Intermediate hosts as source communities

We describe helminth communities in two sympatric species of intertidal crabs (Pachygrapsus transversus and Panopeus lacustris) that serve as intermediate hosts for helminth parasites. We suggest that a single definitive host feeding briefly on Pachygrapsus transversus may be colonized simultaneously by up to six species of microphallid trematodes and that infrapopulations can increase rapidly by a definitive host feeding on Panopeus lacustris. Therefore, we argue that consideration of colonization processes in definitive hosts may be a crucial underpinning to many community-level studies. We show that, in Florida, colonization of Cerithidea scalariformis by miracidia is markedly different from observations made on Cerithidea californica in California. Also, different populations of C. scalariformis are highly variable in the helminths they support. We conclude that community-level studies on invertebrate intermediate hosts may be easier and more informative than similar studies on definitive hosts.