The ichthyofauna of the Lake Victoria ecosystem are some of the most globally threatened biodiversity as a result of anthropogenic and other ecological impacts. The morphological plasticity of barbs (genus Barbus) makes them ideal models for studying evolutionary phenomenon in freshwater fishes. Barbus altianalis populations have declined in Lake Victoria probably due to anthropogenic activities and hence there is need to identify remaining populations for purposes of conservation and management. In this study, morphological and genetic characterization of the endangered cyprinid a species known to be potamodramous in four main rivers draining Lake Victoria was carried out. Morphological characterization was based on 21 morphometric characters on samples from rivers Nzoia, Nyando, Yala and Sondu-Miriu. Principal Component Analysis (PCA) showed partial separation of Rivers Yala from Nzoia, Nyando, and Sondu-Miriu fish populations. Factor loadings established that 11 characters were morphologically informative. PCA1 accounted for 43.25% of the difference while PCA2 accounted for 19.44% of the difference. Mann-Whitney U Test (α =0.05) indicated lack of significanct difference in morphological characteristics between Sondu-Miriu and Nyando, but significant intra-specific morphological difference between all the other pairs of rivers. Growth variability analysis based on 19 characters indicated negative allometric growth of B. altianalis in the four populations. The results suggest presence of intra-specisfic morphometric variation between the four populations. To assess genetic diversity, population structure, demographic expansion and phylogeny of this species, 850bp of the mitochondrial control region and 658bp of CO1 were used. The 196 samples yielded 49 mitochondrial DNA haplotypes and 83.7% of these haplotypes were private haplotypes restricted to particular rivers. The overall mean haplotype diversity was high (0.936±0.008) and ranged between 0.566 (Sondu–Miriu) and 0.944 (Nzoia). The overall mean nucleotide diversity was low (0.013±0.001). The B. altianalis populations in the Lake Victoria have thus maintained high genetic diversity despite adverse ecological changes in the catchment. Population differentiation tests revealed unexpected strong and highly significant (P≤ 0.001) segregation of populations in the four river basins. FST values for comparison of mtDNA among the four river-based populations ranged from 0.052 to 0.443. The samples formed two main haplotype networks based on a 95% parsimony criterion, each exhibiting a strong signature of past population differentiation. The smaller network was restricted to the river Nzoia and Uganda (secondary data) populations, whereas the larger network contained representatives from all four rivers; within this the central haplotypes were found in more than one river, whereas the peripheral haplotypes tended to be river-specific. Phylogenetic trees from the two markers display two distinct Clades. Clade I having samples from Nzoia and Uganda while Clade II had samples from all the four Kenyan rivers population. River Nzoia and Ugandan populations probably represents phylogenetically different populations or sub-species of B. altianalis. The degree of population differentiation and the high number of river specific haplotypes, and the highly supported bootstrap values 100/100/1.0, NJ/MP/Bayesian tree respectively of phylogenetic trees is too high to be explained by recent anthropogenic impacts alone and suggests that the species has probably existed in the Lake Victoria catchment as two populations; the now ‘extinct’ migratory population and the extant river restricted non migratory population. The decline of migratory populations could have created opportunities for population expansion. The existence of genetically robust population of Barbus altianalis in the L. Victoria catchment rivers should provide new impetus for conservation of these species. The four populations should be regarded as Evolutionary Significant Units (ESUs) and river basin specific management measures instituted to protect these populations.

University of Eldoret



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