09SexSelect06x - Sexual selection"The season of love is the...

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Sexual selection “The season of love  is the season of battle.”   (Darwin 1872)
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Sexual selection - if survive, might mate 1. intra- (usu. ♂-♂) - outcompete rivals; usu. aggression 2. inter- (= mate (♀) choice , epigamic ) - sing, .., smell good - overlap
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Mating systems 1. monogamy (& communal) - when 1 parent insufficient - very rare (Ribble & Chatelaine) - enforced by synchronous fertility - social vs. genetic 2. polygyny 3. polyandry 4. promiscuity (no bond, multiple mates, incl. leks), polygynandry (dunnocks) polygamy
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Why sex-biased courting  (whether  s  bigger or not)? - generalities & determinism! - how does each sex maximise fitness? - both via production of young - but, e.g., human ♀ max. is ~ 1 ea. 9 mos. - human ♂s max. theoretically all - why? - gamete size
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Sexual dimorphism - consequence of different selection pressures on ♀s & ♂s (independent of gonads, = 2 o traits) - selection on ♀s to survive, on ♂s to look & act silly - esp. where payoff greatest; polygyny
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Announce 1. limited info on parasites in leks versus other mating systems 2. Mean for 1 st lab = 77%
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Dimorphic strategies - ♀s ↑ initial investment in young (eggs, etc. vs. sperm), so choosy about mates (control access to eggs) - ↑ # of mates has ↓ influence on ♀ fitness - # mates ~ linearly related to ♂ fitness; cost of mating low, ↓ need to be choosy 0 1 2 3 4 5 6 7 8 0 1 2 3 4 Number of mates Number of offspring Female mating success Male mating success
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Bateman's principle - ↑ variation in ♂ vs. ♀ mating success; many ♂s never mate, most ♀s do - Drosophila , 5 ♂s, 5 ♀s, replicates % not If mating, Corr. btwn. # mating avg. # mates kids, mates ♂s 21 >2 ++ ♀s 0 1-2 0 - sp.-specific, but partly generalisable - bias in literature
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  rationale for   #  mates?
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