Experimental approach to the importance of parasitism in biological conservation

Recolonisation of protected areas by new host species, and their parasites, or the translocation of individuals (accidentally or intentionally) to new locations may induce new host-parasite associations. Parasites are usually found to be less well-adapted and more virulent to newly colonized host sp ecies. Such new host-parasite associations may represent threats to the sur vival of the host populations. Our study compared the reaction of a naive h ost facing a new parasite with the reaction of a host in a population alrea dy associated with that parasite. We collected 305 Pomatoschistus microps ( Kroyer, 1838), second intermediate host of the digenean Labratrema minimus (Stossich, 1887), from 4 regions around Europe. The fish were experimentall y exposed to the parasite strain endemic to one of these regions. The initi al step consisted of evaluating the genetic variation among the different f ish populations. The genetic results, based on isozyme electrophoresis, rev ealed a significant differentiation among the populations studied. The seco nd step determined both the quantitative and qualitative success of infesta tion of the different host populations. Our results show that there is no q uantitative difference between sympatric host-parasite success and allopatr ic success. However. at the ultrastructural level, sympatric infection appe ars to be more successful. The results are discussed in terms of the local adaptation of host-parasite associations and the consequences to biological conservation.