Extreme individual flexibility of heterothermy in free-ranging Malagasy mouse lemurs (Microcebus griseorufus)

Abstract

Flexibility in physiological processes is essential to adequately respond to changes in environmental conditions. Madagascar is a particularly challenging environment because climatic conditions seem less predictable than in comparative ecosystems in other parts of the world. We used the reddish-gray mouse lemur (Microcebus griseorufus) from the most unpredictable environment in Madagascar as a model to investigate the flexibility of energy saving strategies to cope with the unpredictability of their habitat. For this we measured T (sk) of free-ranging mouse lemurs throughout the year using temperature data loggers. M. griseorufus showed a very strong seasonal as well as an individual flexibility in thermoregulation. During the rainy season all M. griseorufus remained normothermic. At the beginning of the dry season individuals started to exhibit different energy saving strategies: irregular short torpor bouts, regular daily torpor, prolonged torpor of a few days, and hibernation over several weeks. The accumulation of sufficient seasonal body fat was the crucial factor determining the thermal behavior of individuals. The observed intraspecific and sex independent variation in thermoregulatory patterns within one population inhabiting the same small geographical area is exceptional and gives M. griseorufus the ability to respond to current environmental as well as individual conditions. This thermal plasticity might be seen as a key to success and survival for M. griseorufus in an extremely unpredictable environment.

Modelling mammalian energetics: the heterothermy problem

“…Similar to the vast differences in the daily T b amplitudes, torpor patterns are highly variable both among and within species (Fig. 2) [10,29,36,53,97,98]. However, a decrease in T b during winter can not only be observed in heterothermic species, but also, to a lesser degree, in homeothermic species.…”

“…For example, in southern African hedgehogs (Atelerix frontalis) and mouse lemurs, only heavy individuals will undergo hibernation during the winter period, whereas individuals with a lower body mass will only use shorter bouts of torpor [98,131,132]. Similarly, throughout summer when T a is mild and insects are abundant, individuals of the Australian subtropical/ tropical insectivorous Eastern long-eared bat (Nyctophilus bifax) employ more torpor if they are in better body condition in comparison to individuals in poorer body condition [133].…”

When to initiate torpor use? Food availability times the transition to winter phenotype in a tropical heterotherm

“…3). These sex-specific differences in seasonal timing of daily torpor use might result from reduced body condition of males relative to females during the dry season (Schmid and Kappeler 1998), and associated reduced propensity to use daily torpor (Kobbe et al 2011;Vuarin et al 2013), or from sex-differences in energetic requirements to engage in reproduction just after the dry season (Schmid and Kappeler 1998;Canale et al 2012; see also Munro et al 2005;Sheriff et al 2013b). Our study is the first to document, in free-ranging grey mouse lemurs, that sex differences in activity patterns (Rasoazanabary 2006) result from the fact that males and females do not start using daily torpor at the same period of the dry season, males entering daily torpor later than females.…”

Habitat Separation of Sympatric Microcebus spp. in the Dry Spiny Forest of South-Eastern Madagascar

“…In sympatry, the diameters of trees used by M. murinus and hybrids are larger compared to those used by M. griseorufus . Large trees might provide more holes for shelter than smaller trees and may be important for nest sites that, in the case of Microcebus , allow the species to enter prolonged phases of reduced energy metabolism Andrianasolo et al, 2006;Kobbe and Dausmann, 2009;Schmid and Ganzhorn, 2009;Kobbe et al, 2011]. Visual night surveys at the beginning of the dry season in the Mikea for-est at a site where both species occur sympatrically left the impression that M. murinus had accumulated body fat and was not encountered during transect walks while fat accumulation was not obvious in M. griseorufus and the latter was still seen on the walks [Ganzhorn and Randriamanalina, 2004].…”