Mate guarding, male attractiveness, and paternity under social monogamy

Socially monogamous species vary widely in the frequency of extrapair offspring, but this is usually discussed assuming that females are free to express mate choice. Using game-theory modeling, we investigate the evolution of male mate guarding, and the relationship between paternity and mate-guarding intensity. We show that the relationship between evolutionarily stable mate-guarding behavior and the risk of cuckoldry can be complicated and nonlinear. Because male fitness accumulates both through paternity at his own nest and through his paternity elsewhere, males evolve to guard little either if females are very, faithful or if they are very unfaithful. Attractive males are usually expected to guard less than unattractive males, but within-pair paternity may correlate either positively or negatively with the number of extrapair offspring fertilized by a male. Negative correlations, whereby attractive males are cuckolded more, become more likely if the reason behind female extrapair behavior applies to most females (e.g., fertility insurance) rather than the subset mated to unattractive males (e.g., when females seek "good genes") and if mate guarding is efficient in controlling female behavior. We discuss the current state of empirical knowledge with respect to these findings