Comparative Energetics of the Subterranean Ctenomys Rodents: Breaking Patterns

Abstract

Subterranean mammals show lower mass independent basal metabolic rates (BMR), and several competing hypotheses were suggested to explain how microenvironmental conditions and underground life affect subterranean mammalian energetics. Two of these are the thermal-stress and the cost-of- burrowing hypotheses. The thermal-stress hypothesis posits that a lower massindependent BMR reduces overheating in burrows where convective and evaporative heat loss is low, whereas the cost-of- burrowing hypothesis states that a lower mass-independent BMR may compensate for the high energy expenditure of digging. In this paper we assessed the relationship between BMR of Ctenomys and environmental variables through conventional statistics as well independent contrasts. Moreover, we tested both, thermal-stress and cost of burrowing hypotheses at an interspecific level in a very homogenous genus of subterranean rodents, the South American genus Ctenomys. We compared species from different geographic localities with contrasting habitat conditions. We measured BMR through open flow respirometry. After conventional as well independent contrast analyses, our results support neither the thermal stress nor the cost of burrowing hypotheses. We observed that only body mass affect the variability in BMR. No contrasting climatic and soil conditions, habitat productivity, or net primary productivity were correlated with BMR variability. We suggested that since BMR and maximum metabolic rates (MMR) are correlated, low BMR´s among Ctenomys species could be also determined by factors that affect MMR rather BMR.