A COMPARATIVE STUDY OF THE SERUM PROTEINS OF THE SPECIES OF TARICHA AND THEIR HYBRIDS.

Abstract

One objective of the extensive investigation of the salamander genus Taricha (Twitty, 1955, 1959, 1961a, 1961b, 1964) is to gain knowledge of the evolutionary events which led to the present diversity within the genus. The study about to be described was undertaken to determine if an electrophoretic analysis of the serum proteins of Taricha could contribute useful information toward this end. Additional systematic characters are needed for Taricka, since many of the morphological characters which are used with facility for studying variation in other vertebrates, such as external meristic characters in fish and reptiles, are nonexistent or of a rather plastic nature in salamanders. Furthermore, since individual protein molecules are the expression of relatively few genes the present study was initiated with the belief that certain differences in serum proteins within the genus would lend themselves to genetic analysis. There is thus a possibility of determining, with a fair degree of precision, the number of gene differences separating the species of Taricha at this level. Pertinent in this regard is the finding by Twitty (1961b) that some of the most conspicuous characters separating the species of Taricha are based on a limited number of gene differences. This is indicated by the segregation ratios, in secondgeneration interspecific hybrids, of such features as presence or absence of a balancer, adult coloration, and especially larval pigment pattern. In order to determine the potential usefulness of electrophoretic analysis of serum proteins the following three requirements were established: The patterns obtained must be 1) genetically based and not modified by environmental factors, 2) different enough so that species and their subgroups may be distinguished, and yet 3) sufficiently conservative to reflect accurately the relationships within the genus. Other workers investigating quantitative variation in serum and other systems of proteins have in some cases encountered much intraspecific and individual variation in many fractions, which has led them to conclude that these characters are not particularly useful for systematic study of closely related groups (Starr and Fosberg, 1957; Sibley and Johnsgard, 1957; Sibley, 1960; Mairs and Sinderman, 1962). Variation of this type is expected since environmental and physiological factors may have profound effects on the amount of protein present at any instant. For this reason it was decided to concentrate in this study on qualitative differences in the serum proteins, and the method of electrophoresis used was chosen on this basis. Disc electrophoresis has been shown to give greatly increased resolution of individual protein bands compared with paper and in some applications with starch-gel electrophoresis (Ornstein, 1964; personal observation). To determine if the first of the above requirements could be satisfied, the influence of environmental and physiological factors on the patterns obtained was observed. This was possible because Taricha may be kept indefinitely in the laboratory under constant environmental conditions which are considerably different from those in nature. Furthermore, it is possible to capture Taricka at various times during the breeding season when the environment and physiology of individuals are undergoing substantial changes. During the breeding season the animals migrate to water for the purpose of spawning and