Impact saisonnier de l'environnement sur la structure génétique de trois populations de Ruditapes decussatus dans lécosystème lagunaire de Bizerte

Abstract

Bizerte Lagoon is subjected to natural and anthropic disturbances which can modify the genetic structure of clam populations (Ruditapes decussatus). In an attempt to evaluate the impact of the environmental variations on populations, genetic analysis has been carried out on three clam populations sampled from Echaara, Menzel Jemil and Faroua sites between June 2000 and February 2001. This present study allowed genetic and protein markers to be specifically characterized. Four allozymic markers have been examined to reveal the genetic structure of these populations; glucosephosphate isomerase (Gpi), phosphoglucomutase (Pgm), malate deshydrogenase (Mdh), and leucine aminopeptidase (Lap). A significant genetic differentiation between the three populations of clams has been observed, as well as for every one of two populations between the sampling periods. This analysis also detected the existence of an heterozygote deficiency and a seasonal decrease of the allelic diversity for each of them. A positive correlation between the decrease of diversity and the metallothionein contents seems to be occurring for every population. These results suggests a possible relationship with the existence of heavy metals flow graduation between Menzel Jemil, Faroua et Echaara. Heavy metals seems to be a major selective strength among the lagoon clams