Geographical patterns of genetic subdivision in the cellar spider Pholcus phalangioides (Araneae)

Geographical patterns of gene flow and drift were analysed in the commensal cellar spider Pholcus phalangioides to get insight into the causes affecti ng genetic variation in this species strictly associated with man. Our samp ling consisted of 23 subpopulations collected over five urban regions in ce ntral Europe (distances ranged from 920 km to sites within the same buildin g complex). Five variable allozyme loci showed significant interpopulation subdivision (0-0.146) and isolation by distance over the area studied. On a regional scale (up to 70 km) significant differentiation was found, but th e genetic pattern did not correlate with distance. Moreover, significant tw o-locus disequilibria welt detected and a recent reduction in the effective population size was indicated within six sites. These results suggest that in P. phalangioides a high potential of dispersal and strong effects of dr ift within small, demographically unstable mating units seem to cause signi ficant, but unpredictable genetic differentiation patterns at lower geograp hical scales. Our study documents strong effects of drift in a strictly com mensal species outside the murine rodents.