COS 118-5 - CANCELLED - The effects of infection by a non-trophically transmitted parasite on snail host behavior

Abstract:
Many parasites have been documented altering the behavior of their hosts, especially in those with complex life cycles where transmission occurs via predation (i.e., trophic transmission). Less is known about how parasites alter hosts behavior when intermediate life stages are motile, such as trematode cercariae which are abundant and diverse across many aquatic ecosystems. Here, we aimed to study the behavior of infected and uninfected intermediate host snails across different ecological contexts. Planorabella trivolvis is a freshwater air-breathing snail, known to be an intermediate host for many parasites but is predominantly associated with Echinostoma spp. trematodes. Across their life cycle, these multi-host parasites infect a wide range of taxa from freshwater snails to amphibians, fish, and wading birds, and impose public health concerns to human populations.


The goals of this project were to: (1) assess infection prevalence and intensity across four P. trivolvis populations in Gainesville FL, (2) quantify differences in the behavior of infected and uninfected snails, and (3) measure snail movement in the presence of predation cues. We checked field-caught snails for infection with Echinostoma trematodes using environmental chambers to stimulate cercarial shedding and tested snails’ righting behavior and phototaxis in the laboratory. Infected snails were slower to right themselves after being placed on their side and were slower to emerge from a retreat into the light compared to uninfected snails. We then measured snails’ responses to varying levels of predation risk cues: control with no predator cues, exposure to a caged crayfish, and exposure to a crayfish plus a conspecific alarm cue. Infected snails moved further away under all conditions compared to uninfected snails.


These data show that, although it is uncertain if these trematode parasites manipulate snail host behavior, infected snails exhibit context-dependent altered behaviors. Freshwater snails are intermediate hosts for many parasites and studying the behavior of infected snails will help us understand the impact of multi-host parasites on ecosystems, and can inform the conservation efforts of imperiled species which may be potential hosts.