Metabolic and affective consequences of fatherhood in male California mice

Physiological and affective condition can be modulated by the social environment and parental state in mammals. However, in species in which males assist with rearing offspring, the metabolic and affective effects of pair bonding and fatherhood on males have rarely been explored. In this study we tested the hypothesis that fathers, like mothers, experience energetic costs as well as behavioral and affective changes (e.g., depression; anxiety) associated with parenthood. We tested this hypothesis in the monogamous, biparental California mouse (Peromyscus californicus). Food intake, blood glucose and lipid levels, blood insulin and leptin levels, body composition, pain sensitivity, and depression-like behavior were compared in males from three reproductive groups: virgin males (VM, housed with another male), non-breeding males (NB, housed with a tubally ligated female), and breeding males (BM, housed with a female and their first litter). We found statistically significant (P < 0.007, when modified for Adaptive False Discovery Rate) or nominally significant (0.007 < P < 0.05) differences among reproductive groups in relative testis mass, circulating glucose, triglyceride, and insulin concentrations, pain sensitivity, and anxiety-like behaviors. A priori contrasts indicated that VM produced significantly more fecal pellets than BM in the tail-suspension test, had significantly higher glucose levels than NB, and had significantly lower average testis masses than did NB and BM. A priori contrasts also indicated that VM had a nominally longer latency to the pain response than NB and that VM had nominally higher insulin levels than did NB. For breeding males, litter size (one to three pups) was a nominally significant positive predictor of body mass, food consumption, fat mass, and plasma leptin concentration. These results indicate that cohabitation with a female and/or fatherhood influences several metabolic, morphological, and affective measures in California mouse males. Overall, the changes we observed in breeding males were minor, but stronger effects might occur in long-term breeding males and/or under more challenging environmental conditions.