Strangers and brothers: a paternity game between house mice

Using a framework based on the Hawk–Dove game, we constructed a model of the interaction between two males, which may or may not be related, competing for access to females. We parameterized the model with laboratory data from size-matched house mice and tested the model's predictions against independent laboratory data. The predictions that mate sharing is more frequent, fighting is less frequent and reproductive skew is lower when males are brothers than when they are unrelated were supported by the data. The qualitative and quantitative match between the model's predictions and the frequencies of fighting, sharing and dominance outcomes were generally good, except that the model predicts occasional fighting between brothers when none was observed. The empirically corroborated prediction on relatedness and reproductive skew is consistent with incomplete control of the subordinate male by the dominant, rather than with reproductive incentives, although the magnitude of skew in the model arises from frequencies of outcomes and not from these more specific mechanisms. The analysis demonstrates that these types of male–male interactions and their frequencies may be adequately characterized by a few main features such as relatedness of males, reproductive skew associated particularly with social dominance, and the costs of fighting. The model also makes testable predictions about results to be expected under more natural conditions.