Population differentiation of the woodlouse Oniscus asellus in Central Europe (Isopoda: Oniscoidea)

Thirteen allozyme gene loci were assayed in 264 Oniscus asellus L. from 10 collection sites in Central Europe. Three biallelic polymorphisms (glutamate-oxaloacetate transaminase Got-2*, glucose-phosphate, and isocitrate Icd-2*) and 1 triallelic system (Got-1*) are described. The questionably biallelic Icd-1* was omitted from subsequent data analysis. Optimized conditions for an allozymic survey of O. asellus are presented. The G(ST)-fixation indices and the genetic interpopulation distances generally increased with the geographic distance separating population pairs. However, the geographic differentiation appeared very low when considering that a woodlouse lacks efficient means for active, locomotory dispersal. Moreover, the population samples could not be combined to geographically meaningful groupings. Three reasons possibly explaining the notable genetic population cohesion of a soil-dwelling isopod are discussed: the recent postglacial colonization of the Central European study area by O. asellus, human-aided passive dispersal an a large scale, and very abundant population sizes which minimize the among-stock differentiation by genetic drift.