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1. Reproductive Proteins Evolve Faster Than Non-reproductive Proteins Among Solanum Species

   https://doi.org/10.3389/fpls.2021.635990  

   Moyle, Leonie C.; Wu, Meng; Gibson, Matthew J. (April 2021, Frontiers in Plant Science)

   null (Ed.)

   Elevated rates of evolution in reproductive proteins are commonly observed in animal species, and are thought to be driven by the action of sexual selection and sexual conflict acting specifically on reproductive traits. Whether similar patterns are broadly observed in other biological groups is equivocal. Here, we examine patterns of protein divergence among wild tomato species ( Solanum section Lycopersicon ), to understand forces shaping the evolution of reproductive genes in this diverse, rapidly evolving plant clade. By comparing rates of molecular evolution among loci expressed in reproductive and non-reproductive tissues, our aims were to test if: (a) reproductive-specific loci evolve more rapidly, on average, than non-reproductive loci; (b) ‘male’-specific loci evolve at different rates than ‘female’-specific loci; (c) genes expressed exclusively in gametophytic (haploid) tissue evolve differently from genes expressed in sporophytic (diploid) tissue or in both tissue types; and (d) mating system variation (a potential proxy for the expected strength of sexual selection and/or sexual conflict) affects patterns of protein evolution. We observed elevated evolutionary rates in reproductive proteins. However, this pattern was most evident for female- rather than male-specific loci, both broadly and for individual loci inferred to be positively selected. These elevated rates might be facilitated by greater tissue-specificity of reproductive proteins, as faster rates were also associated with more narrow expression domains. In contrast, we found little evidence that evolutionary rates are consistently different in loci experiencing haploid selection (gametophytic-exclusive loci), or in lineages with quantitatively different mating systems. Overall while reproductive protein evolution is generally elevated in this diverse plant group, some specific patterns of evolution are more complex than those reported in other (largely animal) systems, and include a more prominent role for female-specific loci among adaptively evolving genes. 

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2. Monoicy, dioicy, and genetic structure in three species of Sheathia (Batrachospermales, Rhodophyta)

   https://doi.org/10.1111/jpy.70032  

   Shainker‐Connelly, Sarah_J; Stoeckel, Solenn; Vis, Morgan_L; Krueger‐Hadfield, Stacy_A (May 2025, Journal of Phycology)

   Abstract Sexual systems (i.e., separate vs. combined sexes) vary widely among eukaryotes and influence the evolution of reproductive systems, which shape genetic structure and evolutionary trajectories. In diploid‐dominant angiosperms, combined (i.e., hermaphroditism) and separate sexes are expected to correlate with selfing and outcrossing, respectively. When sex is determined in the haploid phase, selfing is possible even when there are separate sexes. The freshwater red macroalgal genusSheathia(Batrachospermales) displays sexual system variation within and among populations, but no prior data exist on the reproductive systems of these populations. We developed 16 polymorphic microsatellite loci to characterize the reproductive system and genetic structure of threeSheathiaspecies. We observed cross‐amplification of loci across the three targeted species, suggesting these markers may be useful in otherSheathiaspp. We observed variation in monoicy (i.e., hermaphroditism) versus dioicy (i.e., separate sexes) in each species, includingS. americana, which was previously believed to be obligately dioicous. Our data suggest thatS. americanaandS. involutadisplay more variation in their prevailing reproductive modes as compared toS. grandis. Generally, dioicy resulted in greater diversity in contrast to monoicy. We observed strong population structure that is likely driven by uniparental reproduction and limited dispersal; however, there is limited population connectivity that may be facilitated by long‐distance dispersal events. Overall, these data contribute to our knowledge of the relationship between the sexual system, reproductive system, and population genetic structure in haploid‐diploid taxa, thereby informing a broader understanding of the evolution of sex. 

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3. A test of Haldane’s rule in Neodiprion sawflies and implications for the evolution of postzygotic isolation in haplodiploids

   https://doi.org/10.1086/724820  

   Bendall, Emily E.; Mattingly, Kayla M.; Moehring, Amanda J.; Linnen, Catherine R. (January 2023, The American Naturalist)

   Haldane’s rule—a pattern in which hybrid sterility or inviability is observed in the heterogametic sex of an interspecific cross—is one of the most widely obeyed rules in nature. Because inheritance patterns are similar for sex chromosomes and haplodiploid genomes, Haldane’s rule may apply to haplodiploid taxa, predicting that haploid male hybrids will evolve sterility or inviability before diploid female hybrids. However, there are several genetic and evolutionary mechanisms that may reduce the tendency of haplodiploids to obey Haldane’s rule. Currently, there are insufficient data from haplodiploids to determine how frequently they adhere to Haldane’s rule. To help fill this gap, we crossed a pair of haplodiploid hymenopteran species (Neodiprion lecontei and Neodiprion pinetum) and evaluated the viability and fertility of female and male hybrids. Despite considerable divergence, we found no evidence of reduced fertility in hybrids of either sex, consistent with the hypothesis that hybrid sterility evolves slowly in haplodiploids. For viability, we found a pattern opposite of Haldane’s rule: hybrid females, but not males, had reduced viability. This reduction was most pronounced in one direction of the cross, possibly due to a cytoplasmic-nuclear incompatibility. We also found evidence of extrinsic postzygotic isolation in hybrids of both sexes, raising the possibility that this form or reproductive isolation tends to emerge early in speciation in host-specialized insects. Our work emphasizes the need for more studies on reproductive isolation in haplodiploids, which are abundant in nature, but under-represented in the speciation literature. 

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4. Fisher vs. the Worms: Extraordinary Sex Ratios in Nematodes and the Mechanisms that Produce Them

   https://doi.org/10.3390/cells10071793  

   Van Goor, Justin; Shakes, Diane C.; Haag, Eric S. (July 2021, Cells)

   Parker, Baker, and Smith provided the first robust theory explaining why anisogamy evolves in parallel in multicellular organisms. Anisogamy sets the stage for the emergence of separate sexes, and for another phenomenon with which Parker is associated: sperm competition. In outcrossing taxa with separate sexes, Fisher proposed that the sex ratio will tend towards unity in large, randomly mating populations due to a fitness advantage that accrues in individuals of the rarer sex. This creates a vast excess of sperm over that required to fertilize all available eggs, and intense competition as a result. However, small, inbred populations can experience selection for skewed sex ratios. This is widely appreciated in haplodiploid organisms, in which females can control the sex ratio behaviorally. In this review, we discuss recent research in nematodes that has characterized the mechanisms underlying highly skewed sex ratios in fully diploid systems. These include self-fertile hermaphroditism and the adaptive elimination of sperm competition factors, facultative parthenogenesis, non-Mendelian meiotic oddities involving the sex chromosomes, and environmental sex determination. By connecting sex ratio evolution and sperm biology in surprising ways, these phenomena link two “seminal” contributions of G. A. Parker. 

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5. Drosophila female reproductive tract gene expression reveals coordinated mating responses and rapidly evolving tissue-specific genes

   https://doi.org/10.1093/g3journal/jkab020  

   McDonough-Goldstein, Caitlin E; Borziak, Kirill; Pitnick, Scott; Dorus, Steve (March 2021, G3 Genes|Genomes|Genetics)

   Civetta, A (Ed.)

   Abstract Sexual reproduction in internally fertilizing species requires complex coordination between female and male reproductive systems and among the diverse tissues of the female reproductive tract (FRT). Here, we report a comprehensive, tissue-specific investigation of Drosophila melanogaster FRT gene expression before and after mating. We identified expression profiles that distinguished each tissue, including major differences between tissues with glandular or primarily nonglandular epithelium. All tissues were enriched for distinct sets of genes possessing secretion signals that exhibited accelerated evolution, as might be expected for genes participating in molecular interactions between the sexes within the FRT extracellular environment. Despite robust transcriptional differences between tissues, postmating responses were dominated by coordinated transient changes indicative of an integrated systems-level functional response. This comprehensive characterization of gene expression throughout the FRT identifies putative female contributions to postcopulatory events critical to reproduction and potentially reproductive isolation, as well as the putative targets of sexual selection and conflict. 

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