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1. Positive Selection and Horizontal Gene Transfer in the Genome of a Male-Killing Wolbachia

   https://doi.org/10.1093/molbev/msab303  

   Hill, Tom; Unckless, Robert L; Perlmutter, Jessamyn I (January 2022, Molecular Biology and Evolution)

   Rogers, Rebekah (Ed.)

   Abstract Wolbachia are a genus of widespread bacterial endosymbionts in which some strains can hijack or manipulate arthropod host reproduction. Male killing is one such manipulation in which these maternally transmitted bacteria benefit surviving daughters in part by removing competition with the sons for scarce resources. Despite previous findings of interesting genome features of microbial sex ratio distorters, the population genomics of male-killers remain largely uncharacterized. Here, we uncover several unique features of the genome and population genomics of four Arizonan populations of a male-killing Wolbachia strain, wInn, that infects mushroom-feeding Drosophila innubila. We first compared the wInn genome with other closely related Wolbachia genomes of Drosophila hosts in terms of genome content and confirm that the wInn genome is largely similar in overall gene content to the wMel strain infecting D. melanogaster. However, it also contains many unique genes and repetitive genetic elements that indicate lateral gene transfers between wInn and non-Drosophila eukaryotes. We also find that, in line with literature precedent, genes in the Wolbachia prophage and Octomom regions are under positive selection. Of all the genes under positive selection, many also show evidence of recent horizontal transfer among Wolbachia symbiont genomes. These dynamics of selection and horizontal gene transfer across the genomes of several Wolbachia strains and diverse host species may be important underlying factors in Wolbachia’s success as a male-killer of divergent host species. 

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2. Effect of gut microbiota on α‐amanitin tolerance in Drosophila tripunctata

   https://doi.org/10.1002/ece3.6630  

   Griffin, Logan H.; Reed, Laura K. (August 2020, Ecology and Evolution)

   Abstract The bacterial gut microbiota of many animals is known to be important for many physiological functions including detoxification. The selective pressures imposed on insects by exposure to toxins may also be selective pressures on their symbiotic bacteria, who thus may contribute to the mechanism of toxin tolerance for the insect. Amatoxins are a class of cyclopeptide mushroom toxins that primarily act by binding to RNA polymerase II and inhibiting transcription. Several species of mycophagousDrosophilaare tolerant to amatoxins found in mushrooms of the genusAmanita, despite these toxins being lethal to most other known eukaryotes. These species can tolerate amatoxins in natural concentrations to utilize toxic mushrooms as larval hosts, but the mechanism by which these species are tolerant remains unknown. Previous data have shown that a local population ofD. tripunctataexhibits significant genetic variation in toxin tolerance. This study assesses the potential role of the microbiome in α‐amanitin tolerance in six wild‐derived strains ofDrosophila tripunctata. Normal and antibiotic‐treated samples of six strains were reared on diets with and without α‐amanitin, and then scored for survival from the larval stage to adulthood and for development time to pupation. Our results show that a substantial reduction in bacterial load does not influence toxin tolerance in this system, while confirming genotype and toxin‐specific effects on survival are independent of the microbiome composition. Thus, we conclude that this adaptation to exploit toxic mushrooms as a host is likely intrinsic to the fly's genome and not a property of their microbiome. 

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3. An orphan gene is essential for efficient sperm entry into eggs in Drosophila melanogaster

   https://doi.org/10.1093/genetics/iyaf008  

   Guay, Sara_Y; Patel, Prajal_H; Thomalla, Jonathon_M; McDermott, Kerry_L; O’Toole, Jillian_M; Arnold, Sarah_E; Obrycki, Sarah_J; Wolfner, Mariana_F; Findlay, Geoffrey_D; Begun, ed., D. (February 2025, GENETICS)

   Abstract While spermatogenesis has been extensively characterized in the Drosophila melanogaster model system, very little is known about the genes required for fly sperm entry into eggs. We identified a lineage-specific gene, which we named katherine johnson (kj), that is required for efficient fertilization. Males that do not express kj produce and transfer sperm that are stored normally in females, but sperm from these males enter eggs with severely reduced efficiency. Using a tagged transgenic rescue construct, we observed that the KJ protein localizes around the edge of the nucleus at various stages of spermatogenesis but is undetectable in mature sperm. These data suggest that kj exerts an effect on sperm development, the loss of which results in reduced fertilization ability. Interestingly, KJ protein lacks detectable sequence similarity to any other known protein, suggesting that kj could be a lineage-specific orphan gene. While previous bioinformatic analyses indicated that kj was restricted to the melanogaster group of Drosophila, we identified putative orthologs with conserved synteny, male-biased expression, and predicted protein features across the genus, as well as likely instances of gene loss in some lineages. Thus, kj was likely present in the Drosophila common ancestor. It is unclear whether its role in fertility had already evolved at that time or developed later in the lineage leading to D. melanogaster. Our results demonstrate a new aspect of male reproduction that has been shaped by a lineage-specific gene and provide a molecular foothold for further investigating the mechanism of sperm entry into eggs in Drosophila. 

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4. Experimental assessment of 3D-printed traps and chemical attractants for the collection of wild Drosophila melanogaster

   https://doi.org/10.1101/2025.01.28.635319  

   Keene-Snickers, Alexandra H; Dunham, Tillie J; Stenglein, Mark D (January 2025, bioRxiv)

   ABSTRACT Drosophila melanogaster, the common fruit fly, has been instrumental to our understanding of evolution, genetics and disease. There are benefits to studying these flies in the wild, including assessment of their naturally occurring microbiota. To facilitate efforts to catch wildD. melanogaster, we designed two fly traps and evaluated several candidate attractants. The first trap utilized a stable food substrate that can be used to catch live flies to establish new lab colonies. The second trap was designed to be reusable and easy to ship to enable the collection of flies over time from diverse locations. We evaluated several chemical attractants derived from banana and from marula fruit, which is the proposed ancestral food host ofD. melanogaster. We found that wild flies were preferentially attracted to banana-based odorants over marula-derived ones. Overall, these traps and attractants represent an inexpensive and simple option for the collection of wildD. melanogasterand related species for sampling or colony establishment. 

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5. A fast‐evolving X‐linked duplicate of importin‐α2 is overexpressed in sex‐ratio drive in Drosophila neotestacea

   https://doi.org/10.1111/mec.14928  

   Pieper, Kathleen E.; Unckless, Robert L.; Dyer, Kelly A. (December 2018, Molecular Ecology)

   Abstract Selfish genetic elements that manipulate gametogenesis to achieve a transmission advantage are known as meiotic drivers.Sex‐ratioX chromosomes (SR) are meiotic drivers that prevent the maturation of Y‐bearing sperm in male carriers to result in the production of mainly female progeny. The spread of an SR chromosome can affect host genetic diversity and genome evolution, and can even cause host extinction if it reaches sufficiently high prevalence. Meiotic drivers have evolved independently many times, though only in a few cases is the underlying genetic mechanism known. In this study we use a combination of transcriptomics and population genetics to identify widespread expression differences between the standard (ST) andsex‐ratio(SR) X chromosomes of the flyDrosophila neotestacea.We found the X chromosome is enriched for differentially expressed transcripts and that many of these X‐linked differentially expressed transcripts had elevatedK_a/K_svalues between ST and SR, indicative of potential functional differences. We identified a set of candidate transcripts, including a testis‐specific, X‐linked duplicate of the nuclear transport geneimportin‐α2that is overexpressed in SR.We find suggestions of positive selection in the lineage leading to the duplicate and that its molecular evolutionary patterns are consistent with relaxed purifying selection in ST. As these patterns are consistent with involvement in the mechanism of drive in this species, this duplicate is a strong candidate worthy of further functional investigation. Nuclear transport may be a common target for genetic conflict, as the mechanism of the autosomalSegregation Distorterdrive system inD. melanogasterinvolves the same pathway. 

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