The effects of genome size and climate on basal metabolic rate variation in rodents

Basal metabolic rate (BMR) is the most commonly measured energetic variable in endothermic animals. Identifying the underlying factors driving interspecific variation in BMR remains a major question in the field of energetics. While body size (M) and taxonomic affiliation are the intrinsic factors that account for most of the interspecific variation in BMR, haploid genome size (C-value) is hypothesized to directly influence cell size and, indirectly, the specific metabolic rate. Climatic variables, mostly ambient temperature, have also been proposed as predictors of mass-independent BMR for endotherms. Therefore, in this study, we aimed to investigate the relative importance of intrinsic (C-value: CV) and extrinsic (climatic variables) factors as predictors of BMR in 67 rodent species in a phylogenetic context. The best ordinary least square (OLS) and phylogenetic generalized least squares (PGLS) models explaining interspecific variation in BMR included the variables logM, logCV, maximum temperature of the warmest month (Tmax), minimum temperature of the coldest month (Tmin) and net primary productivity (NPP). logM was the main determinant of logBMR variation in the rodents analyzed. Part of the remaining variation was attributed to a negative effect of genome size, explaining 14% of the BMR variance when Tmin was included in the model. As expected, one or two climatic variables were involved in explaining the remaining BMR variation (Tmin, Tmax and NPP). Our study highlights the importance of a denser sampling within vertebrate clades and the use of a phylogenetic context to elucidate the factors that contribute to explain BMR variation.