Studies of linkage in populations. X. Altitude and autosomal gene arrangements in Drosophila robusta.

Data are presented concerning the gene arrangements in the second and third chromosomes of Drosophila robusta in eight altitudinal transects. A consistent change is the increase in the arrangement 2L-3, particularly in the linkage combination 2L-3.2R, with increasing altitude. The reciprocal decrease with increasing altitude affects several different 2-left arrangements, most consistently 2L-1. The arrangements of 2-right show no significant variation with altitude, and those of 3-right do so only in a few samples of the two northern transects studied, none in any of the southern ones. These results confirm previous evidence for the significant role of the arrangements of the left arm of the second chromosome in the adaptations of this species to altitude and suggest further that interactions of linked arrangements are involved in these adaptations. The data also indicate that the factors responsible for the altitudinal adaptations of this species are in many cases not the same ones that are responsible for variations in its gene arrangements with latitude.