This study quantified the intra‐specific diversity and characterized the population structure of the Asian snakehead fish, Channa striata in Sabah, North Borneo by determining the variability at six microsatellite loci. Range of genetic diversity across all sampled populations was comparatively moderate in relation to levels reported for C. striata populations occurring elsewhere and the overall Sabah population is highly structured, reflecting isolations across geological and ecological time scales. Two reciprocally monophyletic genodemes were identified along the west and east coast that may have been separated by mountain upthrusts throughout the central region of Sabah. Despite kinship among populations within each genodeme, individual demes were discrete as indicated by significant genotypic differentiation (all P < 0.0014) and low estimates of gene flow between them that likely reflect natural fragmentation of freshwater habitats they occupy. Our findings underline the potential of molecular markers in delimiting and delineating geospatial units of conservation in Sabah. Lowland freshwater ecosystems in the area may comprise two geographically isolated ecoregions, in which each hypothetically harbours biota that have evolved allopatrically. Additionally, identification of biodiversity hotspots within these putative ecoregions can be greatly facilitated with genetic‐level investigations as the rate by which freshwater communities are inventoried has been extremely slow in most habitats.
This study is aimed at establishing a baseline on the genetic diversity of the Acropora corals of Sabah, North Borneo based on variations in the partial COI and CYB nucleotide sequences. Comparison across 50 shallow-water Acropora morphospecies indicated that the low substitution rates in the two genes were due to negative selection and that rate heterogeneity between them was asymmetric. CYB appeared to have evolved faster than COI in the Acropora as indicated by differences in the rate of pairwise genetic distance, degrees of transition bias (T/T), synonymous-to-nonsynonymous rate ratio (d/d), and substitution patterns at the three codon positions. Despite the relatively high haplotype diversity (H), nucleotide diversity (π) of the haplotype datasets was low due to stringent purifying selection operating on the genes. Subsequently, we identified individual COI and CYB haplotypes that were each extensively shared across sympatrically and allopatrically distributed Indo-Pacific Acropora. These reciprocally common mtDNA types were suspected to be ancestral forms of the genes whereas other haplotypes have mostly evolved from autoapomorphic mutations which have not been fixed within the species even though they are selectively neutral. To our knowledge, this is the first report on DNA barcodes of Acropora species in North Borneo and this understanding will play an important role in the management and conservation of these important reef-building corals.
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