1. Signal honestySignal honesty –“Good genes” models versus runaway models Conditional handicapConditional handicap Revealing handicap or “index”Revealing handicap or “index” From Zahavi 1975 J. Theor. Biol. 53:205-214

2. Predation costsPredation costs Physiological costsPhysiological costs From Ryan et al. 1982. Am. Nat. 119:136-139 http://gallery.pictopia.com/natgeo/photo/1112965/

3. LeksLeks Theory: Heritability of fitness relevant traits should rapidly declineTheory: Heritability of fitness relevant traits should rapidly decline SolutionsSolutions –Accumulation of deleterious mutations –Selection pressure varies over time & space –Females seek compatible genes http://www.arthurgrosset.com/sabirds/photos/ manman8933.jpg Video by Mark E. Berres 2002

4. A form of changing selection pressureA form of changing selection pressure –Coevolving “parasites” are a moving target –Mixed results Immunocompetence handicapsImmunocompetence handicaps From Milinski & Bakker 1990 Nature 344:330-333

5. Female sensory or cognitive biasFemale sensory or cognitive bias –Origin PracticalPractical IncidentalIncidental Males ‘exploit’ biasMales ‘exploit’ bias In tungara frogsIn tungara frogs –Chuck is derived, relative to basilar papilla tuning From Ryan et al. 1990 Nature 343:66-67

6. GeneticGenetic –Heterozygosity masks deleterious recessives –MHC –Evidence Inbreeding avoidanceInbreeding avoidance Female preference for genetically dissimilar malesFemale preference for genetically dissimilar males http://lancaster.unl.edu/pest/images/Cockroaches/gm_roaches.jpg From Lihoreau et al. 2007 Behav. Ecol. 20:46-53

9. Competition in female genital tract between sperm of two or more malesCompetition in female genital tract between sperm of two or more males As scramble competitionAs scramble competition As interference competitionAs interference competition –May exist

10. Sperm removalSperm removal Toxic ejaculatesToxic ejaculates –Protect own sperm –Harm other males’ sperm –Alter female behavior Higher fecundityHigher fecundity Lower promiscuityLower promiscuity –Harm to female is a byproduct

11. Female choice that occurs within a female’s bodyFemale choice that occurs within a female’s body Sperm selectionSperm selection Copulatory performanceCopulatory performance –Intromission rate and paternity in –Intromission rate and paternity in Linyphia litigiosa Implantation & abortionImplantation & abortion From Watson & Lighton 1994 Anim. Behav. 48:615-626

12. Forced monogamy on fruit fliesForced monogamy on fruit flies –Monogamous Less toxic ejaculatesLess toxic ejaculates Lower male courtship rateLower male courtship rate Less female resistance to toxic ejaculatesLess female resistance to toxic ejaculates Lower body / testes size, sperm countLower body / testes size, sperm count –Polygamous Females laid more eggsFemales laid more eggs

14. “The worst blunder in sexual preference”“The worst blunder in sexual preference” Now thought that species recognition relies on subset of mate choice traitsNow thought that species recognition relies on subset of mate choice traits Two mechanismsTwo mechanisms –Allopatric divergence –Reinforcement Negative selection on marginal types if hybrid matings produce less viable offspringNegative selection on marginal types if hybrid matings produce less viable offspring –Reproductive character displacement

15. Pre-reproductive isolationPre-reproductive isolation –Sexually selected characters can diversify rapidly given small initial changes DriftDrift Founder effectsFounder effects Local conditionsLocal conditions –Many closely related species differ primarily in sexually selected traits Natural selection could drive divergenceNatural selection could drive divergence –Isolated populations adapt to environment … –… and these adaptations affect their sexual signals

16. From Podos 2001 Nature 409:185-188