Testing the effects of drought, parasite infection, and their interaction on freshwater snails

Increased drought intensity and frequency pose a risk to freshwater ecosystems around the globe. We investigated the effects of water loss on snail–trematode interactions to determine how Helisoma trivolvis (Say, 1816) might respond to anticipated drought in natural systems and whether parasites might modify this response. Trematode-infected and uninfected H. trivolvis snails were experimentally subjected to drought conditions in microcosms over a 6-week (44 day) period. We found that drought-altered snail behavior but not mortality. Snails maintained under desiccated conditions were more likely to bury themselves under the sediment than snails that were maintained with constant water levels. Snails in the drought treatment did not exhibit higher rates of mortality than those in the perennial treatment. Rather, mortality appeared to be driven by an interaction between trematode infection and body size. Infected snails of all sizes and across treatments were more likely to die than uninfected snails, and within uninfected snails, larger individuals had increased odds of mortality. Infection also had pronounced effects on snail behavior, as snails with trematode infections were less likely to bury themselves. Our experiment highlights the potential interplay between drought and parasitism in affecting freshwater snail populations, warranting further investigation through larger-scale experiments and field research.