Systematics and Evolution of Western North American Frogs Allied to Rana Aurora and Rana Boylii: Karyological Evidence

Abstract

C-banded karotypes of five species of frogs endemic to western North America were analyzed to investigate the use of such chromosomal data in determining their systematic interrelationships. Morphologically, three of the species (Rana aurora, R. cascadae and R. pretiosa) may be considered generalized brown while the other two species (R. boylii and R. muscosa) are morphologically divergent and may be termed stream frogs. The peculiar karyo- type of R. muscosa, with its three pairs of telocentric chromosomes, can be derived from that of R. boylii by postulating a series of chromosomal inversions. Based on karyotypic character anal- ysis, R. boylii and R. muscosa constitute a pair of sister taxa that appears to have arisen from within the western Rana. The chromosomal evidence, while concordant with morphological considerations, conflicts with various systematic hypotheses that have been proposed concern- ing these frogs based on immunological distance studies and reanalyses. (Anura; Ranidae; Rana; systematics; evolutionary relationships; chromosomes; C-bands; western North America.) Five species of frogs, genus Rana, are en- demic to the far western United States and Canada. The relationships of these species-R. aurora, R. boylii, R. cascadae, R. pretiosa and R. muscosa-that constitute the R. boylii group (sensu Case, 1978a) have been the subject of repeated analyses by various means, including study of mor- phology, comparative biochemistry and karyology (Boulenger, 1920; Zweifel, 1955;