting ability leads to sexual dimorphism
males more likely to develope armaments (weapons) e.g. convergent evolution of horns
avoidance of battle
to mitigate cost of battle
threat behaviours!!! used to intimidate potential competitors into backing off
impacts of threat displays
separate males into dominancy heirarchy
deters fighting
resolves conflict
possible signals of dominance
acoustic signal
mate guarding behaviour
after mating, one member of the pair prevent the other from seeking additional mates/prevent other bates from approaching
extra-pair copulations
even if monogamous, not always faithful
in female birds, sperm stored in tiny tubules in uterus, last sperm to be stored more likely to be used to fertilize
mate guarding behaviour more likely
why would females undergo extra pair copulation??
monogamy - direct benefit from monogomous mate
extra-pair - indirect, if mating with more fit male!
female is maximizing fitness benefits
4 mechanisms of sexual selection by female choice
Direct benefits
good genes, honest signals
sensory bias
runaway
When do benefits occur for each mechanism of sex. sel. by fem choice?
Direct - benefit in female’s generation to her directly or to resources she gives her offspring
Good genes - benefit in next gen via genes inherited from the male
Sensory bias - there may be no benefit at all (though female could assess multiple signals to make an informed choice)
Runaway - could be no survival or fecundity benefit at all
