From: New Scientist, Sept. 26, 2007 *FROG DEFORMITIES LINKED TO FARM POLLUTION*
By Catherine Brahic Fertiliser run-off could be causing an increase in frog deformities in North American lakes, according to a new study. Frogs with extra or malformed legs have been a focus of attention in North America since 1995, when schoolchildren in Minnesota studying wetlands found a high number of frogs with missing or extra legs. Theories abounded on what was causing the malformations (see Freak frogs <http://www.newscientist.com/article/mg15520993.000-freak-frogs.html>). Some said pollution was to blame, but in 1999, Pieter Johnson of Stanford University in California, US, showed that a flatworm parasite (Ribeiroia ondatrae) was a major culprit <http://www.newscientist.com/article/mg16221852.200-flukey-frogs.html>. But, "at low abundance, Ribeiroia ondatrae does not cause much damage," says Johnson, now a researcher at the University of Colorado. He now believes fertiliser pollution may be to blame for boosting the number of parasites in lakes and ponds. Pollution-parasite link Run-off from non-organic farms contains large amounts of nutrients contained in fertilisers such as phosphorus and nitrogen, which eventually end up enriching the waters in nearby ponds, lakes and rivers -- a phenomenon known as eutrophication. According to Johnson, the amount of phosphorus that runs from rivers into the oceans has increased about three-fold since the industrialisation of agriculture. These enriched waters boost the growth of algae within them, which in turn has a cascade of effects on the local food chain. Johnson and his colleagues created 36 mini ponds in isolated tubs that were filled with clear, non-polluted lake water. In half the tubs, they added 200 micrograms of phosphorus per litre of lake water. Polluted lakes can have up to five times that concentration, according to Stephen Carpenter of the University of Wisconsin, a study co- author. The tubs were populated with algae, as well as frogs and small aquatic snails. The snails, which feed on algae, are key to the flatworm parasite's life-cycle -- it is inside them that the worm reproduces before infecting frogs. The researchers found that by boosting the growth of algae, the nutrients eventually increase the number and size of the water snails. In turn, this pushed up parasite numbers. "When their eggs hatch, the parasites have to find a snail within 12 hours or else they die," explains Johnson. Infected tadpoles In tubs containing additional nutrients, snail biomass increased by 50% and infected snails produced twice as many parasitic worms. The infection rate in frogs increased between two and five fold. "If there are more snails, the parasites are more likely to find a snail. And if the snails have more food, they survive longer. Once infected they become zombies whose sole function is to release parasites," Johnson told New Scientist. The parasites then attack the frogs at the tadpole stage, infecting the cells that eventually give rise to the frog's limbs. Cysts form in the infected areas as the frogs develop, causing missing limbs, extra limbs, and other malformations. The discovery of deformed frogs has caused concern for the survival of their populations. Without normal limbs, the frogs are easy targets for predatory birds. What is more, many die long before they metamorphose from tadpoles to adult frogs. Journal reference: Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.0707763104) <http://www.pnas.org/cgi/doi/10.1073/pnas.0707763104> Copyright Copyright Reed Business Information Ltd. -- "Fool's gold exists because there is real gold." -Rumi _______________________________________________ RSS, archives, subscription & listserv information for: [email protected] http://lists.mutualaid.org/mailman/listinfo/sustainabletompkins free hosting by http://www.mutualaid.org
