Age-related changes of physiological performance and survivorship of bank voles selected for high aerobic capacity

Variation in lifespans is an intriguing phenomenon, but how metabolic rate influence this variation remains unclear. High aerobic capacity can result in health benefits, but also in increased oxidative damage and accelerated ageing. We tested these contradictory predictions using bank voles (Myodes=Clethrionomys glareolus) from lines selected for high swim-induced aerobic metabolism (A), which had about 50% higher maximum metabolic rate and a higher basal and routine metabolic rates, than those from unselected control lines (C). We measured sprint speed (VSmax), forced-running maximum metabolic rate (VO_{2}run), maximum long-distance running speed (VLmax), running speed at VO_{2}run (VVO_{2}), and respiratory quotient at VO_{2}run (RQ) at three age classes (I: 3-5, II: 12-14, III: 17-19 months), and analysed survivorship. We asked if ageing, understood as the age-related decline of the performance traits, differs between the A and C lines. At age class I, voles from A lines had 19% higher VO_{2}run, and 12% higher VLmax, but tended to have 19% lower VSmax, than those from C lines. RQ was nearly 1.0 for both A and C lines. The pattern of age-related changes differed between the lines mainly between age classes I and II, but not in older animals. VSmax increased by 27% in A lines and by 10% in C lines between age class I and II, but between classes II and III, it increased by 16% in both selection directions. VO_{2}run decreased by 7% between age class I and II in A lines only, but in C lines it remained constant across all age classes. VLmax decreased by 8% and VVO_{2} by 12% between age classes II and III, but similarly in both selection directions. Mortality was higher in A than in C lines only between the age of 1 and 4 months. The only trait for which the changes in old animals differed between the lines was RQ. In A lines, RQ increased between age classes II and III, whereas in C lines such an increase occurred between age classes I and II. Thus, we did not find obvious effects of selection on the pattern of ageing. However, the physiological performance and mortality of bank voles remained surprisingly robust to ageing, at least until the age of 17-19 months, similar to the maximum lifespan under natural conditions. Therefore, it is possible that the selection could affect the pattern of ageing in even older individuals when symptoms of senility might be more profound