HYBRIDIZATION BETWEEN SPECIES OF THE RANA PIPIENS COMPLEX IN CENTRAL TEXAS.

Abstract

Widespread acceptance and application of the polytypic species concept in the 1930s and 1940s resulted in the taxonomic lumping of many allopatric nominal species on the basis of the assumption of conspecificity. Consequently, for many groups of organisms one can cite cases of what Vaurie (1955) called pseudo-subspecies-good species taxonomically confused as subspecies. The example provided by leopard frogs of the Rana pipiens complex is particularly important because of the prominent place they have had in relation to theories of intraspecific variation and the evolution of isolating mechanisms. Analysis of patterns of geographic variation in morphology and the ability of individuals from some widely separated areas to produce viable offspring in laboratory crosses led Moore (1944) to regard many forms of the Rana pipiens complex as members of one polytypic species. Moore's (1946a, 1946b, 1949a, 1949b, 1950) extensive and influential work on the effects of temperature on embryonic and larval development and on genetic compatibility between frogs from different areas was interpreted within the framework of intraspecific variation. His demonstration that degree of abnormality in embryonic development is related to latitudinal distance (and, to a lesser degree, longitudinal distance) between parental populations provided a model of the manner in which differences accumulate between conspecific populations along environmental gradients. As Moore's interpretation gained wide acceptance, Rana pipiens became a standard textbook