Sex differences and behaviour in the pace-of-life of rodents

Male and female rodents experience different selective pressures associated with reproductive costs. Thus, we may expect the expression of different Pace-of-life (POL) strategies between sexes. Further, the pace-of-life syndrome (POLS) hypothesis and anisogamy predict differences in the costs of gamete production, where variation in life history trait expression should follow a fast-slow continuum such that males and females might exist on opposite ends of the spectrum. However, males and females could express a similar POL strategy in systems where the reproductive costs are consistent between sexes or where selective pressures force a similar directionality of traits. We used standardized behavioural tests and fecal glucocorticoid metabolite (FGM) concentrations to measure potential differences in POL strategies among three rodent species in Algonquin Provincial Park. We hypothesized that differences in reproductive costs between males and females would result in differences in POL traits along the fast-slow continuum. We predicted that males would express more explorative behaviours and have a higher level FGMs than female counterparts. We found little support for the POLS hypothesis between sexes. Instead, we suggest that the species observed may express a similar directionality of selection for the observed behavioural traits, where both sexes express similar relationships in POL. Thus, some male rodents may be more explorative to accommodate the increase of energetic stress associated with mate acquisition, while females may share similar trait expressions to accommodate the increased metabolic demand for the care and development of young. Significance statementDocility and exploration are measurements of how species or individuals react to novel and sometimes risky stimuli. Further, reproduction is an energetically expensive and inherently risky process. In seasonally breeding rodents, males often invest in fast pace-of-life behaviours that accommodate an increased necessity to disperse and find a mate. Meanwhile, females often invest in metabolically expensive physiological processes, including pregnancy and lactate development, increased protection of the young and the need for self-maintenance. Using a series of behavioural tests and fecal glucocorticoid metabolites (FGMs), we measured the relationship between metabolic stress, docility and exploration in three species of rodents during the breeding season. We observed consistent relationships in behaviour and FGMs, indicating uniformity between sexes regarding these behaviours. We posit that the costs associated with mate acquisition for males and the care and development of young for females can influence similar behavioural strategies.