Systematics and Evolution of Western North American Frogs Allied to Rana aurora and Rana boylii: Karyological Evidence

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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 determinng their systematic interrelationships. Morphologically, three of the species (Rana aurora, R. cascadae and R. pretiosa) may be considered generalized "brown frogs", while the other two species (R. boylii and R. mucosa) are morphologically divergent and may be termed "stream frogs". The peculiar karyotype of R. mucosa, 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 analysis, R. boylii and R. mucosa 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 sytematic hypotheses that have been proposed concerning these frogs based on immunological distance studies and reanalyses.