NESPOLO, RF; Universidad Austral de Chile: The G-matrix of energetics and life histories in a wild mammal

How close are endotherm physiological traits to fitness? Can maximum capacities for energy expenditure in endotherms respond to natural selection? Is the aerobic model a plausible explanation for the evolution of endothermy? These are implicit, yet strongly debated questions in studies of animal evolutionary physiological ecology. To address these questions we measured energetics and life history variables in the wild mouse, Phyllotis darwini. We determined narrow-sense heritabilities and genetic correlations (i.e., the G-matrix). Our results (1) provide the first evidence of high, significant heritable variation in maximum metabolic rate, suggesting that this trait could respond directly to natural selection, (2) do not support the aerobic model for the evolution of endothermy, since no genetic correlation was detected between maximum and basal metabolic rate, and (3) support a link between life histories and energetics, however not through basal metabolic rate, as formerly suggested, instead, through non-shivering thermogenesis (NST) and factorial aerobic scope (FAS). It appears that physiological adaptive evolution could occur in this rodent population if selection acts directly on maximum metabolic rate, or indirectly on NST and FAS.