Different tools for different trades: contrasts in specialized metabolite chemodiversity and phylogenetic dispersion in fruit, leaves, and roots of the neotropical shrubs Psychotria and Palicourea (Rubiaceae).

Abstract

Plants produce an astonishingly diverse array of specialized metabolites. A crucial step in understanding the origin of such chemodiversity is describing how chemodiversity manifests across the spatial and ontogenetic scales relevant to plant-biotic interactions. Focusing on 21 sympatric species of Psychotria and Palicourea sensu lato (Rubiaceae), we describe patterns of specialized metabolite diversity across spatial and ontogenetic scales using a combination of field collections, untargeted metabolomics, and ecoinformatics. We compare α, β, and γ diversity of specialized metabolites in expanding leaves, unripe pulp, immature seed, ripe pulp, mature seed, and fine roots. Within species, fruit tissues from across ontogenetic stages had ≥α diversity than leaves, and ≤β diversity than leaves. Pooled across species, fruit tissues and ontogenetic stages had the highest γ diversity of all organs, and fruit tissues and ontogenetic stages combined had a higher incidence of organ-specific mass spectral features than leaves. Roots had ≤α diversity than leaves and the lowest β and γ diversity of all organs. Phylogenetic correlations of chemical distance varied by plant organ and chemical class. Our results describe patterns of specialized metabolite diversity across organs and species and provide support for organ-specific contributions to plant chemodiversity. This study contributes to the growing understanding within plant evolutionary ecology of the biological scales of specialized metabolite diversification. Future studies combining our data on specialized metabolite diversity with biotic interaction data and experiments can test existing hypotheses on the roles of ecological interactions in the evolution of chemodiversity.