Life history of voles: growth and maturation in seasonal cohorts of the root vole

Abstract

Seasonal differences in growth and maturation patterns in voles can be direct effects of changing environmental factors or indirect, evolutionary selected responses to environrnental signals. The airn of the study is to examine growth and maturation in seasonal cohorts of wild populations of the root vole, Microtus oeconomus, and to investigate causes for stated differences in the patterns. Three cohorts of young of the year (KI-K3) and one of overwintered old individuals (KO) were distinguished. Young born in different seasons differed in continuity of growth throughout the breeding season and in maturity. The first signs of the seasonal inhibition of growth and maturation in subadult sumrner born voles (K2) were found before mid-July. The inhibition is interpreted as an adaptive response which increases chances of these individuals to survive the winter. The possible environmental cue to which they respond, and the possible advantages of refraining from further growth are discussed. Existing rnodels of optirnal energy allocation to growth and reproduction, which do not fit small rodents, appear to be inadequate.