ABSTRACT
Abnormal amphibians have been reported in the literature for centuries. Since at least the 1700s, malformed amphibians, especially frogs with multiple hind limbs, have been documented in research articles, illustrated in atlases, and preserved in museums (Vallisneri 1706; de Superville 1740; Van Valen 1974; Ouellet 2000). Generally, such reports have involved an isolated individual or, in rare cases, a few animals. But it was not until August 1995, when a group of Minnesota middle school students discovered a pond in which 50% of the frogs had missing limbs, extra limbs or feet, bony protrusions, and skin webbings, that the issue of malformed amphibians was catapulted to the forefront of the public’s attention (Kaiser 1997, 1999; Schmidt 1997; Souder 2000). Subsequent field surveys discovered large numbers of abnormal frogs in other regions of North America (NARCAM 2008), particularly parts of the Midwest (Helgen et al. 1998; Hoppe 2000, 2005; Vandenlangenberg et al. 2003), the West (Johnson et al. 1999, 2002, 2003), Alaska (Reeves et al. 2008), and the Northeast (Converse et al. 2000; Kiesecker 2002; Eaton-Poole et al. 2003; Levey 2003). The causes of observed abnormalities and their potential implications for human health and wildlife conservation became a topic of intense scientific debate and controversy. Now, more than a decade later, we revisit the issue and evaluate scientific progress in our understanding of amphibian malformations and their environmental significance.
