Morphological and genetic characterization of the invasive rayed pearl oyster Pinctada imbricata radiata (Mollusca: Bivalvia: Pteriidae) populations from contrasting environments along the Tunisian coast

To understand patterns of genetic and morphological variability, population structure and dispersal dynamics of the invasive bivalve Pinctada imbricata radiata (Leach, 1814) in Tunisian waters, we studied 200 individuals from five different sites (natural, polluted and/or subjected to environmental and anthropogenic pressures) using 10 enzymatic systems and six shell measurements. In this study, we attempt to elucidate the relationship between the spreading ability and the adaptive potential of the species under various environmental stresses. Fourteen putative enzyme-coding loci were resolved, six of which were polymorphic at the level of 99%. P. imbricata radiata maintains a relatively consistent level of polymorphism at the genetic markers studied, since 10% of individuals were heterozygous. The mean F-IS value was positive and significant in two samples. However, the remaining samples collected from the disturbed marine sites (polluted, urban and lagoon areas) were at Hardy-Weinberg equilibrium. Highly significant genetic (mean F-ST=0.022, P<0.001) and morphological (Wilks' lambda=0.0814, approximate F-20,F- 627=35.484, P<0.001) differentiations between samples were observed, with no evidence of isolation caused by geographic distance. However, the Mantel test performed between genetic and morphological distances revealed a significant correlation. Our results indicate that natural selection seems to have a greater influence on genetic differentiation in P. imbricata radiata than genetic drift. The combination of genetic and morphological data provided important theoretical information for determining the invasion mechanisms of the species.

Automated summary

The study on the invasive bivalve Pinctada imbricata radiata in Tunisian waters revealed stable genetic polymorphism and significant genetic differentiation between samples under different environmental stresses, with a greater influence of natural selection on genetic differentiation.