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You could study…

You could study…. Birds in Costa Rica Bats in Israel Squirrels in Canada Monkeys in Ethiopia Pronghorn in Montana www.animalbehavior.org. Sexual selection. Sex (the basics). Asexual and sexual organisms Sex and gender Sexual selection Selection affecting access to gametes.

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You could study…

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  1. You could study… • Birds in Costa Rica • Bats in Israel • Squirrels in Canada • Monkeys in Ethiopia • Pronghorn in Montana • www.animalbehavior.org

  2. Sexual selection

  3. Sex (the basics) • Asexual and sexual organisms • Sex and gender • Sexual selection • Selection affecting access to gametes http://www.micrographia.com/specbiol/cnidari/hydrozo/hydr0100/hydra-01.htm http://flickr.com/photos/billwalker/2521121709/

  4. Sex is a mixed bag • 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

  5. Hermaphroditism • 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/196/800px-Mating_earthworms.jpg http://throughthestatic.wordpress.com/category/idiots/

  6. Anisogamy • 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

  7. Kinds of sexual selection • 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

  8. Intra-sexual selection

  9. The evolution of size dimorphism • 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

  10. Caveats on size dimorphism • 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

  11. Precopulatory guarding • Amplexus • Female receptivity is limited, cyclic, asynchronous • Males are available to reproduce almost continuously • Mate guarding in birds http://www.treknature.com/gallery/Middle_East/Turkey/photo164737.htm From Birkhead 1979 Anim. Behav. 27:866-874

  12. Inter-sexual selection

  13. Which sex chooses? • 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

  14. Direct benefits • Definition • Kinds • Fertilization success • Protection • Resources • Territories • Parental care • Nuptial gifts • Nutritious ejaculates • Sexual cannibalism http://www.biology.au.dk/trine.bilde.htm

  15. Indirect benefits Photograph by Medford Taylor

  16. Fisher’s runaway model Benefit of trait Male cost Different genes promoting trait / preference Genetic linkage Trait size Female preference Generations

  17. Quantifying the runaway model • 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

  18. Testing for runaway • 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

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