sexual selection 2

it is in a particular alleles best interest to act in such a way that it promotes its own chance of successful tranmission to next generation

• ensuring other copies of the gene itself reproduces/survives
• these copies are likely to be found in relatives
• leads to evolution of behaviour that promotes reproduction by your relatives or protection of kin from danger

• fitness of an allele can be related to how well it promotes reproduction/survival of copies of itself in other individuals 
• females have greater individual success by staying in related groups + communally raising young

evolutionists response - look for mechanisms that allow evolution of altruistic behaviour without contravening selfish gene, ESS, game theory etc.

• vampire bats - unrelated adults share blood meals on return to roost
• rule - if ive not fed for 36hrs and will die within 24hrs you must feed me, ill do the same one day

1. direct selection on female preference
2. sensory bias - can't help herself
3. indirect selection

• all 3 lead to evolution of choosy females + showy males
• all involve heritable variation

• if male provides access to resources he may be selected on basis of large territory, high quality territory, parenting investment etc.
• may also be selected on basis of resource provision

• females are polyandrous - multiple mates
• competition for fertilisation = giant testes (5% body weight) make giant sperm
• accessory gland proteins carried on giant sperm passed to females in seminal fluid
• sex peptide makes female unreceptive to other males for days rather than hours
• giant sperm have evolved to facilitate the gradual release of these

• female preference may have pre-existed, preferred trait in males comes later + selected
• examples = colour, size etc.
• tungara frogs - female preference for males with complex song

• preference in female is indirectly selected via direct selection on preferred male trait
• preference expressed in choosy sex

• a gene variant arises causing female preference for that male trait
• assortative mating occurs for new extreme trait
• offspring likely to carry trait + preference gene
• after generations, trait + preference gene become genetically correlated
• runaway selection can start