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Behavioral mechanisms for avoiding inbreeding are common in the natural world and are believed to have evolved as a response to the negative consequences of inbreeding. However, despite a fundamental role in fitness, we have a limited understanding of the cues that individuals use to assess inbreeding risk, as well as the extent to which individual inbreeding behavior is repeatable. We used piecewise structural equation modeling of 24 years of data to investigate the causes and consequences of within- versus extra-group paternity in banded mongooses. This cooperatively breeding mammal lives in tight-knit social groups that often contain closely related opposite-sex breeders, so inbreeding can be avoided through extra-group mating. We used molecular parentage assignments to show that, despite extra-group paternity resulting in outbred offspring, within-group inbreeding occurs frequently, with around 16% litters being moderately or highly inbred. Additionally, extra-group paternity appears to be plastic, with females mating outside of their social group according to individual proxies (age and immigration status) and societal proxies (group size and age) of within-group inbreeding risk but not in direct response to levels of within-group relatedness. While individual repeatability in extra-group paternity was relatively low, female cobreeders showed high repeatability, suggesting a strong constraint arising from the opportunities for extra-group mating. The use of extra-group paternity as an inbreeding avoidance strategy is, therefore, limited by high costs, opportunity constraints, and the limited reliability of proxies of inbreeding risk. [ABSTRACT FROM AUTHOR]

Many recent models of reproductive skew explain subordinate reproduction s a staying incentive offered by dominants, who can produce moreyoung with a helper present than without. Here, we present a new, alternative explanation for subordinate reproduction, which applies whenever the fitness cost to a parent of producing young is an accelerating function of the number produced (as commonly assumed in optimal clutch size theory). Under these circumstances, a dominant individual may be selected to offer a share of reproduction to a related subordinate, not as an incentive to stay, but because additional offspring that would be expensive for the dominant to produce are cheap for the subordinate. 'Beneficial sharing' of this kind is more likely the more closely related the subordinate is to the dominant, so that the model predicts a negative relationship between skew and relatedness. This result runs directly counter to the positive relationship predictedby previous incentive-based models. We explore the interaction of these contrasting effects by developing an integrated model that allowsfor both beneficial sharing and staying incentives. When offspring are cheap to produce, this integrated model predicts that the incentive effect will dominate, and skew will increase with relatedness. Whenyoung are costly, in contrast, beneficial sharing will be of greaterimportance, and skew will decrease with relatedness. [ABSTRACT FROM AUTHOR]