Latitudinal relationships of esterase-6 and phosphoglucomutase gene frequencies in Drosophila melanogaster

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Abstract
Geographic variation in Esterase-6 (Est-6) and Phosphoglucomutase (Pgm) gene frequencies in Australasian populations of Drosophila melanogaster are compared with analogous data collated from 16 previous reports for North America and Europe/Asia. A large-scale latitudinal cline is found on all three Zoogeographic zones for Est-6 and overall, Est-61·00 frequency increases from about 20 per cent around 20° latitude to about 80 per cent approaching 50° latitude. In contrast, there is no consistent evidence for a latitudinal cline in Pgm gene frequencies in any of the three zones, with Pgm1·00 frequency generally about 85 per cent and Pgm1·20 and Pgm0·70 frequencies each between 5 per cent and 10 per cent. The consistent Est-6 clines are attributed to latitudinal selection gradients but no consistent correlations are found between Est-6 gene frequencies and maximum or minimum temperature or rainfall which might be associated with these gradients. The directions of the Est-6 clines in fact run counter to expectations based on the in vitro thermostabilities of the respective allozymes.