Whole genome sequences of 23 species from the Drosophila montium species group (Diptera: Drosophilidae): A resource for testing evolutionary hypotheses

Abstract

Large groups of species with well-defined phylogenies are excellent systems for testing evolutionary hypotheses. In this paper, we describe the creation of a comparative genomic resource consisting of 23 genomes from the species-rich Drosophila montium species group, 22 of which are presented here for the first time. The montium group is uniquely positioned for comparative studies. Within the montium clade, evolutionary distances are such that large numbers of sequences can be accurately aligned while also recovering strong signals of divergence; and the distance between the montium group and D. melanogaster is short enough so that orthologous sequence can be readily identified. All genomes were assembled from a single, small-insert library using MaSuRCA, before going through an extensive post-assembly pipeline. Estimated genome sizes within the montium group range from 155 Mb to 223 Mb (mean=196 Mb). The absence of long-distance information during the assembly process resulted in fragmented assemblies, with the scaffold NG50s varying widely based on repeat content and sample heterozygosity (min=18 kb, max=390 kb, mean=74 kb). The total scaffold length for most assemblies is also shorter than the estimated genome size, typically by 5 -15 %. However, subsequent analysis showed that our assemblies are highly complete. Despite large differences in contiguity, all assemblies contain at least 96 % of known single-copy Dipteran genes (BUSCOs, n=2,799). Similarly, by aligning our assemblies to the D. melanogaster genome and remapping coordinates for a large set of transcriptional enhancers (n=3,457), we showed that each montium assembly contains orthologs for at least 91 % of D. melanogaster enhancers. Importantly, the genic and enhancer contents of our assemblies are comparable to that of far more contiguous Drosophila assemblies. The alignment of our own D. serrata assembly to a previously published PacBio D. serrata assembly also showed that our longest scaffolds (up to 1 Mb) are free of large-scale misassemblies. Our genome assemblies are a valuable resource that can be used to further resolve the montium group phylogeny; study the evolution of protein-coding genes and cis -regulatory sequences; and determine the genetic basis of ecological and behavioral adaptations.

Evolutionary diversification reveals distinct somatic versus germline cytoskeletal functions of the Arp2 branched actin nucleator protein

“…We queried the Arp2D2 locus by PCR in 18 additional montium species, whose genomes were unsequenced. Together with recently published montium genomes 26 , we concluded that Arp2D2 is present in a shared syntenic location in 27 montium species with no exceptions (Figure 1B, Figure S1A, Data S1-3). Based on this, we conclude that Arp2D2 arose in the common ancestor of the montium group at least 15 million years ago 27 (Figure S1A).…”

Putative condition-dependent viability selection in wild type stocks ofDrosophila pseudoobscura

“…For example, cactophilic (Markow, 2019) and mushroom feeding (Scott Chialvo et al, 2019) Drosophila represent recent adaptive radiations with growing potential for ecological genomics. Additionally, the montium species group has recently become genome-enabled and is well suited for testing various evolutionary hypotheses (Bronski et al, 2020).…”

cifB-transcript levels largely explain cytoplasmic incompatibility variation across divergentWolbachia

“…Coding sequences for these genes in D. melanogaster and D. simulans were obtained from FlyBase. Orthologs in D. teissieri ( 65 ), D. auraria and D. triauraria ( 66 ), D. baimaii, D. bocki , and D. tsacasi ( 67 ), and D. anomalata ( 38 ) were obtained with BLAST using the D. melanogaster sequences. The resulting sequences were aligned with MAFFT v. 7 ( 62 ) and hand curated to remove fragments of introns that could cause frameshifts.…”