Beyond Names: Phylogeographic Insights into the Mahseer (Teleostei: Cyprinidae: Tor) of Sarawak, Malaysia Using the Mitochondrial COI Gene
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Abstract
The mahseer (Teleostei: Cyprinidae: Tor) are highly valued freshwater fishes in Southeast Asia, with ecological, fisheries, and cultural importance. However, their taxonomy and biogeography remain unresolved, especially in Sarawak, Malaysia. This study assessed genetic divergence and phylogeographic structure of Sarawak Tor using the mitochondrial cytochrome oxidase subunit I (COI) gene. Ninety-four (94) COI sequences were analysed, comprising 19 newly determined sequences from specimens referable to T. tambroides and T. douronensis from North and South Sarawak and 75 GenBank sequences. Mean interspecific divergence between the nominal taxa was 3.62%, compared with intraspecific divergence of 2.24% for T. douronensis and 1.16% for T. tambroides, yielding a narrow difference of 1.38% between interspecific and the higher intraspecific divergence. Geographic differentiation was clearer, with 1.93% divergence between North and South Sarawak populations, compared with 0.04% and 0.62% within regions. Phylogenetic analyses recovered two major regional lineages, with the Sarawak specimens forming a distinct lineage subdivided into northern and southern subclades. The nominal taxa were not reciprocally monophyletic, and T. tambroides from Baram was nested within the North Sarawak T. douronensis lineage. These results indicate that mitochondrial variation is structured more strongly by geography than by nominal species designation and support interpreting Sarawak T. tambroides and T. douronensis as an unresolved, geographically structured species complex. Historical isolation with incomplete lineage sorting provides the most parsimonious explanation, although introgression and reference misidentification cannot be excluded. Broader sampling, nuclear or genomic data, and integrated morphological analyses are required to resolve their taxonomy and support provenance-based conservation.
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