Biochemical Systematics of Members of the Genus Rana Native to Western North America

Case, S. M. (Museum of Vertebrate Zoology and Departments of Zoology and Biochemistry, University of California, Berkeley, California 94720) 1978. Biochemical systematics of members of the genus Rana native to western North America. Syst. Zool. 27:299-311. -Few supraspecific groups have been defined in North American ranids and the informal groupings which are recognized are often poorly characterized. Two biochemical methods, starch gel electrophoresis and microcomplement fixation, have been used in an examination of the evolutionary relationships among western North American frogs of the genus Rana. Both the electrophoretic and albumin comparisons indicate that the Rana boylii species group presently includes two very different evolutionary lineages. Rana aurora, R. boylii, R. cascadae, R. muscosa, and R. pretiosa are all members of one lineage allied to R. temporaria of Europe. A Mexican species traditionally included in this group, R. tarahumarae, is most closely related to other members of the genus that occur in Mexico and is part of a larger lineage that also includes R. pipiens. Frogs found in eastern North America diverged from western European frogs in mid-Eocene; estimates of divergence time are consistent with the hypothesis that separation of these lineages coincided with the end of a land connection between Europe and North America. The catesbeiana, pipiens, and tarahumarae groups diverged from each other in the Oligocene. Western North American Rana diverged from a Eurasian ancestor in the Oligocene and radiated in this area to form the five members of the boylii group. [Evolutionary relationships; electrophoresis; microcomplement fixation; Rana; western North America.] There have been conflicting views about the relationships among North American species of the genus Rana, particularly of the western forms. The traditional species groups, which are primarily defined by similarities in external morphology, are presented in Table 1. The results of two recent studies, one which examined several osteological features (Chantell, 1970) and the other utilizing biochemical comparisons (Wallace et al., 1973), have suggested that the composition of the species groups of western ranids needs to be reevaluated. Their data suggested that R. boylii and R. muscosa were closely allied with the members of the aurora group, with the possible exception of R. sylvatica. This study deals primarily with Rana aurora, R. boylii, R. cascadae, R. musI Present address: Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138. cosa, and R. pretiosa, all of which are native to the western United States, and R. tarahumarae which occurs primarily in Mexico. The geographical ranges of these six species are shown in Figs. 1 and 2. The methods of starch gel electrophoresis and microcomplement fixation have been utilized here in an analysis of the evolutionary relationships among members of the genus Rana in western North America. MATERIALS AND METHODS Rana boylii from six localities, R. muscosa from eight localities, R. aurora draytoni from seven localities, R. pretiosa from two localities, R. tarahumarae and R. catesbeiana from one locality each were examined (see Appendix for locality data). Eleven enzymes encoded ly 15 loci and five serum proteins were examined electrophoretically in horizontal starch gel. These were: lactate dehydrogenase (LDH-1 and 2), malate dehy-