Multiple stressors and the cause of amphibian abnormalities

Mari K. Reeves, Peter Jensen, Christine L. Dolph, Marcel Holyoak, Kimberly A. Trust

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


The repeated occurrence of abnormal amphibians in nature points to ecological imbalance, yet identifying causes of these abnormalities has proved complex. Multiple studies have linked amphibian abnormalities to chemically contaminated areas, but inference about causal mechanisms is lacking. Here we use a high incidence of abnormalities in Alaskan wood frogs to strengthen inference about the mechanism for these abnormalities. We suggest that limb abnormalities are caused by a combination of multiple stressors. Specifically, toxicants lead to increased predation, resulting in more injuries to developing limbs and subsequent developmental malformations. We evaluated a variety of putative causes of frog abnormalities at 21 wetlands on the Kenai National Wildlife Refuge, south-central Alaska, USA, between 2004 and 2006. Variables investigated were organic and inorganic contaminants, parasite infection, abundance of predatory invertebrates, UVB, and temperature. Logistic regression and model comparison using the Akaike information criterion (AIC) identified dragonflies and both organic and inorganic contaminants as predictors of the frequency of skeletal abnormalities. We suggest that both predators and contaminants alter ecosystem dynamics to increase the frequency of amphibian abnormalities in contaminated habitat. Future experiments should test the causal mechanisms by which toxicants and predators may interact to cause amphibian limb abnormalities.

Original languageEnglish (US)
Pages (from-to)423-440
Number of pages18
JournalEcological Monographs
Issue number3
StatePublished - Aug 2010


  • Abnormality
  • Alaska, USA
  • Amphibian
  • Invertebrate predators
  • Kenai National Wildlife Refuge
  • Lithobates sylvaticus
  • Malformation
  • Metals
  • Rana sylvatica
  • Wood frog


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