Lagoonal sand smelts (Atherina lagunaea, Teleostei, Atherinidae) inhabit marine shallow waters of the coasts of Djerba island (Tunisia)

Abstract

The Mediterranean Atherina boyeri species complex has been recently divided into three species, two living in marine environments (A. boyeri and A. punctata) and one found in lagoons and in shallow coasts of the Tunisian Kerkennah islands (A. lagunae) (Trabelsi et al. 2009). Genetic variation in a portion of the cytochrome b gene was examined for two populations belonging to the A. boyeri complex which have been caught in shallow waters of another Tunisian southern Island (Djerba). Similarly to the Kerkennah fish, molecular studies have shown that fish from Djerba, inspite of their marine habitat, belong to the A. lagunae species. All the phylogenetic analysis showed that the sequences of the Djerba insular fish constitute with the lagoon Atherina of the Lake of Tunis and Kerkennah insular fish a clade which is strongly statistically supported. In addition, within this clade, the both sequences from fish caught Djerba and Kerkennah coasts exhibit a great level of intrapopulational divergence between them. Whereas, analysis of partial cytochrome b gene of fish from the Lake of Tunis suggests a very low level of sequence heterogeneity. These results could suggest a metapopulation pattern with core-satellite structure in which cores are insular populations; whereas population of Lake of Tunis would be an example of satellite population. The ancestors of the A. lagunae can considered marine fish adaptated in a first step to shallow waters of the island coasts and in a second step, they have colonized lagoons; or some lagoon fish could have migrated and lived on similar habitats such as island coasts. However, according to the core-satellite hypothesis, the first scenario could be the most realistic according to the fish colonization of lagoon habitats with reduction of its gene diversity.