{"paper_id":"01640050-bea1-47b6-94ef-e4c7e451d30c","body_text":"Lineage-Specific Adaptive Evolution of the Growth Arrest–Specific Protein 8 (GAS8) Domain Protein in Trypanosoma melophagium | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Lineage-Specific Adaptive Evolution of the Growth Arrest–Specific Protein 8 (GAS8) Domain Protein in Trypanosoma melophagium Anumita Das, Arnab Ghosh, Swarnamoy Pal, Sonali Biswas, Krishnendu Sinha, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8921716/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 15 You are reading this latest preprint version Abstract The Growth arrest–specific protein 8 (GAS8) domain-containing gene family (Orthogroup 6127at5690) is a strictly single-copy, highly conserved orthologous group across the genus Trypanosoma. Present in all 16 examined species, this family encodes a microtubule-associated protein implicated in cytoskeletal organization and flagellar motility. We conducted a genus-wide evolutionary analysis of the GAS8-domain protein, focusing on the Trypanosoma melophagium ortholog LSM04 004638. Maximum likelihood phylogenetic reconstruction, branch-specific and site-level codon-based selection analyses, ancestral sequence reconstruction, and Rosetta-based energetic estimation were performed. Despite strong purifying constraint consistent with essential cytoskeletal function , branch-level models detected significant episodic diversifying selection along the T. melophagium lineage. Site-level analyses identified three codon positions under episodic selection, two of which correspond to derived non-synonymous substitutions relative to the reconstructed ancestor (P2G and V106L). Ancestral-state back-mutation and energetic estimation indicate that individual substitutions exert modest stability effects relative to cumulative divergence between ancestral and extant sequences. These results demonstrate that highly conserved, single-copy cytoskeletal regulators can undergo limited lineage-specific adaptive refinement without disruption of core structural architecture. Our findings highlight the evolutionary plasticity of essential microtubule-associated proteins under ecological specialization. Biological sciences/Evolution Biological sciences/Genetics GAS8 domain Orthogroup 6127at5690 cytoskeleton flagellar motility adaptive evolution Trypanosoma Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 17 Mar, 2026 Reviews received at journal 16 Mar, 2026 Reviews received at journal 14 Mar, 2026 Reviewers agreed at journal 13 Mar, 2026 Reviewers agreed at journal 12 Mar, 2026 Reviewers agreed at journal 08 Mar, 2026 Reviewers agreed at journal 07 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers agreed at journal 06 Mar, 2026 Reviewers invited by journal 06 Mar, 2026 Editor assigned by journal 06 Mar, 2026 Editor invited by journal 06 Mar, 2026 Submission checks completed at journal 04 Mar, 2026 First submitted to journal 26 Feb, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {\"props\":{\"pageProps\":{\"initialData\":{\"identity\":\"rs-8921716\",\"acceptedTermsAndConditions\":true,\"allowDirectSubmit\":false,\"archivedVersions\":[],\"articleType\":\"Article\",\"associatedPublications\":[],\"authors\":[{\"id\":603947239,\"identity\":\"6fbf3b03-20f9-457e-9070-1a891002d92d\",\"order_by\":0,\"name\":\"Anumita Das\",\"email\":\"\",\"orcid\":\"\",\"institution\":\"Maulana Azad College, India\",\"correspondingAuthor\":false,\"prefix\":\"\",\"firstName\":\"Anumita\",\"middleName\":\"\",\"lastName\":\"Das\",\"suffix\":\"\"},{\"id\":603947240,\"identity\":\"2baec48e-112f-4d1f-bb3c-c6b713f563f9\",\"order_by\":1,\"name\":\"Arnab 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