Using polyclonal antibodies to detect predation by dogwhelks Nucella lapillus (L.)

Interactions between predators and their multiple prey species can vary greatly among locations where they coexist. As a method to assess spatial variation in predation by intertidal dogwhelks on their dominant prey, immunoassays of dogwhelk gut contents from experimental populations and field collected individuals were evaluated using polyclonal antibodies raised separately to soluble proteins from Mytilus edulis L. mussels and Semibalanus balanoides (L.) barnacles. Both antisera produced strong reactions against their homologous antigens but no cross reactions between prey species. Experimental trials tested the critical hypothesis that prey species had equal detection intervals in dogwhelk guts. Two groups of 225 dogwhelks were starved for 14 days, provided with either mussels or barnacles for five days, and then sampled over 22 days. Independent immunoassays of dogwhelk gut contents against each antibody revealed a consistent, weak cross reaction between the anti-mussel antibody and dogwhelk gut tissues. After accounting for this cross reaction, the strength of immunoassays against both prey species declined exponentially and at similar rates. The proportions of dogwhelks that tested positive for their provided prey species declined linearly through time and were not significantly influenced by prey type. Prey were detectable throughout the sampled post-feeding period and were projected to have detection limits of 24.4 days (barnacles) and 26.5 days (mussels), demonstrating that immunoassay results are not biased by dissimilar prey detection intervals. Reactions against the antibody from the non-provided prey were time invariant and occurred at relatively low frequencies. Immunoassays of dogwhelks collected from five intertidal sites on Swans Island, Maine, USA revealed patterns similar to field observations, though immunoassays classified far fewer individuals as non-feeders and more as barnacle feeders than indicated by direct field observations. Unlike single observations, immunoassays also revealed the presence of both prey in dogwhelks from four sites, though most individuals tested positive for only a single prey type. Immunoassays facilitate concurrent collections of predation data from many individuals and will enable further local- to regional-scale assessments of dogwhelk predation at additional sites around the Gulf of Maine.