Mate guarding, male attractiveness, and paternity under social monogamy

Socially monogamous species vary widely in the frequency ofextrapair offspring, but this is usually discussed assumingthat females are free to express mate choice. Using game-theorymodeling, we investigate the evolution of male mate guarding,and the relationship between paternity and mate-guarding intensity.We show that the relationship between evolutionarily stablemate-guarding behavior and the risk of cuckoldry can be complicatedand nonlinear. Because male fitness accumulates both throughpaternity at his own nest and through his paternity elsewhere,males evolve to guard little either if females are very faithfulor if they are very unfaithful. Attractive males are usuallyexpected to guard less than unattractive males, but within-pairpaternity may correlate either positively or negatively withthe number of extrapair offspring fertilized by a male. Negativecorrelations, whereby attractive males are cuckolded more, becomemore likely if the reason behind female extrapair behavior appliesto most females (e.g., fertility insurance) rather than thesubset mated to unattractive males (e.g., when females seek"good genes") and if mate guarding is efficient in controllingfemale behavior. We discuss the current state of empirical knowledgewith respect to these findings.