Comparison of gene flow estimates between species of darters in different streams

Allozyme variation was assessed at two localities for 38 loci in Etheostoma blennioides and 43 loci in E. flabellare. Percent polymorphism (P) ranged from 18 .4 to 31 .6 and average heterozygosity (H) ranged from 0 . 026 to 0 . 079. Estimates of gene flow indicated panmictic populations of E. blenni oides and sub-divided populations of E. flabellare, with significantly more substructuring of E. flabellare from one population. Population structurin g of E. flabellare and no structuring of E. blennioides is consistent with predictions based on life history data. Significantly different gene flow e stimates for E. flabellare between streams imply that each stream environme nt induced different population structures. Reduced heterozygosity for both species and significantly less population structuring in one population ar e consistent with drought-induced extinction and recolonization that probab ly occurs in the smaller stream. (C) 2000 The Fisheries Society of the Brit ish Isles.