High altitude favours long-chained cuticular hydrocarbons in <i>Drosophila</i>

Cuticular hydrocarbons (CHCs) are key components of the insect cuticle and contribute to the wide geographical distribution of this taxon. Many studies have investigated sex and population differences in CHC profiles, with these investigations mostly focusing on latitudinal CHC variation, whereas CHC variation across altitudinal transects is less well-studied. Here, we tested whether CHC profiles vary along an altitudinal gradient in the cosmopolitan vinegar fly Drosophila melanogaster. We collected from three populations of D. melanogaster in the Western Himalayas at altitudes ranging from 760 to 2,592 m above sea level and tested their CHC profiles for standing and plastic variation. We found quantitative differences in 25 CHCs across populations, and at higher elevations, males and females expressed higher amounts of particular long-chained hydrocarbons. We also found plastic shifts in CHC profiles in all three populations when flies were exposed to desiccating conditions. Overall, our findings suggest that there is an altitudinal cline in CHCs. However, this does not mirror the well-established latitudinal clines in fly hydrocarbons.