Host range expansion of asexual parasite can be explained by loss of adaptions in Muller’s Ratchet

Host range expansion of asexual parasite can be explained by loss of adaptions in Muller’s Ratchet | 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 Host range expansion of asexual parasite can be explained by loss of adaptions in Muller’s Ratchet Aaron Jex, Swapnil Tichkule, Cock van Oosterhout, Simone Cacciò, and 10 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5154616/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 01 Dec, 2025 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Sexual recombination is a hallmark of eukaryotic evolution. Without recombination, asexual eukaryotes should succumb to deleterious mutations and more rapidly evolving pathogens. Giardia duodenalis, a parasitic protist, sits within one of the earliest-branching eukaryotic lineages and has no known sexual stage. Whether Giardia are ‘ancient asexuals’ is long explored but unresolved. Here, we find clear evidence of sex in Giardia but also discover an asexual sublineage that has a broader host range than its sexual ancestor. This asexual lineage is not ancient, and is accumulating deleterious mutations. Unlike its sexual counterparts, its genetic variation lacks the signatures of selection and Red Queen coevolution. We propose a new hypothesis that explains how a mutational meltdown during Muller’s Ratchet might enable asexual pathogens to expand their host ranges transiently. Fittingly, Giardia is not the last exception to but further proof of the essentiality of eukaryotic sex. Biological sciences/Microbiology/Parasitology/Parasite evolution Biological sciences/Microbiology/Microbial genetics Biological sciences/Evolution/Evolutionary genetics Biological sciences/Genetics/Population genetics/Genetic variation Full Text Additional Declarations There is NO Competing Interest. Supplementary Files Tichkule.SSupplementaryFigures125andTables18.pdf Cite Share Download PDF Status: Published Journal Publication published 01 Dec, 2025 Read the published version in Nature Communications → Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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