Population Genomics Reveals Genetic Divergence and Adaptive Differentiation of Chinese Sea Bass (Lateolabrax maculatus).

The marine species usually show high dispersal capabilities accompanied by high levels of gene flow. On the other hand, many physical barriers distribute along the continental marginal seas and may prevent dispersals and increase population divergence. These complexities along the continental margin generate serious challenges to population genetic studies of marine species. Chinese sea bass Lateolabrax maculatus distributes broad latitudinal gradient spanning from the tropical to the mid-temperate zones in the continental margin seas of the Northwest Pacific Ocean. Using the double digest restriction-site-associated DNA tag sequencing (ddRAD) approach, we genotyped 10,297 SNPs for 219 Chinese seabass individuals of 12 populations along the Chinese coast in the Northwest Pacific region. Genetic divergence among these populations was evaluated, and population structure was established. The results suggested that geographically distant populations in the Bohai Gulf and the Beibu Gulf retain significant genetic divergence, which are connected by a series of intermediate populations in between. The results also suggested that Leizhou Peninsula, Hainan Island, and Shandong Peninsula are major physical barriers and substantially block gene flow and genetic admixture of L. maculatus. We also investigated the potential genetic basis of local adaptation correlating with population differentiation of L. maculatus. The sea surface temperature is a significantly differentiated environmental factor for the distribution of L. maculatus. The correlation of water temperature and genetic variations in extensively distributed populations was investigated with Bayesian-based approaches. The candidate genes underlying the local selection in geographically divergent populations were identified and annotated, providing clues to understand the potential mechanisms of adaptive evolution. Overall, our genome scale population genetic analysis provided insight into population divergence and local adaptation of Chinese sea bass in the continental marginal seas along Chinese coast.