Tropical Heterothermy: Does the Exception Prove the Rule or Force a Re-Definition?

Abstract

Recent interest in heterothermy in the tropics and the subtropics has raised issues with the existing definitions of torpor. The current methods used to distinguish and define patterns of heterothermy are insufficient in face of the numerous forms of torpor expression and high daily variation in normothermic body temperature (T b) observed in species inhabiting the tropics. Tropical heterothermy often occurs at highly variable ambient temperatures that may lead to a continuum between hibernation, daily torpor and normothermia with no clear distinction between states. While we do not seek to redefine torpor in this review, by listing torpor patterns that fall outside the usual categories (the exceptions to the rule), we discuss these thermoregulatory behaviours in terms of the energetics and evolution of heterothermy under warm climates.