Pigmentation of the Western Spotted Frog, Rana p. pretiosa, in Yellowstone Park, Wyoming

Abstract

Information on the amount of variation in the pigmentation of Rana pretiosa has usually been scanty and based on subjective appraisals of a small number of individuals (Dickerson, 1920; Blanchard, 1921; Patch, 1922; Tanner, 1931; Logier, 1932; Gordon, 1939). All these color descriptions are perfectly valid as generalizations but were not intended to serve as expressions of the variation existing in natural populations. Color and pattern differences are useful characteristics in attempting to assess inter- and intraspecific relationships but the proper evaluation of pigment variation depends upon adequate understanding of the differences exhibited by the species as a whole, and hence by its component populations. For example, in her description of the new race Rana pretiosa luteiventris Thompson (1913) contrasted, among other characteristics, the yellow ventral pigmentation of the new form with the red or salmon coloring of the nominate subspecies. One may wonder whether such a difference is actually of taxonomic significance or whether ventral coloration varies so greatly over the entire range, or even within adjacent populations, of Rana pretiosa as to negate its diagnostic value. Slevin (1928) did not recognize Rana pretiosa as a polytypic species and there are others (Stebbins, 1951) who are at least skeptical as regards the validity of R. p. luteiventris. However, the purpose of this study is not to attempt to settle this taxonomic issue but rather to gain some conception of the amount of variation that may be expected in several localized populations of Rana p. pretiosa in Yellowstone Park, Wyoming. The expansion of this approach to embrace other populations in other parts of the range of Rana pretiosa will eventually permit a decision as to the status of R. p. luteiventris. A similar study of pigmentation has already been carried out in Oregon by Dunlap (1955). His remarks are based largely on preserved material (at least for melanin distribution) with additional notes on ventral color differences based on field observations. In this study a more restricted geographic area was chosen for