Dietary Protein Deficiency Affects Food Consumption and Torpor in the African Woodland Dormouse (Graphiurus murinus)

Abstract

Many heterotherms employ torpor to conserve energy to cope with food shortage. Food shortage affects not only energy budgets but also other aspects of nutritional status. In addition to serving as an energy substrate, dietary proteins also provide vital nutrients including essential amino acids, some of which cannot be synthesized de novo. We evaluated the hypothesis that dietary protein deficiency induces torpor as a means of adjusting protein metabolism in the African woodland dormouse (Graphiurus murinus), a rodent with a protein-rich diet and lacking a cecum, which limits the potential for hindgut fermentation and coprophagy. Dormice were fed control and non-protein diets with equivalent energy content every two weeks under thermoneutral conditions. While the dormice did not express torpor under control conditions, some did under protein-deficient conditions. Among dormice expressing torpor, one maintained energy intake comparable to that during the control diet period, whereas the other reduced energy intake due to spontaneously reduced food consumption. These results suggest that torpor can be induced directly or indirectly by dietary protein deficiency even in the absence of energy constraints and thermal stress. In either case, torpor in response to deficiency in certain nutrients can reduce demands of the nutrient.