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Does An Asexual Endophyte Symbiont Alter Life Stage and Long-Term Survival in a Perennial Host Grass?

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Abstract

Asexual, seedborne endophytic fungi in perennial grasses are often viewed as strong mutualists because fitness of the symbiont and host grass are closely coupled. However, at least for some native grasses, the asexual endophyte, Neotyphodium, acts parasitically, yet remains at high frequencies in natural populations. Most previous studies of Neotyphodium effects on host survival have been short term relative to the long life span of the perennial grass host. We therefore tested the hypothesis that Neotyphodium alters the survival in various life stages and long-term survival of adult native Arizona fescue (Festuca arizonica). To test the former, we planted 40 infected (E+) and 40 uninfected (E−, endophyte removed) seeds from four different maternal plants in the field under ambient conditions. We followed survival of seeds, seedlings, and adult plants over a 5-year period. To test the latter, we determined the infection of 1633 adult plants and followed their survival over the next 5–7 years. E+ seeds did not differ from uninfected seeds in terms of overall survival from seed germination to seedling to adult. However, the shape of the survival curve differed, with E+ plants showing higher mortality in early life stages. E+ adult plants did not differ from E− plants in long-term survival. Survival was generally very high during the study, which included a severe and prolonged drought. Infection by asexual Neotyphodium does not increase survival in early life stages or that of adult plants. Because asexual, vertically transmitted symbionts are predicted by evolutionary theory to be strong mutualists, the persistence of high infection frequencies in natural populations without long-term benefits to the host remains enigmatic. One possible explanation is that the long life span of the perennial host and low seedling recruitment may obscure either the costs or benefits of endophyte infection.

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Acknowledgments

We thank Laura Beard, Natalie Fuller, Hilary Gan, Cinnamon Hayes, Jean Horne, Andrea Jani, Morgan MacCallum, Wendy Marussich, Vivian Miller, Jennie Rambo, Stephanie Steele, Phil Steiner, T.J. Sullivan and Sally Wittlinger for assistance in the field and in the laboratory. Jesse Brunner provided statistical advice. We are also grateful to the Sally Haase and Steve Sackett of USDA Forest Service–Fire Research Lab, Riverside, CA, for their generous help in accessing the experimental fire rotation sites, and the Arboretum of Flagstaff for use of experimental plots. We are especially grateful to Dr. and Mrs. Meyer for use of their cabin during field observations. This research was supported by NSF grants DEB 9727020 and 0128343 to S.H.F.

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  1. School of Life Sciences, Arizona State University, PO BOX 874501, Tempe, AZ, 85287-4501, USA

    Stanley H. Faeth & Cyd E. Hamilton

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Correspondence to Stanley H. Faeth.

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Faeth, S.H., Hamilton, C.E. Does An Asexual Endophyte Symbiont Alter Life Stage and Long-Term Survival in a Perennial Host Grass?. Microb Ecol 52, 748–755 (2006). https://doi.org/10.1007/s00248-006-9123-z

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