Journal
ECOLOGY LETTERS
Volume 22, Issue 6, Pages 914-924Publisher
WILEY
DOI: 10.1111/ele.13247
Keywords
Acmispon strigosus; Bradyrhizobium; cheating; legume-rhizobium mutualism; maladaptation; mutualism breakdown; sanctions; symbiosis
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Funding
- University of California Riverside
- NSF [DEB 1150278, 1738028]
- Division Of Environmental Biology
- Direct For Biological Sciences [1738028] Funding Source: National Science Foundation
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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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