evolution of antiherbivore defenses and their contribution to species coexistence in the tropical tree genus Inga

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 43; pp. 18073 - 18078
• Main Authors: Kursar, Thomas A, Dexter, Kyle G, Lokvam, John, Pennington, R. Toby, Richardson, James E, Weber, Marjorie G, Murakami, Eric T, Drake, Camilla, McGregor, Ruth, Coley, Phyllis D
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 27.10.2009; National Acad Sciences
• Series: Plant and Insect Biodiversity Special Feature
• Subjects: Animals; Ants; Ants - physiology; Biodiversity; Biological Evolution; Biological Sciences; Biological taxonomies; Botany; chemical ecology; Chemicals; Chlorophyll - biosynthesis; Chlorophyll - chemistry; Coexistence; Differentiation; Evolution; Fabaceae; Fabaceae - chemistry; Fabaceae - genetics; Fabaceae - growth & development; Fabaceae - metabolism; Fitness; Food Chain; Forests; Formicidae; Herbivores; Inga; Inga (Fabaceae); Insect genetics; insect pests; Leaves; Molecular Sequence Data; Multivariate analysis; mutualism; pest resistance; Phenotypic traits; Phylogenetics; Phylogeny; phytophagous insects; Plant and Insect Biodiversity Special Feature; plant diversity; Plant Leaves - chemistry; Plant Leaves - genetics; Plant Leaves - growth & development; Plant Leaves - metabolism; plant-insect relations; Plants; resistance mechanisms; secondary metabolites; Selection, Genetic; species diversity; Trees; Tropical environments; tropical forests; Tropical rain forests; tropics; Peru; Panama
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0904786106

Plants and their herbivores constitute more than half of the organisms in tropical forests. Therefore, a better understanding of the evolution of plant defenses against their herbivores may be central for our understanding of tropical biodiversity. Here, we address the evolution of antiherbivore defenses and their possible contribution to coexistence in the Neotropical tree genus Inga (Fabaceae). Inga has >300 species, has radiated recently, and is frequently one of the most diverse and abundant genera at a given site. For 37 species from Panama and Peru we characterized developmental, ant, and chemical defenses against herbivores. We found extensive variation in defenses, but little evidence of phylogenetic signal. Furthermore, in a multivariate analysis, developmental, ant, and chemical defenses varied independently (were orthogonal) and appear to have evolved independently of each other. Our results are consistent with strong selection for divergent defensive traits, presumably mediated by herbivores. In an analysis of community assembly, we found that Inga species co-occurring as neighbors are more different in antiherbivore defenses than random, suggesting that possessing a rare defense phenotype increases fitness. These results imply that interactions with herbivores may be an important axis of niche differentiation that permits the coexistence of many species of Inga within a single site. Interactions between plants and their herbivores likely play a key role in the generation and maintenance of the conspicuously high plant diversity in the tropics.