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1. The seminal odorant binding protein Obp56g is required for mating plug formation and male fertility in Drosophila melanogaster

   https://doi.org/10.7554/eLife.86409  

   Brown, Nora C; Gordon, Benjamin; McDonough-Goldstein, Caitlin E; Misra, Snigdha; Findlay, Geoffrey D; Clark, Andrew G; Wolfner, Mariana Federica (December 2023, eLife)

   In Drosophila melanogaster and other insects, the seminal fluid proteins (SFPs) and male sex pheromones that enter the female with sperm during mating are essential for fertility and induce profound post-mating effects on female physiology. The SFPs in D. melanogaster and other taxa include several members of the large gene family known as odorant binding proteins (Obps). Work in Drosophila has shown that some Obp genes are highly expressed in the antennae and can mediate behavioral responses to odorants, potentially by binding and carrying these molecules to odorant receptors. These observations have led to the hypothesis that the seminal Obps might act as molecular carriers for pheromones or other compounds important for male fertility, though functional evidence in any species is lacking. Here, we used functional genetics to test the role of the seven seminal Obps in D. melanogaster fertility and the post-mating response (PMR). We found that Obp56g is required for male fertility and the induction of the PMR, whereas the other six genes are dispensable. We found males lacking Obp56g fail to form a mating plug in the mated female’s reproductive tract, leading to ejaculate loss and reduced sperm storage, likely due to its expression in the male ejaculatory bulb. We also examined the evolutionary history of these seminal Obp genes, as several studies have documented rapid evolution and turnover of SFP genes across taxa. We found extensive lability in gene copy number and evidence of positive selection acting on two genes, Obp22a and Obp51a. Comparative RNAseq data from the male reproductive tract of multipleDrosophilaspecies revealed that Obp56g shows high male reproductive tract expression in a subset of taxa, though conserved head expression across the phylogeny. Together, these functional and expression data suggest that Obp56g may have been co-opted for a reproductive function over evolutionary time. 

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2. Gene age shapes functional and evolutionary properties of the Drosophila seminal fluid proteome

   https://doi.org/10.1073/pnas.2505490122  

   Ranz, Jose M; Flacchi, Carolina; Hariyani, Imtiyaz E; Civetta, Alberto (October 2025, Proceedings of the National Academy of Sciences)

   Seminal fluid proteins (Sfps) are crucial for animal reproductive success, with Sfp-encoding genes believed to be evolutionarily young due to heightened rates of gene loss and gain and rapidly evolving at the sequence level relative to other genes. Using estimates of the phylogenetic origin of eachDrosophila melanogasterSfp gene, based on genomic resources that include outgroup species to theDrosophilagenus, we examined the functional attributes and evolutionary characteristics of 357 Sfp genes relative to their evolutionary age. Contrary to the perception that many Sfp genes are evolutionarily young, 62% existed in the genome of the ancestor to this genus. These ancient genes have broader expression profiles, more expansive biological roles, and have more interactions with non-Sfp genes. This increased pleiotropy has imposed constraints on the rate of sequence evolution in ancient Sfp genes compared to younger ones. Notably, these younger Sfp genes evolve substantially faster as a result of both adaptive and nonadaptive evolutionary forces. Within the Sfp interactome, we identified a fast-evolving core subnetwork of younger genes with more restricted tissue expression and functions. Our systematic approach has uncovered a large set of ancient Sfp genes with distinct genomic, functional, and evolutionary characteristics compared to the younger, more commonly studied Sfp genes. With increased refined genomic and functional data acquisition across a wider variety of taxa, our approach and results serve as proof of the importance of systemic strategies applied to broadly defined gene sets based on their time of evolutionary origination. 

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3. Sperm length and seminal fluid proteins promote male reproductive success in Drosophila melanogaster

   https://doi.org/10.1093/jeb/voaf065  

   Galvin, Jake; Yedigarian, Sevan; Rahman, Mohammad; Borziak, Kirill; DeNieu, Michael; Larson, Erica L; Manier, Mollie K (April 2025, Journal of Evolutionary Biology)

   Bilde, Trine; Rowe, Melissah (Ed.)

   Abstract Spermatozoal morphology varies widely within and among species, often corresponding to the shape of the female sperm storage organs in ways that can impact fertilization. To understand genetic mechanisms of sperm length variation, we compared gene expression patterns in the testes of Drosophila melanogaster males that produce either long or short sperm. We found that genes upregulated in long sperm testes are enriched for long noncoding RNAs and seminal fluid proteins (Sfps). Transferred to the female during mating, Sfps are secreted by the male accessory glands and affect female remating rate, physiology, and behavior. While sperm and Sfps are both critical for male reproductive success, they are largely considered to be functionally and genetically independent, and Sfps have no known function in testes. Knockouts of two Sfps upregulated in long sperm males, Sex Peptide and ovulin, resulted in shorter sperm, suggesting Sfps may contribute to sperm length development. Consistent with this, knockout of accessory gland function did not affect sperm length, indicating accessory gland expression had no influence on spermatogenesis. We also found that long sperm males were better able to delay female remating, suggesting a dual advantage in sperm competition by both delaying female remating and resisting sperm displacement. However, we found that the delay in female remating does not necessarily increase progeny or paternity success. Thus, multiple components of the ejaculate promote male reproductive success at different stages of reproduction, but the realized fitness advantages in sperm competition are uncertain. 

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4. Still Enigmatic: Innate Immunity in the Ctenophore Mnemiopsis leidyi

   https://doi.org/10.1093/icb/icz116  

   Traylor-Knowles, Nikki; Vandepas, Lauren E; Browne, William E (August 2019, Integrative and Comparative Biology)

   Abstract Innate immunity is an ancient physiological response critical for protecting metazoans from invading pathogens. It is the primary pathogen defense mechanism among invertebrates. While innate immunity has been studied extensively in diverse invertebrate taxa, including mollusks, crustaceans, and cnidarians, this system has not been well characterized in ctenophores. The ctenophores comprise an exclusively marine, non-bilaterian lineage that diverged early during metazoan diversification. The phylogenetic position of ctenophore lineage suggests that characterization of the ctenophore innate immune system will reveal important features associated with the early evolution of the metazoan innate immune system. Here, we review current understanding of the ctenophore immune repertoire and identify innate immunity genes recovered from three ctenophore species. We also isolate and characterize Mnemiopsis leidyi cells that display macrophage-like behavior when challenged with bacteria. Our results indicate that ctenophores possess cells capable of phagocytosing microbes and that two distantly related ctenophores, M. leidyi and Hormiphora californiensis, possess many candidate innate immunity proteins. 

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5. Strong postmating reproductive isolation in Mimulus section Eunanus

   https://doi.org/10.1111/jeb.14219  

   Farnitano, Matthew C; Sweigart, Andrea L (October 2023, Journal of Evolutionary Biology)

   Abstract Postmating reproductive isolation can help maintain species boundaries when premating barriers to reproduction are incomplete. The strength and identity of postmating reproductive barriers are highly variable among diverging species, leading to questions about their genetic basis and evolutionary drivers. These questions have been tackled in model systems but are less often addressed with broader phylogenetic resolution. In this study we analyse patterns of genetic divergence alongside direct measures of postmating reproductive barriers in an overlooked group of sympatric species within the model monkeyflower genus, Mimulus. Within this Mimulus brevipes species group, we find substantial divergence among species, including a cryptic genetic lineage. However, rampant gene discordance and ancient signals of introgression suggest a complex history of divergence. In addition, we find multiple strong postmating barriers, including postmating prezygotic isolation, hybrid seed inviability and hybrid male sterility. M. brevipes and M. fremontii have substantial but incomplete postmating isolation. For all other tested species pairs, we find essentially complete postmating isolation. Hybrid seed inviability appears linked to differences in seed size, providing a window into possible developmental mechanisms underlying this reproductive barrier. While geographic proximity and incomplete mating isolation may have allowed gene flow within this group in the distant past, strong postmating reproductive barriers today have likely played a key role in preventing ongoing introgression. By producing foundational information about reproductive isolation and genomic divergence in this understudied group, we add new diversity and phylogenetic resolution to our understanding of the mechanisms of plant speciation. Abstract Hybrid seed inviability and other postmating reproductive barriers isolate species in Mimulus section Eunanus. Variation in seed size may help explain hybrid seed failure. Whole-genome sequencing indicates a complex history of divergence, including signals of ancient introgression and cryptic diversity. 

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