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1. Sperm and alternative reproductive tactics: a review of existing theory and empirical data

   https://doi.org/10.1098/rstb.2020.0075  

   Kustra, Matthew C. ; Alonzo, Suzanne H. ( December 2020 , Philosophical Transactions of the Royal Society B: Biological Sciences)

   Males that exhibit alternative reproductive tactics (ARTs) often differ in the risk of sperm competition and the energetic trade-offs they experience. The resulting patterns of selection could lead to between-tactic differences in ejaculate traits. Despite extensive research on male ARTs, there is no comprehensive review of whether and what differences in sperm traits exist between male ARTs. We review existing theory on ejaculate evolution relevant to ARTs and then conduct a comprehensive vote-counting review of the empirical data comparing sperm traits between males adopting ARTs. Despite the general expectation that sneaker males should produce sperm that are more competitive (e.g. higher quality or performance), we find that existing theory does not predict explicitly how males adopting ARTs should differ in sperm traits. The majority of studies find no significant difference in sperm performance traits between dominant and sneaker males. However, when there is a difference, sneaker males tend to have higher sperm performance trait values than dominant males. We propose ways that future theoretical and empirical research can improve our understanding of the evolution of ejaculate traits in ARTs. We then highlight how studying ejaculate traits in species with ARTs will improve our broader knowledge of ejaculate evolution. This articlemore »is part of the theme issue ‘Fifty years of sperm competition’.« less
2. Evaluation of Additional Drosophila suzukii Male-Only Strains Generated Through Remobilization of an FL19 Transgene

   https://doi.org/10.3389/fbioe.2022.829620  

   Yamamoto, Akihiko ; Yadav, Amarish K. ; Scott, Maxwell J. ( March 2022 , Frontiers in Bioengineering and Biotechnology)

   Drosophila suzukii (D. suzukii) (Matsumura, 1931; Diptera: Drosophilidae), also known as spotted wing Drosophila , is a worldwide pest of fruits with soft skins such as blueberries and cherries. Originally from Asia, D. suzukii is now present in the Americas and Europe and has become a significant economic pest. Growers largely rely on insecticides for the control of D. suzukii . Genetic strategies offer a species-specific environmentally friendly way for suppression of D. suzukii populations. We previously developed a transgenic strain of D. suzukii that produced only males on a diet that did not contain tetracycline. The strain carried a single copy of the FL19 construct on chromosome 3. Repeated releases of an excess of FL19 males led to suppression of D. suzukii populations in laboratory cage trials. Females died as a consequence of overexpression of the tetracycline transactivator (tTA) and tTA-activated expression of the head involution defective proapoptotic gene. The aim of this study was to generate additional male-only strains that carried two copies of the FL19 transgene through crossing the original line with a piggyBac jumpstarter strain. Males that carried either two chromosome 3 or a singleX-linked transgene were identified through stronger expression of the red fluorescent proteinmore »marker gene. The brighter fluorescence of the X-linked lines was likely due to dosage compensation of the red fluorescent protein gene. In total, four X-linked lines and eleven lines with two copies on chromosome 3 were obtained, of which five were further examined. All but one of the strains produced only males on a diet without tetracycline. When crossed with wild type virgin females, all of the five two copy autosomal strains examined produced only males. However, the single copy X-linked lines did not show dominant female lethality. Five of the autosomal lines were further evaluated for productivity (egg to adult) and male competition. Based on these results, the most promising lines have been selected for future population suppression experiments with strains from different geographical locations.« less
3. How female × male and male × male interactions influence competitive fertilization in Drosophila melanogaster

   https://doi.org/10.1002/evl3.193  

   Lüpold, Stefan ; Reil, Jonathan Bradley ; Manier, Mollie K. ; Zeender, Valérian ; Belote, John M. ; Pitnick, Scott ( October 2020 , Evolution Letters)

   How males and females contribute to joint reproductive success has been a long-standing question in sexual selection. Under postcopulatory sexual selection, paternity success is predicted to derive from complex interactions among females engaging in cryptic female choice and males engaging in sperm competition. Such interactions have been identified as potential sources of genetic variation in sexually selected traits but are also expected to inhibit trait diversification. To date, studies of interactions between females and competing males have focused almost exclusively on genotypes and not phenotypic variation in sexually selected traits. Here, we characterize within- and between-sex interactions in Drosophila melanogaster using isogenic lines with heritable variation in both male and female traits known to influence competitive fertilization. We confirmed, and expanded on, previously reported genotypic interactions within and between the sexes, and showed that several reproductive events, including sperm transfer, female sperm ejection, and sperm storage, were explained by two- and three-way interactions among sex-specific phenotypes. We also documented complex interactions between the lengths of competing males’ sperm and the female seminal receptacle, which are known to have experienced rapid female-male co-diversification. Our results highlight the nonindependence of sperm competition and cryptic female choice and demonstrate that complex interactionsmore »between the sexes do not limit the ability of multivariate systems to respond to directional sexual selection.

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4. Sexual Dichromatism Drives Diversification within a Major Radiation of African Amphibians

   https://doi.org/10.1093/sysbio/syz023  

   Portik, Daniel M. ; Bell, Rayna C. ; Blackburn, David C. ; Bauer, Aaron M. ; Barratt, Christopher D. ; Branch, William R. ; Burger, Marius ; Channing, Alan ; Colston, Timothy J. ; Conradie, Werner ; et al ( April 2019 , Systematic Biology)

   Theory predicts that sexually dimorphic traits under strong sexual selection, particularly those involved with intersexual signaling, can accelerate speciation and produce bursts of diversification. Sexual dichromatism (sexual dimorphism in color) is widely used as a proxy for sexual selection and is associated with rapid diversification in several animal groups, yet studies using phylogenetic comparative methods to explicitly test for an association between sexual dichromatism and diversification have produced conflicting results. Sexual dichromatism is rare in frogs, but it is both striking and prevalent in African reed frogs, a major component of the diverse frog radiation termed Afrobatrachia. In contrast to most other vertebrates, reed frogs display female-biased dichromatism in which females undergo color transformation, often resulting in more ornate coloration in females than in males. We produce a robust phylogeny of Afrobatrachia to investigate the evolutionary origins of sexual dichromatism in this radiation and examine whether the presence of dichromatism is associated with increased rates of net diversification. We find that sexual dichromatism evolved once within hyperoliids and was followed by numerous independent reversals to monochromatism. We detect significant diversification rate heterogeneity in Afrobatrachia and find that sexually dichromatic lineages have double the average net diversification rate of monochromaticmore »lineages. By conducting trait simulations on our empirical phylogeny, we demonstrate that our inference of trait-dependent diversification is robust. Although sexual dichromatism in hyperoliid frogs is linked to their rapid diversification and supports macroevolutionary predictions of speciation by sexual selection, the function of dichromatism in reed frogs remains unclear. We propose that reed frogs are a compelling system for studying the roles of natural and sexual selection on the evolution of sexual dichromatism across micro- and macroevolutionary timescales.

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5. The contribution of sex chromosome conflict to disrupted spermatogenesis in hybrid house mice

   https://doi.org/10.1093/genetics/iyac151  

   Kopania, Emily E. K. ; Watson, Eleanor M. ; Rathje, Claudia C. ; Skinner, Benjamin M. ; Ellis, Peter J. I. ; Larson, Erica L. ; Good, Jeffrey M. ; Barbash, ed., D. ( October 2022 , Genetics)

   Incompatibilities on the sex chromosomes are important in the evolution of hybrid male sterility, but the evolutionary forces underlying this phenomenon are unclear. House mice (Mus musculus) lineages have provided powerful models for understanding the genetic basis of hybrid male sterility. X chromosome–autosome interactions cause strong incompatibilities in M. musculus F1 hybrids, but variation in sterility phenotypes suggests a more complex genetic basis. In addition, XY chromosome conflict has resulted in rapid expansions of ampliconic genes with dosage-dependent expression that is essential to spermatogenesis. Here, we evaluated the contribution of XY lineage mismatch to male fertility and stage-specific gene expression in hybrid mice. We performed backcrosses between two house mouse subspecies to generate reciprocal Y-introgression strains and used these strains to test the effects of XY mismatch in hybrids. Our transcriptome analyses of sorted spermatid cells revealed widespread overexpression of the X chromosome in sterile F1 hybrids independent of Y chromosome subspecies origin. Thus, postmeiotic overexpression of the X chromosome in sterile F1 mouse hybrids is likely a downstream consequence of disrupted meiotic X-inactivation rather than XY gene copy number imbalance. Y chromosome introgression did result in subfertility phenotypes and disrupted expression of several autosomal genes in mice withmore »an otherwise nonhybrid genomic background, suggesting that Y-linked incompatibilities contribute to reproductive barriers, but likely not as a direct consequence of XY conflict. Collectively, these findings suggest that rapid sex chromosome gene family evolution driven by genomic conflict has not resulted in strong male reproductive barriers between these subspecies of house mice.

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