GENETIC DIVERSITY OF ASIAN WATER-BUFFALO (BUBALUS-BUBALIS) - MICROSATELLITE VARIATION AND A COMPARISON WITH PROTEIN-CODING LOCI

Twenty-one microsatellite loci in 11 populations of Asian water buffal o (eight swamp, three river type) were analysed and, within and among populations, genetic variability was compared with results from 25 pol ymorphic protein-coding loci. Within-population mean heterozygosity ra nged from 0.380-0.615, approximately twice that estimated from the pro tein-coding loci (0.184-0.346). Only eight significant departures from Hardy-Weinberg equilibrium (involving four loci) were detected; globa l tests showed significant heterozygote deficiencies for these four lo ci. Non-amplifying alleles are likely to be segregating in some or all populations for one of these loci, and probably far the other three. There was significant differentiation between the swamp and river type s of water buffalo, and among populations within each buffalo type. Es timates of theta (measure of population differentiation) for each locu s for the eight swamp populations were all highly significant (mean th eta = 0.168 +/- 0.018). Mean theta for protein-coding loci was not sig nificantly different (0.182 +/- 0.041). The variance among protein-cod ing loci was significantly higher than among microsatellite loci, sugg esting balancing selection affecting allele frequencies at some protei n-coding loci. Genetic distances show clear separation of the swamp an d river types, which were estimated to have diverged at least 10 000-1 5 000 years ago. The topology of the swamp populations' microsatellite tree is consistent with their geographical distribution and their pre sumed spread through south-east Asia. By contrast, the tree based on t he protein-coding loci distances is quite different, being clearly dis torted by a bottleneck effect in one population, and possibly in at le ast two others. As many domestic livestock breeds are possibly descend ed from small numbers of founders, microsatellite-based trees are to b e preferred in assessing breed genetic relationships.