Run off from farming is driving up numbers of horrifically deformed frogs (AP, Reuters, Wisconsin State Journal, Rocky Mountain News). New research from the University of Colorado at Boulder shows that nitrogen and phosphorus used to increase crop yields are leading to the amphibians sprouting extra legs and other malformations (research abstract). “You can get five or six extra limbs. You can get no hind limbs. You can get all kinds of really bizarre, sick and twisted stuff,” evolutionary biologist Pieter Johnson told Reuters.

The problem first came to light in the 1990s when a group of Minnesota school children stumbled across a pond full of deformed frogs. Suspects included pesticides, parasites and UV rays. Actually, according to Johnson and colleagues the extra limbs are caused by trematode parasites – parasites that are increasingly prevalent due to farming run off (press release). By constructing artificial ponds to recreate frog / parasite habitats they determined the key role of nutrients.

Nutrients promote algae growth; algae growth increases snail populations that host parasites; snails then release the parasites into ponds and lakes; here they prey on tadpoles, causing cysts in developing limbs which cause the malformations. The finding could be important for other parasite-spread problems linked to nutrient supply, including cholera, malaria and West Nile virus.

Image: University of Colorado & Peiter Johnson