Testosterone, paternal behavior, and aggression in the monogamous California mouse (Peromyscus californicus)

Testosterone (T) mediates a trade-off, or negative correlation, between pat ernal behavior and aggression in several seasonally breeding avian species. However, the presence or absence of a T-mediated trade-off in mammals has received less attention. We examined the relationship between paternal beha vior and territorial aggression in the biparental California mouse, Peromys cus californicus. In contrast to seasonally breeding birds, T maintains pat ernal behavior in this year-round territorial species. Castration reduced p aternal behavior, whereas T replacement maintained high levels of paternal behavior. We hypothesize that T is aromatized in the brain to estradiol, wh ich in turn stimulates paternal behavior. In contrast to paternal behavior, aggressive behavior was not reduced by castration. Interestingly, only sha m males showed an increase in aggression across three aggression tests, whi le no change was detected in castrated or T-replacement males. Overall, tra de-offs between aggression and paternal behavior do not appear to occur in this species. Measures of paternal behavior and aggression in a correlation al experiment were actually positively correlated. Our data suggest that it may be worth reexamining the role that T plays in regulating mammalian pat ernal behavior. (C) 2001 Academic Press.