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RESEARCH PRODUCT

The association between body mass, metabolic rates and survival of bank voles

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Summary 1Many studies have been performed in an attempt to explain physiological, ecological and evolutionary factors behind inter- and intraspecific variation in basal metabolic rate (BMR) and maximum aerobic metabolic rate (VO2max). However, very little is known about the association between the traits and fitness components in populations of free-living animals. 2We studied the association between body size and the metabolic rates of bank voles Myodes (= Clethrionomys) glareolus and their survival, measured by repeated trappings across 2 years in an isolated, island population. All measured traits (body mass, BM; head width, HW; VO2max and BMR) were significantly repeatable over short (mean 5·4 days) and long (mean 56·4 days) intervals. 3Logistic regression analyses showed no consistent relationship between the measured traits and survival until the next trapping session. The correlations, if present, differed in direction between sessions and sexes. Survival over winters was negatively correlated with BM in males (P = 0·001) but not in females (P = 0·43). The logistic regression with quadratic effects revealed stabilizing selection on VO2max in males (across all sessions: P = 0·010; in breeding seasons only: P = 0·001). 4Both the presence of stabilizing selection and the opposite direction of the selection between sexes and/or seasons could contribute to the relatively high additive genetic variance of metabolic rates, reported earlier in the bank voles. 5The results indicate that the maximum rather than the basal rate of metabolism is important to individual fitness of the voles. However, lack of consistency in the association between survival and the metabolic traits casts doubt on previous assumptions regarding the importance of the level of metabolism to an individual's fitness.