MOLLUSCAN DEFENSE-MECHANISMS - IMMUNITY OR POPULATION BIOLOGY

In recent studies of associations between host and parasite, there has been a tendency to consider the internal defence mechanisms of the mo llusc as pivotal in the relationship However, evolution is a populatio n-based phenomenon, and it is by considering populations rather than i ndividuals that the success of these associations can best be apprecia ted. Among susceptible host species within the biocoenosis, truly resi stant strains appear to be remarkably rare, Clive Shiff here examines mechanisms of defence or avoidance among molluscan hosts of trematodes from both the internal and ecological perspective.