ebonyaffects pigmentation divergence and cuticular hydrocarbons inDrosophila americanaandD. novamexicana

Abstract

16Drosophila pigmentation has been a fruitful model system for understanding the genetic and 17 developmental mechanisms underlying phenotypic evolution. For example, prior work has shown 18 that divergence of the tan gene contributes to pigmentation differences between two members of the 19 virilis group: Drosophila novamexicana, which has a light yellow body color, and D. americana, 20which has a dark brown body color. Quantitative trait locus (QTL) mapping and expression analysis 21 has suggested that divergence of the ebony gene might also contribute to pigmentation differences 22 between these two species. Here, we directly test this hypothesis by using CRISPR/Cas9 genome 23 editing to generate ebony null mutants in D. americana and D. novamexicana and then using 24 reciprocal hemizygosity testing to compare the effects of each species' ebony allele on pigmentation. 25 We find that divergence of ebony does indeed contribute to the pigmentation divergence between 26 species, with effects on both the overall body color as well as a difference in pigmentation along the 27 dorsal abdominal midline. Motivated by recent work in D. melanogaster, we also used the ebony null 28 mutants to test for effects of ebony on cuticular hydrocarbon (CHC) profiles. We found that ebony 29 affects CHC abundance in both species, but does not contribute to qualitative differences in the CHC 30 profiles between these two species. Additional transgenic resources for working with D. americana 31 and D. novamexicana, such as white mutants of both species and yellow mutants in D. novamexicana, 32were generated in the course of this work and are also described. Taken together, this study advances 33 our understanding of loci contributing to phenotypic divergence and illustrates how the latest genome 34 editing tools can be used for functional testing in non-model species. 35 36 ebony affects pigmentation and CHCs 2 This is a provisional file, not the final typeset article

A shift to shorter cuticular hydrocarbons accompanies sexual isolation amongDrosophila americanagroup populations

“…First, the distribution of both "long" versus "short" CHC phenotypes (shown here and in Lamb et al 2020), and allelic variation in CG17821, indicate that the "short" phenotype and the CG17821 (Frentiu and Chenoweth 2010, Rajpurohit et al 2017, but see Gibbs et al 2003, and physiological traits such as desiccation resistance (reviewed Chung and Carroll 2015), that suggest a role for natural selection in shaping CHC composition, but the specific sources(s) of selection can be challenging to pinpoint. In the D. americana group, species habitats are differentiated primarily on the basis of water availability, and species differ in key physiological traits such as desiccation resistance (Davis and Moyle 2019).…”

“…Our candidate list was generated by searching Flybase (Flybase.org) for annotated Drosophila melanogaster genes with protein-coding domains (as identified by InterProt) that have known functions in CHC synthesis (Pardy et al 2018), resulting in an initial list of 34 genes. To this we added the pigmentation genes ebony and tan as they have been shown to alter CHC variation among D. americana group species (Lamb et al 2020, Massey et al 2019. With these 36 genes, we identified orthologs in Drosophila virilis (as annotated in Flybase) and evaluated whether each of these loci had transcript expression in our three species, using previously published whole-body transcriptome data generated from the same three populations using RNA-seq (Davis and Moyle 2020).…”

From simplicity to complexity: The gain or loss of spot rows underlies the morphological diversity of threeDrosophilaspecies

“…Investigating how pigmentation develops in D. melanogaster provided the foundation to understand the same processes in other fruit flies. This knowledge, in turn, has facilitated studies of species divergence (Lamb et al, 2020) and positioned Drosophila pigmentation as a model to study how gene-regulatory networks – the regulatory mechanisms responsible for organismal development (Davidson and Levin, 2005) – evolved (Camino et al, 2015; Gibert et al, 2018; Grover et al, 2018; Ordway et al, 2014; Rebeiz and Williams, 2017; Roeske et al, 2018). The Drosophila pigmentation pathway with the enzymes and reactions necessary to produce black, brown, and yellow coloration seen on the bodies of fruit flies, is shown in Figure 1 (Rebeiz and Williams, 2017; True et al, 2005; Wittkopp et al, 2003).…”