Geographic variation of the chromosomal polymorphism in Drosophila flavopilosa.

Natural populations of the Chilean species Drosophila flavopilosa Frey are polymorphic for the banding sequences in the fifth chromosome due to the existence of four paracentric inversions. Qualitative analysis of the polymorphism demonstrated that there are seasonal fluctuation and geographic variations of two kinds: altitudinal gradients and a north-south gradient. In addition, the northernmost and southernmost samples examined are polymorphic only for one inversion (inversion "B"). In the light of previous experimental evidence, it was concluded that the seasonal fluctuations and elevational differences are probably controlled by weather conditions, especially temperature. However, the observed differences between the central and marginal populations require another type of interpretation, similar to that postulated for other species that exhibit the same pattern of chromosomal variation. A photomicrographic map of the Standard banding pattern of the salivary gland polytene chromosomes of D. flavopilosa is presented.