Genetic dissection of intraspecific variation in a male-specific sexual trait in Drosophila melanogaster

Abstract

An open question in evolutionary biology is the relationship between standing variation for a trait and the variation that leads to interspecific divergence. By identifying loci underlying phenotypic variation in intra- and interspecific crosses we can determine the extent to which polymorphism and divergence are controlled by the same genomic regions. Sexual traits provide abundant examples of morphological and behavioral diversity within and among species, and here we leverage variation in the Drosophila sex comb to address this question. The sex comb is an array of modified bristles or ‘teeth' present on the male forelegs of several Drosophilid species. Males use the comb to grasp females during copulation, and ablation experiments have shown that males lacking comb teeth typically fail to mate. We measured tooth number in >700 genotypes derived from a multiparental advanced-intercross population, mapping three moderate-effect loci contributing to trait heritability. Two quantitative trait loci (QTLs) coincide with previously identified intra- and interspecific sex comb QTL, but such overlap can be explained by chance alone, in part because of the broad swathes of the genome implicated by earlier, low-resolution QTL scans. Our mapped QTL regions encompass 70–124 genes, but do not include those genes known to be involved in developmental specification of the comb. Nonetheless, we identified plausible candidates within all QTL intervals, and used RNA interference to validate effects at four loci. Notably, TweedleS expression knockdown substantially reduces tooth number. The genes we highlight are strong candidates to harbor segregating, functional variants contributing to sex comb tooth number.

Dissecting the Genetic Basis of Variation in Drosophila Sleep Using a Multiparental QTL Mapping Resource

“…We generated estimates of broad-sense heritability for sleep phenotypes in the DSPRF1 by estimating variance components from a linear mixed model using the nlme R package [36], nesting genotype within subpopulation (see also [37]). Heritability for all traits in our mapping population is substantial: light-phase sleep time (51.4%), dark-phase sleep time (53.5%), light waking activity (46.3%), dark waking activity (36.0%), light bout number (47.5%), dark bout number (38.2%), light bout length (25.0%), and dark bout length (37.1%).…”

The developmental and genetic architecture of the sexually selected male ornament of swordtails

“…The evolutionary mechanism driving their origin, maintenance and role in speciation have been widely studied, but today little is known about the proximate causes, i.e. the genes encoding sexually selected traits and their function in development of the structure, aside a few examples from Drosophila [43,44]. The sword is a male specific outgrowth of the lower margin of the caudal fin and we wanted to know what genes provoke its sex-specific elongation.…”