Genetic variability and divergence of Neutrodiaptomus tumidus Kiefer 1937 (Copepoda: Calonida) among 10 subpopulations in the high mountain range of Taiwan and their phylogeographical relationships indicated by mtDNA COI gene

Abstract

Background: In the mountain area of Taiwan, we investigated 10 subpopulations of Neutrodiaptomus tumidus Kiefer 1937 living in isolated alpine ponds or lakes. We used mitochondrial DNA cytochrome C oxidase subunit I (COI) sequence as molecular marker to investigate the population genetic structure and their phylogeographical relationships. Results: We obtained 179 sequences from 10 subpopulations and found 94 haplotypes. Nucleotide composition was AT-rich. Haplotype diversity (Hd) and nucleotide diversity (p) indicated significant genetic differences between subpopulations (Hd = 0.131 similar to 0.990; pi = 0.0002 similar to 0.0084); genetic differentiation index (F-st) and gene flow index (N-m) also exhibited significant genetic diversification between subpopulations (F-st = 0.334 similar to 0.997; N-m = 0 similar to 1). Using Tajima's D and Fu and Li's D* and F* as neutrality tests, we found that the nucleotide variation within the population was consistent with the neutral theory except in the JiaLuoHu subpopulation. The JiaLuoHu subpopulation significantly deviated from the neutral theory and was speculated to have experienced a bottleneck effect. According to the phylogenetic tree, these alpine lake subpopulations could be divided into four phylogroups (northern region, Xueshan group, central region, and southwestern region). Xueshan group contains one subpopulation, DuRongTan, which is a unique group relative to other groups. It is close to northern group geographically but closer to southwestern group genetically. According to AMOVA, the major genetic variation came from different geographical distribution of subpopulations. Molecular clock estimates that the northern and southern regional divergence time was about 2.2 similar to 3.9 MYA, when the Central Mountain Range uplift (3 similar to 5 MYA) caused the population of N. tumidus to be segregated into northern and southern parts. Conclusions: Significant genetic divergence between each subpopulation of N. tumidus was found in this study. This result indicated the low dispersion ability of planktonic copepods with limited gene flow between each subpopulation.