Microphallus turgidus lives in brackish water habitats on the coast of Georgia. This little parasite rarely infects people but is common in wild animals that live in salt marshes. Microphallus turgidus has a typical, intricate trematode life cycle that requires multiple hosts. An immature stage of the parasite called a metacercaria encysts in the abdominal muscles of Palaemonetes spp. grass shrimp. When a bird or mammal eats an infected shrimp, the parasite excysts in the intestine and matures into an egg-laying adult. The eggs enter the water in the host's feces and are consumed by tiny hydrobiid snails. Another immature form of the parasite called a cercaria develops in the snail. Cercariae leave the snail and swim through the water until they find a grass shrimp to infect, thus completing the life cycle.
Research Projects: A good deal of our research has examined the relationship between the parasite and its second intermediate host, Palaemonetes spp. grass shrimp. Grass shrimp are common inhabitants of estuaries and tidal marshes along the north Atlantic and Gulf coasts of the U.S.A. These small decapod crustaceans are an abundant and integral component of estuarine and marsh food webs. They are opportunistic feeders, preying on small invertebrates and consuming living and dead plant and animal matter. Grass shrimp are themselves prey to fish, birds, mammals, and other crustaceans.
Grass shrimp are easily collected in brackish water all along the coast of Georgia. The parasite, M. turgidus is also quite abundant. In fact, it is rare are to find a locality where the grass shrimp Palaemonetes pugio is not infected. At certain shrimp collection sites, near all specimens of P. pugio are infected, some with more than 100 parasites. The intensity of infection varies from one locality to another and may be due, at least partially, to geographic differences in salinity.
The other brackish water grass shrimp common in Georgia is Palaemonetes vulgaris. The parasite M. turgidus infects P. vulgaris but the percentage of shrimp infected and the number of parasites/shrimp is always dramatically lower than what is observed in P. pugio. This is surprising because P. pugio and P. vulgaris are often found together in the same habitat. We are now trying to figure out why these two shrimp species are so different from each with respect to parasite infection. To do this we need to figure out how to infect hydrobiid snails in the laboratory to produce large numbers of M. turgidus cercariae for experimental grass shrimp infections.
One way to infect hydrobiids in the lab would be by feeding them eggs produced by the adult worm in culture. We are currently culturing the worms in the laboratory and optimizing the conditions needed to enhance their egg production.
I am also interested in the effect of M. turgidus on the behavior of the grass shrimp P. pugio. We have found that heavily infected shrimp are more likely to be eaten by a predator than uninfected shrimp, have lower swimming stamina, and spend more time swimming and less time motionless in the presence of a predator. Thus, M. turgidus may increase the predation of P. pugio in the wild.
Kunz, A.K. and O.J. Pung. 2004. Effects of Microphallus turgidus (Trematoda: Microphallidae) on the predation, behavior, and swimming stamina of the grass shrimp Palaemonetes pugio. Journal of Parasitology. 90: 443-445.
Flowers, M.A., Q.Q. Fang, and O.J. Pung. 2005. Population genetic analysis of the grass shrimp Palaemonetes pugio using DNA single-strand conformation polymorphism. Georgia Journal of Science. 63: 232-242.
Kunz, A.K., M. Ford, and O.J. Pung. 2006. Behavior of the grass shrimp Palaemonetes pugio and its response to the presence of the predatory fish Fundulus heteroclitus. American Midland Naturalist. 155:286-294.
Pung, O.J., C.B. Grinstead, and S.P. Vives. 2006. Variation in the temporal and geographic distribution of Microphallus turgidus (Trematoda: Microphallidae) in grass shrimp (Palaemonetes spp.) on tidal rivers in southeast Georgia, U.S.A. Comparative Parasitolgy. 73: 172-178.
Pung, Oscar J., Christopher Brad Grinstead, Kraig Kersten, and Catherine L. Edenfield. 2008. Spatial Distribution of hydrobiid snails in salt marsh along the Skidaway River in Southeastern Georgia with notes on their larval trematode parasites. Southeastern Naturalist. 7: 717-728.Pung, Oscar J., Ashley R. Burger, Michael F. Walker, Whitney L. Barfield, Micah H. Lancaster, and Christina E. Jarrous. 2009. In vitro cultivation of Microphallus turgidus (Trematoda: Microphallidae) from metacercaria to ovigerous adult with continuation of the life cycle in the laboratory. Journal of Parasitology. 95: 913-919.