Thoracic trident pigmentation in Drosophila melanogaster: Latitudinal and altitudinal clines in Indian populations

Abstract

Wild populations of Drosophila melanogaster were collected along a latitudinal transect between Ernaculum (10°latitude) and Jammu (32.4°). Altitudes were also highly variable, from sea level up to more than 2 000 m. The intensity of dark pigmentation on the thorax (trident) was estimated visually using four phenotypic classes, in flies grown at 17 and 25 °C. Significant clines of increasing pigmentation were observed according to latitude and altitude. A multiple regression technique permitted improvement of the relationship between pigmentation and geographic parameters, so that 93% of the pigmentation variations among populations could be predicted by knowing both the latitude and altitude of original populations. These data strongly suggest an adaptive response of thoracic pigmentation to physical factors of the environment, and especially to temperature.