Physiological Responses to Starvation in Snakes: Low Energy Specialists

Abstract

Many types of snakes are capable of surviving over a year of complete starvation. The physiological effects of food limitation on snakes can be appreciated both by controlled studies of individuals and wild populations of snakes. Here we summarize morphological, physiological, and biochemical responses to food limitation among several distantly related snake species. Controlled studies revealed that the three traditional phases of fasting (i.e., stress, transition, adaptation), observed among endotherms, may not be clearly differentiated among fasting snakes. Nevertheless, starving snakes exhibited various potentially adaptive strategies for tolerating food limitation including the ability to: (1) reduce resting energy expenditure by entering a hypometabolic state, (2) regulate levels of circulating metabolites, (3) remodel tissues and increase body length, and (4) prioritize mass loss among different organs. Not surprisingly, the magnitude to which different species relied upon these different strategies varied, and was in part correlated with their ecological background and phylogenetic history. Starvation is a part of the natural history of many wild snake populations. Snakes inhabiting islands often experience boom and bust cycles where food is only available seasonally, usually corresponding to unpredictable allochthonous resources from birds that use islands for migratory stopovers and rookeries. Insular snakes have apparently adjusted to limited food supplies by morphological and behavioral modifications and shifting reproductive windows to minimize risk of starvation to mothers and offspring. The overall success of these strategies is evidenced in the comparatively dense population of snakes on many islands. Food available to snakes inhabiting forested areas can be influenced by land management practices (e.g., logging and fire supression) which indirectly affect the health of snake populations. Long-term mark-recapture and radiotelemetry studies reveal dramatic interannual shifts in mean body condition and extended periods of starvation driven by variation in mast crop in a degraded upland oak ecosystem.