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Historical Observations and Recent Species Diversity of Deformed Anurans

David M. Hoppe

Reports of abnormal amphibians, mostly multilegged frogs, have appeared in the past, both in publication and anecdotally. None of those reports appear remotely comparable to the frequency or geographic distribution of abnormalities found in Minnesota in 1995-96. Two other observations lead me to believe this is a recent, rapid-onset phenomenon:

1. In observing and handling thousands of Minnesota frogs from 1975-1995, I had seen only 2 with macroscopic limb defects; in 1996 I have seen over 200.

2. Among 6 west-central Minnesota populations where I have examined 200-600 frogs each in the past showing no abnormalities, 4 populations showed 1-4% abnormalities in 1996.

During the summer of 1996 I found limb and/or eye abnormalities in 6 species of Minnesota anurans: Northern leopard frog (Rana pipiens), mink frog (R. septentrionalis), wood frog (R. sylvatica), spring peeper (Pseudacris crucifer), gray treefrog (Hyla versicolor), and American toad (Bufo americanus). The array of abnormalities includes missing limbs, missing portions of limbs, malformed limbs, extra limbs or limb portions, fusion of skin of upper and lower legs, and missing eyes.

Of particular interest are data from one Crow Wing County site where all 6 species breed in the same small lake. The species with the worst array and highest frequency of abnormalities was the mink frog, with 50% abnormalities. This is also the most aquatic of the 6, as adults breed in water, feed in or very near water, and over-winter in water, and tadpoles spend a whole year in water before metamorphosing. The next most aquatic species, the Northern leopard frog, which feeds terrestrially but also breeds and over-winters in water, and usually reaches metamorphosis in about 12 weeks, had 10% abnormalities. The other 4 species are highly terrestrial, feeding and over-wintering on land, returning to water only to breed, and spending 6-12 weeks as tadpoles. The collective frequency of abnormalities in those 4 species was 3%.

If an environmental agent is responsible for the abnormalities, my data suggest that (1) it is an agent that has achieved higher concentration and/or wider distribution in recent years, and (2) it is most likely acting in the water where the anurans breed and their larvae develop.

U.S. Department of the Interior
U.S. Geological Survey
Patuxent Wildlife Research Center
Laurel, MD, USA 20708-4038
http://www.pwrc.usgs.gov/naamp3/naamp3.html
Contact: Sam Droege, email: Sam_Droege@usgs.gov
Last Modified: June 2002