Defense mutualisms enhance plant diversification

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Abstract
The ability of plants to form mutualistic relationships with animal defenders has long been suspected to influence their evolutionary success, both by decreasing extinction risk and by increasing opportunity for speciation through an expanded realized niche. Nonetheless, the hypothesis that defense mutualisms consistently enhance plant diversification across lineages has not been well tested due to a lack of phenotypic and phylogenetic information. Using a global analysis, we show that the >100 vascular plant families in which species have evolved extrafloral nectaries (EFNs), sugar-secreting organs that recruit arthropod mutualists, have twofold higher diversification rates than families that lack species with EFNs. Zooming in on six distantly related plant clades, trait-dependent diversification models confirmed the tendency for lineages with EFNs to display increased rates of diversification. These results were consistent across methodological approaches. Inference using reversible-jump Markov chain Monte Carlo (MCMC) to model the placement and number of rate shifts revealed that high net diversification rates in EFN clades were driven by an increased number of positive rate shifts following EFN evolution compared with sister clades, suggesting that EFNs may be indirect facilitators of diversification. Our replicated analysis indicates that defense mutualisms put lineages on a path toward increased diversification rates within and between clades, and is concordant with the hypothesis that mutualistic interactions with animals can have an impact on deep macroevolutionary patterns and enhance plant diversity.
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Proceedings of the National Academy of Sciences
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A.A.A. was supported by Grant 1118783 of the Division of Environmental Biology of the National Science Foundation (NSF) and by the John Templeton Foundation. M.G.W. was supported by the Society for the Study of Evolution’s Rosemary Grant Award and by the NSF (Graduate Research Fellowship and Doctoral Dissertation Improvement Grant).
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2014-09-22
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National Academy of Sciences
Keywords
mutualism; extrafloral nectaries; plant-insect interactions; lineage diversification rates; plant defense
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Weber, M. G., & Agrawal, A. A. (2014). Defense mutualisms enhance plant diversification. Proceedings of the National Academy of Sciences, 111(46), 16442–16447.
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