sexual selection theory Flashcards
lecture 2
sexual selection results from… (Darwin)
advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction
sexually selected traits
may be disadvantageous in everyday life
waste time, energy, reduce survival
as long as the mating advantage compensates the cost in everyday life, these traits are expected to occur
2 models of sexual selection
intrasexual selection (fighting) and intersexual selection (mate choice)
intrasexual selection
evolution of dimorphism in armaments and aggression
male-male competition
in many animals, males fight over females and defend them, also mate guard females when fertile
post-copulatory competition - sperm removal
males scoop the stored sperm from the female reproductive tract
post-copulatory competition - copulatory plugs
males cement the female genitalia after copulation
post-copulatory competition - sperm competition
males produce large quantities of sperm that out competing males sperm from the female reproductive tract
sperm competition
occurs when a female mates with 2 or more males during 1 conceptive cycle
females may promote it, to confuse paternity and increase genetic quality
breeding system correlates with testes size, ejaculate volume and quality
Anderssons work on widow birds
experimental groups - shortened tails and lengthened tails
control group - cut tail, but glued back to original length
result - prefer longer tails
preference for paternal males
high investors, non-infanticidal
how can females tell what males will be like
fitness traits and random (exaggerated) traits
benefits of mate choice - female preferences are adaptive
non genetic, material benefits - adaptive directly
genetic benefits - adaptive indirectly, sexy sons/good genes
non-genetic, material benefits
resources and parental core - for reasons of fertilisation ability, nutrition, parental ability of males, territory quality, avoiding venereal disease
Fishers ‘runaway’ theory for evolution of extravagant male traits
genes for female preference for long tails -> genes for long tails
initial imbalance between female preference and male trait
genetic covariance
problems for the Fisher process
how does it get started
choosiness genes should go extinct after male trait reaches fixation
solution for the Fisher process
male traits indicate genetic quality
Zahavi - handicap models
exaggerated traits re costly to produce and therefore a handicap - only fit males can afford it
revealing handicap - costliness of signal indicates genetic quality of male
Hamilton + Zuk - handicap model
sexual displays are indicators of genetic resistance to disease and parasites
are females choosing genetic resistance to parasites
females offered a choice, preferred more brightly coloured males
colour was the cue
brightness inversely related to parasites load
