Quantitative Trait Loci for Cuticular Hydrocarbons Associated With Sexual Isolation Between Drosophila simulans and D. sechellia

Abstract

The identification of genes with large effects on sexual isolation and speciation is an important link between classic evolutionary genetics and molecular biology. Few genes that affect sexual isolation and speciation have been identified, perhaps because many traits influencing sexual isolation are complex behaviors. Cuticular hydrocarbons (CHs) of species of the Drosophila melanogaster group play a large role in sexual isolation by functioning as contact pheromones influencing mate recognition. Some of the genes that play key roles in determining species-specific CHs have been identified. We have performed separate quantitative trait locus (QTL) analyses of 7-tricosene (7-T) and 7,11-heptacosadiene (7,11-HD), the two major female CHs differing between D. simulans and D. sechellia. We find that 40% of the phenotypic variance in each CH is associated with two to four chromosomal regions. A region on the right arm of chromosome 3 contains QTL that affect both traits, but other QTL are in distinct chromosomal regions. Epistatic interactions were detected between two pairs of QTL for 7,11-HD such that if either were homozygous for the D. simulans allele, the fly was similar to D. simulans in phenotype, with a low level of 7,11-HD. We discuss the location of these regions with regard to candidate genes for CH production, including those for desaturases.

Identification of quantitative trait loci function through analysis of multiple cuticular hydrocarbons differing between Drosophila simulans and Drosophila sechellia females

“…These include Sexlethal (Sxl), transformer (tra), intersex (ix), doublesex (dsx) and fruitless (fru). In our previous work (Gleason et al, 2005), Sxl, tra and ix were not near QTL. The remaining two genes are both on chromosome 3. dsx, which influences the production of female dienes in D. melanogaster, (Jallon et al, 1988) was on the edge of a QTL (Gleason et al, 2005).…”

“…As there are multiple compounds requiring different biosynthetic pathways, there is the potential for the interaction of multiple genes through both additive and epistatic effects: some enzymes may be required for the synthesis of precursor molecules, whereas other enzymes may modify precursors to final products. In Drosophila, multiple gene effects and epistatic interactions have been found for interspecific differences between D. simulans and D. sechellia, as well as between D. pseudoobscura and D. persimilis (Coyne, 1996;Noor and Coyne, 1996;Gleason et al, 2005).…”

“…The overall pattern is that CHCs in D. sechellia have longer chains and are less saturated than those found in D. simulans. In a previous study we used a quantitative trait locus (QTL) approach to examine differences in the amount of 7-T and 7,11-HD in females of D. simulans and D. sechellia (Gleason et al, 2005). Through composite interval mapping (CIM), we found at least four QTLs for the monoene 7-T, three on chromosome 3 and one on the X, and two QTLs for the diene 7,11-HD on chromosome 3.…”

“…Through composite interval mapping (CIM), we found at least four QTLs for the monoene 7-T, three on chromosome 3 and one on the X, and two QTLs for the diene 7,11-HD on chromosome 3. Although genes have been identified that may influence CHC biosynthesis (candidate genes), very few were included as markers in that study, though the approximate locations of these genes were determined (Table 6 in Gleason et al, 2005). Of the possible candidate genes, only those on chromosome 3 were close to QTL.…”

“…Of the possible candidate genes, only those on chromosome 3 were close to QTL. Gleason et al (2005) did not study the other CHCs that differ between these two species.…”