Multiple paternity in a philopatric rodent: the interaction of competition and choice

Paternity confusion is often suggested as the benefit that female mammals accrue by mating with multiple males, but genetic advantages are also possible. Microsatellite-based parentage analyses demonstrate that female banner-tailed kangaroo rats (Dipodomys spectabilis) commonly mate with more than one male; we asked how male and female behaviors interact to influence the characteristics of males that sire offspring. Specifically, we compared attributes (age, weight, mobility, relatedness, proximity) of the fathers of 229 known-maternity offspring with those of the other males accessible to the mothers. Adult males living adjacent to each female attempt to monopolize access to her, and the nearest male sires a plurality of offspring, but most mothers' young are fathered by more than one male and littermates are usually half-sibs. Male proximity and mobility, but not size, influence the probability of paternity, suggesting a role for competitive mate searching. Females significantly reduce the inbreeding coefficient of their offspring by mating with males other than (or in addition to) the nearest male. Fathers are less closely related to the mother in years of high density when unrelated males are more accessible to the female. Our results favor the genetic bet-hedging hypothesis, whereby females actively but unselectively seek matings with additional males when the male most likely to win in mate competition is costly to her (in this case, genetically less compatible). We anticipate that genetic bet hedging will be common in species whose females are defendable, especially if they are also philopatric.