| UC Toxics News: Spring 2006
Valerie McKenzie, winner of the 2005 TSR&TP Best Poster Award and now a postdoctoral researcher at University of Colorado in Boulder opened her talk with an explanation of her field, “I’m a parsitologist, not to be confused with parapsychologist. I can’t help you with your ghosts, but I may be able to help with your worms.” She said parasites are one of the leading causes of amphibian decline in North America. Understanding how pollutants affect parasite density can help solve this problem. McKenzie’s doctoral research focused on an ecological model of the trematode parasite Ribeiroia ondatrae, which is known to cause malformations in amphibians. Ribeiroia has multiple hosts in its lifecycle – snails, birds and frogs. The intermediate host is often prey of the first host. There has been a huge increase in parasites in the last hundred years. McKenzie hypothesized that eutrophication of ponds and lakes is the cause. Nutrients stimulate algal and snail density, which leads to larval parasites infecting more frogs, which increases food sources and results in a higher number of birds. Because this phenomenon is too complicated to model, McKenzie developed a simulation model to examine two parameters, algal carrying capacity and parasite input rate. Through the model she found that nutrient inputs are the defining factor for parasite levels. Excess nutrients can trigger a bottom up effect leading to the increase in trematodes. The research has some real world applications as well. Catfish plague Bolbophorus damnificus, named for its terrible impact on the catfish industry, has a life cycle involving pelicans and cormorants, with snails and catfish as intermediate hosts. Catfish are grown in dense ponds and excess feed and waste result in dense snail populations. “This is like a fast food stop for all the birds,” said McKenzie. All the hosts for this parasite are concentrated in the farms. Some catfish farms have closed because the parasite can’t be controlled. One treatment strategy is the addition of copper sulfate and citric acid. Copper sulfate is toxic to the snails, but not to the fish at relatively low levels. She’s suggesting that addressing the bottom-up eutrophication could be a better source of control for the parasite. McKenzie thanked the TSR&TP for her grant support.
“It was great to get one of the fellowships and the iPod totally
rules!” |
