Alcohol Dehydrogenase and Glycerol-3-Phosphate Dehydrogenase Clines in Drosophila melanogaster on Different Continents

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Abstract
This paper describes geographic variation in alcohol dehydrogenase (Adh) and glycerol-3-phosphate dehydrogenase (Gpdh) gene frequencies in Australasian populations of D. melanogaster and compares it with analogous data collated from published reports on North American and Asian populations. On each region there are widespread polymorphisms and large-scale latitudinal clines for 2 electrophoretic variants at each locus; in all 3 regions, AdhS frequency decreases markedly and GpdhF frequency decreases to a lesser extent with increasing distance from the equator. The occurrence of such complementary latitudinal clines in Asia, Australasia and North America is interpreted as evidence that the clines are maintained by selection gradients. No consistent evidence that they are directly related to temperature gradients, as has been predicted from reported differences in thermostability between the ADH and GPDH allozymes was found. Geographic variation in AdhS frequencies on all 3 regions is related to maximum rainfall, but the mechanisms underlying this relationship remain obscure.