In lieu of an abstract, here is a brief excerpt of the content:

103 Sporadic reports of malformed amphibians are abundant in the literature, and these reports have been thoroughly reviewed prior to the recent “outbreak” of malformations (Van Valen, 1974) as well as in papers related to the current malformation phenomenon (Ouellet, 2000; Lannoo et al., 2003). Merrell (1969) reported finding limb malformations in northern leopard frogs (Rana pipiens) from a Minnesota site at a frequency of 14.8% during late July 1965. There were no subsequent Minnesota reports until 1993, when residents near Granite Falls, Minnesota, reported “large numbers” of abnormal leopard frogs exhibiting extra limbs, missing limbs, and a missing eye (Helgen, 1996). Investigators did not find malformed frogs in that area during the summer of 1994, nor did the residents report additional abnormal animals. Major media attention first focused on malformed Minnesota frogs in 1995 after a group of students reported abnormal leopard frogs near Henderson, Minnesota (Helgen et al., 1998). The frequency of malformations was about 33%, with a more serious array of defects reported. These defects were described at that time as “webbed” leg skin, “bony protrusions,” “contorted legs,” missing legs, extra legs, and missing eyes, as illustrated in Helgen et al. (1998). Newspaper coverage of these frogs led to more reports by citizens in 1995, including a site near Litchfield where more than 90% of the leopard frogs were missing limbs or parts of limbs. One of those citizen reports came to me from a landowner near Brainerd; that site subsequently became an important study site coded “CWB,” to which I refer extensively in following sections. I joined the Minnesota investigations in 1993 as a herpetological consultant, and I began field surveys in 1994 that continue today. Here I report findings relative to two questions about frog malformations: (1) Is this anything new? Because deformed frogs have both an anecdotal and a literary history, are the types of malformations or their frequencies any different in the 1990s? (2) Which anuran species are affected and are they affected differently? Historical Comparisons Literature Comparisons Interviews with David Merrell of the University of Minnesota revealed that his 1965 findings were quite different from what we were seeing in the 1990s. Merrell saw only two types of malformation, ectromelia and “deformed toes” (Merrell, 1969); I have seen up to 12 different types of malformation in single collections from my intensive sites. Other differences also exist. The 1965 malformation frequency decreased as the season progressed, from 14.8% in July to 3.6% in September; at sites where I am able to do multiple surveys throughout the season, the malformation frequency increases later in the season. Merrell did not see a recurrence of malformations in subsequent years, while my intensive sites have had numerous malformations during 5 consecutive years. Museum Comparisons I also made historical comparisons in two other ways (reported in Hoppe, 2000). One was to examine northern leopard frogs in the collections of the Bell Museum of Natural History, University of Minnesota, particularly a large set of frogs collected from 1958–63 by David Merrell and his collaborators. Only 18 abnormal frogs were found among 2,433 juvenile museum specimens examined in collections representing 43 sites in 26 counties, a “background frequency” of 0.7% abnormalities. These consisted of 12 predator amputations (0.5%) based on scar tissue and 6 malformations (0.2%). From anecdotal information and a few published findings, investigators have been using “about 1%” as a background level of frog abnormalities. Read and Tyler (1994) reported “natural levels of abnormalities ” in Neobatrachus centralis to be about 1.6%. Ouellet et al. (1997a) reported 0.7% malformations among four ranid species sampled at pesticide-free sites in Canada. Gray (2000b) reported 0.39% abnormalities among nearly 10,000 northern cricket frogs (Acris crepitans) in Illinois surveys from 1968–71. The 0.2% historical frequency of malformations in northern leopard frogs based on the Bell Museum collections is lower than other published estimates, and it is considerably lower than the arbitrary “about 1%” value. Literature reports often do not distinguish age categories and, hence, are hard to compare. Because malformations are scarce among adult frogs regardless of the frequency among juveniles (Helgen et al., 2000), it is best to exclude adults when reporting malformation frequencies or to report them separately. E I G HTE E N Malformed Frogs in Minnesota: History and Interspecific Differences DAVID M. HOPPE 104 MALFORMED FROGS IN MINNESOTA From 1996–99, I surveyed many of the same sites represented by the Merrell collections. I...

Share