Climatic Adaptation and the Evolution of Basal and Maximum Rates of Metabolism in Rodents

Abstract

Abstract. Metabolic rate is a key aspect of organismal biology and the identification of selective factors that have led to species differences is a major goal of evolutionary physiology. We tested whether environmental characteristics and/or diet were significant predictors of interspecific variation in rodent metabolic rates. Mass-specific basal metabolic rates (BMR) and maximum metabolic rates (MMR, measured during cold exposure in a He-O 2 atmosphere) were compiled from the literature. Maximum (Tmax) and minimum (Tmin) annual mean temperatures, latitude, altitude, and precipitation were obtained from field stations close to the capture sites reported for each population (N ϭ 57). Diet and all continuous-valued traits showed statistically significant phylogenetic signal, with the exception of masscorrected MMR and altitude. Therefore, results of phylogenetic analyses are emphasized. Body mass was not correlated with absolute latitude, but was positively correlated with precipitation in analyses with phylogenetically independent contrasts. Conventional multiple regressions that included body mass indicated that Tmax (best), Tmin, latitude, and diet were significant additional predictors of BMR. However, phylogenetic analyses indicated that latitude was the only significant predictor of mass-adjusted BMR (positive partial regression coefficient, one-tailed P ϭ 0.0465). Conventional analyses indicated that Tmax, Tmin (best), and altitude explained significant amounts of the variation in mass-adjusted MMR. With body mass and Tmin in the model, no additional variables were significant predictors. Phylogenetic contrasts yielded similar results. Both conventional and phylogenetic analyses indicated a highly significant positive correlation between residual BMR and MMR (as has also been reported for birds), which is consistent with a key assumption of the aerobic capacity model for the evolution of vertebrate energetics (assuming that MMR and exercise-induced maximal oxygen consumption are positively functionally related). Our results support the hypothesis that variation in environmental factors leads to variation in the selective regime for metabolic rates of rodents. However, the causes of a positive association between BMR and latitude remain obscure. Moreover, an important area for future research will be experiments in all taxa are raised under common conditions to allow definitive tests of climatic adaptation in endotherm metabolic rates and to elucidate the extent of adaptive phenotypic plasticity.

Cold- and exercise-induced peak metabolic rates in tropical birds

“…Therefore, unlike temperate residents, tropical birds are presumably not under strong selection for high thermogenic capacity and cold tolerance. This hypothesis is supported by data on 57 rodent species that show a negative correlation between PMR C and mean minimum annual T a (37). Hence, one might predict a lower PMR C in tropical birds.…”

Basal metabolic rate, maximum thermogenic capacity and aerobic scope in rodents: interaction between environmental temperature and torpor use

“…I used a recently compiled dataset [7] on VO 2 -sum elicited by cold exposure in a mixture of helium and oxygen (i.e. heliox), a widely used method to measure the thermogenic capacity of wild endotherms [15].…”

“…While BMR and VO 2 -sum generally increase at low T a s or high latitudes [7], it may not necessarily be the case for species using torpor. One may expect that a low metabolic rate during torpor will maximize chances of survival on limited energy stores (body fat or larder hoards).…”

“…There have been many comparative studies on the selective forces that led to the evolution of metabolic rates that deviate substantially from allometric predictions [6,7]. Latitude and T a have been repeatedly shown to be correlated with metabolism, with species living at extreme latitudes and in cold environments having higher daily energy expenditure, BMR and VO 2 -sum [7][8][9].…”

“…Latitude and T a have been repeatedly shown to be correlated with metabolism, with species living at extreme latitudes and in cold environments having higher daily energy expenditure, BMR and VO 2 -sum [7][8][9]. Moreover, species using torpor have lower BMR during non-torpor periods than euthermic species, as suggested by two large (but non-phylogenetic) comparative analyses in 533 bird and 639 mammal species, respectively [10,11].…”