Evolutionary patterns of naticid gastropods of the Chesapeake Group: an example of coevolution?

The naticid gastropod predator–prey system has been cited as a possible example of coevolution. Previous work indicated that Miocene bivalves from the Chesapeake Group responded to naticid drilling with a predation-avoidance strategy of gradual thickness increase over evolutionary time. The present study examined whether the predators, Euspira heros (Say) and Neverita duplicata (Say), coevolved by increasing their efficiency in response to prey adaptation.Neither predator showed significant trends in most characters thought to affect predator efficiency, including measures of globosity and aperture size relative to shell height. Stasis occurred for all such characters except Euspira aperture height, which showed a statistically significant decrease of 9 percent through the section. Morphologic trends occurred in two additional characters, shell thickness relative to height, and shell height. Euspira increased in thickness by 63 percent through the section; Neverita decreased in thickness by 37 percent (through slightly less section) and simultaneously increased mean height by 60 percent.The size increase exhibited by Neverita could be interpreted as a coevolutionary response to increased prey defenses. Naticids are subject to predation by other naticids, however; the trends in size and thickness may be viewed instead as an evolutionary strategy to escape naticid predation, including cannibalism. Although the possibility of coevolution is difficult to eliminate, Chesapeake Group naticids appear to have evolve more in response to their own predators than to evolution of their prey.