DOI: 10.5061/dryad.gmsbcc2vc
title: High altitude favours long chained cuticular hydrocarbons in Drosophila

description: 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 three
 populations of D. melanogaster from the Western Himalayas at altitudes
 ranging from 760 to 2592 m above sea level and studied their CHC profiles
 for standing and plastic differences. 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 an overall shift in CHCs 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.
description: <em>Drosophila melanogaster</em> populations were
 collected from three altitudinal locations in the Western Himalayas
 (between 760-2592 metres above sea level (a.s.l); Rohru (31.2°N, 77.81°E,
 2592.84 m), Chamba (32°N, 76°E, 996 m), and Mandi (31°N, 76.9°E, 760 m).
 Hereafter, HL (highland), ML (midland), and LL (lowland) correspond to
 Rohru, Chamba, and Mandi, respectively. Fly collection was undertaken in
 and around apple orchards during the winter months (Oct and Nov 2019)
 using both mouth aspirators and bait-trap methods. Field-collected flies
 were transported to the laboratory, sorted by sex under a stereo-zoom
 microscope (Leica S9i) using a mild CO<sub>2</sub> stream, and
 placed under controlled conditions: 23 ± 0.5°C, 12:12 light: dark cycle.
 The females were placed individually in fresh food vials and allowed to
 oviposit until larval activity was visible. In total, 120 founder
 iso-female lines (from three sites; HL, 41 lines; ML, 53 lines; and LL, 26
 lines) were established and maintained under controlled conditions (see
 above 23± 0.5 °C). Successful lines were scanned for species
 identification based on taxonomic keys (e.g. sex combs arrangement,
 pigmentation, and genitalia structures). Of the 120 iso-female lines, 58
 were identified as <em>D. melanogaster</em> (37 lines: HL; 15
 lines: ML; 6 lines: LL). Three separate population cages (one for each
 altitude) were created by pooling iso-female lines from the respective
 collection sites (LL, ML, and HL). Each population cage was then
 maintained for five, non-overlapping, generations (ca. 1000-1200
 flies/cage). All stocks (iso-female lines and population cages) were
 maintained on ad libitum corn-meal agar food medium under controlled
 conditions (23±0.5 °C) and a 12:12h light: dark cycle). These conditions
 were maintained throughout the experiment unless stated
 otherwise. <strong><em>Experimental
 Design</em></strong> Eggs were collected
 from the three population cages (LL, ML, and HL) by placing two food
 plates (per cage) containing active yeast for 3-4 hours. Food chunks with
 ca. 30 eggs were handpicked from these plates and transferred into
 separate vials containing fresh food medium (n=20 vials per population
 cage). The vials were then incubated at 23°C until adults eclosed. A total
 of 600 virgin flies were sorted within 8 hours of eclosion from each
 population and kept isolated for 3 days. On the fourth day, these flies
 were split across two experimental treatments: control (no desiccation)
 and desiccation (8 hours desiccation). Five replicates (R1-R5) were
 created for each sex with each replicate consisting of 20 adults (see
 S1).
description: # High altitude favours long chained cuticular hydrocarbons in Drosophila
 [https://doi.org/10.5061/dryad.gmsbcc2vc](https://doi.org/10.5061/dryad.gmsbcc2vc) Our dataset comprises 25 peaks of cuticular hydrocarbons (CHCs) extracted from Drosophila melanogaster collected from three different altitudes. The first column in the dataset contains Sample IDs followed by "Population", "Treatments", "Replicates" and "Sex". This is followed by relative CHC values of the 25 identified CHC peaks. For example, consider the sample ID: "1HL0MR1" where: "HL/ML/LL" indicates the altitude of collection (highland, midland, and lowland). However, in the first column HL is denoted by AS, ML is denoted by CH and LL is denoted by M. In "0/8", "0" denotes flies collected at the 0th hour which is the "control". Whereas the "8" denotes the time duration of 8 hours till which the flies were exposed to desiccation treatment; "Desiccated". "M/F" represents the sex (male and female). "R1-R5" represents five replicates for each population, R1, R2, R3, R4 and R5. "CHC1-CHC25" denotes the relative abundance CHC values.