Lower body mass and higher metabolic rate enhance winter survival in root voles,Microtus oeconomus

Abstract

Although the biological significance of individual variation in physiological traits is widely recognized, studies of their association with fitness in wild populations are surprisingly scarce. We investigated the effect of individual phenotypic variation in body mass, resting (RMR) and peak metabolic rates (PMR) on mortality of the root vole Microtus oeconomus. Body mass and metabolic rates varied significantly among consecutive years and were also age dependent, as individuals born in late summer and autumn were characterized by significantly lower body mass and metabolic rates than animals born earlier. At the beginning of winter voles born in spring and early summer exhibited reduced body mass and metabolic rates, whereas animals born later maintained lower body mass and RMR, which may be interpreted as phenotypic plasticity enhancing the probability of survival. Body mass had no significant effect on vole survival during summer. In contrast, smaller individuals were characterized by lower mortality during early winter, whereas higher body mass was positively associated with survival later in the season. High body‐mass‐corrected RMR positively affected survival in both summer and winter. The effect of PMR was apparent only during winter, though its direction (and correlation with RMR) varied among years. Deep snow cover negatively affected the survival of voles in both early and late winter. Ambient temperature was positively associated with winter survival, except for late winter, when rising temperature caused flooding of vole habitat. We conclude that the lack of consistency in the directionality and strength of the effects of body mass and metabolic rates on winter survival does not undermine their importance, but rather demonstrates the ability of individuals to adjust metabolic rate to changing environmental conditions. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 297–309.

Effect of abrasive properties of sedges on intestinal absorptive surface and Resting Metabolic Rate of the root voles

“…Under natural conditions the root voles feed almost exclusively on sedges (Tast, 1966), and therefore they probably suffer from even more intense mucosal shedding than that reported here. In our recent study, we found that high densities of the root vole population inhabiting homogenous sedge wetland induces an increase of the silicon concentration in sedges at the end of summer , which, in turn, is followed by an increased mortality of larger (heavier) individual voles during early winter Zub et al, 2014). Thus, our laboratory experiment provides a mechanistic explanation to the field observations by showing that a sedge-dominated diet can reduce the intestinal absorptive surface.…”

“…Our previous studies showed that changes in the silicon concentration in fibrous tussock sedge (Carex appropinquata Schumacher 1801) were induced by a high density of cyclical population of the root voles (Microtus oeconomus Pallas 1776) at the end of the previous summer. We also found that smaller (lighter) voles were characterised by lower mortality during early winter Zub et al, 2014), which might be correlated with the low quality of their food base. However, the underlying proximate mechanism promoting smaller individuals is not known.…”

Immunocompetence and high metabolic rates enhance overwinter survival in the root vole, Microtus oeconomus

“…If positive associations between N/L ratio, body mass and survival hold, they indicate that the high N/L ratio manifests in the ability to combat already developing infection, rather than its contraction. This is in agreement with the analyses of Zub et al [10], which show that survival was not significantly affected by age of individual root voles in either early or late winter.…”

“…Our results concur with Zub et al's study [10] in demonstrating that cPMR in voles is positively associated with winter survival (figure 2a), most likely through enhancing swim-elicited aerobic performance in a frequently flooded habitat. Our findings from early winter also agree with Downs et al [5], who demonstrated an inverse association between induced (not constitutive) innate immunity and cPMR (elicited by forced exercise) in laboratory mice.…”

“…We also measured the swim-elicited peak metabolic rate (PMR), the level of which may influence the survival probability of root voles living in periodically flooded sedge meadows [10]. By definition, PMR does not constitute a significant part of energy expenditures.…”