THE molecular basis for the maintenance of a gene–enzyme polymorphism in natural populations of Drosophila melanogaster has been reported1. The locus under analysis codes for the subunit of α-glycerophosphate dehydrogenase, (α-GDH; E.C. 18.104.22.168) a homodimeric enzyme: the primary function of this enzyme in adult muscle is to provide metabolic energy during flight2–7, and these alleles showed both spatial and temporal variations in frequency. A latitudinal cline was identified, in which the frequency of the α-GDHS allele decreases southwards along the eastern US coast8. The α-GDHS allele was also found to increase in frequency during cooler months in several New England populations6. We evaluated several biochemical parameters using partially purified enzyme from the three common genotypes and uncovered temperature-dependent differences in Km, specific activity, and reaction rate constancy1. Based on the population and biochemical data an argument was provided that environmental temperature was operating as a selective agent in demanding the relative frequencies of the two alleles at this metabolically important locus. We present here additional evidence to support this proposal, based on an evolutionary pattern of coincidence.
S. Alahiotis, Steve Miller, E. Berger