Size and Metabolic Differences in Pseudacris Triseriata (Anura) from Different Elevations

Abstract

An altitudinal cline in body size is described. Frogs from higher elevations are larger than those from prairie populations. Oxygen consumption per unit of body weight is shown to be inversely related to size. The ecological relation- ships of these two parameters and their possible adaptive significance are discussed. The phenomenon of geographic variation has been so amply illus- trated by the description of numerous subspecies that it has come to be expected in any wide-ranging species. However, too little attention has been given the mechanisms responsible for generating the observed variations. This report summarizes some of the differences found in populations of the chorus-frog Pseudacris triseriata (Weid) occurring at different elevations in northern Colorado and includes certain pre- liminary data from experiments designed to determine the adaptive significance of the observed differences. Perhaps the greatest contrast between populations from different elevations in the area studied is in body size. This trait together with its relationship to oxygen consumption will be the major topics of this paper, but other striking differences have been found. There are highly significant differences in egg size, number and color, as well as adult coloration and larval developmental. The latter three cate- gories will be discussed in later papers. The present study is similar to those of Moore (1942, 1949) and Ruibal (1955, 1957) in that frogs from contrasting environments have been compared in an attempt to find differentially adaptive charac- ters. A major difference is in the distance involved. While Moore and Ruibal compared populations living hundreds of miles apart at the extremes, this study has been primarily concerned with popula- tions separated by only 40 miles. This difference should be of impor- tance if, in fact, distance alone may deter gene flow between popula- tions. It should however be noted that since different species with presumably different dispersal abilities are being considered, statute