Skimping as an Adaptive Strategy in Social Fossorial Rodents: The Mole Vole (Ellobius talpinus) as an Example

Abstract

Most fossorial or subterranean rodents show similar physiological adaptations to subterranean life. The physical properties of the soil – high density, thermostability, low partial pressure of oxygen and high concentration of carbon dioxide – result in a decrease in basal and maximal metabolic rate, and thermoregulatory ability in fossorial rodents (Ar 1987). Good protection against predators and parasites, together with low dispersion rates (Lovegrove 1991) are assumed to lead to the reduction of reproductive activity and enormously high longevity typical of these species (Jarvis and Bennett 1991; O’Connor et al. 2002). One of the main evolutionary consequences of these adaptations is a social existence with communal nesting and reproductive skew (Jarvis andBennett 1991; Faulkes andBennett 2001) that reduces the costs of body maintenance, reproduction and thermoregulation. On the other hand, energetic expenditure on burrowing (Vleck 1979) dramatically increases the metabolic costs of foraging. Selection pressures exerted by ecological factors lead to the evolution of integratedmorphological, physiological and behavioral adaptations (Pianka 1994), so onemight expect that all life history and physiological traits of fossorial rodents will, to some extent, reflect trade-offs between burrowing and other activities. Hitherto, however, there have been no studies of overall energy budgeting in fossorial rodents from the perspective of optimal resource allocation theory (Stearns 1992). We have examined species specific adaptive traits in mole-voles (Ellobius spp.) and compared these with dwarf hamsters (Phodopus spp.) and voles of the genusClethrionomys. These two taxonomically related and sympatric, surface-dwelling rodents have bodymasses comparable to those of mole-voles. Besides examination of major metabolic demands – cellular maintenance, somatic and generative production, locomotion, thermoregulation and immunity –we include in our analysis an estimation of the adrenocortical response to stress as