A novel test for host-symbiont codivergence indicates ancient origin of fungal endophytes in grasses

C. L. Schardl, K. D. Craven, S. Speakman, A. Stromberg, A. Lindstrom, R. Yoshida

Research output: Contribution to journalArticlepeer-review

93 Scopus citations


Significant phylogenetic codivergence between plant or animal hosts (H) and their symbionts or parasites (P) indicates the importance of their interactions on evolutionary time scales. However, valid and realistic methods to test for codivergence are not fully developed. One of the systems where possible codivergence has been of interest involves the large subfamily of temperate grasses (Pooideae) and their endophytic fungi (epichloae). These widespread symbioses often help protect host plants from herbivory and stresses and affect species diversity and food web structures. Here we introduce the MRCALink (most-recent-common-ancestor link) method and use it to investigate the possibility of grass-epichloë codivergence. MRCALink applied to ultrametric H and P trees identifies all corresponding nodes for pairwise comparisons of MRCA ages. The result is compared to the space of random H and P tree pairs estimated by a Monte Carlo method. Compared to tree reconciliation, the method is less dependent on tree topologies (which often can be misleading), and it crucially improves on phylogeny-independent methods such as ParaFit or the Mantel test by eliminating an extreme (but previously unrecognized) distortion of node-pair sampling. Analysis of 26 grass species-epichloë species symbioses did not reject random association of H and P MRCA ages. However, when five obvious host jumps were removed, the analysis significantly rejected random association and supported grass-endophyte codivergence. Interestingly, early cladogenesis events in the Pooideae corresponded to early cladogenesis events in epichloae, suggesting concomitant origins of this grass subfamily and its remarkable group of symbionts. We also applied our method to the well-known gopher-louse data set.

Original languageEnglish
Pages (from-to)483-498
Number of pages16
JournalSystematic Biology
Issue number3
StatePublished - Jun 2008

Bibliographical note

Funding Information:
ACKNOWLEDGMENTS We thank Adrian Leuchtmann (ETH Zürich, Switzerland) for providing biological materials, Walter Hollin (University of Kentucky) for technical support, Stephane Aris-Brosou for very useful conversation, and Mark Hafner for providing the gopher-louse data sets. Also, we would like to thank Roderic Page, Francois-Joseph Lapointe, Michael Charleston, Jack Sullivan, and an anonymous referee for very useful comments to improve this paper. This work was supported by National Science Foundation grant DEB–9707427, National Institutes of Health grant KY–INBRE P20 RR16481, U.S. Department of Agriculture CSREES grant 2005-34457-15712, and the Harry E. Wheeler Endowment to the University of Kentucky Department of Plant Pathology. This is publication 08–12–034 of the Kentucky Agricultural Experiment Station, published with approval of the director.


  • Coevolution
  • Endophytes
  • Grasses
  • Phylogenetic trees

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Genetics


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