Genetic Diversity and Genetic Structure of Phascolosoma esculenta Populations in Southeastern China Based on 16S rRNA Gene Sequences

Here, we investigated the population genetic structure and genetic diversity of the endemic Chinese oceanic sipuncula Phascolosoma esculenta by using partial mitochondrial DNA 16S rRNA sequences. In total, 80 samples were collected from Xiangshan, Wenling, Ningde, and Zhanjiang, which are four muddy intertidal zones of southeastern China. Results showed that of the 80 16S rRNA gene fragments, 5 were 1010 bp in length, 73 were 1011 bp in length, and 2 were 1012 bp in length. The A+T content (67.7%) was signifi cantly higher than the C+G content (32.3%), thus exhibiting obvious AT biases. In addition, 27 different haplotypes were defi ned by 33 polymorphic sites, giving an overall haplotype diversity of 0.908 and a nucleotide diversity of 0.00247. The topological structure of the haplotype neighbor-joining tree was extremely simple, without any obvious geographical structures within the four groupings. The genetic distances among populations ranged from 0.0022 to 0.0031, and those within populations ranged from 0.002 to 0.0028. The results of AMOVA revealed a low level of genetic differentiation among the four populations. A neutral test and mismatch analysis indicated a recent population expansion for P. esculenta.