IYENGAR, E.V.: To steal or not to steal? That is the question. Suspension feeding versus kleptoparasitism in a marine snail.

Although suspension feeding is a dominant feeding mode in the marine realm, is performed by members of many diverse taxa, and has evolved at least seven times within the prosobranchs, suspension feeding is rare among snails. In a group that appears extremely versatile, why aren’t more snails suspension feeders? In order to approach this question, I am studying the marine caenogastropod Trichotropis cancellata. This snail is capable of suspension feeding, but the majority of its populations also participate in kleptoparasitism, usually stealing food from tube-dwelling worms. The Trichotropis/worm symbiosis is a system where a suspension feeding snail is facing limitations that can at least be reduced by a shift to parasitism. Kleptoparasitism is common for snails of all sizes at sites from Washington to Alaska, and proportions of the population involved in parasitism varies seasonally. In the San Juan Islands, Washington, parasitic snails have faster growth rates and correspondingly higher fecundities than suspension feeding snails. Host size does not affect growth rates in parasitic snails. Although host species does not appear to influence snail growth rate in the summer, snails grow faster on sabellids than on serpulids in the winter. Finally, the discovery that another species within the Trichotropis genus is restricted to suspension feeding indicates that kleptoparasitism has arisen at least twice within the superfamily and suggests possible factors driving the shift to parasitism.