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Article Abstract – Gano-Cohen et al. (2019)

Title:

Interspecific conflict and the evolution of ineffective rhizobia

Authors and affiliations:

Kelsey A. Gano-Cohen^1,2, Camille E. Wendlandt^2,3, Peter J. Stokes², Mia A. Blanton², Kenjiro W. Quides², Avissa Zomorrodian², Eunice S. Adinata², and Joel L. Sachs^1,2,3,4.

¹Department of Microbiology & Plant Pathology, University of California, Riverside, CA
²Department of Evolution, Ecology & Organismal Biology, University of California, Riverside, CA
³Department of Botany & Plant Sciences, University of California, Riverside, CA
⁴Institute for Integrative Genome Biology, University of California, Riverside, CA,

Citation:

Ecology Letters 221: 914-924 (2019)

Abstract:

Microbial symbionts exhibit broad genotypic variation in their fitness effects on hosts, leaving hosts vulnerable to costly partnerships. Interspecific conflict and partner-maladaptation are frameworks to explain this variation, with different implications for mutualism stability. We investigated the mutualist service of nitrogen fixation in a metapopulation of root-nodule forming Bradyrhizobium symbionts in Acmispon hosts. We uncovered Bradyrhizobium genotypes that provide negligible mutualist services to hosts and had superior in planta fitness during clonal infections, consistent with cheater strains that destabilise mutualisms. Interspecific conflict was also confirmed at the metapopulation level – by a significant negative association between the fitness benefits provided by Bradyrhizobium genotypes and their local genotype frequencies – indicating that selection favours cheating rhizobia. Legumes have mechanisms to defend against rhizobia that fail to fix sufficient nitrogen, but these data support predictions that rhizobia can subvert plant defenses and evolve to exploit hosts.

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