Amphibian Malformations

Scientific research suggests that amphibian malformations can be caused by a variety of abiotic and biotic agents in the environment. It is likely that many of these factors work together to cause abnormalities in amphibians, e.g., parasite infection and chemical toxins in the water. Moreover, studies have shown that these various agents likely vary in importance across sites and years, and no single cause is likely to explain all high-frequency accounts of amphibian deformities in nature.

The amphibian malformation phenomenon and potential implications for human health and wildlife conservation remain a topic of intense scientific debate and controversy. Below, we review available evidence for the best-supported potential causes of amphibian abnormalities.

Common Types of Amphibian Malformations

Extra digits
Extra limb or limb elements
Missing or partially missing limbs
Missing or partially missing digits
Bony triangles
Skin webbings
Abnormal bone formation
Missing or abnormal eyes

Factors known to cause Malformations:

  • Pollution
  • Predation

  • Parasites and Disease
  • UVB Radiation
  • Unknown Factors/Interactions

Blaustein, A.R., et al. (1994) UV repair and resistance to solar UV-B in amphibian eggs: a link to population declines? Proceedings of the National Academy of Sciences 91:1791-1795.
Bowerman, J., et al. (2010) Sublethal predators and their injured prey: linking aquatic predators and severe limb abnormalities in amphibians. Ecology 91:242-51.
Diamond, S.A., et al. (2002) Assessment of the risk of solar ultraviolet radiation to amphibians. Prediction of impacts in selected northern Midwestern wetlands. Environmental Science and Technology 36:2866-2874.
Hopkins, W.A., et al. (2000) Incidence and impact of axial malformations in larval bullfrogs (Rana catesbeiana) developing in sites polluted by coal-burning power plant. Environmental Toxicology and Chemistry 19:862-868.
Johnson, P.T.J., et al. (1999) The effect of trematode infection on amphibian limb development and survivorship. Science 284:802-804.
Johnson, P.T.J., et al. (2007) Aquatic eutrophication promotes pathogenic infections in amphibians. Proceedings of the National Academy of Sciences 104:15781-15786.
Reeves, M.K., et al. (2008) Road proximity increases risk of skeletal abnormalities in wood frogs from the National Wildlife Refuges in Alaska. Environmental Health Perspectives 116:1009-1015.
Relyea, R.A. (2005) The lethal impacts of Roundup and predatory stress on six species of North American tadpoles. Archives of Environmental Contamination and Toxicology 48:351-357.
Sessions, S.K., and S.B. Ruth. (1990) Explanation for naturally-occurring supernumerary limbs in amphibians. Journal of Experimental Zoology 254:38-47.