The role of plant secondary metabolites in shaping regional and local plant community assembly

Abstract

1. The outstanding diversity of Amazonian forests is predicted to be the result of several processes. While tree lineages have dispersed repeatedly across the Amazon, interactions between plants and insects may be the principal mechanism structuring the communities at local scales.2. Using metabolomic and phylogenetic approaches, we investigated the patterns of historical assembly of plant communities across the Amazon based on the Neotropical genus of trees Inga (Leguminosae) at four, widely separated sites.3. Our results show a low degree of phylogenetic structure and a mixing of chemotypes across the whole Amazon basin, suggesting that although biogeography may play a role, the metacommunity for any local community in the Amazon is the entire basin. Yet, local communities are assembled by ecological processes, with the suite of Inga at a given site more divergent in chemical defences than expected by chance 4. Synthesis. To our knowledge, this is the first study to present metabolomic data for nearly 100 species in a diverse Neotropical plant clade across the whole Amazonia.Our results demonstrate a role for plant-herbivore interactions in shaping the clade's community assembly at a local scale, and suggest that the high alpha diversity in Amazonian tree communities must be due in part to the interactions of diverse tree lineages with their natural enemies providing a high number of niche dimensions.

Diversity and Divergence: Evolution of defense chemistry in the tropical tree genusInga

“…To test for phylogenetic signal of the entire chemical profile and quantify divergence between species, we developed a method for quantifying overall chemical similarity between two species (17). This provides a challenge because few compounds are shared between species, making classic distance metrics such as Bray-Curtis uninformative (17,32).…”

“…To test for phylogenetic signal of the entire chemical profile and quantify divergence between species, we developed a method for quantifying overall chemical similarity between two species (17). This provides a challenge because few compounds are shared between species, making classic distance metrics such as Bray-Curtis uninformative (17,32). Our method, which is similar to but distinct from one developed by Sedio et al (32), accounts for the fact that two species may have different compounds that are structurally similar (4,7,17).…”

“…This provides a challenge because few compounds are shared between species, making classic distance metrics such as Bray-Curtis uninformative (17,32). Our method, which is similar to but distinct from one developed by Sedio et al (32), accounts for the fact that two species may have different compounds that are structurally similar (4,7,17). Specifically we leverage MS/MS spectra as a proxy for structural similarity between compounds (31).…”

“…For example, increased phytochemical diversity in tropical forests decreases the number of herbivore species associated with a given host (12,14) and can reduce rates of herbivory (15). In addition to producing a diverse set of compounds, recent studies have highlighted the importance for a given species to maintain a unique chemical profile relative to other species in its community (7,16,17).…”

Ontogenetic Changes in the Chemical Profiles of Piper Species

“…In addition, across species, herbivory is particularly limiting in dense patches of conspecific seedlings [31][32][33][34]. Plant chemotypes are more variable than phylogeny would suggest [35,36], further indicating that variation in plant chemistry enables survival by limiting herbivory. Together, these patterns suggest that studying plant secondary metabolites early in ontogeny may lead to a better understanding of phytochemical diversity.…”