Adaptive value of PGM polymorphism in laboratory populations ofDrosophila melanogaster

Abstract

SUMMARYExperiments have been performed to show that PGM polymorphism for the two common electrophoretic allozymes, PGMAand PGMB, inDrosophila melanogasterhas adaptive value. Firstly, the allele frequencies converge to the same equilibrium value in six experimental populations. Secondly, density-dependent selection operates. Thirdly, the relative fitness of the three genotypes varies in modified culture media. PGM polymorphism is maintained by frequency-dependent selection and heterotic selection: the first mechanism operates to reach equilibrium frequency, the second cooperates to maintain it. The experiments performed with modified culture media favour the view that the two allozymes have different affinities for two components which are present in the nutritional environment. These components may be either substrates or other factors involved in the reaction catalyzed by PGM.