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Evolution of variance in mate choice. Deena Schmidt MBI Postdoctoral Fellow July 31, 2009 dschmidt@mbi.osu.edu. Definition of Mate Choice. Process where members of one sex mate non-randomly with respect to one or more varying traits in members of the other sex.
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Evolution of variance in mate choice Deena Schmidt MBI Postdoctoral FellowJuly 31, 2009 dschmidt@mbi.osu.edu
Definition of Mate Choice • Process where members of one sex mate non-randomly with respect to one or more varying traits in members of the other sex. • Typically, female choice of male mate • How and why mate choice evolves has been vigorously debated in the field of evolutionary biology.
Definition of Lek • A gathering of males of a certain species for the purpose of competitive mating display. Females visit the lek and choose a mate. • Common in fish, birds, and insects • Lekking is a model system for understanding sexual selection and the benefits of group living. • Lekking males are thought to face strong directional selection on secondary sexual traits.
“Lek Paradox” • The maintenance of variation in the face of strong directional selection on a trait is a general problem in evolutionary biology. • Lek paradox: maintenance of variation in female mate choice and male quality on leks. • Paradoxical because variation in male traits should decrease rapidly due to selection imposed by female choice.
Influence of “Enemies” on Leks • Enemies = predators, egg predators, brood parasites (or sneaker males) • Enemies congregate around higher quality males. • Females must then trade-off the benefits of mating with high quality males against the increased risk of enemies. • Interaction with enemies fitness cost to both females and males
Game Theoretic Model • 3 classes of individuals: • Females, males, and enemies • Males are ranked according to quality: • i.e. high or low • Basic assumptions: • All females rank males the same way. • Ranking is based on some trait that is a measure of quality (“good genes”). • In absence of enemies, females choose high quality males.
Game Theoretic Model • Focus on the game between females and enemies. • Use this model to predict how interactions between females and enemies influence the frequency of high and low quality males. Main idea: Avoidance of costly enemies can lead to variation in female mate choice. This can result in maintenance of variation in male quality.
Game Theoretic Model • Main Reference: Hamilton, I.M. et al. Behav. Ecol. 17:97-107 (2006). • Studied the influence of the female-enemy game on the maintenance of variation in male quality. • Project: We will be extending this model.
Possible Extensions to the Model • In this model, males do not make decisions. • Add male strategies: • Invest in safety, defend against enemies • Males might reject some females: • Consider female vs. male game (instead of female vs. enemy game) • Add differences in female quality. • Add continuous variation in qualities. • Something else you might come up with!
Math Involved • Evolutionary game theory model • Model interactions within a population: females choosing a mate in the presence of enemies • Main parameter = fitness (or payoff) • Replicator dynamics • Identify evolutionary stable strategies (ESS) • Matlab code – run simulations
References • Hamilton, I.M. et al. 2006. Predators, reproductive parasites, and the persistence of poor males on leks. Behav. Ecol. 17:97-107. • Kokko, H. et al. 2003. The evolution of mate choice and mating biases. Proc. R. Soc. Lond. B 270:653-664. (review article) • Alonzo, S.H. and Warner, R.R. 1999. Behav. Ecol. 10:105-111. • Alonzo, S.H. and Warner, R.R. 2000. Behav. Ecol. 11:56-70.
