Term of Award

Fall 2010

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)

Department

Department of Biology

Committee Chair

Oscar J. Pung

Committee Member 1

Stephen P. Vives

Committee Member 2

Sophie George

Abstract

The hydrobiid snail and grass shrimp hosts of the microphallid trematode Microphallus turgidus are found in specific microhabitats. The primary second intermediate host of this parasite is the grass shrimp Palaemonetes pugio. The behavior of trematode cercaria often reflects the habitat and behavior of the host species. The objective of my study was to examine the behavior of M. turgidus in relation to the microhabitat selection of the second intermediate host. To do so, I established a behavioral ethogram for the cercariae of M. turgidus and compared the behavior of these parasites to the known host behavior. I tested the phototactic, geotactic, and chemical responses of the parasite. When M. turgidus cercariae are placed in a half covered Petri dish I predicted that the cercariae would have negative phototaxis. For the control experiment, in the absence of light, I predicted an equal distribution of cercariae throughout the entire Petri dish. I also predicted that the cercariae would prefer the bottom of the water column, and that their behavior would change in response to chemicals in shrimp conditioned water. Both the phototaxis and geotaxis trials used lighted conditions as the experimental and unlighted conditions as the control. The phototaxis trials were performed using a half covered Petri dish and the geotaxis trials used a graduated cylinder. The chemical response trials used water from a container which housed grass shrimp for 72 hr or unconditioned water for the control. The behavioral ethogram was based on the data of the chemical response trials. The majority of M. turgidus cercariae swam horizontally towards the covered side of the Petri dish for both lighted and unlighted trials; however a significantly higher percentage of cercariae swam horizontally towards the covered side of the Petri dish during the lighted trials suggesting that light affects the horizontal distribution of cercariae. Microphallus turgidus was also found to prefer the bottom of the water column in both lighted and unlighted trials. The behavior of the cercariae was not affected by shrimp/conditioned water. The ethogram showed that cercaria spent the largest percentage of time swimming on the bottom. The bottom dwelling behavior of M. turgidus cercariae corresponds to the demersal behavior of P. pugio. The cercariae do not appear to use chemical cues to find the host directly, rather the innate search pattern allows M. turgidus cercariae to find areas where the probability of encountering the primary host is highest. My findings show that the behavior of M. turgidus cercariae follows the demersal behavior of the grass shrimp P. pugio and may explain why this host is so frequently and heavily infected.

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