ARE FASTER MODES OF PREDATION EVOLUTIONARILY DERIVED IN THE BUSYCONINAE?: A TEST WITH MOLECULES AND FOSSILS

The escalation hypothesis predicts that selection has repeatedly emphasized offensive speed and force among top predators over the course of evolution, resulting in a trend, among others, of evolutionarily derived predatory weapons and behaviors that increase the speed of killing prey.

The evolutionary history of busyconine whelk feeding behavior is ideal to test this prediction. Whelks have been conspicuous gastropod predators in shallow-water marine communities along the Atlantic and Gulf coasts of North and Central America since at least the Early Miocene. Living whelk species either wedge or chip open the shell of their bivalve prey. When feeding on the same hard-shelled prey species, wedging is much slower than chipping behavior because it requires the predator to wait for the prey’s valves to gape before its shell lip can be inserted between the valves. Chipping, however, is a more active and forceful behavior that involves repeated application of the predator’s shell lip against the prey’s shell to create an opening sufficient for wedging the valves apart.

With this understanding of the ecology of living species, we hypothesized that wedging behavior is the ancestral condition within the clade. To test our hypothesis, the evolutionary relationships among living busyconines were estimated using partial sequences of a rapidly evolving mitochondrial gene (cytochrome oxidase I) from representative members of the clade. Tracing the feeding ecology of living busyconines onto the phylogenetic hypothesis indicates that wedging is the ancestral behavior within the whelk clade. This inference is strengthened by the post-Oligocene history of characteristic whelk predation traces on the shells of hard-shelled prey species, which first appear in the fossil record during the Late Miocene.

The selective advantages of killing prey faster for whelk predators include creating opportunities for more effective exploitation of available prey resources and reducing exposure to enemies, especially in highly competitive environments where the bar of performance is set high.