Intraspecific Variation in Metabolic Rate and Its Relationship with Productivity in the Cotton Rat, Sigmodon hispidus

Abstract

We investigated the relationship between basal metabolic rate and production rates (i.e., tissue biosynthesis) at the intraspecific level in Sigmodon hispidus from seven distinct geographic locations. Variation in metabolic and production rates did not correlate with a latitudinal or longitudinal gradient. No evidence was found that intraspecific variation in basal metabolic rate influences variation in production rates. Rates of basal metabolism were not correlated significantly with rates of energy investment in postnatal growth, reproduction, or rates of assimilation of energy at the intraspecific level. In general, allocation of energy to production was constant regardless of the basal metabolic rate of each individual. In contrast, allocation of energy to activities other than basal metabolism and production was lower in cotton rats with high basal rates. Differences in metabolic capacity and metabolic scope are suggested as an alternative explanation for simultaneous increases in basal metabolism and production rates documented at the interspecific level.