Abstract: 【Aim】 This study aims to reveal the impact of island isolation on the genetic diversity of Geisha distinctissima inhabiting in the Zhoushan Archipelago in East China. 【Methods】 Based on 16S rRNA gene fragments of 247 individuals from 15 populations of G. distinctissima in 11 islands and adjacent mainland obtained in this study, the population genetic diversity of G. distinctissima in this region was assessed. The phylogenetic analysis was conducted using Bayesian inference method and the haplotype network was constructed to resolve genetic structures among G. distinctissima populations. The demographic history of G. distinctissima populations was also evaluated by neutrality test, mismatch distribution analysis and Bayesian skyline plots (BSP). 【Results】 Both Bayesian phylogenetic analysis and haplotype network showed that the G. distinctissima populations in the Zhoushan Archipelago did not develop distinct genetic structure. Moreover, the molecular analysis of variance (AMOVA) showed that genetic differentiation mainly occurred within population (68.26%), suggesting that G. distinctissima populations of this region are homogeneous in genetic diversity. No correlation was found between the haplotype and nucleotide diversity and the isolated time and distance of islands. In addition, the neutral test showed that both Tajima’s D and Fu’s Fs exhibited prominent negative values, and there was a single peak in mismatch distribution analysis with canonical unimodal format, suggesting that G. distinctissima populations in the Zhoushan Archipelago may suffer from population expansion events. The BSP analysis showed that the expansion events occurred between 0.5-3.5 thousand years ago (kya). 【Conclusion】 Island isolation might have not exerted visible impacts on the divergence of genetic diversity among G. distinctissima populations in the Zhoushan Archipelago and adjacent mainland.

Key words: Geisha distinctissima, island isolation, 16S rRNA, haplotype, genetic diversity; demographic history, Zhoushan Archipelago