Evaluating sex differences in behaviour and glucocorticoids of rodents

Abstract In rodents, different selective pressures influence behavioural, physiological and life-history strategies between sexes. Anisogamy and the reproductive cost hypothesis suggests that differences in gamete size and trade-offs in reproduction are driving mechanisms of sex-specific reproductive strategy. However, relationships between behaviour and energetic investment in income-breeding rodents are not fully explored. We investigated behavioural and physiological traits in two rodent species from Algonquin Provincial Park, Canada using two standardized behavioural assays and faecal glucocorticoid metabolites (FGMs) as a proxy for movement and energetic stress. We hypothesized that sex differences in reproductive investment throughout a single breeding season would influence behavioural and physiological traits. We predicted that males would be more explorative and less docile than females due to increased risks associated with mate acquisition. We also predicted that FGMs would be greater in females compared to males due to the increased investment in the development and care of young. In contrast to our hypothesis, we observed some differences in behaviour between sexes in the opposite direction. Male deer mice ( Peromyscus maniculatus ) were more docile (mean difference = 0.312, 95% CI = [−0.24; 0.87], ), and male red-backed voles ( Clethrionomys gapperi ) were less explorative (mean difference =-73.8 s, 95% CI = [−127.5; −19.029], ) than female counterparts. There was also a high degree of within-individual variation in FGMs in both species. Between-individual variation was only observed in red-backed voles (26.7%), however neither species had a significant relationship between sex and FGMs. Our findings reveal some relationships between behaviour and physiology in income-breeding rodents.