COMPARATIVE-ANALYSIS OF MICROSATELLITE AND ALLOZYME MARKERS - A CASE-STUDY INVESTIGATING MICROGEOGRAPHIC DIFFERENTIATION IN BROWN TROUT (SALMO-TRUTTA)

A comparative study between microsatellite and allozyme markers was co nducted on natural populations of resident brown trout.(Salmo trutta) sampled over a reduced geographical stale and on hatchery strains. The higher level of polymorphism observed at microsatellite loci resulted in higher power of statistical tests for differentiation among popula tion samples and for genotypic linkage disequilibrium. Genetic distanc es of Cavalli-Sforza and Edwards were on average two times larger for microsatellites than for allozymes but multilocus F-ST estimates compu ted over the entire set of populations were not significantly differen t for both categories of markers. Assignment tests of individual fish to the set of sampled populations demonstrated a much higher efficienc y of microsatellites compared to allozymes. Pairwise multilocus F-ST e stimates were significantly correlated to waterway distances and there was a significant tendency for the incorrectly classified individuals to be assigned to one of the nearest populations, indicating that iso lation-by-distance acted significantly on brown trout populations. The increase of differentiation with distance was higher for allozymes th an for microsatellites. Traditional measures of genetic differentiatio n (Cavalli-Sforza and Edwards' chord distance and F-ST) were compared for microsatellites to recently proposed statistics taking into accoun t allele size differences (Goldstein's distance and rho(ST)). Using Go ldstein's distance for neighbour-joining analysis did not improve the tree structure resolution. Multilocus estimates of rho(ST) and F-ST we re not significantly different when computed over the entire set of po pulations but no significant correlation was detected between matrices of pairwise multilocus rho(ST) estimates and waterway distances.