Transcript Evolution of variance in mate choice

Evolution of variance in mate
choice
Deena Schmidt
MBI Postdoctoral Fellow
July 31, 2009
[email protected]
Definition of Mate Choice
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Process where members of one sex mate nonrandomly with respect to one or more varying
traits in members of the other sex.
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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
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A gathering of males of a certain species for the
purpose of competitive mating display. Females
visit the lek and choose a mate.
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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.
Diagram of a Lek
“Lek Paradox”
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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.
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Paradoxical because variation in male traits should
decrease rapidly due to selection imposed by
female choice.
Influence of “Enemies” on Leks
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Enemies = predators, egg predators, brood
parasites (or sneaker males)
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Enemies congregate around higher quality males.
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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
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3 classes of individuals:
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Males are ranked according to quality:
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Females, males, and enemies
i.e. high or low
Basic assumptions:
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All females rank males the same way.
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Ranking is based on some trait that is a measure of
quality (“good genes”).
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In absence of enemies, females choose high quality
males.
Game Theoretic Model
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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
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Main Reference: Hamilton, I.M. et al. Behav.
Ecol. 17:97-107 (2006).
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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
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In this model, males do not make decisions.
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Add male strategies:
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Invest in safety, defend against enemies
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Males might reject some females:
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Consider female vs. male game (instead of female vs.
enemy game)
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Add differences in female quality.
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Add continuous variation in qualities.
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Something else you might come up with!
Math Involved
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Evolutionary game theory model
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Model interactions within a population: females
choosing a mate in the presence of enemies
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Main parameter = fitness (or payoff)
Replicator dynamics
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Identify evolutionary stable strategies (ESS)
Matlab code – run simulations
References
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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 270:653664. (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.