BIODIVERSITY AND BIOGEOGRAPHY IN HETEROSPECIFIC TELEOSTEAN (GADIDAE) - COPEPOD (LERNAEOCERA) ASSOCIATIONS

This genetic study confirms the validity of two controversial parasite species, Lernaeocera branchialis and Lernaeocera lusci (Copepoda, Pen nellidae). These species cohabit throughout a large sector of the Nort h Sea and the Atlantic Ocean, parasitizing Merlangius merlangus and Tr isopterus luscus (Teleostei, Gadidae), respectively. In the Mediterran ean Sea, it was L. branchialis that was described initially. We have s hown, however, that it is L. lusci that parasitizes T. luscus and Merl uccius merluccius in this geographical area. The distribution of L. lu sci, as well as that of its host, T. luscus, must extend into the Medi terranean. 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 existe nce of genetic differentiation between T luscus from the Atlantic and from the western Mediterranean. Thus, it is possible that the speciali zation of L. lusci in a new resource (M. merluccius) in the Mediterran ean ranean might be related to biological changes undergone by this co pepod's original host, Trisopterus luscus. In contrast to other parasi te 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 phylogenet ic constraints. The relationships within these host-parasite systems a re therefore compared with the predator-prey relationships.