• Signal honestySignal honesty– ““Good genes” Good genes”

models versus models versus runaway modelsrunaway models

• Conditional Conditional handicaphandicap

• Revealing Revealing handicap or handicap or “index”“index” From Zahavi 1975 J. Theor. Biol. 53:205-214From Zahavi 1975 J. Theor. Biol. 53:205-214

• Predation Predation costscosts

• Physiological Physiological costscosts

From Ryan et al. 1982. Am. Nat. 119:136-139From Ryan et al. 1982. Am. Nat. 119:136-139

http://gallery.pictopia.com/natgeo/photo/1112965/http://gallery.pictopia.com/natgeo/photo/1112965/

• LeksLeks• Theory: Heritability of Theory: Heritability of

fitness relevant traits fitness relevant traits should rapidly declineshould rapidly decline

• SolutionsSolutions– Accumulation of Accumulation of

deleterious mutationsdeleterious mutations– Selection pressure Selection pressure

varies over time & spacevaries over time & space– Females seek Females seek

compatible genes compatible genes http://www.arthurgrosset.com/sabirds/http://www.arthurgrosset.com/sabirds/photos/manman8933.jpgphotos/manman8933.jpg

Video by Mark E. Berres 2002Video by Mark E. Berres 2002

• A form of changing A form of changing selection pressureselection pressure– Coevolving “parasites” are Coevolving “parasites” are

a moving target a moving target – Mixed resultsMixed results

• Immunocompetence Immunocompetence handicapshandicaps

From Milinski & Bakker 1990 Nature 344:330-333 From Milinski & Bakker 1990 Nature 344:330-333

• Female sensory or Female sensory or cognitive biascognitive bias– OriginOrigin• PracticalPractical• IncidentalIncidental

• Males ‘exploit’ biasMales ‘exploit’ bias• In tungara frogsIn tungara frogs– Chuck is derived, Chuck is derived,

relative to basilar relative to basilar papilla tuningpapilla tuning From Ryan et al. 1990 Nature 343:66-67From Ryan et al. 1990 Nature 343:66-67

• GeneticGenetic– Heterozygosity masks Heterozygosity masks

deleterious recessivesdeleterious recessives– MHCMHC– EvidenceEvidence• Inbreeding avoidanceInbreeding avoidance• Female preference for Female preference for

genetically dissimilar genetically dissimilar malesmales

http://lancaster.unl.edu/pest/images/Cockroaches/gm_roaches.jpghttp://lancaster.unl.edu/pest/images/Cockroaches/gm_roaches.jpg

From Lihoreau et al . 2007 Behav. Ecol. 20:46-53From Lihoreau et al . 2007 Behav. Ecol. 20:46-53

• Competition in Competition in female genital female genital tract between tract between sperm of two or sperm of two or more malesmore males

• As scramble As scramble competitioncompetition

• As interference As interference competitioncompetition– May existMay exist

• Sperm removalSperm removal• Toxic ejaculatesToxic ejaculates– Protect own spermProtect own sperm– Harm other males’ Harm other males’

spermsperm– Alter female behaviorAlter female behavior• Higher fecundityHigher fecundity• Lower promiscuityLower promiscuity

– Harm to female is a Harm to female is a byproductbyproduct

• Female choice that Female choice that occurs within a female’s occurs within a female’s bodybody

• Sperm selectionSperm selection• Copulatory performanceCopulatory performance– Intromission rate and Intromission rate and

paternity in paternity in Linyphia litigiosa

• Implantation & abortionImplantation & abortionFrom Watson & Lighton 1994 Anim. Behav. 48:615-626From Watson & Lighton 1994 Anim. Behav. 48:615-626

• Forced monogamy on Forced monogamy on fruit fliesfruit flies– MonogamousMonogamous• Less toxic ejaculatesLess toxic ejaculates• Lower male courtship rateLower male courtship rate• Less female resistance to Less female resistance to

toxic ejaculatestoxic ejaculates• Lower body / testes size, Lower body / testes size,

sperm count sperm count

– PolygamousPolygamous• Females laid more eggsFemales laid more eggs

• ““The worst blunder in sexual preference”The worst blunder in sexual preference”• Now thought that species recognition Now thought that species recognition

relies on subset of mate choice traitsrelies on subset of mate choice traits• Two mechanismsTwo mechanisms– Allopatric divergenceAllopatric divergence– ReinforcementReinforcement• Negative selection on marginal types if hybrid Negative selection on marginal types if hybrid

matings produce less viable offspringmatings produce less viable offspring– Reproductive character displacementReproductive character displacement

• Pre-reproductive isolationPre-reproductive isolation– Sexually selected characters can diversify Sexually selected characters can diversify

rapidly given small initial changesrapidly given small initial changes• DriftDrift• Founder effectsFounder effects• Local conditionsLocal conditions

– Many closely related species differ primarily in sexually Many closely related species differ primarily in sexually selected traitsselected traits

• Natural selection could drive divergenceNatural selection could drive divergence– Isolated populations adapt to environment …Isolated populations adapt to environment …– … … and these adaptations affect their sexual signalsand these adaptations affect their sexual signals

From Podos 2001 Nature 409:185-188From Podos 2001 Nature 409:185-188