Dissecting the Genetic Basis of Variation in Cocaine and Methamphetamine Consumption in Drosophila melanogaster

We derived an outbred advanced intercross population (AIP) from 37 of the sequenced inbred wild-derived lines of the Drosophila melanogaster Genetic Reference Panel (DGRP) through a round-robin crossing scheme. These lines are maximally genetically divergent, have minimal residual heterozygosity, are not segregating for common inversions, and are not infected with Wolbachia pipientis. We assessed voluntary consumption of sucrose, methamphetamine-supplemented sucrose and cocaine-supplemented sucrose and found significant phenotypic variation in the AIP, in both sexes, for consumption of both drugs. We performed whole genome sequencing and extreme QTL mapping on the top 10% of consumers for each replicate, sex and condition, and an equal number of randomly selected flies. We evaluated changes in allele frequencies genome-wide among high consumers and the control flies and identified 3,033 variants associated with increased consumption that reside in 1,963 genes, enriched for genes associated with nervous system and mesoderm development. We assessed the effects of ubiquitous RNA interference (RNAi) on consumption for 22 candidate genes, of which 14 showed a significant increase or decrease in consumption compared to control. We created AIPs for both alleles of 10 significant SNPs using a round-robin crossing scheme to isolate the particular SNP in an otherwise randomized genetic background. After 5 rounds of random mating, we tested the average consumption of sucrose, cocaine, or methamphetamine for each population. We compared the average consumption for the populations containing the alternate alleles to look for a significant difference in consumption.