PIETER JOHNSON (FROG), DANIEL SUTHERLAND (INSET)
The malformations in this northern leopard frog (Rana pipiens), which was taken from a pond near Minneapolis–St. Paul, Minn., were caused by a trematode parasite. The encysted Ribeiroia ondatrae parasite shown in the inset photo was removed from an infected frog.
is studying a large population of deformed frogs in the eastern United States that are not infected by parasites. Green scummy ponds full of algae and decaying organic matter are just the kind of habitat where “ramshorn” snails of the family Planorbidae thrive, says Chase. The snails are an essential host in the life cycle of the parasitic trematode, Ribeiroia ondatrae, shown by Johnson to cause the frog deformities. These ponds are usually close to farms or cattle operations, notes Johnson. In this latest work, the scientists evaluated total phosphorous concentration in the water of 27 Michigan ponds and characterized each pond’s population of snails and the proportions of different species. They found that ponds with higher phosphorus levels—above approximately 40 micrograms per liter—generally have more of the unwanted ramshorn snails that serve as host for the parasite. Johnson acknowledges that the data have limitations. “Nutrient data are very noisy as a rule, largely because it’s hard to measure productivity in a single variable,” he says. However, he also cites the finding that ponds with low nutrients often do not have any of the host ramshorn snails at all, which
means that the parasite can’t even exist in these ponds. Johnson and Chase also found that the number of amphibian infections was greater when the snail population was higher at 16 malformation hot spots scattered across the western and central United States. The parasite’s life cycle starts with an adult trematode laying an egg inside a heron or other frogeating waterfowl. The bird excretes the parasite eggs into a pond. After hatching, the young parasite finds its first home inside a ramshorn snail and then emerges some 20 days later to embed itself in a tadpole. Inside the tadpole, the parasite forms a cyst at the developing limb bud. By interfering with the tadpole’s limb development, the parasite causes a deformity, most often by making extra limbs. This deformed frog is then easy pickings for wading birds, which simultaneously consume the parasite and complete its life cycle. “The snail, frog, and parasite are entangled with each other in a complicated food web,” says Chase, who has studied the ecology of food webs in small ponds and the role of the snail in that web. This past spring, Johnson and Chase started experiments in artificial ponds to further test their hypothesis. —REBECCA RENNER
News Briefs Gloomy climate for Europe With average temperatures rising faster in Europe than elsewhere, adaptation strategies will be crucial in limiting climate change impacts, according to a report by the European Environment Agency (EEA). EEA predicts more frequent and more costly storms, floods, droughts, and other extreme weather. Over the past 20 years alone, economic losses resulting from weather- and climaterelated events have roughly doubled. While agricultural yields, particularly in northern Europe, are projected to profit from the changing temperature and precipitation patterns, EEA notes that crop harvests in many southern countries were down by as much as 30% following the heat wave in 2003. EEA warns that even with substantial reductions of greenhouse gas emissions over the coming decades, the observed rise in global temperature is expected to rise this century. Impacts of Europe’s Changing Climate: An Indicator-Based Assessment is at http://reports.eea.eu.int/climate_ report_2_2004/en.
EU laws poorly implemented European Union (EU) countries have “serious shortcomings” in how they implement EU environmental laws, according to a report from the European Commission (EC). France, Greece, Ireland, Italy, and Spain were the worst offenders. Across the EU, implementation of directives associated with water, waste, the protection of nature, and environmental impact assessments was particularly poor. In 2003, the EC recorded 88 cases where countries missed deadlines to write environmental directives into national law, and the environmental sector accounted for more than a third of all complaints and ongoing infringement cases concerning noncompliance with EU law. The Fifth Annual Survey on the Implementation and Enforcement of EU Environmental Law, which was released in August, is at http://europa. eu.int/comm/environment/law.
OCTOBER 15, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 385A
