The ecology and evolutionary biology of the marine facultative kleptoparasite Trichotropis cancellata (Mollusca, Gastropoda).

摘要

Kleptoparasitism, the stealing (inter- or intra-specific) of already-procured food, is one of the most common types of exploitation between animals. An overview of the prevalence of kleptoparasitism and evaluation of the conditions favoring kleptoparasitism is given.; The marine snail Trichotropis cancellata, originally described as an independent suspension feeder, also steals food from tube-dwelling polychaetes and other suspension-feeding hosts. At six sites around the San Juan Islands, Washington, USA, field surveys spanning two years showed that facultative kleptoparasitism was the dominant feeding mode in the summer at all sites for all sizes of T. cancellata. The prevalence of kleptoparasitism fluctuated seasonally, with the highest levels in the summer and the lowest in the winter (snail mating season).; Worms infected with T. cancellata grew significantly more slowly than uninfected worms, thus parasitism was experimentally demonstrated. T. cancellata is a generalist parasite, potentially parasitizing at least nine hosts from seven genera and four phyla. In situ experiments showed that all sizes of T. cancellata grew significantly more quickly as kleptoparasites on worm hosts than as independent suspension-feeders or snails on brachiopods. Smaller snails gained a proportionally greater advantage from parasitism than larger ones. There was competition among medium-sized conspecific parasites, resulting in a slower average growth rate. Host worm size did not significantly determine snail growth rate in the summer or winter. Worm host species produced different growth rates by parasites only in the winter, when snails on sabellids grew more quickly than those on serpulids. In the field, the snails did not distribute themselves among live worm hosts based on potential differential growth, but they did choose live worm hosts over empty worm tubes.; Biogeographic surveys determined that kleptoparasitism is pervasive throughout T. cancellata's range. Within the trichotropids, T. conica is the second confirmed kleptoparasite, while T. insignis engages solely in suspension feeding. T. cancellata is a food-limited suspension feeder that has switched to kleptoparasitism to obtain a growth benefit. Identifying the pressures driving the evolution of the different trophic strategies in this species may shed light on the factors historically limiting the radiation of suspension-feeding gastropods.