Symbiosis is an integral part of life. From the pearlfish who inhabit the anuses of sea cucumbers to the chytrid fungus decimating amphibian populations, most life on Earth is engaged in symbiotic interactions ranging from mutualistic to parasitic. Crayfish and their ectosymbiotic annelid worms (Order: Branchiobdellida) engage in a density-dependent cleaning symbiosis that shifts between a mutualism and a parasitism. This shift provides us with an effective tool to study the nature of symbioses. Multiple factors shape the worm community on each host crayfish; grooming behaviors tend to shape the symbiont community on smaller crayfish, while intraguild predation among the worms shape it on larger crayfish. Our current work utilizes metacommunity theory, which describes the interactions between spatially disparate communities of organisms, to model and predict these symbiotic associations. A metacommunity is a community of communities, groups of interacting organisms that affect each other through dispersal. Traditionally, this framework has been used to study communities along connected environmental patches. However, if we consider a host crayfish to be a patch, we can use this framework to study how host controls and symbiont interactions with the host and each other affect the structure of the symbiont communities on each crayfish.
In September 2016, we began a year long survey of the crayfish and worm communities at Sinking Creek in Newport, VA. The study has provided information on seasonal variation in worm communities on crayfish of different sizes. For instance, worm abundance has a tendency to decrease in the winter; we found that, on large crayfish, when the weather warmed, the populations of the two smaller species of worms began to recover first, while the populations of the two larger species of worms were still declining. This study has also provided us with insights on how the worm communities develop on each crayfish after a disturbance event by looking at crayfish molting. Previous literature indicated that a crayfish loses 75% of its worm community when it molts, and we have indeed found that worm communities on recently molted crayfish consist mostly of worms that we know are early colonizers. These data are providing us with insights on how host heterogeneity, symbiont characteristics, and symbiont dispersal affect the assembly of worm communities on crayfish.