Regional structuring of genetic variation in short-lived rock pool populations of Branchipodopsis wolfi (Crustacea : Anostraca)

The genetic structure of three metapopulations of the southern African anos tracan Branchipodopsis,sis wolfi was compared by analysing allozyme variati on at four loci (PGM, GPI, APK, AAT). In total, 17 local populations from t hree sites (metapopulations) were analysed from rock pools in south-eastern Botswana ranging from 0.2 to 21 m(2) in surface area. In three populations we found significant deviations from Hardy-Weinberg (H-W) equilibrium at o ne or more loci due to heterozygote deficiencies. Genetic variability at on e site was significantly lower than at the other sites, which may be linked to a greater incidence of extinction and recolonisation, as the basins at this site are shallower and have shorter hydrocycles. Across all local popu lations, a significant level of population differentiation was revealed. Mo re than 90% of this variation was explained by differentiation among sites (metapopulations), although this differentiation did not correlate with geo graphic distance, or with environmental variables. Genetic differentiation among populations within metapopulations was low, but significant at ail si tes. At only one of the sites was a significantly positive association meas ured between genetic and geographic distance among local populations. Our d ata suggest that persistent stochastic events and limited effective long-ra nge dispersal appear to dominate genetic differentiation among populations of B. wolfi inhabiting desert rock pools. The lack of association between g eographic distance and genetic or ecological differences between rock pool sites is indicative of historical stochastic events. Low heterozygosity, th e significant deviations From H-W equilibrium, and the large inter- but low intra-site differentiation are suggestive of the importance of short-range dispersal. Gene now between metapopulations of B. wolfi appears to be seri ously constrained by distances of 2 km or even less.