Investigations of the mechanisms of particle selection in suspension-feeding mollusks
Bivalve molluscs (e.g., clams, oysters, scallops) are among the most important members of bottom-dwelling communities, both for their environmental impacts and commercial value. They possess highly efficient and complicated mechanisms for filtering the water , and capturing and sorting their food particles. Their feeding processes strongly couple water-column and bottom communities, and thus they can influence the general well-being of other organisms as well as the overall environment. Because these organisms play such a key role in ecosystems, it is important to understand how they process particulate matter, sorting food from non-food particles, and what factors control the process.
Although a rich body of literature exists describing diet selection, the actual mechanism(s) of suspension feeding bivalves rely upon to discriminate among particles is unknown. In prior investigations, we developed new technical approaches (microcapsulation) and demonstrated that oysters are able to selectively ingest or reject in pseudofeces alginate microcapsules based on the algal species entrapped within. Since microcapsule material (alginate matrix) prevented physical contacts between algae cells and oyster feeding organs, this study demonstrated that extracellular metabolites produced by microalgae could play a crucial role in the preingestive selection of particles in suspension feeding bivalves.
In the ongoing activities, we have developed two major lines of research to investigate the most plausible mechanisms involved in the selection process. We manipulate particle surfaces to determine if selection is a function of surface properties (charge, wettability, protein coating, carbohydrate coating, etc) and determine if there are patterns in the types of particles that are accepted versus rejected. We also focus our investigations on whether bivalves mediate selection through the production of specific compounds associated with mucus produced by feeding organs. Here we provided evidence on the involvement of immune-related molecules embedded in mucus in the capture of food particles based on their cell surface characteristics.