Effects of age at first fatherhood on parental behavior and offspring outcomes in the biparental California mouse.

According to life history theory and the terminal investment hypothesis, older animals should invest more in current reproduction than younger animals because the likelihood of future reproduction decreases with age. Therefore, older parents may provide more and/or higher-quality parental care than younger parents. However, the ability of older animals to provide parental care may decline due to physiological senescence. We examined parental care and reproductive outcomes in biparental California mouse (Peromyscus californicus) families in which males were paired when either young (4 months) or old (16 months) adults. Age did not affect males' responses to unfamiliar pups shortly before pairing, days from pairing until parturition, litter composition, pup survival, or pup development. We also compared fathers' behavior in an open field, an anxiogenic situation, before and after the introduction of a pup into the arena. Old fathers traveled longer distances in the open field than young fathers but did not differ in their pup-directed behaviors. In observations of undisturbed families in their home cages, we found few differences in parental behavior between old and young fathers and those of their mates. Our results suggest that males' age influences exploratory behavior but has little effect on paternal behavior and offspring outcomes, within the age range studied.