Variation in Rana pipiens (Anura: Ranidae) of Eastern Colorado

Abstract

Examination of 621 individuals of Rana pipiens from 54 localities in eastern Colorado revealed two character complexes within this species. These complexes may be distinguished on the basis of five contrasting traits. The complexes were never found to overlap geographically. At four localities they were collected less than 40 miles from one another and yet maintained their character consistency and discreteness. This study indicates there is little, if any, gene flow between the two complexes. Moreover, clinal variation within one species is not represented here. Much of our knowledge of the geographic variability of Rana pipiens is due to the work of Moore and his students (Moore 1944, 1946a, 1946b, 1947, 1949a, 1949b, 1950, 1957; Volpe 1954; Ruibal 1955, 1957). Unfortunately interest in this complex species has flagged somewhat in recent years, and many critical problems concerning it remain unresolved. For example, Moore (1949b) suggests . . the sharp differences between the northern and southern populations (of R. pipiens) is probably due in part to the absence of data from localities between 320 and 40' N. latitude. Moore (1944) presents a map showing geographic distribution of the traits, presence or absence of vestigial oviducts, in mature male Rana pipiens. Since both types are present in eastern Colorado and this species has received relatively little attention in this area, we decided to investigate the geographic relationships of these two morphotypes more intensively. The research reported here was conducted to investigate the existence of additional morphological differences as well as to clearly define the distribution of the two phenotypic complexes. An understanding of these variations may demand a re-interpretation of earlier studies which imply that these differences are clinal variations rather than sharp discontinuities between subunits of the species. The study was restricted to collections of Rana pipiens from eastern Colorado, east of 105930' west longitude. The study was not concerned with the adaptive significances between the two phenotypic complexes. METHODS AND MATERIALS. The initial phase of the study was made using preserved specimens from the Colorado Museum of Natural