A Significant Genetic Admixture in Farmed Populations of the Noble Scallop Chlamys nobilis Revealed by Microsatellite DNA Analysis in Southern China

Haitao Ma,Yuehuan Zhang,Jun Li,Yang Zhang,Shu Xiao,Yanping Qin,Dongmei Yu,Ziniu Yu

doi:10.3389/fmars.2021.721292

Abstract

The noble scallop, Chlamys nobilis, is an important bivalve mollusk with high commercial value and is usually farmed in the waters of southern China. To date, very little is known about the genetic diversity and population structure of C. nobilis. In this study, 10 microsatellite loci of four farmed C. nobilis populations were compared with one another and compared wild population in southern China. A total of 83 alleles were found. Surprisingly, the level of genetic diversity of the farmed C. nobilis populations was higher than that of the wild population. Although the population genetic of wild population was completely in the Hardy–Weinberg equilibrium, due to heterozygote deficiency, significant deviations from the Hardy–Weinberg equilibrium were found in all farmed populations, suggesting a genetic admixture caused by the mixing of seeds from various hatcheries. The Fst and AMOVA values showed significant genetic differences between wild and farmed populations. The Bayesian assignment also confirmed that genetic admixture was significant and widespread in artificial breeding of C. nobilis. Furthermore, the UPGMA tree topology and PCA demonstrated that the genetic diversity of wild population can be clearly distinguished from farmed populations. In a nutshell, the findings of this study not only fill the knowledge gaps in genetic diversity of wild and farmed C. nobilis populations, but also serve as a guide for maintaining the genetic diversity of C. nobilis in both farmed and wild populations.

Highlights

Scallops are important animal protein source for humans (Liu et al, 2007; Tan et al, 2019)
The aim of this study was to use microsatellites to explore the genetic variation of C. nobilis among hatcheries, and between hatchery and wild populations
All 10 microsatellite loci were polymorphic in all five C. nobilis populations. 83 different alleles were observed in these 10 loci, ranging in size from 66 to 464 bp

Summary

Introduction

Scallops are important animal protein source for humans (Liu et al, 2007; Tan et al, 2019). It is generally believed that the reproduction of animals in small or isolated populations will result in reduced heterozygosity and inbreeding depression, as well as reduced survival rates (Reed and Frankham, 2003). To avoid those potential problems, scallop farmers usually purchase scallop seeds from various sources or use seeds produced by mixing broodstocks obtained from various sources. There are significant variations in aquaculture traits among scallops in different farms, such as growth, survival rate, and disease resistance. It is worth noting that mixing population seeds from different sources may lead to a higher levels of genetic diversity and fewer heterozygotes in the populations (Ferguson, 1995; Thai et al, 2007), which might explain the high mortalities within scallop populations (Nagashima et al, 2005)

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Conclusion