Abstract: 【Aim】This study aims to clarify the genetic differentiation among populations and to reveal the cause of the geographical distribution pattern of Sigmella biguttata. 【Methods】 The sequences of mitochondrial genes COI, COII and ND1 and nuclear gene ITS of 284 individuals from 19 geographic populations of S. biguttata were amplified by PCR. The genetic diversity and genetic differentiation of S. biguttata geographic populations were analyzed using MEGA v.7.0, DnaSP v.5.0 and Arlequin v.3.5, and the population historical dynamics was detected by neutrality test and mismatch distribution analysis. The phylogenetic trees were constructed using maximum likelihood (ML) and Bayesian inference (BI) methods and the haplotype network was constructed using median joining network algorithm. The divergence time of S. biguttata populations was inferred based on the substitution rate of mitochondrial gene COI.【Results】The overall genetic diversity of the geographic populations of S. biguttata was relatively high (Hd=0.98835, π=0.02777). The ML and BI trees yielded almost identical topologies with generally high support values, and all geographic populations of eight groups were clustered together to form three lineages and showed obvious phylogeographic structure, which was consistent with the result of SAMOVA analysis. There was no haplotype shared by different geographic populations according to the haplotype network. The genetic differentiation and gene flow (N_m) analysis showed that the Fst values among populations were more than 0.25 and the maximum N_m value was less than 1. The population historic dynamics analysis showed that Group 2, Group 4, Group 6 and Group 7 experienced population expansion, occurring in the last interglacial period, but Group 1, Group 3, Group 5 and Group 8 did not. The divergence time of lineages and groups was estimated in the Mid-Pleistocene (0.5391-0.1544 Ma). 【Conclusion】 There is significant genetic differentiation among populations of S. biguttata. A warm and humid climate contributes to the population expansion of S. biguttata, and the genetic structure and geographic distribution pattern of the populations are mainly affected by geographic barriers and climatic oscillation in the Quaternary Pleistocene.

Key words: Sigmella biguttata, phylogeography, population historic dynamics, genetic differentiation, geographic distribution pattern