Field Investigations of Malformed Frogs in Minnesota 1993-97

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Journal of the Iowa Academy of Science, Vol: 107, Issue: 3, Page: 96-112

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Helgen, Judy C.; Gernes, Mark C.; Kersten, Susan M.; Chirhart, Joel W.; Canfield, Jeff T.; Bowers, Dorothy; Haferman, Jon; McKinnell, Robert G.; Hoppe, David M.
malformations; Anura; Rana pipiens; Minnesota; Anthropology; Life Sciences; Physical Sciences and Mathematics; Science and Mathematics Education
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Reports of malformed frogs were made to the Minnesota Pollution Control Agency (MPCA) from different parts of Minnesota in 1993, 1995, 1996, and 1997 and one, nine, 190, and 172 reports were received, respectively. MPCA field crews and Drs. Hoppe and McKinnell documented malformed frog locations starting in 1993. By 1997, MPCA field crews documented malformed frogs at 62 locations in Minnesota, in 29 of 87 counties. Most malformations were in young metamorphs of Rana pipiens but they were observed also in R. clamitans, R. septentrionalis, R. sylvatica, Bufo americanus, and Hyla spp. Frequencies of malformations varied by time of year. Most malformations occurred in rear limbs, with some in front limbs, eye, jaw or skin. Frequencies of limb duplications at the Ney Pond were higher in 1995 (11.7%) than in subsequent years. Malformations were equally likely to be left- or right-sided. A study design in which malformed frog sites were paired with 'reference' sites was attempted, although some reference sites had, or developed, malformed frogs. In some sites, body weights of malformed metamorphs were significantly lower than normal ones, while in two sites both normal and abnormal metamorphs were quite reduced in size compared with frogs from reference sites. There is the possibility of a developmental delay in some of the metamorphs.