Genetic Diversity and Population Structure of Portunustrituberculatus in Released and Wild Populations Based on Microsatellite DNA Markers from the Yangtze Estuary

Abstract

Portunus trituberculatus is an important economic species of crab that is artificially bred and released in the Yangtze River Estuary and its adjacent sea areas. Based on six microsatellite markers, we investigate the genetic diversity and structure of 101 P. trituberculatus specimens collected from two hatcheries in Nantong and Zhoushan that participated in stock enhancement in the year 2019. We compared these with 124 wild specimens caught from 13 localities in the estuary. Analysis of several genetic diversity parameters (NA, RS, I, HO, HE, FIS, and FST) for the 15 populations demonstrates that both released and wild populations possess relatively rich genetic diversity. Furthermore, the released groups demonstrate no less genetic variation between themselves than do the wild crabs. Most FIS values are greater than zero, which shows inbreeding is common among specimens with geographically open sites. However, insufficient sampling may have led to a wide distribution of null alleles, a Hardy–Weinberg test disequilibrium in microsatellite markers PN22 and P04, and a lack of crab genetic diversity in site 14. All populations (except locality 14) have not suffered the bottleneck effect. Four subgroups can be seen to roughly spread longitudinally along the sample area by performing pairwise comparisons of genetic distance and FST values among the populations. No obvious topological heterogeneity is discovered among the four subgroups in a phylogenetic tree. The existence of genetic exchange and differentiation among the subgroups is also verified using structure analysis. Therefore, based on this evidence, we propose that the hatchery stock enhancements performed in Nantong and Zhoushan result in no reduction in genetic diversity for wild populations in the Yangtze Estuary in 2019.