Genetic diversity and structure of potamodromous Opsaridium microlepis (Günther) populations in the inlet rivers of Lake Malawi

Abstract

Studies were carried out to determine the genetic diversity and structure of endangered Opsaridium microlepis (Mpasa) populations in the affluent rivers of Lake Malawi; Linthipe, Bua, Dwangwa and North Rukuru. A total of 200 DNA samples of O. microlepis from four river populations were analyzed at 20 microsatellite loci. The primers’ discriminating power was high (mean PIC, 0.76) yielding a total of 295 alleles with a range of 10-22 and an average of 15 alleles per locus. All the populations were not in Hardy Weinberg Equilibrium probably due to outbreeding that leads to heterozygosity excess. This observation was further supported by heterozygosity excess exhibited by 100% of the population-locus combinations (mean F_IS, -0.30) and lack of  evidence for genetic bottleneck. The populations exhibited high genetic diversity as evidenced by high mean Shannon information Index (I=1.64) and high observed heterozygosity (H_o = 0.98). Genetic relationships among the populations appear to be less  influenced by geographical distance (Mantel’s statistics Z, 0.18; p = 0.6369) implying that the populations do not fit into the  isolation by distance model. Nevertheless, the populations are highly differentiated (F_ST = 0.17; AMOVA among populations = 16%). This is supported by inter-deme migration of less than one individual per generation (Nm=0.91) as determined by Slatkin’ private allele method. Therefore, these populations are probably still large and distinct requiring separate monitoring  and management due to inferred restricted gene flow and considerable population differentiation.

Keywords: Mpasa, Lake Malawi, population structure, genetic diversity, microsatellites, threatened species, conservation.