A phylogenetic examination of host use evolution in the quinaria and testacea groups of Drosophila

The genome sequence of the drosophilid fruit fly, Drosophila phalerata (Meigen, 1830)

We present a genome assembly from an individual male Drosophila phalerata (drosophilid fruit fly, Arthropoda; Insecta; Diptera; Drosophilidae). The genome sequence is 223.9 megabases in span. Most of the assembly is scaffolded into 7 chromosomal pseudomolecules, including the X and Y sex chromosomes. The mitochondrial genome has also been assembled and is 16.14 kilobases in length. Gene annotation of this assembly on Ensembl identified 18,973 protein coding genes.

Examining the associations between a generalist feeder and a highly toxic host

Understanding the often antagonistic plant-herbivore interactions and how host defenses can influence herbivore dietary breadth is an area of ongoing study in ecology and evolutionary biology. Typically, host plants/fungi that produce highly noxious chemical defenses are only fed on by specialists. We know very little about generalist species that can feed and develop on a noxious host. One such example of generalists feeding on toxic host occurs in the mushroom-feeding Drosophila found in the immigrans-tripunctata radiation. Although these species are classified as generalists, their acceptable hosts include deadly Amanita species. In this study, we used behavioral assays to assess associations between one mushroom-feeding species, Drosophila guttifera, and the deadly Amanita phalloides. We conducted feeding assays to confirm the presence of cyclopeptide toxin tolerance. We then completed host preference assays in female flies and larvae and did not find a preference for toxic mushrooms in either. Finally, we assessed the effect of competition on oviposition preference. We found that the presence of a competitor's eggs on the preferred host was associated with the flies increasing the number of eggs laid on the toxic mushrooms. Our results highlight how access to a low competition host resource may help to maintain associations between a generalist species and a highly toxic host.

Investigating the phylogenetic history of toxin tolerance in mushroom-feeding Drosophila

Understanding how and when key novel adaptations evolved is a central goal of evolutionary biology. Within the immigrans-tripunctata radiation of Drosophila, many mushroom-feeding species are tolerant of host toxins, such as cyclopeptides, that are lethal to nearly all other eukaryotes. In this study, we used phylogenetic and functional approaches to investigate the evolution of cyclopeptide tolerance in the immigrans-tripunctata radiation of Drosophila. First, we inferred the evolutionary relationships among 48 species in this radiation using 978 single copy orthologs. Our results resolved previous incongruities within species groups across the phylogeny. Second, we expanded on previous studies of toxin tolerance by assaying 16 of these species for tolerance to α-amanitin and found that six of them could develop on diet with toxin. Finally, we asked how α-amanitin tolerance might have evolved across the immigrans-tripunctata radiation, and inferred that toxin tolerance was ancestral in mushroom-feeding Drosophila and subsequently lost multiple times. Our findings expand our understanding of toxin tolerance across the immigrans-tripunctata radiation and emphasize the uniqueness of toxin tolerance in this adaptive radiation and the complexity of biochemical adaptations.

Investigating the phylogenetic history of toxin tolerance in mushroom-feeding Drosophila

Understanding how and when key novel adaptations evolved is a central goal of evolutionary biology. Within the immigrans-tripunctata radiation of Drosophila , many mushroom-feeding species are tolerant of host toxins, such as cyclopeptides, that are lethal to nearly all other eukaryotes. In this study, we used phylogenetic and functional approaches to investigate the evolution of cyclopeptide tolerance in the immigrans-tripunctata radiation of Drosophila . We first inferred the evolutionary relationships among 48 species in this radiation using 978 single copy orthologs. Our results resolved previous incongruities within species groups across the phylogeny. Second, we expanded on previous studies of toxin tolerance by assaying 16 of these species for tolerance to α-amanitin and found that six of these species could develop on diet with toxin. Third, we examined fly development on a diet containing a natural mix of toxins extracted from the Death Cap Amanita phalloides mushroom. Both tolerant and susceptible species developed on diet with this mix, though tolerant species survived at significantly higher concentrations. Finally, we asked how cyclopeptide tolerance might have evolved across the immigrans-tripunctata radiation and inferred that toxin tolerance was ancestral and subsequently lost multiple times. Our results suggest the evolutionary history of cyclopeptide tolerance is complex, and simply describing this trait as present or absent does not fully capture the occurrence or impact on this adaptive radiation. More broadly, the evolution of novelty can be more complex than previously thought, and that accurate descriptions of such novelties are critical in studies examining their evolution.

Ecology-relevant bacteria drive the evolution of host antimicrobial peptides in Drosophila

Antimicrobial peptides are host-encoded immune effectors that combat pathogens and shape the microbiome in plants and animals. However, little is known about how the host antimicrobial peptide repertoire is adapted to its microbiome. Here, we characterized the function and evolution of the Diptericin antimicrobial peptide family of Diptera. Using mutations affecting the two Diptericins (Dpt) of Drosophila melanogaster, we reveal the specific role of DptA for the pathogen Providencia rettgeri and DptB for the gut mutualist Acetobacter. The presence of DptA- or DptB-like genes across Diptera correlates with the presence of Providencia and Acetobacter in their environment. Moreover, DptA- and DptB-like sequences predict host resistance against infection by these bacteria across the genus Drosophila. Our study explains the evolutionary logic behind the bursts of rapid evolution of an antimicrobial peptide family and reveals how the host immune repertoire adapts to changing microbial environments.

Analytical methods for amatoxins: A comprehensive review

Amatoxins are toxic bicyclic octapeptides found in certain wild mushroom species, particularly Amanita phalloides. These mushrooms contain predominantly α- and β-amanitin, which can lead to severe health risks for humans and animals if ingested. Rapid and accurate identification of these toxins in mushroom and biological samples is crucial for diagnosing and treating mushroom poisoning. Analytical methods for the determination of amatoxins are critical to ensure food safety and prompt medical treatment. This review provides a comprehensive overview of the research literature on the determination of amatoxins in clinical specimens, biological and mushroom samples. We discuss the physicochemical properties of toxins, highlighting their influence on the choice of the analytical method and the importance of sample preparation, particularly solid-phase extraction with cartridges. Chromatographic methods are emphasised with a focus on liquid chromatography coupled to mass spectrometry as one of the most relevant analytical method for the determination of amatoxins in complex matrices. Furthermore, current trends and future perspectives in amatoxin detection are also suggested.

The regulation of a pigmentation gene in the formation of complex color patterns in Drosophila abdomens

Changes in the control of developmental gene expression patterns have been implicated in the evolution of animal morphology. However, the genetic mechanisms underlying complex morphological traits remain largely unknown. Here we investigated the molecular mechanisms that induce the pigmentation gene yellow in a complex color pattern on the abdomen of Drosophila guttifera. We show that at least five developmental genes may collectively activate one cis-regulatory module of yellow in distinct spot rows and a dark shade to assemble the complete abdominal pigment pattern of Drosophila guttifera. One of these genes, wingless, may play a conserved role in the early phase of spot pattern development in several species of the quinaria group. Our findings shed light on the evolution of complex animal color patterns through modular changes of gene expression patterns.

Phylogenetic resolution of the fly superfamily Ephydroidea-Molecular systematics of the enigmatic and diverse relatives of Drosophilidae

The schizophoran superfamily Ephydroidea (Diptera: Cyclorrhapha) includes eight families, ranging from the well-known vinegar flies (Drosophilidae) and shore flies (Ephydridae), to several small, relatively unusual groups, the phylogenetic placement of which has been particularly challenging for systematists. An extraordinary diversity in life histories, feeding habits and morphology are a hallmark of fly biology, and the Ephydroidea are no exception. Extreme specialization can lead to "orphaned" taxa with no clear evidence for their phylogenetic position. To resolve relationships among a diverse sample of Ephydroidea, including the highly modified flies in the families Braulidae and Mormotomyiidae, we conducted phylogenomic sampling. Using exon capture from Anchored Hybrid Enrichment and transcriptomics to obtain 320 orthologous nuclear genes sampled for 32 species of Ephydroidea and 11 outgroups, we evaluate a new phylogenetic hypothesis for representatives of the superfamily. These data strongly support monophyly of Ephydroidea with Ephydridae as an early branching radiation and the placement of Mormotomyiidae as a family-level lineage sister to all remaining families. We confirm placement of Cryptochetidae as sister taxon to a large clade containing both Drosophilidae and Braulidae-the latter a family of honeybee ectoparasites. Our results reaffirm that sampling of both taxa and characters is critical in hyperdiverse clades and that these factors have a major influence on phylogenomic reconstruction of the history of the schizophoran fly radiation.

Inter- and intraspecific variation in mycotoxin tolerance: A study of four Drosophila species

Many mycophagous Drosophila species have adapted to tolerate high concentrations of mycotoxins, an ability not reported in any other eukaryotes. Although an association between mycophagy and mycotoxin tolerance has been established in many Drosophila species, the genetic mechanisms of the tolerance are unknown. This study presents the inter‐ and intraspecific variation in the mycotoxin tolerance trait. We studied the mycotoxin tolerance in four Drosophila species from four separate clades within the immigrans‐tripunctata radiation from two distinct locations. The effect of mycotoxin treatment on 20 isofemale lines per species was studied using seven gross phenotypes: survival to pupation, survival to eclosion, development time to pupation and eclosion, thorax length, fecundity, and longevity. We observed interspecific variation among four species, with D. falleni being the most tolerant, followed by D. recens, D. neotestacea, and D. tripunctata, in that order. The results also revealed geographical variation and intraspecific genetic variation in mycotoxin tolerance. This report provides the foundation for further delineating the genetic mechanisms of the mycotoxin tolerance trait.

Putative Condition-Dependent Viability Selection in Wild-Type Stocks of <b><i>Drosophila pseudoobscura</i></b>

Meiotic recombination rates vary in response to intrinsic and extrinsic factors. Recently, heat stress has been shown to reveal plasticity in recombination rates in <i>Drosophila pseudoobscura.</i> Here, a combination of molecular genotyping and X-linked recessive phenotypic markers were used to investigate differences in recombination rates due to heat stress. In addition, haplotypes from the genetic crosses were compared to test if they deviated from equal proportions, which would indicate viability selection. To avoid this potential bias, SNP genotyping markers overlapping the regions assayed with mutant markers were used to further investigate recombination rate. Interestingly, skews in haplotype frequency were consistent with the fixation of alleles in the wild-type stocks used that are unfit at high temperature. Evidence of viability selection due to heat stress in the wild-type haplotypes was most apparent on days 7–9 when more mutant non-crossover haplotypes were recovered in comparison to wild type (<i>p</i> &#x3c; 0.0001). Recombination analysis using SNP markers showed days 9–10 as significantly different due to heat stress in 2 pairs of consecutive SNP markers (<i>p</i> = 0.018; <i>p</i> = 0.015), suggesting that during this time period the recombination rate is most sensitive to heat stress. This peak timing for recombination plasticity is consistent with <i>Drosophila melanogaster</i> based on a comparison of similarly timed key meiotic events, enabling future mechanistic work of temperature stress on recombination rate.

From Aedes to Zeugodacus: a review of dipteran body coloration studies regarding evolutionary developmental biology, pest control, and species discovery

Over the past two decades, evo-devo (evolution of development) studies have elucidated genetic mechanisms underlying novel dipteran body color patterns. Here we review the most recent developments, which show some departure from the model organism Drosophila melanogaster, leading the field into the investigation of more complex color patterns. We also discuss how the robust application of transgenic techniques has facilitated the study of many non-model pest species. Furthermore, we see that subtle pigmentation differences guide the discovery and description of new dipterans. Therefore, we argue that the existence of new field guides and the prevalence of pigmentation studies in non-model flies will enable scientists to adopt uninvestigated species into the lab, allowing them to study novel morphologies.

Phylogeny and evolution of mycophagy in the Zygothrica genus group (Diptera: Drosophilidae)

Despite numerous phylogenetic studies on the family Drosophilidae, relationships among some important lineages are still poorly resolved. An example is the equivocal position of the Zygothrica genus group that is mostly comprised of the mycophagous genera Hirtodrosophila, Mycodrosophila, Paramycodrosophila, and Zygothrica. To fill this gap, we conducted a phylogenetic analysis by assembling a dataset of 24 genes from 92 species, including 42 species of the Zygothrica genus group mainly from the Palearctic and Oriental regions. The resulting tree shows that the Zygothrica genus group is monophyletic and places it as the sister to the genus Dichaetophora, and the clade Zygothrica genus group + Dichaetophora is sister to the Siphlodora + Idiomyia/Scaptomyza clade. Within the Zygothrica genus group, the genera Mycodrosophila and Paramycodrosophila are both recognized as monophyletic, while neither the genus Zygothrica nor Hirtodrosophila is monophyletic. We also used this phylogenetic tree to investigate the evolution of mycophagy by reconstructing ancestral food habit in the Drosophilidae. We found that fungus-feeding habit has been gained independently in two lineages. The most recent common ancestor (MRCA) of the subgenus Drosophila was estimated to have acquired mycophagy by expanding its ancestral feeding niche on fermenting fruits to decayed fungi, while the MRCA of the Zygothrica genus group shifted its niche from fruits to fungi as a specialist probably preferring fresh fruiting bodies.

The modular expression patterns of three pigmentation genes prefigure unique abdominal morphologies seen among three Drosophila species

To understand how novel animal body colorations emerged, one needs to ask how the development of color patterns differs among closely related species. Here we examine three species of fruit flies - Drosophila guttifera (D. guttifera), D. palustris, and D. subpalustris - displaying a varying number of abdominal spot rows. Through in situ hybridization experiments, we examine the mRNA expression patterns for the pigmentation genes Dopa decarboxylase (Ddc), tan (t), and yellow (y) during pupal development. Our results show that Ddc, t, and y are co-expressed in modular, identical patterns, each foreshadowing the adult abdominal spots in D. guttifera, D. palustris, and D. subpalustris. We suggest that differences in the expression patterns of these three genes partially underlie the morphological diversity of the quinaria species group.

Transcriptome analysis reveals wingless regulates neural development and signaling genes in the region of wing pigmentation of a polka-dotted fruit fly

How evolutionary novelties have arisen is one of the central questions in evolutionary biology. Preexisting gene regulatory networks or signaling pathways have been shown to be co-opted for building novel traits in several organisms. However, the structure of entire gene regulatory networks and evolutionary events of gene co-option for emergence of a novel trait are poorly understood. In this study, to explore the genetic and molecular bases of the novel wing pigmentation pattern of a polka-dotted fruit fly (Drosophila guttifera), we performed de novo genome sequencing and transcriptome analyses. As a result, we comprehensively identified the genes associated with the pigmentation pattern. Furthermore, we revealed that 151 of these associated genes were positively or negatively regulated by wingless, a master regulator of wing pigmentation. Genes for neural development, Wnt signaling, Dpp signaling, and effectors (such as enzymes) for melanin pigmentation were included among these 151 genes. None of the known regulatory genes that regulate pigmentation pattern formation in other fruit fly species were included. Our results suggest that the novel pigmentation pattern of a polka-dotted fruit fly might have emerged through multistep co-options of multiple gene regulatory networks, signaling pathways, and effector genes, rather than recruitment of one large gene circuit.

Evolution of wing pigmentation in Drosophila: Diversity, physiological regulation, and cis-regulatory evolution

Fruit flies (Drosophila and its close relatives, or “drosophilids”) are a group that includes an important model organism, Drosophila melanogaster, and also very diverse species distributed worldwide. Many of these species have black or brown pigmentation patterns on their wings, and have been used as material for evo‐devo research. Pigmentation patterns are thought to have evolved rapidly compared with body plans or body shapes; hence they are advantageous model systems for studying evolutionary gains of traits and parallel evolution. Various groups of drosophilids, including genus Idiomyia (Hawaiian Drosophila), have a variety of pigmentations, ranging from simple black pigmentations around crossveins to a single antero‐distal spot and a more complex mottled pattern. Pigmentation patterns are sometimes obviously used for sexual displays; however, in some cases they may have other functions. The process of wing formation in Drosophila, the general mechanism of pigmentation formation, and the transport of substances necessary for pigmentation, including melanin precursors, through wing veins are summarized here. Lastly, the evolution of the expression of genes regulating pigmentation patterns, the role of cis‐regulatory regions, and the conditions required for the evolutionary emergence of pigmentation patterns are discussed. Future prospects for research on the evolution of wing pigmentation pattern formation in drosophilids are presented, particularly from the point of view of how they compare with other studies of the evolution of new traits.

Evolutionary genomics of host plant adaptation: insights from Drosophila

Variation in gene expression in response to the use of alternate host plants can reveal genetic and physiological mechanisms explaining why insect-host relationships vary from host specialism to generalism. Interpreting transcriptome variation relies on well-annotated genomes, making drosophilids valuable model systems, particularly those species with tractable ecological associations. Patterns of whole genome expression and alternate gene splicing in response to growth on different hosts have revealed expression of gene networks of known detoxification genes as well as novel functionally enriched genes of diverse metabolic and structural functions. Integrating trancriptomic responses with fitness differences and levels of phenotypic plasticity in response to alternate hosts will help to reveal the general nature of genotype-phenotype relationships.

Dynamic Evolution of Antimicrobial Peptides Underscores Trade-Offs Between Immunity and Ecological Fitness

There is a developing interest in how immune genes may function in other physiological roles, and how traditionally non-immune peptides may, in fact, be active in immune contexts. In the absence of infection, the induction of the immune response is costly, and there are well-characterized trade-offs between immune defense and fitness. The agents behind these fitness costs are less understood. Here we implicate antimicrobial peptides (AMPs) as particularly costly effectors of immunity using an evolutionary framework. We describe the independent loss of AMPs in multiple lineages of Diptera (true flies), tying these observations back to life history. We then focus on the intriguing case of the glycine-rich AMP, Diptericin, and find several instances of loss, pseudogenization, and segregating null alleles. We suggest that Diptericin may be a particularly toxic component of the Dipteran immune response lost in flies either with reduced pathogen pressure or other environmental factors. As Diptericins have recently been described to have neurological roles, these findings parallel a developing interest in AMPs as potentially harmful neuropeptides, and AMPs in other roles beyond immunity.

Ongoing hybridization obscures phylogenetic relationships in the Drosophila subquinaria species complex

Inferring evolutionary relationships among recently diverged lineages is necessary to understand how isolating barriers produce independent lineages. Here, we investigate the phylogenetic relationships between three incompletely isolated and closely related mushroom-feeding Drosophila species. These species form the Drosophila subquinaria species complex and consist of one Eurasian species (D. transversa) and two widespread North American species (D. subquinaria and D. recens) that are sympatric in central Canada. Although patterns of pre- and post-mating isolation among these species are well characterized, previous work on their phylogenetic relationships is limited and conflicting. In this study, we generated a multi-locus data set of 29 loci from across the genome sequenced in a population sample from each species, and then, we inferred species relationships and patterns of introgression. We find strong statistical support that D. subquinaria is paraphyletic, showing that samples from the geographic region sympatric with D. recens are most closely related to D. recens, whereas samples from the geographic region allopatric with D. recens are most closely related to D. transversa. We present several lines of evidence that both incomplete lineage sorting and gene flow are causing phylogenetic discordance. We suggest that ongoing gene flow primarily from D. recens into D. subquinaria in the sympatric part of their ranges causes phylogenetic uncertainty in the evolutionary history of these species. Our results highlight how population genetic data can be used to disentangle the sources of phylogenetic discordance among closely related species.