The Genetic Architecture of Cold Tolerance in Natural-Populations of Drosophila-Melanogaster and Drosophila-Simulans

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Abstract
Genetic analysis of cold tolerance was applied to samples of recently collected isofemale strains of Drosophila melanogaster and D. simulans from natural populations from diverse climates. The temperate zone locality of Melbourne was sampled twice for both species, once in 1986 and again in 1987. In 1987, D. melanogaster collections were also made in the humid tropics at Townsville and the wet/dry tropical locality of Darwin. D. simulans was also collected in Townsville in 1987 but it was not found in Darwin. Diallel analysis was performed for each population sample, so there were seven diallels, each with from 9 to 12 strains which were randomly chosen. Diallel analyses showed that cold tolerance was mainly controlled by additive genetic effects. This pattern was consistent across time, across populations and across species. It is proposed that natural populations of both members of the sibling species have the genetic architecture necessary for adaptive phenotypic response to selection by intermittent periods of low temperature.