The effects of a digenetic trematode on snail movement and morphology.

Abstract

Digenetic trematodes can affect their first intermediate gastropod hosts in a number of ways. Effects may be adaptive to the gastropod host, to the parasite, or simply a byproduct of infection. Effects of digenetic trematodes have been shown to depend largely on the specific life-cycle of the trematode as well as the microhabitat and behavior of its host (Bernot, 2003). Some studies on various species of snails documented reduced movement, varying relationship of size and infection rate, and snail induced growth. In this study, the efects of a digenetic trematode on the snail Physa gyrina were experimentally observed. Infected and uninfected snails were collected and motion was recorded experimentally in a 30 gallon glass aquarium and then crushed to assess infection. Larval stages of the trematode within the collected snails were not able to be identified, leaving the exact trematode life cycle unknown. Nevertheless, data collected showed no significant differences with respect to size and infection status. Infected snails were found to move slower and travel shorter distances. A common explanation for alterations in snail behavior is based on adaptive changes of the host snail which increases rates of transmission of the parasite. Another explanation is a proposed life-history trade-off which states that infected snails requiring more energy to produce cercariae (the larval stages of the trematode), have less resources for immune response and locomotion (Sandland and Minchella, 2002). Both of these explanations are important in understanding snail behavior and morphology in response to parasite infection, and consequently, it is important that whenever possible the trematode life-cycle and the specific microhabitat of the intermediate host be known.