HAMMOND, K.A.*; CHAPPELL, M.A.: Age and Aerobic Performance in Deer Mice

While it is common to examine the effects of aging on whole animal performance between juvenile and adult stages there is less of a focus on how performance changes with age within the adult animal. We examined 197 deer mice (Peromyscus maniculatus) to determine how basal (BMR) and maximal metabolism resulting from either intense exercise (aerobic performance–VO_2max) or extreme cold exposure using heliox (summit metabolism– VO_2sum) changed throughout their adult lifetime. In addition we determined the relationship between aerobic performance and summit metabolism in adult mice. Mice continued to grow between sexual maturity and old age (20 and 36% for males and females respectively), and males were up to14% larger than females so we corrected all metabolic data for body mass. After body mass corrections we did not find an effect of age on BMR for either sex but female BMR was 12% higher than male BMR (P=0.002). There was a small but significant and steady decline (about 25% between 100 and 1400 days of age) in both aerobic performance and summit metabolism with age (r²= 0.02-0.04, P<0.05) for both males and females. There was also a positive correlation between VO_2max and VO_2sum (r=0.42; P<0.0001) which was not affected by age. Finally we estimated the factorial scope (Maximal metabolism / BMR) for both exercise and cold exposure and found that it was 16% higher for males than that for females (P < 0.01 for both exercise and cold exposure). We conclude that the effects of aging in adult deer mice are primarily visible on maximal metabolic output but that they do not influence exercise capacity or thermogenesis differentially.