Sexual and natural selection on body mass and metabolic rates in free-living bank voles

P>1. Because energy is a crucial resource, adaptive significance of variation in the rate of energy metabolism, and especially in basal (BMR) and maximum aerobic (VO2max) metabolic rates, is a popular theme in evolutionary and ecological physiology. However, little is known about the association of these traits with fitness components in populations of free-living animals. 2. We studied the association between body size, the metabolic rates, and reproductive success in bank voles (Myodes glareolus) in an isolated, small island population. Correlation analyses were performed for two measures of reproductive performance: mating success (the number of partners with which an individual had any offspring), and overall reproductive success (the number of offspring trapped in the field, calculated for all individuals, including those with no offspring). 3. Direction of the selection on metabolic traits varied between sexes and over time, which could contribute to maintaining a high additive genetic variance of the traits. 4. Mating success and overall reproductive success of males were positively correlated with body size (head width), but not with mass-independent VO2max. The latter result undermines the hypothesis that evolution of high aerobic capacity could be driven by a selection for traits important in male competition. 5. Overall reproductive success was positively correlated with basal metabolic rate. The result corroborates the hypothesis that high BMR and endothermy in mammals could evolve as consequences of intensive parental care evolution. However, the generality of such a correlation remains uncertain and warrants further research.