Albumin Differences among Ranid Frogs: Taxonomic and Phylogenetic Implications

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Abstract
Wallace, D. G., M. C. King and A. C. Wilson (Biochemistry Dept., University of California, Berkeley, California 94720) 1973. Albumin differences among ranid frogs: taxonomic and phylogenetic implications. Syst. Zool., 22:1–13.—Since morphological analysis of living and fossil material has provided little information on taxonomic and phylogenetic relationships among species in the frog family Ranidae, an attempt was made to obtain such information by comparing their serum albumins. Rabbit antisera were prepared against the purified serum albumins of seven ranid species and tested by the microcomplement fixation method for reactivity with the albumins of 36 ranid species. This method provides a measure of the degree of amino acid sequence difference between albumins. The taxonomic and phylogenetic schemes we have derived from the albumin comparisons are generally in agreement with nonmolecular evidence. In some cases, they go beyond it, permitting demarcations among taxa that were previously unresolved. For example, it is proposed that the North American species of Rana are divisible into at least two major subgroups; an eastern subgroup, which includes R. pipiens and R. catesbeiana, and a western cluster, which includes R. aurora. The nearest relatives of the western cluster appear from albumin comparisons to be the R. temporaria cluster of the Palearctic region. The albumin results also permitted the construction of a phylogenetic tree with a very low percent standard deviation. With the aid of this tree and the molecular clock hypothesis we have estimated the approximate divergence times of various groups, subgroups and clusters of Holarctic ranid species. The molecular differences among Rana species are at least as large as those usually found within orders of placental mammals. This raises an important question regarding the ranking of taxonomic categories. If the genus Rana is equivalent in terms of genetic dispersion to an order of mammals, should one elevate the rank of Rana to the ordinal level? We believe that the molecular findings provide taxonomists with a dilemma.

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