{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,6,16]],"date-time":"2026-06-16T16:04:41Z","timestamp":1781625881271,"version":"3.54.5"},"reference-count":0,"publisher":"Cold Spring Harbor Laboratory","funder":[{"DOI":"10.13039\/501100004359","name":"Swedish Research Council","doi-asserted-by":"publisher","award":["2016-05138"],"award-info":[{"award-number":["2016-05138"]}],"id":[{"id":"10.13039\/501100004359","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100004359","name":"Swedish Research Council","doi-asserted-by":"publisher","award":["2020-04631"],"award-info":[{"award-number":["2020-04631"]}],"id":[{"id":"10.13039\/501100004359","id-type":"DOI","asserted-by":"publisher"}]},{"name":"Swedish Agricultural Agency","award":["9\/16"],"award-info":[{"award-number":["9\/16"]}]},{"name":"Swedish Agricultural Agency","award":["5.2.18-13223\/17"],"award-info":[{"award-number":["5.2.18-13223\/17"]}]},{"DOI":"10.13039\/501100004357","name":"Swedish Environmental Protection Agency","doi-asserted-by":"crossref","award":["NV-01203-8"],"award-info":[{"award-number":["NV-01203-8"]}],"id":[{"id":"10.13039\/501100004357","id-type":"DOI","asserted-by":"crossref"}]},{"DOI":"10.13039\/501100004357","name":"Swedish Environmental Protection Agency","doi-asserted-by":"crossref","award":["NV-02622-20"],"award-info":[{"award-number":["NV-02622-20"]}],"id":[{"id":"10.13039\/501100004357","id-type":"DOI","asserted-by":"crossref"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Genome Res."],"accepted":{"date-parts":[[2026,4,22]]},"abstract":"<jats:p>Spermatogenesis is a complex process in which spermatogonia differentiate into haploid sperm cells. Genes guiding this process are subject to an evolutionary trade-off between purifying selection preserving basic functions and positive selection favoring fast gamete production and innovative sperm traits. The outcome of this trade-off varies across the spermatogenesis stages in mammals but remains unexplored for species with ZW sex chromosomes, such as birds. Here, we identify 20 cell clusters comprising somatic and germline cells across stages of spermatogenesis by using single-cell RNA sequencing of collared and pied flycatcher testis. Based on an ortholog comparison with mammals and analyses of differential gene expression between two closely related flycatcher species and lineage-specific protein sequence evolution, we find evidence for rapid divergence of genes expressed during the second and last major stages of spermatogenesis (meiosis and spermiogenesis). The genes that are differentially expressed between the two flycatcher species are enriched for Gene Ontology biological processes that are fundamental for sperm function. Although genes expressed during spermiogenesis are known to evolve fast in mammals, our results imply that gene expression at meiosis is subject to stronger positive selection or is less constrained by purifying selection and\/or by intralocus sexual conflict in birds compared with mammals. We also find signals of fast-evolving Z-linked genes expressed during meiosis, consistent with the lack of sex chromosome silencing during meiosis (i.e., meiotic sex chromosome inactivation [MSCI]) in birds.<\/jats:p>","DOI":"10.1101\/gr.281911.126","type":"journal-article","created":{"date-parts":[[2026,5,14]],"date-time":"2026-05-14T16:25:23Z","timestamp":1778775923000},"source":"Crossref","is-referenced-by-count":0,"title":["Single-cell transcriptomics reveals rapid divergence of genes guiding meiosis and spermiogenesis in two passerine birds"],"prefix":"10.1101","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9885-1537","authenticated-orcid":false,"given":"J. Carolina","family":"Segami","sequence":"first","affiliation":[{"name":"Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala 75236, Sweden;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3479-7524","authenticated-orcid":false,"given":"Marie","family":"S\u00e9mon","sequence":"additional","affiliation":[{"name":"Laboratoire de Biologie et Mod\u00e9lisation de la Cellule, \u00c9cole Normale Sup\u00e9rieure de Lyon, CNRS UMR5239, Universit\u00e9 Claude Bernard Lyon 1, 69007 Lyon, France;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9038-2337","authenticated-orcid":false,"given":"Catarina","family":"Cunha","sequence":"additional","affiliation":[{"name":"Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala 75236, Sweden;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7960-1789","authenticated-orcid":false,"given":"Claudia","family":"Bergin","sequence":"additional","affiliation":[{"name":"Science for Life Laboratory, Molecular Evolution, Uppsala University, Uppsala 75237, Sweden;"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4220-4928","authenticated-orcid":false,"given":"Carina F.","family":"Mugal","sequence":"additional","affiliation":[{"name":"Department of Ecology and Genetics, Evolutionary Biology, Uppsala University, Uppsala 75236, Sweden;"},{"name":"Laboratory of Biometry and Evolutionary Biology (LBBE), University of Lyon 1, CNRS, UMR 5558, 69622 Villeurbanne, France"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1178-4053","authenticated-orcid":false,"given":"Anna","family":"Qvarnstr\u00f6m","sequence":"additional","affiliation":[{"name":"Department of Ecology and Genetics, Animal Ecology, Uppsala University, Uppsala 75236, Sweden;"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"246","published-online":{"date-parts":[[2026,5,14]]},"container-title":["Genome Research"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/syndication.highwire.org\/content\/doi\/10.1101\/gr.281911.126","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,6,16]],"date-time":"2026-06-16T15:05:28Z","timestamp":1781622328000},"score":1,"resource":{"primary":{"URL":"http:\/\/genome.cshlp.org\/lookup\/doi\/10.1101\/gr.281911.126"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,5,14]]},"references-count":0,"alternative-id":["10.1101\/gr.281911.126"],"URL":"https:\/\/doi.org\/10.1101\/gr.281911.126","relation":{},"ISSN":["1088-9051","1549-5469"],"issn-type":[{"value":"1088-9051","type":"print"},{"value":"1549-5469","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,5,14]]}}}