• 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• www.animalbehavior.orgwww.animalbehavior.org

• Asexual and Asexual and sexual organismssexual organisms

• Sex and genderSex and gender• Sexual selectionSexual selection– Selection affecting Selection affecting

access to gametesaccess to gametes

http://flickr.com/photos/billwalker/2521121709/http://flickr.com/photos/billwalker/2521121709/

http://www.micrographia.com/specbiol/cnidari/hydrozo/http://www.micrographia.com/specbiol/cnidari/hydrozo/hydr0100/hydra-01.htmhydr0100/hydra-01.htm

• Costs of sexCosts of sex– Cost of meiosisCost of meiosis– Breakup gene combinationsBreakup gene combinations– Mate acquisitionMate acquisition– STDsSTDs

• Benefits of sexBenefits of sex– Adapt to changing Adapt to changing

environmentenvironment• AbioticAbiotic• BioticBiotic

http://porpax.bio.miami.edu/~cmallery/150/life/meiosis.pics.jpghttp://porpax.bio.miami.edu/~cmallery/150/life/meiosis.pics.jpg

• Pathological in tetrapodsPathological in tetrapods• SimultaneousSimultaneous

– Earthworms, gastropods, hamlet fishEarthworms, gastropods, hamlet fish– Self fertilization is rareSelf fertilization is rare– Costs: Double the sex organsCosts: Double the sex organs– Benefits: When optimal sex for relative size of Benefits: When optimal sex for relative size of

mates changes mates changes

• SequentialSequential– TeleostsTeleosts– Usually a one way ticketUsually a one way ticket– Female Female male in reef fish 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 Male female in sea bass female in sea bass• Female reproductive output increases with sizeFemale reproductive output increases with size

http://www.fsbio-hannover.de/oftheweek/196/800px-http://www.fsbio-hannover.de/oftheweek/196/800px-Mating_earthworms.jpgMating_earthworms.jpghttp://throughthestatic.wordpress.com/category/http://throughthestatic.wordpress.com/category/idiots/idiots/

http://www.microscopy-uk.org.uk/thedark/eggbigx.jpghttp://www.microscopy-uk.org.uk/thedark/eggbigx.jpg

• The evolution of AnisogamyThe evolution of Anisogamy– Females and malesFemales and males

• Consequences of anisogamyConsequences of anisogamy– Unequal parental investmentUnequal parental investment– Unequal variance in fitnessUnequal variance in fitness• Ornamented malesOrnamented males• Choosy femalesChoosy females

– Easy malesEasy males

• Intra-sexual selectionIntra-sexual selection– Interference competitionInterference competition

• Armaments (displays)Armaments (displays)• SizeSize• Badges of statusBadges of status

• Inter-sexual selectionInter-sexual selection– Scramble competitionScramble competition

• Locomotion and mate seekingLocomotion and mate seeking

– Mate choiceMate choice• Ornamentation (displays)Ornamentation (displays)• Alternative tactics (e.g, coercion, Alternative tactics (e.g, coercion,

female mimicry)female mimicry)

• Sperm competitionSperm competition

• Given interference Given interference competitioncompetition– Directional selection for male Directional selection for male

size, armamentssize, armaments– Decrease in males’ mean Decrease in males’ mean

viability viability – Evolutionary “arms race”Evolutionary “arms race”– Distribution of male size as Distribution of male size as

costs balance benefitscosts balance benefits– Mean investment is proportional Mean investment is proportional

to number of defended females to number of defended females (reproductive variance)(reproductive variance)

http://www.innatmorrobay.com/elephant_seals_color.jpghttp://www.innatmorrobay.com/elephant_seals_color.jpg

• Male size vs. male Male size vs. male trait sizetrait size

• Shrinking femalesShrinking females• Alternative Alternative

strategiesstrategies• Small male Small male

advantageadvantage

http://crawford.tardigrade.net/journal/album/lillivatia.jpghttp://crawford.tardigrade.net/journal/album/lillivatia.jpg

From Legrand and Morse 2000 Biol. J. Lin. Soc. 71:643-664From Legrand and Morse 2000 Biol. J. Lin. Soc. 71:643-664

• AmplexusAmplexus– Female receptivity Female receptivity

is limited, cyclic, is limited, cyclic, asynchronous asynchronous

– Males are available Males are available to reproduce to reproduce almost almost continuouslycontinuously

• Mate guarding in Mate guarding in birdsbirds

http://www.treknature.com/gallery/http://www.treknature.com/gallery/Middle_East/Turkey/photo164737.htmMiddle_East/Turkey/photo164737.htm

From Birkhead 1979 Anim. Behav. 27:866-From Birkhead 1979 Anim. Behav. 27:866-874874

• The importance of the The importance of the questionquestion

• The operational sex ratio The operational sex ratio (OSR)(OSR)

• The potential reproductive The potential reproductive rate (PRR)rate (PRR)

• The differential cost of The differential cost of reproductionreproduction– Covaries with OSR and PRRCovaries with OSR and PRR

From Amundsen & Forsgren 2001 PNAS 98:13155-13160From Amundsen & Forsgren 2001 PNAS 98:13155-13160

• DefinitionDefinition• KindsKinds– Fertilization successFertilization success– ProtectionProtection– ResourcesResources• TerritoriesTerritories• Parental careParental care• Nuptial giftsNuptial gifts

– Nutritious ejaculates Nutritious ejaculates – Sexual cannibalismSexual cannibalism

http://www.biology.au.dk/trine.bilde.htmhttp://www.biology.au.dk/trine.bilde.htm

Photograph by Medford TaylorPhotograph by Medford Taylor

Generations

Ge

ne

tic

lin

kag

e

Different genes promoting trait /

preferenceFemale preference

Ben

efit

of

trai

t

Trait sizeM

ale

cost

• Lande’s versionLande’s version– Quantitative geneticQuantitative genetic– Runaway when B / G > (vRunaway when B / G > (v22 / w / w22 ) + 1 ) + 1– In other words, when CVIn other words, when CVAA (B) is high relative to V (B) is high relative to VA A of of

trait (G) with low variance in female preference (vtrait (G) with low variance in female preference (v22), ), weak utilitarian selection on trait (high wweak utilitarian selection on trait (high w22) )

– Requires initial Requires initial preference!preference!• Natural selectionNatural selection• DriftDrift• Sensory Sensory

exploitation exploitation

• P1: Additive genetic variance for trait and P1: Additive genetic variance for trait and preferencepreference– Generally supportedGenerally supported– Traits are influenced by several lociTraits are influenced by several loci

• P2: Genetic co-variation between trait and P2: Genetic co-variation between trait and preferencepreference– Method 1: Select for trait, see if preference also changesMethod 1: Select for trait, see if preference also changes

• Generally supportiveGenerally supportive

– Method 2: Is there covariation among traits in brothers Method 2: Is there covariation among traits in brothers and preferences in sisters?and preferences in sisters?• Supported in sticklebacks and cricketsSupported in sticklebacks and crickets