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• • • • • • Birds in Costa Rica Bats in Israel Squirrels in Canada Monkeys in Ethiopia Pronghorn in Montana www.animalbehavior.org • Asexual and sexual organisms • Sex and gender • Sexual selection – Selection affecting access to gametes http://www.micrographia.com/specbiol/cnidari/hydrozo/hydr010 0/hydra-01.htm http://flickr.com/photos/billwalker/2521121709/ • Costs of sex – Cost of meiosis – Breakup gene combinations – Mate acquisition – STDs • Benefits of sex – Adapt to changing environment • Abiotic • Biotic http://porpax.bio.miami.edu/~cmallery/150/life/meiosis.pics.jpg • Pathological in tetrapods • Simultaneous – – – – Earthworms, gastropods, hamlet fish Self fertilization is rare Costs: Double the sex organs Benefits: When optimal sex for relative size of mates changes • Sequential – – – Teleosts Usually a one way ticket Female male in reef fish • • – When harem male dies Only large males can defend a territory Male female in sea bass • Female reproductive output increases with size http://www.fsbio-hannover.de/oftheweek/196/800pxMating_earthworms.jpg http://throughthestatic.wordpress.com/category/idio ts/ • The evolution of Anisogamy – Females and males • Consequences of anisogamy – Unequal parental investment – Unequal variance in fitness • Ornamented males • Choosy females – Easy males http://www.microscopy-uk.org.uk/thedark/eggbigx.jpg • Intra-sexual selection – Interference competition • • • Armaments (displays) Size Badges of status • Inter-sexual selection – Scramble competition • Locomotion and mate seeking – Mate choice • • Ornamentation (displays) Alternative tactics (e.g, coercion, female mimicry) • Sperm competition • Given interference competition – Directional selection for male size, armaments – Decrease in males’ mean viability – Evolutionary “arms race” – Distribution of male size as costs balance benefits – Mean investment is proportional to number of defended females (reproductive variance) http://www.innatmorrobay.com/elephant_seals_color.jpg • Male size vs. male trait size • Shrinking females • Alternative strategies • Small male advantage http://crawford.tardigrade.net/journal/album/lillivatia.jpg From Legrand and Morse 2000 Biol. J. Lin. Soc. 71:643-664 • Amplexus – Female receptivity is limited, cyclic, asynchronous – Males are available to reproduce almost continuously http://www.treknature.com/gallery/Middl e_East/Turkey/photo164737.htm • Mate guarding in birds From Birkhead 1979 Anim. Behav. 27:866-874 • The importance of the question • The operational sex ratio (OSR) • The potential reproductive rate (PRR) • The differential cost of reproduction – Covaries with OSR and PRR From Amundsen & Forsgren 2001 PNAS 98:13155-13160 • Definition • Kinds – Fertilization success – Protection – Resources • Territories • Parental care • Nuptial gifts – – Nutritious ejaculates Sexual cannibalism http://www.biology.au.dk/trine.bilde.htm Photograph by Medford Taylor Male cost trait linkage Genetic of Benefit Female preference Generations Different genes promoting trait / preference Trait size • Lande’s version – Quantitative genetic – Runaway when B / G > (v2 / w2 ) + 1 – In other words, when CVA (B) is high relative to VA of trait (G) with low variance in female preference (v2), weak utilitarian selection on trait (high w2) – Requires initial preference! • • • Natural selection Drift Sensory exploitation • P1: Additive genetic variance for trait and preference – Generally supported – Traits are influenced by several loci • P2: Genetic co-variation between trait and preference – Method 1: Select for trait, see if preference also changes • Generally supportive – Method 2: Is there covariation among traits in brothers and preferences in sisters? • Supported in sticklebacks and crickets