Flexible patterns in energy savings: heterothermy in primates

Heterothermy is an energy-saving strategy usually employed in response to environmental bottlenecks, which is common in almost all mammalian orders. Within the order primates, heterothermy has been physiologically confirmed only in the family Cheirogaleidae (Cheirogaleus, Microcebus, Allocebus, Mirza) of the Malagasy lemurs, and the southern lesser bushbaby (Galago moholi) of the family Galagonidae. These closely related species employ a spectrum of daily torpor, prolonged torpor and obligate hibernation under tropical, but nevertheless seasonal and energetically demanding conditions. There is a remarkable physiological flexibility in regard to their thermoregulatory adaptations not only between species of the same genera within one habitat, but also between populations of the same species, within populations and even within the same individual, permitting immediate responses in seasonal and unpredictable environments, and possibly aiding these species to master challenges of globally changing climatic conditions. Whereas heterothermy is a flexible, but regular seasonal response in the Cheirogaleidae, it is only used as a last emergency strategy in G.moholi. In the other primate species, there is either no or only anecdotal evidence of only minor reductions in metabolic rate, presumably rather reflecting pronounced circadian cycles in body temperature, or local heterothermy. Maybe because of their relatively high degree of sociality and larger body sizes, behavioural and ecological adaptations to seasonality are selected for in other primates.