Term of Award

Spring 2003

Degree Name

Master of Science

Document Type and Release Option

Thesis (restricted to Georgia Southern)


Department of Biology

Committee Chair

Oscar J. Pung

Committee Member 1

Bruce A. Schulte

Committee Member 2

Stephen P. Vives


To facilitate transmission between hosts, parasites are thought to induce changes in intermediate host behavior. These altered behaviors potentially influence predatorprey dynamics whereby the infected animal is more likely to be eaten by the definitive host of the parasite. I tested this hypothesis by studying the impact of the trematode Microphallus turgidus on the behavior and predator susceptibility of its intermediate host, the grass shrimp, Palaemonetes pugio. I hypothesized that the presence of a large quantity of encysted parasites (>30) alters both the activity and swimming ability of infected grass shrimp, and as such alters its susceptibility to predation to mummichog fish, Fundulus heteroclitus. Uninfected grass shrimp were predicted to display longer swimming endurance, higher activity rates in the absence of a predator, and be less susceptible to predation by fish than M. turgidus infected conspecifics. The effect of parasite infection on intermediate host predation was evaluated by exposing infected and uninfected grass shrimp to a predatory fish. The swimming stamina of infected shrimp was examined using a flow tank apparatus. The behavioral activities of infected and uninfected shrimp in the presence or absence of a predator were compared using a scan sampling method. I found that M. turgidus-infected grass shrimp are more susceptible to predation by mummichog fish. The increased susceptibility of the grass shrimp to predation could be the result of reduced stamina or altered behavioral activities of the infected shrimp. Infected grass shrimp fatigued more rapidly against a current when compared to uninfected conspecifics. The lowered endurance of the infected grass shrimp could influence the ability of the shrimp to escape predation events. It was also observed that in the absence of a predator the uninfected shrimp spend more time swimming than the infected shrimp whereas in the presence of a predator the uninfected shrimp are spending more time motionless. The results of this study indicate that M. turgidus does alter the behavior of the infected grass shrimp, which may increase predation by the definitive host in the wild.


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