Genetic diversity analysis of Arius manillensis (Siluriformes: Ariidae) using the mitochondrial control region.

Arius manillensis is a Philippine endemic species and is an economically important fishery resource in Laguna de Bay, the largest lake in the country. Drastic reduction in population sizes of A. manillensis has been recorded in the past, which may have resulted in genetic bottleneck. In this study, the genetic diversity and population structure of A. manillensis in Laguna de Bay were assessed using the mitochondrial DNA control region. Specimens were obtained from three localities along Laguna de Bay, namely Binangonan (n = 27), Tanay (n = 29), and Calamba (n = 30). Of the 86 DNA sequences generated, 22 distinct haplotypes were observed. There were four unique haplotypes for Binangonan, six for Calamba, and five for Tanay. There were two haplotypes common to the three sites. The maximum likelihood tree and median-joining network showed little geographic separation among the haplotypes. Chi-square test showed no significant differentiation in A. manillensis from the three sites. The overall computed F(ST) was 0.0144, indicating small genetic differentiation in A. manillensis from the three localities sampled. Likewise, analysis of molecular variance showed a greater percentage of variation within population (98.62%) than variation among populations (1.38%; P = 0.21). Total haplotype diversity and nucleotide diversity among the specimens from the three sites were 0.775 and 0.013, respectively. The high haplotype diversity coupled with low nucleotide diversity observed in this study confirms that genetic bottleneck occurred in A. manillensis which was followed by population expansion. This is also supported by the non-significant values for both Tajima's D and Fu's F. Furthermore, multimodal mismatch distribution plots were generated, which is consistent with the model of spatial range expansion followed by demographic expansion.