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Long-term ungulate exclusion reduces fungal symbiont prevalence in native grasslands

  • Plant-microbe-animal interactions - original research
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Abstract

When symbionts are inherited by offspring, they can have substantial ecological and evolutionary consequences because they occur in all host life stages. Although natural frequencies of inherited symbionts are commonly <100 %, few studies investigate the ecological drivers of variation in symbiont prevalence. In plants, inherited fungal endophytes can improve resistance to herbivory, growth under drought, and competitive ability. We evaluated whether native ungulate herbivory increased the prevalence of a fungal endophyte in the common, native bunchgrass, Festuca campestris (rough fescue, Poaceae). We used large-scale (1 ha) and long-term (7–10 year) fencing treatments to exclude native ungulates and recorded shifts in endophyte prevalence at the scale of plant populations and for individual plants. We characterized the fungal endophyte in F. campestris, Epichloë species FcaTG-1 (F. campestris taxonomic group 1) for the first time. Under ungulate exclusion, endophyte prevalence was 19 % lower in plant populations, 25 % lower within plant individuals, and 39 % lower in offspring (seeds) than in ungulate-exposed controls. Population-level endophyte frequencies were also negatively correlated with soil moisture across geographic sites. Observations of high within-plant variability in symbiont prevalence are novel for the Epichloë species, and contribute to a small, but growing, literature that documents phenotypic plasticity in plant-endophyte symbiota. Altogether, we show that native ungulates can be an important driver of symbiont prevalence in native plant populations, even in the absence of evidence for direct mechanisms of mammal deterrence. Understanding the ecological controls on symbiont prevalence could help to predict future shifts in grasslands that are dominated by Epichloë host plants.

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Acknowledgments

J. M. and D. E. P. were supported by the US National Science Foundation DEB-0614406. J. A. R. was supported by the US National Science Foundation DEB-1354972 and 1145588. The authors have no other conflicts of interest to declare. Thanks to Beth Haley and Ben Goodheart for field and laboratory assistance. This article does not contain any studies with human participants or animals performed by any of the authors.

Author contribution statement

J. L. M. and D. E. P. conceived, designed, and performed the experimental manipulations. R. A. F., E. O., and J. A. R. collected the endophyte data. J. A. R. analyzed the data. C. A. Y. and N. D. C. characterized the endophyte identity. J. A. R. led the writing, with substantial contributions from co-authors.

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Authors and Affiliations

  1. Department of Biology, University of New Mexico, Albuquerque, NM, 87131, USA

    Jennifer A. Rudgers & Eric Olivas

  2. Division of Biological Sciences, University of Montana, Missoula, MT, 59812, USA

    Rebecca A. Fletcher, Dean E. Pearson & John L. Maron

  3. The Samuel Roberts Noble Foundation, Ardmore, OK, 73401, USA

    Carolyn A. Young & Nikki D. Charlton

  4. Rocky Mountain Research Station, USDA, Forest Service, Missoula, MT, 59812, USA

    Dean E. Pearson

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  1. Jennifer A. Rudgers
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  2. Rebecca A. Fletcher
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Correspondence to Jennifer A. Rudgers.

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Communicated by Maria J. Pozo.

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Rudgers, J.A., Fletcher, R.A., Olivas, E. et al. Long-term ungulate exclusion reduces fungal symbiont prevalence in native grasslands. Oecologia 181, 1151–1161 (2016). https://doi.org/10.1007/s00442-016-3620-7

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