Effects of digenetic trematode infection on Physa gyrina.

Abstract

The digenetic trematode characteristically has a complex three-host life cycle. Completion of this cycle may be made more successful as a result of both behavioral and morphological host adaptations. These parasite-induced changes may evolve as mechanisms to increase the fitness of the parasite by increasing the probability of transmission. In this study, the effects of digenetic trematode infection on Physa gyrina were investigated in order to better understand how both behavioral and morphological changes may assist in parasite transmission. The study examined thre possible parasite-induced host adaptations: size of snail, directional preference, and speed of travel. Physa gyrina were collected from their natural environment. Subsequently, snail motion was experimentally tested, size of snails was recorded and snails were crushed to identify infection by digenetic trematodes. Results showed no significant relationship between size of snail and infection status. Infected snails moved significantly slower and traveled less distance than uninfected snails. The observed behavioral changes may potentially be attributed to the fact that infected snails requiring more energy to produce cercariae, have less available resources for immune response and locomotion. In conclusion, based on observed results and previous studies, adaptations leading to increased probability of parasite transmission are very specific to the particular host-parasite interaction. Information regarding the specific species of the trematode as well as the species involved in the life cycle would assist in understanding parasite-induced changes in snail behavior and morphology.