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Document Type

Research

Keywords

anurans, leopard frogs, Rana pipiens, abnormalities, malformations, Minnesota

Abstract

Two lines of investigation were used to determine whether recent Minnesota reports of frog abnormalities differ from historical reports: (1) museum collection studies paired with follow-up field surveys, and (2) comparison of recent and earlier field surveys in west-central Minnesota. For the museum study I examined 2433 northern leopard frogs (Rana pipiens) in the Bell Museum of Natural History collections of the University of Minnesota, collected during 1958-63. 0.7% of frogs were found to have abnormalities, consisting of 0.5% predator amputations and 0.2% malformations. Three types of malformation were found: missing hindlimbs, vestigial feet, and fused digits. Conspicuously absent from the museum collections were the malformation categories of extra limbs, split limbs, webbing of hindlimbs (cutaneous fusions), and bent/twisted limbs (anteversions). Postmetamorphic field surveys at some of the museum collection sites were attempted in 1997. One finding was that frogs were much more easily collected in 1958-63! During surveys in 1997 I found frogs at only 5 of 14 museum sites on record. Fifteen malformed frogs were recorded among 611 examined (2.5%), compared to one malformed frog among 276 (0.4%) in the corresponding museum collections. Field surveys of more museum sites are in progress. Frog surveys conducted in west-central Minnesota from 1976-97 were also analyzed for differences in abnormality frequencies and types. Nine sites were identified as having reasonable (>50) sample sizes in both pre-1993 and post-1995 surveys. Pre-1993 data included three abnormal frogs among 1772 examined (0.2%), compared to 59 abnormal frogs among 2548 (2.3%) in 1996-97. Only 2 categories of abnormality were found in the pre-1993 data, partial limbs and vestigial foot. I conclude that recent findings of anuran abnormalities in Minnesota do represent a new phenomenon. Frog abnormalities were more frequent, more varied, more severe, and more widely distributed in 1996 and 1997 than in 1958-93.

Publication Date

September-December 2000

Journal Title

Journal of the Iowa Academy of Science

Volume

107

Issue

3-4

First Page

86

Last Page

89

Copyright

© Copyright 2000 by the Iowa Academy of Science, Inc.

Language

EN

File Format

application/pdf