Genetic Architecture of Abdominal Pigmentation in Drosophila melanogaster

Abstract

Pigmentation varies within and between species and is often adaptive. The amount of pigmentation on the abdomen of Drosophila melanogaster is a relatively simple morphological trait, which serves as a model for mapping the genetic basis of variation in complex phenotypes. Here, we assessed natural variation in female abdominal pigmentation in 175 sequenced inbred lines of the Drosophila melanogaster Genetic Reference Panel, derived from the Raleigh, NC population. We quantified the proportion of melanization on the two most posterior abdominal segments, tergites 5 and 6 (T5, T6). We found significant genetic variation in the proportion of melanization and high broad-sense heritabilities for each tergite. Genome-wide association studies identified over 150 DNA variants associated with the proportion of melanization on T5 (84), T6 (34), and the difference between T5 and T6 (35). Several of the top variants associated with variation in pigmentation are in tan, ebony, and bric-a-brac1, genes known to affect D. melanogaster abdominal pigmentation. Mutational analyses and targeted RNAi-knockdown showed that 17 out of 28 (61%) novel candidate genes implicated by the genome-wide association study affected abdominal pigmentation. Several of these genes are involved in developmental and regulatory pathways, chitin production, cuticle structure, and vesicle formation and transport. These findings show that genetic variation may affect multiple steps in pathways involved in tergite development and melanization. Variation in these novel candidates may serve as targets for adaptive evolution and sexual selection in D. melanogaster.

Pigmentation and fitness trade-offs through the lens of artificial selection

“…Selection for both increased and decreased pigmentation in replicate populations was associated with a decrease in longevity and increase in age-specific mortality rates relative to the paired unselected, control populations that were maintained on a similar demographic culture regime. The off-selection experiment demonstrated that 100 generations of artificial selection was sufficient to effectively fix phenotypes at their respective extremes, presumably owing to the fixation or near fixation of various alleles associated with dark and light pigmentation phenotype [20,21]. The correlated phenotypic responses are not simply the product of reduction in genetic diversity or increased inbreeding in the selected populations, as the control populations were simultaneously cultured with the same reduction in population size across generations.…”

Genetic basis of natural variation in body pigmentation inDrosophila melanogaster

“…Dembeck et al 26 assessed natural variation in female abdominal pigmentation in 175 sequenced inbred lines of the D. melanogaster Genetic Reference Panel (DGRP), derived from the Raleigh, NC population. The two most posterior abdominal segments, tergites 5 and 6 (T5, T6), were scored for the approximate percentage of the tergite colored with black or dark brown melanin.…”

“…2 The genome-wide association (GWA) studies identified 155 DNA variants in or near ( § 1 kb) 84 genes associated with the proportion of melanization on T5 (84), T6 (34), and the difference between T5 and T6 (35). 26 Several of the top variants associated with variation in pigmentation were in tan (t), ebony (e), and brica-brac1 (bab1). Mutational analyses and targeted RNAi-knockdown showed that 17 out of 28 (61%) novel candidate genes implicated by the genome-wide association study affected abdominal pigmentation.…”

“…Two methods are often used to provide additional support for the GWA results, functional testing such as RNAi or mutant analysis or replication in other populations. Dembeck et al 26 assessed changes in pigmentation using RNAi knockdown and mutant alleles of selected candidate genes. This approach is limited by the availability of these resources.…”

“…These data provide additional evidence supporting the results of the DGRP GWA analysis and previous functional validation experiments. 26 Methodology Drosophila stocks and phenotyping From the 175 DGRP lines scored by Dembeck et al 26 we selected 3 lightly and 3 darkly melanized lines that were scored on a scale from 0 (no dark melanin) to 4 (100% pigmented with dark melanin) for the proportion of dark melanin on T5 and T6. The light lines were DGRP_217 (1.8, 4).…”