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First published online December 26, 2008
Journal of Experimental Biology 212, 297-304 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.021212
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Bioenergetics and inter-individual variation in physiological capacities in a relict mammal – the Monito del Monte (Dromiciops gliroides)

Pablo Cortés, Silvia A. Quijano and Roberto F. Nespolo*

Instituto de Ecología y Evolución, Universidad Austral de Chile, Casilla 567, Valdivia, Chile

* Author for correspondence (e-mail: robertonespolo{at}uach.cl)

Accepted 10 November 2008

In evolutionary physiology, studies of inter-individual variation (i.e. repeatability) in functional capacities are valuable as they indicate – within populations – what attributes could respond to natural selection. Although repeatability and quantitative genetics of physiological traits in energy metabolism of eutherian mammals have been well characterized, few or no studies have been performed on marsupials. We studied the repeatability (i.e. intraclass correlation coefficient, {tau}) of bioenergetics for Monito del Monte (Dromiciops gliroides), the sole living representative of an otherwise extinct marsupial order (Microbiotheria). We measured resting metabolic rate as CO2 production (VCO2) and O2 consumption (VO2) simultaneously, together with minimum thermal conductance (C), evaporative water loss (EWL) and respiratory quotient (RQ), in a sample of ca. 20 individuals. Our results suggest that D. gliroides exhibits poor control of body temperature (Tb), with a thermal amplitude of ca. 10°C in normothermia. As a consequence, repeatability of Tb and metabolic rate (either as VCO2 or VO2) were relatively low ({tau}Tb=0.25±0.04, {tau}VCO2=0.14±0.03, {tau}VO2=0.24±0.02, jackknife estimations of standard errors). Thermal conductance exhibited near-zero or negative repeatability and was lower than expected for marsupials. However, we found significant repeatability for RQ and EWL ({tau}=0.32±0.03 and 0.49±0.09, respectively). In general, these results suggest that Monito del Monte exhibits some `reptilian' physiological characteristics. The relatively low repeatability of physiological variables, which otherwise exhibit large inter-individual and genetic variance in eutherian mammals, suggests that these capacities do not exhibit evolutionary potential in the ancient order Microbiotheria.

Key words: whole-animal metabolism, respiratory quotient, Dromiciops, Australasian fauna, repeatability, evolution of endothermy


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© The Company of Biologists Ltd 2009