Biodiversity and biogeography in heterospecific teleostean (Gadidae) – copepod (Lernaeocera) associations

Abstract

This genetic study confirms the validity of two controversial parasite species, Lernaeocera branchialis and Lernaeocera lusci (Copepoda, Pennellidae). These species cohabit throughout a large sector of the North Sea and the Atlantic Ocean, parasitizing Merlangius merlangus and Trisopterus luscus (Teleostei, Gadidae), respectively. In the Mediterranean Sea, it was L. branchialis that was described initially. We have shown, however, that it is L. lusci that parasitizes T. luscus and Merluccius merluccius in this geographical area. The distribution of L. lusci, as well as that of its host, T. luscus, must extend into the Mediterranean. Lernaeocera lusci has colonized a phylogenetically distant host (Merluccius merluccius) in the Mediterranean and our results show that this species has become the preferred host for the maturation of L. lusci in this region. In addition, we have demonstrated the existence of genetic differentiation between T. luscus from the Atlantic and from the western Mediterranean. Thus, it is possible that the specialization of L. lusci in a new resource (M. merluccius) in the Mediterranean might be related to biological changes undergone by this copepod's original host, Trisopterus luscus. In contrast to other parasite groups such as the Monogenea, the specialization of species of the genus Lernaeocera would appear to depend more on ecological parameters (relative abundance and availability of resources) than on phylogenetic constraints. The relationships within these host–parasite systems are therefore compared with the predator–prey relationships.