title: Macroevolution of plant defenses against herbivores in the evening primroses.
abstract: Plant species vary greatly in defenses against herbivores, but existing theory has struggled to explain this variation. Here, we test how phylogenetic relatedness, tradeoffs, trait syndromes, and sexual reproduction affect the macroevolution of defense. To examine the macroevolution of defenses, we studied 26 Oenothera (Onagraceae) species, combining chemistry, comparative phylogenetics and experimental assays of resistance against generalist and specialist herbivores. We detected dozens of phenolic metabolites within leaves, including ellagitannins (ETs), flavonoids, and caffeic acid derivatives (CAs). The concentration and composition of phenolics exhibited low to moderate phylogenetic signal. There were clear negative correlations between multiple traits, supporting the prediction of allocation tradeoffs. There were also positively covarying suites of traits, but these suites did not strongly predict resistance to herbivores and thus did not act as defensive syndromes. By contrast, specific metabolites did correlate with the performance of generalist and specialist herbivores. Finally, that repeated losses of sex in Oenothera was associated with the evolution of increased flavonoid diversity and altered phenolic composition. These results show that secondary chemistry has evolved rapidly during the diversification of Oenothera. This evolution has been marked by allocation tradeoffs between traits, some of which are related to herbivore performance. The repeated loss of sex appears also to have constrained the evolution of plant secondary chemistry, which may help to explain variation in defense among plants.
authors.affiliation: Department of Biology, University of Toronto-Mississauga, Mississauga, ON, L5L 1C6, Canada.
authors.forename: Marc T J
authors.initials: MT
authors.lastname: Johnson
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Ives
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Ahern
authors.forename: Juha-Pekka
authors.initials: JP
authors.lastname: Salminen
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002109:Caffeic Acids / Q000737:chemistry; D005419:Flavonoids / Q000737:chemistry; D060434:Herbivory; D047348:Hydrolyzable Tannins / Q000737:chemistry; D031664:Oenothera / Q000737:chemistry / Q000145:classification / Q000235:genetics*; D010802:Phylogeny; D018515:Plant Leaves / Q000737:chemistry
chemical_list: D002109:Caffeic Acids; D005419:Flavonoids; D047348:Hydrolyzable Tannins; C040048:caffeic acid
keywords: apomixis; coevolution; evening primrose; phenolics; phylogenetic generalized least squares; plant defense; plant-herbivore interaction; tannins