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Abstract
Until the late 1960's, leopard frogs (Rana pipiens sensu lato) were thought to consist of one broad ranging species with gene flow between adjacent populations. This distribution was thought to be the largest of any anuran encompassing an area from northern Canada south to Panama, and from the eastern to nearly the western coasts of United States (Conant, 1958). This single species concept arose primarily out of diploid hybridization and embryonic temperature adaptation experiments (Moore, 1939; 1942a; 1942b; 1944; 1946; 1947; 1949; 1950; 1957; Volpe, 1954; and Ruibal, 1955). Moore suggested that adjacent (north-south) populations of leopard frogs were capable of genetic exchange, and that as the latitudinal distance between popu- lations increased, genetic compatability decreased. Mayr (1963) cited leopard frogs as a classic example of geographic variation as well as illustrating physiological clines.
This single species paradigm was held in vogue from 1939 to 1966 but fell to more critical external and internal morphological analyses and the advent and quantitative use of modern probes such as tape recorders, sonographs, and electrophoresis (Littlejohn and Oldham, 1968; Brown and Brown, 1972; Post, 1972; Post and Pettus, 1966; Platz, 1972 and 1976; Platz and Platz, 1973; Dunlap and Kruse, 1976; Kruse and Dunlap, 1976; and Frost and Bagnara, 1976).
