Field Investigations of Malformed Frogs in Minnesota 1993-97

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 \u27reference\u27 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

Defining Anuran Malformations in the Context of a Developmental Problem

This paper summarizes terminology and general concepts involved in animal development for the purpose of providing background for the study and understanding of frog malformations. The results of our radiographic investigation of rear limb malformations in Rana pipiens provide evidence that frog malformations are the product of early developmental errors. Although bacteria, parasites and viruses were identified in these metamorphosed frogs, the relevant window to look for the teratogenic affect of these agents is in the early tadpole stage during limb development. As a result, our microbiological findings must be regarded as inconclusive relative to determining their contribution to malformations because we conducted our examinations on metamorphosed frogs not tadpoles. Future studies need to look at teratogenic agents (chemical, microbial, physical or mechanical) that are present in the embryo, tadpole, and their environments at stages of development that are relevant for the malformation type. The impact of these teratogenic agents then needs to be assessed in appropriate animal models using studies that are designed to mimic field conditions. The results of these laboratory tests should then be analyzed in such a way that will allow comparison with the findings in the wild-caught tadpoles and frogs