Reproductive experience drives changes in behavior and physiology in male California mice ( Peromyscus californicus )

Paternal experience improves memory and reduces anxiety-like behavior in males, but it is unclear whether these changes are due to mating, siring offspring, or caregiving behavior. Likewise, paternal males have larger testes, a measure of sperm production, but again, the effects of siring and caregiving experience are difficult to disentangle. We examined behavioral and physiological outcomes in three groups of male mice: 1) virgins, 2) males paired with sterile females (‘non-fathers’), and 3) experienced fathers (Experiment 1). Compared to virgins and non-fathers, experienced fathers exhibited increased recognition memory (novel object recognition) and decreased anxiety-like behavior (elevated plus maze). Virgin males, however, had smaller testes and fewer sperm compared to non-fathers. We then compared the same traits in three additional groups of male mice: 1) non-fathers, 2) non-fathers with experience caring for unrelated pups (‘pup-sensitized non-fathers’), and 3) first-time fathers, to determine whether the behavioral and physiological observations in Experiment 1 were due to siring offspring or caregiving, and how rapidly these changes occur (Experiment 2). Recognition memory and anxiety-like behavior did not differ among these three groups, suggesting that caring for a single litter does not recapitulate the behavioral changes observed in experienced fathers (Experiment 1). Despite equal mating opportunity, we observed larger testes in first-time fathers compared to non-fathers, suggesting that investment in sperm production may be more plastic than behavioral changes. Finally, we compared pup interactions in pup-sensitized non-fathers and first-time fathers. While pup-sensitized non-fathers were slower to approach pups than first-time fathers, they spent more time grooming pups, whereas first-time fathers invested more time in nest building, suggesting different caregiving behaviors in pup-sensitized males and biological fathers. Taken together, our study revealed that mating, siring, and caregiving experience contributes to changes in memory, anxiety-like behavior, and reproductive investment in males of a biparental species.