Melanogaster Species Group Research Articles

Highly contiguous genome assembly of Drosophila prolongata-a model for evolution of sexual dimorphism and male-specific innovations.

Drosophila prolongata is a member of the melanogaster species group and rhopaloa subgroup native to the subtropical highlands of Southeast Asia. This species exhibits an array of recently evolved male-specific morphological, physiological, and behavioral traits that distinguish it from its closest relatives, making it an attractive model for studying the evolution of sexual dimorphism and testing theories of sexual selection. The lack of genomic resources has impeded the dissection of the molecular basis of sex-specific development and behavior in this species. To address this, we assembled the genome of D. prolongata using long-read sequencing and Hi-C scaffolding, resulting in a highly complete and contiguous (scaffold N50 2.2 Mb) genome assembly of 220 Mb. The repetitive content of the genome is 24.6%, the plurality of which are long terminal repeats retrotransposons (33.2%). Annotations based on RNA-seq data and homology to related species revealed a total of 19,330 genes, of which 16,170 are protein-coding. The assembly includes 98.5% of Diptera BUSCO genes, including 93.8% present as a single copy. Despite some likely regional duplications, the completeness of this genome suggests that it can be readily used for gene expression, genome-wide association studies (GWAS), and other genomic analyses.

The Drosophila melanogaster Y-linked gene, WDY, is required for sperm to swim in the female reproductive tract

Unique patterns of inheritance and selection on Y chromosomes have led to the evolution of specialized gene functions. We report CRISPR mutants in Drosophila of the Y-linked gene, WDY, which is required for male fertility. We demonstrate that the sperm tails of WDY mutants beat approximately half as fast as those of wild-type and that mutant sperm do not propel themselves within the male ejaculatory duct or female reproductive tract. Therefore, although mature sperm are produced by WDY mutant males, and are transferred to females, those sperm fail to enter the female sperm storage organs. We report genotype-dependent and regional differences in sperm motility that appear to break the correlation between sperm tail beating and propulsion. Furthermore, we identify a significant change in hydrophobicity at a residue at a putative calcium-binding site in WDY orthologs at the split between the melanogaster and obscura species groups, when WDY first became Y-linked. This suggests that a major functional change in WDY coincided with its appearance on the Y chromosome. Finally, we show that mutants for another Y-linked gene, PRY, also show a sperm storage defect that may explain their subfertility. Overall, we provide direct evidence for the long-held presumption that protein-coding genes on the Drosophila Y regulate sperm motility.

Long-read-based Genome Assembly of Drosophila gunungcola Reveals Fewer Chemosensory Genes in Flower-breeding Species.

Drosophila gunungcola exhibits reproductive activities on the fresh flowers of several plant species and is an emerging model to study the co-option of morphological and behavioral traits in male courtship display. Here, we report a near-chromosome-level genome assembly that was constructed based on long-read PacBio sequencing data (with ∼66× coverage) and annotated with the assistant from RNA-seq transcriptome data of whole organisms at various developmental stages. A nuclear genome of 189 Mb with 13,950 protein-coding genes and a mitogenome of 17.5 kb were acquired. Few interchromosomal rearrangements were found in the comparisons of synteny with Drosophila elegans, its sister species, and Drosophila melanogaster, suggesting that the gene compositions on each Muller element are evolutionarily conserved. Loss events of several OR and IR genes in D. gunungcola and D. elegans were revealed when orthologous genomic regions were compared across species in the D. melanogaster species group. This high-quality reference genome will facilitate further comparative studies on traits related to the evolution of sexual behavior and diet specialization.

Rapid divergence in independent aspects of the compatibility phenotype in a Spiroplasma-Drosophila interaction.

Heritable symbionts represent important components of the biology, ecology and evolution of their arthropod hosts. Particular microbial taxa have become common across arthropods as a consequence of their ability to establish in new host species. For a host shift to occur, the symbiont must be exposed to a novel host and then be compatible: it must not cause excess pathology, must have good vertical transmission and must possess a drive phenotype that enables spread. Here we investigate the lability of compatibility to symbiosis with Spiroplasma. We used transinfection to establish the protective Spiroplasma symbiont from Drosophila hydei in two closely related novel hosts, Drosophila simulans and Drosophila melanogaster. The Spiroplasma had contrasting compatibility in the two species, exhibiting pathology and low vertical transmission but delivering protection from wasp attack in D. melanogaster but being asymptomatic and transmitted with high efficiency but with lower protection in D. simulans. Further work indicated that pathological interactions occurred in two other members of the melanogaster species group, such that D. simulans was unusual in being able to carry the symbiont without damage. The differing compatibility of the symbiont with these closely related host species emphasizes the rapidity with which host-symbiont compatibility evolves, despite compatibility itself not being subject to direct selection. Further, the requirement to fit three independent components of compatibility (pathology, transmission, protection) is probably to be a major feature limiting the rate of host shifts that will likely impact on the utility of Spiroplasma in pest and vector control. Moving forward, the variation between sibling species pairs provides an opportunity to identify the mechanisms behind variable compatibility, which will drive hypotheses as to the evolutionary drivers of compatibility variation.

Evolution of the odorant-binding protein gene family in Drosophila

Odorant-binding proteins (OBPs) are encoded by a gene family involved in the perception of olfactory signals in insects. This chemosensory gene family has been advocated as a candidate to mediate host preference and host shifts in insects, although it also participates in other physiological processes. Remarkable differences in the OBP gene repertoire have been described across insect groups, suggesting an accelerated gene turnover rate. The genus Drosophila, is a valuable resource for ecological genomics studies since it comprises groups of ecologically diverse species and there are genome data for many of them. Here, we investigate the molecular evolution of this chemosensory gene family across 19 Drosophila genomes, including the melanogaster and repleta species groups, which are mostly associated with rotting fruit and cacti, respectively. We also compared the OBP repertoire among the closely related species of the repleta group, associated with different subfamilies of Cactaceae that represent disparate chemical challenges for the flies. We found that the gene family size varies widely between species, ranging from 39 to 54 candidate OBPs. Indeed, more than 54% of these genes are organized in clusters and located on chromosomes X, 2, and 5, with a distribution conserved throughout the genus. The family sizes in the repleta group and D. virilis (virilis-repleta radiation) were smaller than in the melanogaster group. We tested alternative evolutionary models for OBP family size and turnover rates based on different ecological scenarios. We found heterogeneous gene turnover rates (GR) in comparisons involving columnar cactus specialists, prickly pear specialists, and fruit dwellers lineages, and signals of rapid molecular evolution compatible with positive selection in specific OBP genes. Taking ours and previous results together, we propose that this chemosensory gene family is involved in host adaptation and hypothesize that the adoption of the cactophilic lifestyle in the repleta group accelerated the evolution of members of the family.

Functional Divergence of the bag-of-marbles Gene in the Drosophila melanogaster Species Group.

In Drosophila melanogaster, a key germline stem cell (GSC) differentiation factor, bag of marbles (bam) shows rapid bursts of amino acid fixations between sibling species D. melanogaster and Drosophila simulans, but not in the outgroup species Drosophila ananassae. Here, we test the null hypothesis that bam’s differentiation function is conserved between D. melanogaster and four additional Drosophila species in the melanogaster species group spanning approximately 30 million years of divergence. Surprisingly, we demonstrate that bam is not necessary for oogenesis or spermatogenesis in Drosophila teissieri nor is bam necessary for spermatogenesis in D. ananassae. Remarkably bam function may change on a relatively short time scale. We further report tests of neutral sequence evolution at bam in additional species of Drosophila and find a positive, but not perfect, correlation between evidence for positive selection at bam and its essential role in GSC regulation and fertility for both males and females. Further characterization of bam function in more divergent lineages will be necessary to distinguish between bam’s critical gametogenesis role being newly derived in D. melanogaster, D. simulans, Drosophila yakuba, and D. ananassae females or it being basal to the genus and subsequently lost in numerous lineages.

Characterization of Gfat1 (zeppelin) and Gfat2, Essential Paralogous Genes Which Encode the Enzymes That Catalyze the Rate-Limiting Step in the Hexosamine Biosynthetic Pathway in Drosophila melanogaster.

The zeppelin (zep) locus is known for its essential role in the development of the embryonic cuticle of Drosophila melanogaster. We show here that zep encodes Gfat1 (Glutamine: Fructose-6-Phosphate Aminotransferase 1; CG12449), the enzyme that catalyzes the rate-limiting step in the hexosamine biosynthesis pathway (HBP). This conserved pathway diverts 2%–5% of cellular glucose from glycolysis and is a nexus of sugar (fructose-6-phosphate), amino acid (glutamine), fatty acid [acetyl-coenzymeA (CoA)], and nucleotide/energy (UDP) metabolism. We also describe the isolation and characterization of lethal mutants in the euchromatic paralog, Gfat2 (CG1345), and demonstrate that ubiquitous expression of Gfat1+ or Gfat2+ transgenes can rescue lethal mutations in either gene. Gfat1 and Gfat2 show differences in mRNA and protein expression during embryogenesis and in essential tissue-specific requirements for Gfat1 and Gfat2, suggesting a degree of functional evolutionary divergence. An evolutionary, cytogenetic analysis of the two genes in six Drosophila species revealed Gfat2 to be located within euchromatin in all six species. Gfat1 localizes to heterochromatin in three melanogaster-group species, and to euchromatin in the more distantly related species. We have also found that the pattern of flanking-gene microsynteny is highly conserved for Gfat1 and somewhat less conserved for Gfat2.

Resolving between novelty and homology in the rapidly evolving phallus of Drosophila.

The genitalia present some of the most rapidly evolving anatomical structures in the animal kingdom, possessing a variety of parts that can distinguish recently diverged species. In the Drosophila melanogaster group, the phallus is adorned with several processes, pointed outgrowths, that are similar in size and shape between species. However, the complex three-dimensional nature of the phallus can obscure the exact connection points of each process. Previous descriptions based upon adult morphology have primarily assigned phallic processes by their approximate positions in the phallus and have remained largely agnostic regarding their homology relationships. In the absence of clearly identified homology, it can be challenging to model when each structure first evolved. Here, we employ a comparative developmental analysis of these processes in eight members of the melanogaster species group to precisely identify the tissue from which each process forms. Our results indicate that adult phallic processes arise from three pupal primordia in all species. We found that in some cases the same primordia generate homologous structures whereas in other cases, different primordia produce phenotypically similar but remarkably non-homologous structures. This suggests that the same gene regulatory network may have been redeployed to different primordia to induce phenotypically similar traits. Our results highlight how traits diversify and can be redeployed, even at short evolutionary scales.

Phylogenomic analyses of the genus Drosophila reveals genomic signals of climate adaptation.

Many Drosophila species differ widely in their distributions and climate niches, making them excellent subjects for evolutionary genomic studies. Here, we have developed a database of high‐quality assemblies for 46 Drosophila species and one closely related Zaprionus. Fifteen of the genomes were newly sequenced, and 20 were improved with additional sequencing. New or improved annotations were generated for all 47 species, assisted by new transcriptomes for 19. Phylogenomic analyses of these data resolved several previously ambiguous relationships, especially in the melanogaster species group. However, it also revealed significant phylogenetic incongruence among genes, mainly in the form of incomplete lineage sorting in the subgenus Sophophora but also including asymmetric introgression in the subgenus Drosophila. Using the phylogeny as a framework and taking into account these incongruences, we then screened the data for genome‐wide signals of adaptation to different climatic niches. First, phylostratigraphy revealed relatively high rates of recent novel gene gain in three temperate pseudoobscura and five desert‐adapted cactophilic mulleri subgroup species. Second, we found differing ratios of nonsynonymous to synonymous substitutions in several hundred orthologues between climate generalists and specialists, with trends for significantly higher ratios for those in tropical and lower ratios for those in temperate‐continental specialists respectively than those in the climate generalists. Finally, resequencing natural populations of 13 species revealed tropics‐restricted species generally had smaller population sizes, lower genome diversity and more deleterious mutations than the more widespread species. We conclude that adaptation to different climates in the genus Drosophila has been associated with large‐scale and multifaceted genomic changes.

3D genome evolution and reorganization in the Drosophila melanogaster species group.

Topologically associating domains, or TADs, are functional units that organize chromosomes into 3D structures of interacting chromatin. TADs play an important role in regulating gene expression by constraining enhancer-promoter contacts and there is evidence that deletion of TAD boundaries leads to aberrant expression of neighboring genes. While the mechanisms of TAD formation have been well-studied, current knowledge on the patterns of TAD evolution across species is limited. Due to the integral role TADs play in gene regulation, their structure and organization is expected to be conserved during evolution. However, more recent research suggests that TAD structures diverge relatively rapidly. We use Hi-C chromosome conformation capture to measure evolutionary conservation of whole TADs and TAD boundary elements between D. melanogaster and D. triauraria, two early-branching species from the melanogaster species group which diverged ∼15 million years ago. We find that the majority of TADs have been reorganized since the common ancestor of D. melanogaster and D. triauraria, via a combination of chromosomal rearrangements and gain/loss of TAD boundaries. TAD reorganization between these two species is associated with a localized effect on gene expression, near the site of disruption. By separating TADs into subtypes based on their chromatin state, we find that different subtypes are evolving under different evolutionary forces. TADs enriched for broadly expressed, transcriptionally active genes are evolving rapidly, potentially due to positive selection, whereas TADs enriched for developmentally-regulated genes remain conserved, presumably due to their importance in restricting gene-regulatory element interactions. These results provide novel insight into the evolutionary dynamics of TADs and help to reconcile contradictory reports related to the evolutionary conservation of TADs and whether changes in TAD structure affect gene expression.

Production and evolution pattern of “fruity smell” aggregation pheromones in genus Drosophila

AbstractInsects produce pheromones to serve a range of ecological functions throughout their lifetime. The chemical composition, production pattern, and interspecies specificity provide information for carrying out their function and biological significance. Several species of Drosophila produce a class of volatile esters considered as “fruity smells”; however, the production pattern and ecological functions of these “fruity smell” volatiles in genus Drosophila are poorly understood. Here, using the headspace solid‐phase microextraction (SPME) method, we tested the production pattern of volatile pheromones in Drosophila immigrans and factors that possibly affected pheromone production, including mating, feeding conditions, age of adult flies, and geographical distribution. We also explored the evolution and production pattern of volatile pheromones in 14 species of genus Drosophila. Our result showed that male D. immigrans adult flies produce three male‐specific volatile ester pheromones, which are also considered as “fruity smell” chemicals, in a relatively stable pattern. In addition, a series of “fruity smell” ester pheromones with similar structure and chemical properties were found to appear in the species of D. virilis and D. immigrans species group, but not in the species of D. melanogaster species group. The ester volatile pheromone production of male flies has a correspondence with the female's demand for host plants. Integrating the production and evolution pattern of these volatile chemicals, we inferred the interaction between insects and host plants reflected in the Drosophila “fruity smell” pheromones.

Phylogenetic position of the Drosophila fima and dentissima lineages, and the status of the D. melanogaster species group

The subgenus Sophophora of Drosophila, which includes D. melanogaster, is an important model for the study of molecular evolution, comparative genomics, and evolutionary developmental biology. Numerous phylogenetic studies have examined species relationships in the well-known melanogaster, obscura, willistoni, and saltans species groups, as well as the relationships among these clades. In contrast, other species groups of Sophophora have been relatively neglected and have not been subjected to molecular phylogenetic analysis. Here, we focus on the endemic African Drosophila fima and dentissima lineages. We find that both these clades fall within the broadly defined melanogaster species group, but are otherwise distantly related to each other. The new phylogeny supports pervasive divergent and convergent evolution of male-specific grasping structures (sex combs). We discuss the implications of these results for defining the boundaries of the melanogaster species group, and weigh the relative merits of “splitting” and “lumping” approaches to the taxonomy of this key model system.

Diversification and collapse of a telomere elongation mechanism.

In most eukaryotes, telomerase counteracts chromosome erosion by adding repetitive sequence to terminal ends. Drosophila melanogaster instead relies on specialized retrotransposons that insert exclusively at telomeres. This exchange of goods between host and mobile element—wherein the mobile element provides an essential genome service and the host provides a hospitable niche for mobile element propagation—has been called a “genomic symbiosis.” However, these telomere-specialized, jockey family retrotransposons may actually evolve to “selfishly” overreplicate in the genomes that they ostensibly serve. Under this model, we expect rapid diversification of telomere-specialized retrotransposon lineages and, possibly, the breakdown of this ostensibly symbiotic relationship. Here we report data consistent with both predictions. Searching the raw reads of the 15-Myr-old melanogaster species group, we generated de novo jockey retrotransposon consensus sequences and used phylogenetic tree-building to delineate four distinct telomere-associated lineages. Recurrent gains, losses, and replacements account for this retrotransposon lineage diversity. In Drosophila biarmipes, telomere-specialized elements have disappeared completely. De novo assembly of long reads and cytogenetics confirmed this species-specific collapse of retrotransposon-dependent telomere elongation. Instead, telomere-restricted satellite DNA and DNA transposon fragments occupy its terminal ends. We infer that D. biarmipes relies instead on a recombination-based mechanism conserved from yeast to flies to humans. Telomeric retrotransposon diversification and disappearance suggest that persistently “selfish” machinery shapes telomere elongation across Drosophila rather than completely domesticated, symbiotic mobile elements.

First record of the invasive vinegar fly Drosophila suzukii (Matsumura)(Diptera: Drosophilidae) from eastern Turkey

* Correspondence: bdalgic@hacettepe.edu.tr Invasive vinegar fly Drosophila suzukii, commonly known as spotted-wing drosophila (SWD), is a fruit crop pest endemic to Southeast Asia (Walsh et al., 2011) and was first reported outside of this region in Hawaii in the 1980s (Hauser, 2011). The first records from the North American mainland were made in 2008 from central California, USA (Hauser et al., 2009), and it is now widespread throughout the central and southern states, causing agricultural damage to summer fruits such as cherries, strawberries, and peaches (Hauser, 2011). The first records in Europe of D. suzukii were in Spain and Italy in 2008, simultaneously (Raspi et al., 2011; Calabria et al., 2012; Cini et al., 2012). However, spatial analysis of its distribution across Europe suggested the south of France as the most likely spreading center (Cini et al., 2014). Considering the close proximity of these first records to ports, it is likely that the first individuals may have arrived as eggs or larvae in fruits that had been sea-traded from Asia (Rota-Stabelli et al., 2013). The first report of crop damage in Europe was in northern Italy (Grassi et al., 2009; Calabria et al., 2012). It has also been detected in various localities across Europe (as shown in Figure 1), expanding across an altitudinal range from 27 to 1550 m above sea level; SWD has spread approximately 1400 km through infested fruits (Hauser, 2011; Calabria et al., 2012; Kiss et al., 2013). D. suzukii is taxonomically classified under genus Drosophila and subgenus Sophophora as a member of the melanogaster species group and within the suzukii species subgroup (Yang et al., 2004; Ashburner et al., 2005). In contrast to common drosophilids, which oviposit on damaged or rotting fruits, females of D. suzukii lay eggs under the soft skin of healthy, ripening fruits by using their sharp and serrated ovipositor, which wounds the host physically and leaves it vulnerable to secondary contagion by pathogens (Sasaki and Sato, 1995; Cini et al., 2012). Developing larvae, hatched from eggs, cause the fruit to become soft and rotten, which leads to substantial crop deterioration, thus making D. suzukii an economically damaging pest (Goodhue et al., 2011). Although it is difficult to estimate financial damage caused by a scientifically unknown pest such as D. suzukii, yield losses of 20% and 80% were reported in the United States in 2008 and 2009, respectively (Bolda et al., 2010; Walsh et al., 2011). In Europe, losses of up to 80% occurred in the strawberry crops of southern France in 2010 (Lee et al., 2011). Originally described in insect illustrations from Japan, D. suzukii is a red-eyed drosophilid with a yellowish brown thorax and pale brown abdomen with black transverse stripes. Males are easily recognized by having a distinct apical wing spot and 2 sets of short sex Abstract: Drosophila suzukii (Matsumura, 1931) (Diptera: Drosophilidae) is native to East Asia and invasive on the European and American continents. The first records in both Europe and the United States were in 2008. Since that year, it has widely moved across these continents. As D. suzukii females lay eggs in healthy ripening fruits of several species, particularly in small soft fruits and berries, the species causes agricultural damage. The soft thin-skinned fruit pest, identified as D. suzukii, has been found in Erzurum, Turkey, where damaged strawberry crops were observed and cultured in the middle of August and September 2014. Initially, 2 adults, 3 pupae, and several larvae were observed. Emergence of male and female adults continued for 10 more days. Here we report the first finding of D. suzukii in Turkey.

PHYLOGENETIC RELATIONSHIP OF AN INVASIVE DROSOPHILID, Zaprionus indianus AND CLOSELY RELATED SPECIES OF DROSOPHILIDAE (DIPTERA) BASED ON ESTERASE PATTERNS

Two natural populations of Zaprionus indianus; collected from two different cities in Kafr El-Sheikh governorate, Egypt, were analyzed for esterase variability in comparison with natural population of both of D. melanogaster and D. simulans. Drosophila melanogaster (Oregon-K) was also used as a standard laboratory strain. The electrophoresis results gave an evidence of esterase polymorphisms in the studied populations with 88.89% polymorphism. Phylogenetic analysis based on Jaccard’s similarity coefficient of esterase patterns showed that D. melanogaster and D. simulans populations formed one cluster unit of the melanogaster species group whereas other cluster unit consisted of the two Z. indianus populations.

Visualizing Molecular Functions and Cross-Species Activity of Sex-Peptide in Drosophila.

The Drosophila melanogaster sex-peptide (melSP) is a seminal fluid component that induces postmating responses (PMR) of females via the sex-peptide receptor (SPR) . Although SP orthologs are found in many Drosophila species, their functions remain poorly characterized. It is unknown whether SP functions are conserved across species or rather specific to each species. Here, we developed a GFP-tagged melSP (G-SP) and used it to visualize cross-species binding activity to the female reproductive system of various species. First we demonstrated that ectopically expressed G-SP induced PMR in D. melanogaster females and bound to the female reproductive system, most notably to the common oviduct. No binding occurred in the females lacking SPR, indicating that G-SP binding was dependent on SPR. Next we tested whether G-SP binds to the common oviducts from 11 Drosophila species using dissected reproductive tracts. The binding was observed in six species belonging to the D. melanogaster species group, but not to those outside the group. Injection of melSP reduced the receptivity of females belonging to the D. melanogaster species group, but not of those outside the group, being consistent with the ability to bind G-SP. Thus the SP-mediated PMR appears to be limited to this species group. SPR was expressed in the oviducts at high levels in this group; therefore, we speculate that an enhanced expression of SPR in the oviduct was critical to establish the SP-mediated PMR during evolution.

Strange little flies in the big city: exotic flower-breeding drosophilidae (Diptera) in urban Los Angeles.

Urban landscapes are commonly considered too mundane and corrupted to be biotically interesting. Recent insect surveys employing 29 Malaise traps throughout Los Angeles, California, however, have uncovered breeding populations of two unexpected species of one of the most studied and familiar groups of organisms, Drosophila “fruit” flies. Unlike most introduced species of drosophilids, which breed in fresh or decaying fruits, these are specialized flower-breeders. A common species in the survey was Drosophila (Drosophila) gentica Wheeler and Takada, previously collected only once, in El Salvador. It belongs to the flavopilosa species group, all species of which have been known until now from central Chile, Argentina and Uruguay, to Veracruz, Mexico and the Caribbean, breeding in flowers of Cestrum (“jessamine”) and Sessea (Solanaceae). The Los Angeles populations are probably breeding in a native and/or introduced Cestrum; in addition, populations in San Luis Obispo County were visiting ornamental Cestrum. Drosophila gentica occurs as far north as San Francisco, where it was found breeding in Cestrum aurantiacum. D. gentica is redescribed and figured in detail for diagnostic and identification purposes. Specimens from Jamaica previously identified as D. gentica are a distinct species but are not formally described in lieu of complete male specimens. Rare in the Malaise traps was Drosophila (Sophophora) flavohirta Malloch, a common species in Australia on the blossoms of native Myrtaceae, found on introduced Eucalyptus in South Africa and both Eucalyptus and Syzygium in Madagascar; adults feed on myrtaceous pollen and nectar, larvae breed in the flowers. It is also redescribed in detail, including its unusual egg. This is the first New World report of this species; DNA sequences confirm it is a morphologically highly aberrant member of the D. melanogaster species group. This study reveals how intensive field sampling can uncover remarkable biodiversity in even the most urbanized areas.

Simpler is better: fewer non‐target insects trapped with a four‐component chemical lure vs. a chemically more complex food‐type bait for Drosophila suzukii

AbstractBaits – fermented food products – are generally attractive to many types of insects, which makes it difficult to sort through non‐target insects to monitor a pest species of interest. We test the hypothesis that a chemically simpler and more defined attractant developed for a target insect is more specific and attracts fewer non‐target insects than a chemically more complex food‐type bait. A four‐component chemical lure isolated from a food bait and optimized for the spotted wing drosophila (SWD), Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), was compared to the original wine/vinegar bait to assess the relative responses of non‐target insects. In several field experiments in Washington State, USA, it was shown that numbers of pest muscid flies, cutworm and armyworm moths, and pest yellowjackets were reduced in traps baited with the chemical lure compared to the wine/vinegar bait. In other field experiments in the states of Washington, Oregon, and New York, numbers of non‐target drosophilid flies were also reduced in traps baited with the chemical lure relative to wine/vinegar bait. In Washington, numbers of Drosophila melanogaster Meigen and Drosophila obscura Fallen species groups and Drosophila immigrans Sturtevant were reduced in the chemical lure traps, whereas in New York, D. melanogaster and D. obscura species groups, D. immigrans, Drosophila putrida Sturtevant, Drosophila simulans Sturtevant, Drosophila tripunctata Loew, and Chymomyza spp. numbers were reduced. In Oregon, this same effect was observed with the D. melanogaster species group. Taken together, these results indicate that the four‐component SWD chemical lure will be more selective for SWD compared to fermentation baits, which should reduce time and cost involved in trapping in order to monitor SWD.

Dopamine drives Drosophila sechellia adaptation to its toxic host.

Many insect species are host-obligate specialists. The evolutionary mechanism driving the adaptation of a species to a toxic host is, however, intriguing. We analyzed the tight association of Drosophila sechellia to its sole host, the fruit of Morinda citrifolia, which is toxic to other members of the melanogaster species group. Molecular polymorphisms in the dopamine regulatory protein Catsup cause infertility in D. sechellia due to maternal arrest of oogenesis. In its natural host, the fruit compensates for the impaired maternal dopamine metabolism with the precursor l-DOPA, resuming oogenesis and stimulating egg production. l-DOPA present in morinda additionally increases the size of D. sechellia eggs, what in turn enhances early fitness. We argue that the need of l-DOPA for successful reproduction has driven D. sechellia to become an M. citrifolia obligate specialist. This study illustrates how an insect's dopaminergic system can sustain ecological adaptations by modulating ontogenesis and development.

The genetic architecture of coordinately evolving male wing pigmentation and courtship behavior in Drosophila elegans and Drosophila gunungcola.

Many adaptive phenotypes consist of combinations of simpler traits that act synergistically, such as morphological traits and the behaviors that use those traits. Genetic correlations between components of such combinatorial traits, in the form of pleiotropic or tightly linked genes, can in principle promote the evolution and maintenance of these traits. In the Oriental Drosophila melanogaster species group, male wing pigmentation shows phylogenetic correlations with male courtship behavior; species with male-specific apical wing melanin spots also exhibit male visual wing displays, whereas species lacking these spots generally lack the displays. In this study, we investigated the quantitative genetic basis of divergence in male wing spots and displays between D. elegans, which possesses both traits, and its sibling species D. gunungcola, which lacks them. We found that divergence in wing spot size is determined by at least three quantitative trait loci (QTL) and divergence in courtship score is determined by at least four QTL. On the autosomes, QTL locations for pigmentation and behavior were generally separate, but on the X chromosome two clusters of QTL were found affecting both wing pigmentation and courtship behavior. We also examined the genetic basis of divergence in three components of male courtship, wing display, circling, and body shaking. Each of these showed a distinct genetic architecture, with some QTL mapping to similar positions as QTL for overall courtship score. Pairwise tests for interactions between marker loci revealed evidence of epistasis between putative QTL for wing pigmentation but not those for courtship behavior. The clustering of X-linked QTL for male pigmentation and behavior is consistent with the concerted evolution of these traits and motivates fine-scale mapping studies to elucidate the nature of the contributing genetic factors in these intervals.