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

Tichkule, Swapnil, van Oosterhout, Cock, Cacciò, Simone Mario, Weisz, Filip, Balan, Balu, Nohynkova, Eva, Ansell, Brendan R. E., Emery-Corbin, Samantha J., Baker, Louise, Lalle, Marco, Svard, Staffan, Gasser, Robin B., Naung, Myo T. and Jex, Aaron R. (2025) Host range expansion of asexual parasite can be explained by loss of adaptions in Muller’s Ratchet. Nature Communications. ISSN 2041-1723

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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’ has been long explored but is unresolved. Here, we find clear evidence of sex in Giardia and 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, our results suggest that Giardia is not the last exception to, but rather further evidence of, the essentiality of eukaryotic sex.

Item Type:	Article
Faculty \ School:	Faculty of Science > School of Environmental Sciences
UEA Research Groups:	Faculty of Science > Research Centres > Centre for Ecology, Evolution and Conservation
Depositing User:	LivePure Connector
Date Deposited:	14 Jan 2026 15:30
Last Modified:	14 Jan 2026 15:30
URI:	https://ueaeprints.uea.ac.uk/id/eprint/101610
DOI:	10.1038/s41467-025-65843-4

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