High genetic diversity and low differentiation in mud crab (Scylla paramamosain) along the southeastern coast of China revealed by microsatellite markers

The mud crab (Scylla paramamosain) is a carnivorous portunid crab, mainly distributed along the southeastern coast of China. Mitochondrial DNA analysis in a previous study indicated a high level of genetic diversity and a low level of genetic differentiation. In this study, population genetic diversity and differentiation of S. paramamosain were investigated using nine microsatellite markers. In total, 397 wild specimens from 11 locations on the southeastern coast of China were sampled and genotyped. A high level of genetic diversity was observed, with the number of alleles, and the observed and expected heterozygosity per location in the range 7.8-9.6, 0.62-0.77 and 0.66-0.76, respectively. AMOVA analysis indicated a low level of genetic differentiation among the 11 locations, despite the fact that a statistically significant fixation index (F-ST) value was found (F-ST=0.0183, P<0.05). Out of 55 pairwise location comparisons, 39 showed significant F-ST values (P<0.05), but all of them were lower than 0.05, except for one between Sanmen and Shantou locations. No significant deficiency of heterozygotes (inbreeding coefficient F-IS=0.0007, P>0.05) was detected for all locations except Sanmen and Zhanjiang. Cluster analysis using UPGMA showed that all locations fell into one group except Sanmen. Significant association was found between genetic differentiation in terms of F-ST/(1-F-ST) and the natural logarithm of geographical distance (r(2)=0.1139, P=0.02), indicating that the genetic variation pattern closely resembled an isolation by distance model. This study supports the proposal of high genetic diversity and low genetic differentiation in S. paramamosain along the southeastern coast of China.