Evaluation of the effect of longitudinal connectivity in population genetic structure of endangered golden mahseer, Tor putitora (Cyprinidae), in Himalayan rivers: Implications for its conservation

In many aquatic species, alteration of habitats and human-induced barriers shape the population’s genetic structure in rivers with longitudinal connectivity. The golden mahseer, Tor putitora (GM) is an endangered and sensitive cyprinid species. It is considered an indicator of a healthy freshwater ecosystem and is found in cold-water habitats. Therefore, it is crucial to understand how longitudinal connectivity and anthropogenic factors affect the diversity and population genetic structure of GM. The population genetic structure, gene flow and demography of the GM in four Himalayan rivers were investigated by mitochondrial cytochrome b gene (cyt b) as well as microsatellite genotyping. The results showed overall high mtDNA diversity (hd: 0.795) couple with low nucleotide diversity (π: 0.0012) in all GM populations. We also found significant levels of observed heterozygosity (ranging from 0.618 to 0.676), with three genetic clusters. The mtDNA and microsatellite analysis suggested that there are close genetic relationships between the Bhagirathi and Ganga populations; whereas, significant level of genetic differentiation was observed with that of Alaknanda and Yamuna populations. Haplotype distribution, unimodal distribution graph and results of the neutrality test indicated a sign of recent population growth in the GM population. Analysis of molecular variance (AMOVA) and spatial molecular variance (SAMOVA) revealed existence of genetic structures in GM populations. In addition, spatial genetic analysis detected a significant correlation between the pairwise genetic and geographical distances for the entire study area (Mantel test, rM = 0.126; P = 0.010). Considering the significant level of heterozygosity, high rate of unidirectional migration and the intra-population structuring in Alaknanda and Yamuna, it is crucial to propose an effective conservation plan for the GM populations. In general, dams obstruct continuous water flow and create isolated microhabitats. Therefore, we recommend the establishment of microscale protected areas near GM breeding sites and construction of fish pass to maintain the genetic connectivity of fish species that enhance viable populations.