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1. Sperm competition intensity shapes divergence in both sperm morphology and reproductive genes across murine rodents

   https://doi.org/10.1093/evolut/qpae146  

   Kopania, Emily_E_K; Thomas, Gregg_W_C; Hutter, Carl_R; Mortimer, Sebastian_M_E; Callahan, Colin_M; Roycroft, Emily; Achmadi, Anang_S; Breed, William_G; Clark, Nathan_L; Esselstyn, Jacob_A; et al (October 2024, Evolution)

   Abstract It remains unclear how variation in the intensity of sperm competition shapes phenotypic and molecular evolution across clades. Mice and rats in the subfamily Murinae are a rapid radiation exhibiting incredible diversity in sperm morphology and production. We combined phenotypic and genomic data to perform phylogenetic comparisons of male reproductive traits and genes across 78 murine species. We identified several shifts towards smaller relative testes mass (RTM), presumably reflecting reduced sperm competition. Several sperm traits were associated with RTM, suggesting that mating system evolution selects for convergent suites of traits related to sperm competitive ability. We predicted that sperm competition would also drive more rapid molecular divergence in species with large testes. Contrary to this, we found that many spermatogenesis genes evolved more rapidly in species with smaller RTM due to relaxed purifying selection. While some reproductive genes evolved rapidly under recurrent positive selection, relaxed selection played a greater role in underlying rapid evolution in small testes species. Our work demonstrates that postcopulatory sexual selection can impose strong purifying selection shaping the evolution of male reproduction and that broad patterns of molecular evolution may help identify genes that contribute to male fertility. 

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2. Sperm lacking Bindin are infertile but are otherwise indistinguishable from wildtype sperm

   https://doi.org/10.1038/s41598-021-00570-6  

   Wessel, Gary M; Wada, Yuuko; Yajima, Mamiko; Kiyomoto, Masato (December 2021, Scientific Reports)

   Abstract Cell–cell fusion is limited to only a few cell types in the body of most organisms and sperm and eggs are paradigmatic in this process. The specialized cellular mechanism of fertilization includes the timely exposure of gamete–specific interaction proteins by the sperm as it approaches the egg. Bindin in sea urchin sperm is one such gamete interaction protein and it enables species–specific interaction with a homotypic egg. We recently showed that Bindin is essential for fertilization by use of Cas9 targeted gene inactivation in the sea urchin,Hemicentrotus pulcherrimus. Here we show phenotypic details of Bindin-minus sperm. Sperm lacking Bindin do not bind to nor fertilize eggs at even high concentrations, yet they otherwise have wildtype morphology and function. These features include head shape, tail length and beating frequency, an acrosomal vesicle, a nuclear fossa, and they undergo an acrosomal reaction. The only phenotypic differences between wildtype and Bindin-minus sperm identified is that Bindin-minus sperm have a slightly shorter head, likely as a result of an acrosome lacking Bindin. These data, and the observation that Bindin-minus embryos develop normally and metamorphose into normal functioning adults, support the contention that Bindin functions are limited to species–specific sperm–egg interactions. We conclude that the evolutionary divergence of Bindin is not constrained by any other biological roles. 

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3. Flow-induced buckling dynamics of sperm flagella

   https://doi.org/10.1103/PhysRevE.100.063107  

   Kumar, Manish; Walkama, Derek M.; Guasto, Jeffrey S.; Ardekani, Arezoo M. (December 2019, Physical Review E)
4. Flagellar kinematics reveals the role of environment in shaping sperm motility

   https://doi.org/10.1098/rsif.2020.0525  

   Guasto, Jeffrey S.; Estrada, Jonathan B.; Menolascina, Filippo; Burton, Lisa J.; Patel, Mohak; Franck, Christian; Hosoi, A. E.; Zimmer, Richard K.; Stocker, Roman (September 2020, Journal of The Royal Society Interface)

   Swimming spermatozoa from diverse organisms often have very similar morphologies, yet different motilities as a result of differences in the flagellar waveforms used for propulsion. The origin of these differences has remained largely unknown. Using high-speed video microscopy and mathematical analysis of flagellar shape dynamics, we quantitatively compare sperm flagellar waveforms from marine invertebrates to humans by means of a novel phylokinematic tree. This new approach revealed that genetically dissimilar sperm can exhibit strikingly similar flagellar waveforms and identifies two dominant flagellar waveforms among the deuterostomes studied here, corresponding to internal and external fertilizers. The phylokinematic tree shows marked discordance from the phylogenetic tree, indicating that physical properties of the fluid environment, more than genetic relatedness, act as an important selective pressure in shaping the evolution of sperm motility. More broadly, this work provides a physical axis to complement morphological and genetic studies to understand evolutionary relationships. 

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5. The Impacts of Mating System on Sperm Gene Evolution in Primates

   Decamp, RM; Trujillo, AE; Tilton, KM; Blair, ME; Pozzi, L; Disotell, TR; Tosi, AJ; Burrell, AS; Bergey, CM (January 2022, American journal of physical anthropology)