Sexual SelectionSexual Selection
Natural Selection: Individual Lifetime Natural Selection: Individual Lifetime Reproductive SuccessReproductive Success
Survival, ReproductionSurvival, Reproduction
Tradeoff Greater Tradeoff Greater CurrentCurrent Reproduction Reproductionvsvs Survival ( Survival (FutureFuture Reproduction) Reproduction)
Sexual SelectionSexual Selection
Sexual Selection Sexual Selection Does Not OpposeDoes Not Oppose
Natural SelectionNatural Selection
Natural Selection for Traits EnhancingNatural Selection for Traits EnhancingMating SuccessMating Success
May Reduce Survival, But May Reduce Survival, But NotNot Fitness Fitness
Sexual SelectionSexual Selection
Two Processes, Defined by PI DifferenceTwo Processes, Defined by PI Difference
Intrasexual (Direct Male Competition)Intrasexual (Direct Male Competition)
Intersexual (Indirect Male Competition)Intersexual (Indirect Male Competition)
Sexual SelectionSexual Selection
Intrasexual: Intrasexual: DirectDirect Competition among Competition among Members of Sex with Lower PI for Members of Sex with Lower PI for Mating with Sex with Greater PIMating with Sex with Greater PI
““Male-Male Competition”Male-Male Competition”
Sexual SelectionSexual Selection
Intersexual: Indirect Competition among Intersexual: Indirect Competition among Members of Sex with Lower PIMembers of Sex with Lower PI
Sex with Greater PI Increases Mating Sex with Greater PI Increases Mating Variance in Sex with Lower PI Variance in Sex with Lower PI through through Mate ChoiceMate Choice
““Female Choice”Female Choice”
Sexual SelectionSexual Selection
Potential for Sexual SelectionPotential for Sexual Selection
Ratio Variance in Reproductive Success:Ratio Variance in Reproductive Success:Lesser PI Sex / Greater PI SexLesser PI Sex / Greater PI Sex
Small: MonogamySmall: MonogamyLarge: Polygyny (Polyandry)Large: Polygyny (Polyandry)
Sexual Selection: Female DefenseSexual Selection: Female Defense
Sexual Selection: PolygynySexual Selection: Polygyny
V[Male Rep Success] >V[Male Rep Success] >V[Female Rep Success]V[Female Rep Success]
Sexual Selection More Intense in MalesSexual Selection More Intense in Males
Body Size, Aggression, Body Size, Aggression, etcetc..
2014 stop2014 stop
Secondary Sexual CharactersSecondary Sexual Characters
Bright Colors, Ornaments, Bright Colors, Ornaments, Elaborate Displays of MalesElaborate Displays of Males
Sexual Selection: Advance Mating Sexual Selection: Advance Mating Success & Enhance Fitness,Success & Enhance Fitness,
Despite Cost Despite Cost
Evolve?Evolve?
Secondary Sexual CharactersSecondary Sexual Characters
Intrasexual Competition:Intrasexual Competition:Some Display FunctionSome Display Function
Darwin: Sexual Selection through Darwin: Sexual Selection through Intersexual Competition,Intersexual Competition,
Female ChoiceFemale Choice
WhyWhy Females Attracted by Bright Colors? Females Attracted by Bright Colors?Number of HypothesesNumber of Hypotheses
Secondary Sexual CharactersSecondary Sexual Characters
““Sexy Son” Hypothesis:Sexy Son” Hypothesis:Given Female Preference,Given Female Preference,Female Chooses Male Genes Likely Female Chooses Male Genes Likely to Render Her Sons Attractiveto Render Her Sons Attractive
Doesn’t Answer Question ?Doesn’t Answer Question ?
Secondary Sexual Characters & Secondary Sexual Characters & Female ChoiceFemale Choice
Hamilton, W.D. & M. Zuk. 1982. Hamilton, W.D. & M. Zuk. 1982. ScienceScience 218218:384:384..
Females Females AssessAssess Potential Mate’s Ability Potential Mate’s Ability to to Resist ParasitesResist Parasites
Female “Obtains” Parasite-Resistance Female “Obtains” Parasite-Resistance Genes for OffspringGenes for Offspring
Resistance Resistance versusversus Tolerance Tolerance
Secondary Sexual CharactersSecondary Sexual Characters
AssumptionsAssumptions
Expression of Secondary Sexual Traits Expression of Secondary Sexual Traits Increases with Health/Vigor of MaleIncreases with Health/Vigor of Male
Resistance to Parasites HeritableResistance to Parasites Heritable
Parasites Affect Host ViabilityParasites Affect Host Viability
Secondary Sexual CharactersSecondary Sexual Characters
Predict that Species with Greater Predict that Species with Greater Parasite Burdens Would Show Parasite Burdens Would Show Brightest ColorsBrightest Colors
Assumptions Not Met When Prevalence Assumptions Not Met When Prevalence of Parasites Lowof Parasites Low
High Parasite Prevalence: Both Sexes High Parasite Prevalence: Both Sexes May Benefit from Signal of HealthMay Benefit from Signal of Health
Secondary Sexual Characters & Secondary Sexual Characters & Female ChoiceFemale Choice
North American Passerine BirdsNorth American Passerine Birds
Male Brightness (6 point scale)Male Brightness (6 point scale) Correlates Positively withCorrelates Positively withParasite PrevalenceParasite Prevalence(Proportion Males Infected(Proportion Males Infectedby Class of Blood Parasites)by Class of Blood Parasites)
Supports Hypothesis (Tolerance)Supports Hypothesis (Tolerance)
Secondary Sexual Characters & Female Secondary Sexual Characters & Female ChoiceChoice
WithinWithin Population: Population:Parasite Load Parasite Load vsvs Mating Success? Mating Success?
Tolerance Tolerance versusversus Resistance Resistance
Are Brighter Males Withstanding Parasite Load Are Brighter Males Withstanding Parasite Load Physiologically? Are Brighter Males Resistant, Physiologically? Are Brighter Males Resistant, and Parasitized Less?and Parasitized Less?
Open QuestionsOpen Questions
Secondary Sexual CharactersSecondary Sexual Characters
Barn Swallow (Barn Swallow (Hirundo rusticaHirundo rustica))
Males: Long TailfeathersMales: Long Tailfeathers
Female Choice &Female Choice &Males with Larger Tail Ornaments Males with Larger Tail Ornaments SurviveSurvive Better Better
Secondary Sexual CharactersSecondary Sexual Characters
Moller, A.P. 1994. Moller, A.P. 1994. Proc. Natl. Acad. Proc. Natl. Acad. Science USAScience USA 9191:6929.:6929.
Tail Length & HeritabilityTail Length & Heritability
DenmarkDenmark
Secondary Sexual CharactersSecondary Sexual Characters
Secondary Sexual CharactersSecondary Sexual Characters
Barn swallowBarn swallow
Females Choose Ornamental TraitFemales Choose Ornamental Trait
Secondary-Sexual Trait Secondary-Sexual Trait Positively CorrelatedPositively Correlated with with
Survival in Male MateSurvival in Male Mate
Trait Heritable: Son’s Survival Positively Trait Heritable: Son’s Survival Positively Correlated with Father’s SurvivalCorrelated with Father’s Survival
Parasitism & Male TraitsParasitism & Male Traits
Alternative Hypothesis: “Trade-off”Alternative Hypothesis: “Trade-off”Males Pay Cost of Secondary TraitsMales Pay Cost of Secondary Traits
More Testosterone Implies Increase in More Testosterone Implies Increase in Male Secondary Sexual TraitsMale Secondary Sexual Traits
Aggressiveness: Intra-sexual CompetitionAggressiveness: Intra-sexual CompetitionFemale Choice: Intersexual ComponentFemale Choice: Intersexual Component
Parasitism & Male TraitsParasitism & Male Traits
Testosterone: ImmunosuppressiveTestosterone: Immunosuppressive
Increased Male Traits Can DecreaseIncreased Male Traits Can DecreaseImmunocompetenceImmunocompetence
More Testosterone May Imply Greater More Testosterone May Imply Greater Parasite Load, Parasite Load, Decreased SurvivalDecreased Survival ? ?
Maintained by Sexual Selection ?Maintained by Sexual Selection ?
