Serum albumin polymorphisms in natural and laboratory populations of Peromyscus.

-Electrophoresis of serum from 14 species of Peromyscus revealed albumin polymorphisms in samples of P. maniculatus, P. leucopus, P. truei, P. difficilis, P. megalops, and P. floridanus. All samples of P. melanotis, P. crinitis, P. boylii, P. ochraventer, P. eremicus, P. californicus, and P. thomasi were monomorphic. Two samples of P. polionotus were both monomorphic, but they differed from each other. Polymorphisms were found in natural populations of P. maniculatus, P. leucopus, P. truei, and P. megalops. In P. maniculatus the long-tailed, forest dwelling forms of northern and western North America were monomorphic and the short-tailed, grassland inhabiting forms tended to be polymorphic. No relationship between the electrophoretic mobilities of the serum albumins of the different species and the presumed phylogenetic relationships of these species was observed. The analysis of genetic polymorphisms in natural populations of small mammals in general, and of Peromyscus in particular, has largely been neglected by biologists studying vertebrate populations. Among the few exceptions are Blair's (1947a, 1947b) attempts to estimate frequencies of coat color alleles in Peromyscus maniculatus, and the studies of antigenic and transferrin polymorphisms in the same species by Rasmussen (1964) and Rasmussen and Koehn (1966). The development of serological techniques and their application to studies of vertebrate populations promises to contribute significantly to our knowledge of the structure and dynamics of natural populations. The discovery of different serum albumins in laboratory stocks of Peromyscus maniculatus and P. polionotus and the subsequent elucidation of their inheritance (Welser et al., 1965) led us to examine wild populations of P. maniculatus, and wild and laboratory populations of other species of Peromyscus for polymorphic albumins. MATERIALS AND METHODS The natural populations and laboratory stocks used in this study are identified under "Populations Sampled" beyond. Blood samples from healthy, adult (weaned) mice were drawn from the suborbital canthal sinus into heparinized glassware and examined either fresh or after storage at -10? C. Starch gels were prepared after the general method of Smithies (1955). The starch concentration was increased to 1.37 times that recommended by the manufacturer (Connaught). A Tris-Borate-Versene system mixed to buffer at pH 6.7 (90% 0.3M boric acid, 10% 0.3M Tris, and 1.23 grams of Versene per liter) was preferred. Buffer concentration in the finished gel was 0.043M. The gels were left uncovered after pouring in order to minimize internal distortion. To obviate the necessity of a lid, the plastic trays, normally 6 mm deep, were temporarily heightened by winding half-inch masking tape around the perimeter. The trays were filled with excess gel to 2 or 3 mm above the plastic rim.