COEVOLUTION OF A MARINE GASTROPOD PREDATOR AND ITS DANGEROUS BIVALVE PREY: A CRITICAL REAPPRAISAL

In 2003 (Biol. J. Linn. Soc., v. 80: 409-436), I published a study detailing the fossil record of the interaction between the predatory whelk Sinistrofulgur and its dangerous bivalve prey Mercenaria from the Plio-Pleistocene of Florida to test the hypothesis that the species interaction coevolved. Whelks are specialized predators that use their shell lip to chip or wedge open the shell of their bivalve prey, which often results in shell breakage to both predator and prey. Predation intensity (indexed by the frequency of lethal and sublethal whelk predation traces on prey shells) increased over the study interval. Mercenaria and Sinistrofulgur both evolved larger shells (size is the main trait that determines the outcome of encounters between predator and prey). Indices of predator effectiveness in exploiting prey (e.g., degree of stereotypy of attack position) and prey effectiveness (e.g., ratio of unsuccessful to total whelk predation attempts) in deterring predator attacks indicated that predator adaptation had “outpaced” prey antipredatory adaptation. Whelk behavior also evolved to limit performance loss (shell breakage) associated with feeding on Mercenaria.

Despite evidence of reciprocal adaptation between predator and prey in my 2003 study, sites available at that time to collect an adequate number of specimens of both predator and prey for analysis were limited to one to three sample locations per stratigraphic unit. These samples did not adequately account for potential spatial variability in the interaction. In the present study, I report on a nearly decade long effort to collect additional specimens that has nearly tripled the number of samples to assess the robustness of the patterns documented in 2003. A reanalysis of the expanded dataset confirms that the interaction intensified; whelks and Mercenaria increased in body size; prey effectiveness decreased; whelk behavior evolved to limit attacks on prey to when the whelk’s shell lip is thickest and most resistant to breakage; and whelk selection of attack site became more stereotyped.

Further work is needed to determine how the whelk-Mercenaria interaction coevolved amid multiple conflicting abiotic and biotic selection pressures across complex, highly dynamic landscapes.