Forming foci of transmission: the effects of resource utilization, species interaction, and parasitism on molluscan movement

Abstract

Animal aggregation to environmental cues provides opportunities for parasite transmission between individual hosts of the same or different species. Better characterization of host behavioral responses to environmental stimuli in the absence and presence of parasites will improve our understanding of how foci of transmission form. The behavioral response patterns of two co-occurring freshwater snail species ( Lymnaea elodes (Say, 1821) and Helisoma trivolvis (Say, 1817) (=  Planorbella trivolvis (Say, 1817))) were assessed in response to three environmental stimuli (crayfish (genus Orconectes  Cope, 1872) carrion, vegetation, or temperature gradient). Experiments were conducted with single species and species interactions. In addition, parasitized L. elodes were included in a single-species experiment and a species-interaction experiment. Snail species differed in the direction and magnitude of their responses to the environmental stimuli. Species interactions did not affect the responses to two of the stimuli for either species; however, interspecific interactions affected the response to high temperature in both species. Behavioral responses were altered in the presence of parasites for both the infected and uninfected hosts, suggesting parasitism is an important biotic factor in animal movement. This experimental study indicates co-occurring species respond to environmental factors in different ways. Furthermore, species interactions and parasitism within a guild can have strong effects on animal movement and potentially on parasite transmission.