Electrophoretic Heterogeneity of α-Glycerophosphate Dehydrogenase among many Species of Drosophila

Coyne, J. A., W. F. Eanes, J. A. M. Ramshaw (Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts 02138) and R. K. Koehn (Department of Ecology and Evolution, State University of New York, Stony Brook, New York 11794). 1979. Electrophoretic heterogeneity of o-glycerophosphate dehydrogenase among many species of Drosophila. Syst. Zool. 28:164-175.-Electromorphic variation of a-glycerophosphate dehydrogenase in 71 species of Drosophila has been studied using sequential polyacrylamide gel electrophoresis, sequential starch gel electrophoresis, and isoelectric focusing. Although this locus was previously reported as nearly invariant among many species of the genus, this study shows a substantial increase in variation between species which is concordant with the known taxonomy of the genus. However, these methods revealed no additional variation within the species themselves. Each of the three methods found variation not detectable by the other two; thus, all are necessary for maximizing the observed variation between species. In comparison to previous electrophoretic studies of this enzyme in Drosophila, these new data show a much increased concordance with reported immunological and kinetic differences between this enzyme in different species. The implications of these results for electrophoretic studies of speciation and taxonomy are discussed. [Drosophila spp.; a-glycerophosphate dehydrogenase; electrophoresis; heterogeneity.] In recent years electrophoresis has been extensively used to investigate questions of general interest in evolutionary biology and systematics (Ayala et al., 1974; King and Wilson, 1975; Mickevich and Johnson, 1976; and many others). Electrophoretic data is fairly simple to gather, and it has a number of advantages over more traditionally used taxonomic characters (Avise, 1974). Because it is assumed that electromorphs are only a step removed from single genes, differences between them are readily translated into measures of "genetic distance." Inherent in these investigations are assumptions about the nature of electrophoretic variation. It is often recognized that some genetic differences may be mistakenly described as genetic identities due to convergence of different variants to similar mobilities; but this problem is usually ignored, being considered insignificant given the weight of a total data set. Of course the generalities drawn from such data can seriously depend on the safety of these assumptions. Evidence is now accumulating that electrophoretic phenotypes are not necessarily homogeneous molecular entities, but are often heterogeneous classes which will divide when subjected to a series of electrophoretic conditions (e.g., Weitkamp et al., 1973; Bernstein et al., 1973; Singh et al., 1976; Coyne and Felton, 1977). When used to investigate variation within species, this approach has had a significant effect on the interpretation of particular problems, such as descriptions of geographic variation of gene frequencies. So far these analyses have not been extended to comparisons between many species. However, the implications of undetected variation at this level may be even more profound than within species. In this report we examine the apparent electrophoretic identity of a single enzyme a-glycerophosphate dehydrogenase (a-GPDH, Lglycerol-3-phosphate oxidoreductase, E.C. 1.1.1.8.) in many species of the genus Drosophila. Our study clearly demonstrates that judgements of genetic