Genetic Structure and Phylogeography of Commercial Mytilus unguiculatus in China Based on Mitochondrial COI and Cytb Sequences

In order to study the genetic structure and population geographic distribution pattern of coastal mussel populations in the coast of China, mitochondrial DNA (COI and Cytb genes) were used to analyze the genetic diversity, genetic structure, and population history dynamics of Mytilus unguiculatus in the East China Sea and the Yellow Sea. We detected high levels of genetic diversity in seven populations of M. unguiculatus. A total of 34 haplotypes of COI genes and 29 haplotypes of Cytb were obtained. The haplotype diversity of COI ranged from around 0.77 to 0.93 (Cytb: 0.83 similar to 0.91). The nucleotide diversity of COI ranged from around 0.0044 to 0.0064 (Cytb: 0.0049 similar to 0.0063). The coefficient of genetic differentiation (F-ST) of COI ranged from around 0.031 to 0.080, and Cytb ranged from around 0.028 to 0.039. Analysis of molecular variance (AMOVA) and a phylogenetic tree showed that the genetic structure was relatively weak, and there was no clear population differentiation. The neutrality test results showed that Tajima's D value and Fu's Fs value were not significant, and no significant population demographic events, including population expansion or population bottleneck, were detected in the samples. The Bayesian skyline graph analysis showed that the effective population size has been relatively stable for nearly 10,000 years, without any large population fluctuations. It was speculated that the seven populations in the present study should belong to the same group. This study provides a comprehensive survey of the genetic characteristics of M. unguiculatus, filling the gaps among related studies. It provides theoretical support and material accumulation for seed selection and breeding, genetic resources' protection, and breeding management in the future.