UC Riverside

In many species, caring for young is essential for reproductive success because it increases offspring survival, development, and quality. However, parental care can be costly by increasing resource expenditure and mortality risk and decreasing likelihood of future reproduction. Therefore, animals are predicted to adjust their levels of caregiving based on both intrinsic (e.g., sex, physical ability) and extrinsic factors (e.g., season, social interactions). Within-family dynamics are particularly interesting because an animal’s level of care determined by intrinsic factors may be influenced by responses to the behaviors of mates, offspring, or siblings. In biparental species, an individual’s social environment includes not only offspring, which can manipulate parents to garner greater levels of care, but also its mate. Little is known about how interactions within biparental families affect parental behavior. Thus, I examined intrinsic and social influences on caregiving behavior and the consequences for offspring in a biparental mammal, the California mouse (Peromyscus californicus). The first study investigated sex as a factor by determining whether parent-offspring discrimination differs between mothers and fathers. Throughout the pup-rearing period, I presented individual parents simultaneously with two mesh balls containing their own pup in one and an unrelated pup in the other. Although parents behaved similarly on individual test days, fathers showed significant changes in behaviors directed towards the non-kin ball over time, suggesting that fathers may show increased interest in unrelated young as their offspring become independent. In the second study, I examined parental behavior of both parents and offspring quality are affected by paternal age. Mothers mated to young fathers nursed pups more than those mated to old fathers; however, few other measures differed between families of old and young fathers. In the last study, I explored the effects of overlapping litters, in which subsequent litters are raised concurrently, on parent-offspring and sibling-sibling interactions and on offspring development.