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1 March 2009 Phylogenetic Trends in Phenolic Metabolism of Milkweeds (Asclepias): Evidence for Escalation
Anurag A. Agrawal, Juha-Pekka Salminen, Mark Fishbein
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Abstract

Although plant-defense theory has long predicted patterns of chemical defense across taxa, we know remarkably little about the evolution of defense, especially in the context of directional phylogenetic trends. Here we contrast the production of phenolics and cardenolides in 35 species of milkweeds (Asclepias and Gomphocarpus). Maximum-likelihood analyses of character evolution revealed three major patterns. First, consistent with the defense-escalation hypothesis, the diversification of the milkweeds was associated with a trend for increasing phenolic production; this pattern was reversed (a declining evolutionary trend) for cardenolides, toxins sequestered by specialist herbivores. Second, phylogenetically independent correlations existed among phenolic classes across species. For example, coumaric acid derivatives showed negatively correlated evolution with caffeic acid derivatives, and this was likely driven by the fact that the former are used as precursors for the latter. In contrast, coumaric acid derivatives were positively correlated with flavonoids, consistent with competition for the precursor p-coumaric acid. Finally, of the phenolic classes, only flavonoids showed correlated evolution (positive) with cardenolides, consistent with a physiological and evolutionary link between the two via malonate. Thus, this study presents a rigorous test of the defense-escalation hypothesis and a novel phylogenetic approach to understanding the long-term persistence of physiological constraints on secondary metabolism.

© 2009 The Society for the Study of Evolution
Anurag A. Agrawal, Juha-Pekka Salminen, and Mark Fishbein "Phylogenetic Trends in Phenolic Metabolism of Milkweeds (Asclepias): Evidence for Escalation," Evolution 63(3), 663-673, (1 March 2009). https://doi.org/10.1111/j.1558-5646.2008.00573.x
Received: 10 August 2008; Accepted: 1 October 2008; Published: 1 March 2009
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KEYWORDS
Apocynaceae
cardenolide
Coevolution
evolutionary trend
flavonoid
plant-defense theory
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