The effect of body mass and diet composition on torpor patterns in a Malagasy primate (Microcebus murinus).

One of the most obvious physiological changes accompanying seasonal heterothermy in mammals is a fattening stage preceding periods of resource scarcity. This phenomenon reflects the interplay of both diet and physiology. Though the accrual of fat stores is known to be essential for overwintering in some species, the influence of diet on the physiology of torpor is not fully understood. Results from captive studies in heterothermic rodents and marsupials have indicated that when autumn diets are enriched with polyunsaturated fatty acids (PUFAs), animals receiving these diets experience deeper and more frequent torpor bouts than their counterparts receiving a control diet. Our study investigates this potential effect of dietary composition in animals that use daily torpor rather than prolonged torpor (i.e., hibernation). In so doing, we investigate the degree to which dietary effects on torpor are restricted to cold-adapted rodents and marsupials, or are a more general feature of mammalian heterothermy. We examined the effects of a PUFA diet and a control diet on the thermoregulation of one of the few species of primates known to use daily torpor: the grey mouse lemur (Microcebus murinus). Though the results of this study are largely inconclusive regarding the impact of dietary manipulations on torpor frequency and duration, we nonetheless find that the propensity of animals to enter torpor is directly influenced by age and seasonal changes in body mass, and thus reflect important physiological aspects of flexible thermoregulatory responses.