LANNOO, M.J.*; NANJAPPA, P.; BLACKBURN, L.M.: What Amphibian Malformations Tell Us About Causes

Amphibian malformations in northern and eastern regions of North America have generated considerable attention from both the general public and the scientific community. Common malformations of ranid frogs collected by the Minnesota Pollution Control Agency include missing limbs (ectromelia) and multiple limbs (polymelia). Despite the co-occurrence of both types of malformations among animals in any given hot spot, and the disparate locations of hot spots, some researchers argue that discrete factors cause different malformations (Kaiser, 1998, Science, 278:2051-2052; Souder, 2000, A Plague of Frogs, Hyperion Press). Gross and radiographic analyses show that two unusual features — spongiform bone and dorsal pigment abnormalities — appear in a subset (74%) of malformed ranids. Such bone and pigment abnormalities are difficult (bone) or impossible (pigment) to detect in cleared and stained animals. The presence of spongiform bone and dorsal pigment malformations proximal to the missing limb region strongly argue against predation being the main cause of ectromelia. Spongiform bone and pigment malformations also appear in polymelic animals. The presence of these abnormalities in both ectromelic and polymelic animals argues two things: 1) a shared cause, manifested differently depending perhaps on dosage or variations in exposure; and 2) the rejection of hypothesized causes that do not produce these malformations.