Abstract
Since the pioneering work of Dobzhansky in the 1940s, many chromosomal inversions have been identified but how they contribute to adaptation remains poorly understood. In Drosophila melanogaster, the widespread inversion polymorphism In(3R)P is involved in climate adaptation, exhibiting non-neutral latitudinal clines on multiple continents. Here, I summarize new results suggesting that this chromosomal rearrangement represents a long-term (equilibrium) balanced polymorphism of ancestral African origin and that it harbors alleles that are maintained by balancing selection on several continents. Our findings indicate that In(3R)P spread out of its ancestral subtropical/tropical range and then become latitudinally along similar but independent climatic gradients, always being frequent in subtropical/tropical areas but rare or absent in temperate climates.
