Does maternal stress influence winter survival of offspring in root voles Microtus oeconomus? A field experiment

Maternal stress can have long-term adverse consequences on immunocompetence and disease risk of offspring, and winter survival is a crucial demographic parameter in the life-history of an individual that can substantially affect northern rodent population dynamics. An understanding of the effects of maternal stress on winter survival of offspring may help identify mechanisms driving population fluctuations of northern small mammals. Thus, we assessed the effects of maternal stress, resulting from high population densities, on winter survival of first generation (F-1) and second generation (F-2) in root voles Microtus oeconomus. Replicate high- and low-density enclosed parental populations were established, from which we obtained F-1 generation that were used to establish new enclosed, equal-density populations. The adults of the high-density parental populations had higher corticosterone levels, an indication of physiological stress, than did those of the low-density parental populations. Over-winter survival of the F-1 generation voles from the low-density parental populations was greater than that of those from the high-density parental populations. Over-winter survival of F-2 generation voles did not differ between the two treatments. Our results suggest that maternal stress affected over-winter survival of first generations but not second generations. Reduced immunocompetence, resulting from high population density stresses, transferred to offspring may be a factor in annual (winter) population declines. Because the effect is transitory, i.e. immunocompetence of F-2 voles is not affected, reduced immunocompetence resulting from high density stresses would not contribute to lengthy periods of low population densities that are characteristic of multi-annual population fluctuations.