The metabolic determinant underlying the rate of energy use during prolonged fasting for the diamondback watersnake, Nerodia rhombifer (1101.4)

Abstract

During prolonged bouts of fasting, tissues and organs lose mass as a function of their metabolic expenditure and differences in the allocation of endogenous energy. We previously observed considerable variation in the rate at which individual diamondback watersnakes (Nerodia rhombifer) lose body and fat mass during extended fasts. It has also been found that these snakes exhibit variation in their standard metabolic rate (SMR). We therefore hypothesized that individual variation in SMR is responsible for the observed variation in body mass and body fat loss with fasting. Predictably, snakes with relatively high SMR would metabolize fat stores at a greater rate (therefore loss body mass faster) than snakes that possess relatively low SMR. We explored the causal relationships between SMR and body and fat loss during extended bouts of fasting for the diamondback watersnake by examining variation in SMR and differential loss of body, fat, and organ mass over six months of fasting. Baseline SMR and body mass was measured from 55 snakes and organ masses from 10 snakes. For each following month, 5 snakes were dissected, with 10 snakes sampled on the 6th month. SMR of individuals was measured at 2‐month intervals. On average snakes lost 0.1 grams of fat per day while fasting, with a 5‐fold range in daily fat loss among snakes. After 5 months of fasting, variation in body fat loss ranged from 25% to 90%. There was a 2.5‐fold variation in SMR among these same individuals. As predicted, snakes with higher SMR experienced a greater rate of body fat loss. We have demonstrated that basal rates of metabolism can significant determine rates of body fat loss and therefore impact an individual’s capacity to survive long episodes of fasting.