Genetic characterisation of oyster populations along the north-eastern coast of Tunisia

Abstract

The taxonomy of oysters has been traditionally based on characteristics of the shell. More recently, the analysis of protein and DNA polymorphism has provided a means to overcome difficulties in distinguishing the different species of oysters based solely on shell morphology. In order to identify oysters of the Tunisian northeast coast, we sequenced a 16S rRNA mitochondrial fragment from 68 oysters sampled from the Bizert Lagoon and the Gulf of Hammamet in northern Tunisia. Comparison of oyster 16S rRNA sequences available in GenBank showed the presence of both Ostreola stentina and Crassostrea gigas in our samples, which could not be detected on the basis of shell morphology only. These data confirmed that C. gigas, a non-native species, is now naturalised in the Bizert Lagoon. Furthermore, significant levels of genetic divergence among the 16S rRNA haplotypes from O. stentina populations have been observed. Specifically, the haplotypes found in the Bizert Lagoon are closer to those previously detected from Morocco and Portugal, whereas those in the Gulf of Hammamet are closer to the haplotypes from the south of Tunisia, with a divergence ranging from 2.1% to 2.7% between the northern and eastern Tunisian haplotypes. The possible impact of the Siculo-Tunisian Strait on the phylogeography of O. stentina is discussed.

DNA barcoding for assessment of exotic molluscs associated with maritime ports in northern Iberia

“…Although a detailed taxonomical examination is needed for its accurate identification, they exhibit notable genetic differences (Lapegue et al 2006), also confirmed from the phylogenetic trees (Figure 1). In other studies some O. stentina specimens could not be distinguished from C. gigas based on external shell morphology alone (Dridi et al 2008). Therefore, the presence of O. stentina in our study area could most likely remain undetected without the use of genetic markers.…”