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Birds in Costa RicaBirds in Costa Rica Bats in IsraelBats in Israel Squirrels in CanadaSquirrels in Canada Monkeys in EthiopiaMonkeys in Ethiopia Pronghorn.

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Presentation on theme: "Birds in Costa RicaBirds in Costa Rica Bats in IsraelBats in Israel Squirrels in CanadaSquirrels in Canada Monkeys in EthiopiaMonkeys in Ethiopia Pronghorn."— Presentation transcript:

1 Birds in Costa RicaBirds in Costa Rica Bats in IsraelBats in Israel Squirrels in CanadaSquirrels in Canada Monkeys in EthiopiaMonkeys in Ethiopia Pronghorn in MontanaPronghorn in Montana

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3 Asexual and sexual organismsAsexual and sexual organisms Sex and genderSex and gender Sexual selectionSexual selection –Selection affecting access to gametes 0/hydra-01.htm

4 Costs of sexCosts of sex –Cost of meiosis –Breakup gene combinations –Mate acquisition –STDs Benefits of sexBenefits of sex –Adapt to changing environment AbioticAbiotic BioticBiotic

5 Pathological in tetrapodsPathological in tetrapods SimultaneousSimultaneous –Earthworms, gastropods, hamlet fish –Self fertilization is rare –Costs: Double the sex organs –Benefits: When optimal sex for relative size of mates changes SequentialSequential –Teleosts –Usually a one way ticket –Female  male in reef fish When harem male diesWhen harem male dies Only large males can defend a territoryOnly large males can defend a territory –Male  female in sea bass Female reproductive output increases with sizeFemale reproductive output increases with size Mating_earthworms.jpg ts/

6 The evolution of AnisogamyThe evolution of Anisogamy –Females and males Consequences of anisogamyConsequences of anisogamy –Unequal parental investment –Unequal variance in fitness Ornamented malesOrnamented males Choosy femalesChoosy females –Easy males

7 Intra-sexual selectionIntra-sexual selection –Interference competition Armaments (displays)Armaments (displays) SizeSize Badges of statusBadges of status Inter-sexual selectionInter-sexual selection –Scramble competition Locomotion and mate seekingLocomotion and mate seeking –Mate choice Ornamentation (displays)Ornamentation (displays) Alternative tactics (e.g, coercion, female mimicry)Alternative tactics (e.g, coercion, female mimicry) Sperm competitionSperm competition

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9 Given interference competitionGiven 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)

10 Male size vs. male trait sizeMale size vs. male trait size Shrinking femalesShrinking females Alternative strategiesAlternative strategies Small male advantageSmall male advantage From Legrand and Morse 2000 Biol. J. Lin. Soc. 71:

11 AmplexusAmplexus –Female receptivity is limited, cyclic, asynchronous –Males are available to reproduce almost continuously Mate guarding in birdsMate guarding in birds e_East/Turkey/photo htm From Birkhead 1979 Anim. Behav. 27:

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13 The importance of the questionThe importance of the question The operational sex ratio (OSR)The operational sex ratio (OSR) The potential reproductive rate (PRR)The potential reproductive rate (PRR) The differential cost of reproductionThe differential cost of reproduction –Covaries with OSR and PRR From Amundsen & Forsgren 2001 PNAS 98:

14 DefinitionDefinition KindsKinds –Fertilization success –Protection –Resources TerritoriesTerritories Parental careParental care Nuptial giftsNuptial gifts –Nutritious ejaculates –Sexual cannibalism

15 Photograph by Medford Taylor

16 Generations Genetic linkage Different genes promoting trait / preference Female preference Benefit of trait Trait size Male cost

17 Lande’s versionLande’s version –Quantitative genetic –Runaway when B / G > (v 2 / w 2 ) + 1 –In other words, when CV A (B) is high relative to V A of trait (G) with low variance in female preference (v 2 ), weak utilitarian selection on trait (high w 2 ) –Requires initial preference! Natural selectionNatural selection DriftDrift Sensory exploitationSensory exploitation

18 P1: Additive genetic variance for trait and preferenceP1: Additive genetic variance for trait and preference –Generally supported –Traits are influenced by several loci P2: Genetic co-variation between trait and preferenceP2: Genetic co-variation between trait and preference –Method 1: Select for trait, see if preference also changes Generally supportiveGenerally supportive –Method 2: Is there covariation among traits in brothers and preferences in sisters? Supported in sticklebacks and cricketsSupported in sticklebacks and crickets


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