Torpor in Tenrecs, a Basal Protoendothermic Mammal

Abstract

Thirty of the 33 described tenrec species are endemic to Madagascar. These basal mammals possess features such as a cloaca and variable body temperature (Tb). We measured the energetics of common tenrecs, Tenrec ecaudatus, during the hibernation season. Tenrecs are capable of variable arousal from torpor but do not perform the predictable interbout arousals characteristic of all other known small hibernators. At lower ambient temperatures, ventilation may be punctuated with periods of 30 min or more between breaths. We found discordant changes to oxygen consumption (VO2), heart rate (HR), and Tb e.g. a spontaneous 23% decrease in VO2 was accompanied by an 47% decrease in HR and no change in Tb. Marked changes in Tb could occur with little change to VO2. We hypothesize that hibernation in tenrecs may represent a plesiomorphic form that is manifested by poor coordination of key homeostatic processes.