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Genetic Covariation Between the Vertically Transmitted Endophyte Epichloë canadensis and Its Host Canada Wildrye

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Abstract

Symbiotic mutualisms are thought to be stabilized by correlations between the interacting genotypes which may be strengthened via vertical transmission and/or reduced genetic variability within each species. Vertical transmission, however, may weaken interactions over time as the endosymbionts would acquire mutations that could not be purged. Additionally, temporal variation in a conditional mutualism could create genetic variation and increased variation in the interaction outcome. In this study, we assessed genetic variation in both members of a symbiosis, the endosymbiotic fungal endophyte Epichloë canadensis and its grass host Canada wildrye (Elymus canadensis). Both species exhibited comparable levels of diversity, mostly within populations rather than between. There were significant differences between populations, although not in the same pattern for the two species, and the differences were not correlated with geographic distance for either species. Interindividual genetic distance matrices for the two species were significantly correlated, although all combinations of discriminant analysis of principle components (DAPC) defined multilocus genotype groups were found suggesting that strict genotype matching is not necessary. Variation in interaction outcome is common in grass/endophyte interactions, and our results suggest that the accumulation of mutations overtime combined with temporal variation in selection pressures increasing genetic variation in the symbiosis may be the cause.

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Data Availability

The data sets generated during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

The authors would like to thank Mark McKone and Nancy Barker for access to the Carleton College Cowling Arboretum, and the Iowa Department of Natural Resources for access to Hayden Prairie. The authors also thank two anonymous reviewers for their helpful feedback on the manuscript.

Funding

This research was supported by NSF-IOS-1119775 to TJS and TLB.

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Authors and Affiliations

  1. School of Sciences, Indiana University Kokomo, 2300 S. Washington St, Kokomo, IN, 46902, USA

    T. J. Sullivan & Holly Roberts

  2. Department of Biology, Hope College, 35 E. 12th St., Holland, MI, 49423, USA

    Thomas L. Bultman

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Contributions

TJS and TB conceived and designed the study. TJS, HR, and TB contributed to data collection. TJS preformed the analysis and wrote the initial draft, and all authors contributed to the editing. All the authors read and approved the final manuscript.

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Correspondence to T. J. Sullivan.

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Supplementary Information

Supplemental Fig. 1

Panels a (E. canadensis) and b (CWR) are minimum spanning networks for MLGs based on Bruvo’s distances. Node size is proportional to the number of MLGs, and nodes with MLGs represented in more than 1 population are plotted as pie charts (PNG 504 kb)

High resolution image (TIFF 2883 kb)

(PNG 743 kb)

High resolution image (TIFF 2883 kb)

Supplemental Table 1

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Sullivan, T.J., Roberts, H. & Bultman, T.L. Genetic Covariation Between the Vertically Transmitted Endophyte Epichloë canadensis and Its Host Canada Wildrye. Microb Ecol 86, 1686–1695 (2023). https://doi.org/10.1007/s00248-022-02166-7

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