Research in the Sedio Lab seeks to understand the origins and maintenance of biodiversity in forest communities by integrating perspectives from macroevolution, community ecology, historical biogeography, and theoretical ecology. "What determines biological diversity?" is one of the most important outstanding questions in science (Science 309: 5731). The quest to identify the mechanisms responsible for the generation and maintenance of species richness in the world’s most diverse tropical forests lies at the heart of any attempt to answer this question. Plots of only a fraction of a km2 in Amazonia and Borneo contain 1,200 tree species, more than all of the temperate forests of North America, Europe, and Asia combined (Wright 2002). Unlike animals, which can exploit distinct food resources, all plants require a small number of common resources, which seemingly limits the number of resource-based niches along which competing species might differentiate. This paradox between diversity and ecological similarity is an old one (Hutchinson 1961). Our work seeks to generate novel insights into this fundamental problem by combining perspectives from fields that have not traditionally informed one another, such as community ecology, analytical chemistry, phylogenetics, and historical biogeography. In addition, research in the Sedio Lab seeks to gain novel insight by leveraging new technologies to overcome previously insurmountable obstacles to the study of plant chemical traits and herbivore and pathogen associations on the scale of forest communities comprised of hundreds of species of trees.
Chemical ecology
Ecological theory maintains that species must differ in their resource requirements, their “niche”, in order to coexist (Gause 1934). In contrast with plant resource requirements, plant interactions with microbial pathogens and insect herbivores may provide a highly multidimensional space within which species can carve out a “niche” defined by the enemies they support, and those they avoid.
Thousands of secondary metabolites distinguish plants in the eyes of their natural enemies. For example, the Bean Family (Leguminosae) alone synthesizes over 20 major classes of secondary compounds (Wink 2003). This variety of plant chemical defense has long precluded chemical analysis at the large taxonomic scales required for the study of macroevolution and community ecology. Recent advances in mass spectrometry (MS) developed by my collaborator Pieter C. Dorrestein at the University of California, San Diego, however, enable the high-throughput comparison of the structures of unknown compounds (Wang et al. 2016), making possible comparative metabolomics at unprecedented scales necessary for the study of chemical community ecology and macroevolution (Sedio 2017).
Novel methods for generating molecular networks using mass spectra are able to capture the structural similarity of unknown compounds because molecules with similar structures fragment into many of the same sub-structures (Wang et al. 2016). Molecular networks can therefore quantify chemical similarities between samples even though few compounds are unambiguously identified, which is essential in chemically diverse and understudied tropical forests. A molecular network of 7,665 unique molecules derived from the 21 species of Psychotria (Rubiaceae) found on Barro Colorado Island (BCI), Panama, is shown below. Closely related species of Psychotria differ remarkably in their foliar chemistry.
Our recent work has generated community-wide datasets of plant defense chemistry and herbivore relationships in order to test fundamental hypotheses that plant-enemy interactions i) facilitate tree species coexistence in hyperdiverse forest communities (Janzen 1970, Connell 1971), ii) drive the evolutionary diversification of plants by selecting for novel chemical defenses (Ehrlich & Raven 1964), and, by varying in importance over latitude, iii) explain the ten- to hundred-fold disparity in tree diversity at small spatial scales observed between temperate and tropical forests (Fischer 1960, Schemske 2009). In our recent publications, we have found differences in the foliar metabolome among congeneric species to be far greater than sources of within-species variation due to leaf ontogeny, light environment, and precipitation season (Sedio et al. 2017 Ecology). In comparing the metabolomes of tree communities in Maryland and Panama, we observed a profound difference in the chemical diversity of a temperate and a tropical forest, driven by striking differences in secondary metabolites among congeneric species in a handful of species-rich tropical tree genera (Sedio et al. 2018 Ecology). These results suggest that the chemical defenses reflected in plant metabolomes play a fundamental role in plant ecology and evolution. Furthermore, they illustrate the emerging power of metabolomics to shed light on basic questions in community ecology (Sedio 2017 New Phytologist).
Ongoing work: Chemical ecology at the regional scale. In May 2018 we began collecting leaf samples from ca. 500 tree species from the Barro Colorado Nature Monument in Panama. Over the next three years, we aim to analyze secondary metabolites in as many as 2000 tree species in Panama in a network of 1-ha forest dynamics plots established by Rick Condit (Field Museum, ForestGEO) and Jim Dalling (University of Illinois). Our goal is to understand how secondary metabolites affect survival, growth, and recruitment by distinguishing seedlings and saplings from their neighbors, and the strength of such chemical niche differences may vary with precipitation, elevation, and species richness at the regional scale within Panama. If you are interested in joining this project as a postdoc based at the Smithsonian Tropical Research Institute in Panama, please contact Brian (sediob at utexas dot edu) or Joe Wright (wrightj at si dot edu).
Ongoing work: Chemical ecology at the continental and global scale. With support from the National Science Foundation and through collaborations with the PIs of forest dynamics plots in the Forest Global Earth Observatory (ForestGEO) network coordinated by the Smithsonian Institution, we are planning to examine the importance of species differences in secondary metabolites for neighborhood effects on survival, growth, and recruitment in forest dynamics plots spanning a range of variation in climate and latitude, from subarctic boreal forest to tropical rain forest.
Thousands of secondary metabolites distinguish plants in the eyes of their natural enemies. For example, the Bean Family (Leguminosae) alone synthesizes over 20 major classes of secondary compounds (Wink 2003). This variety of plant chemical defense has long precluded chemical analysis at the large taxonomic scales required for the study of macroevolution and community ecology. Recent advances in mass spectrometry (MS) developed by my collaborator Pieter C. Dorrestein at the University of California, San Diego, however, enable the high-throughput comparison of the structures of unknown compounds (Wang et al. 2016), making possible comparative metabolomics at unprecedented scales necessary for the study of chemical community ecology and macroevolution (Sedio 2017).
Novel methods for generating molecular networks using mass spectra are able to capture the structural similarity of unknown compounds because molecules with similar structures fragment into many of the same sub-structures (Wang et al. 2016). Molecular networks can therefore quantify chemical similarities between samples even though few compounds are unambiguously identified, which is essential in chemically diverse and understudied tropical forests. A molecular network of 7,665 unique molecules derived from the 21 species of Psychotria (Rubiaceae) found on Barro Colorado Island (BCI), Panama, is shown below. Closely related species of Psychotria differ remarkably in their foliar chemistry.
Our recent work has generated community-wide datasets of plant defense chemistry and herbivore relationships in order to test fundamental hypotheses that plant-enemy interactions i) facilitate tree species coexistence in hyperdiverse forest communities (Janzen 1970, Connell 1971), ii) drive the evolutionary diversification of plants by selecting for novel chemical defenses (Ehrlich & Raven 1964), and, by varying in importance over latitude, iii) explain the ten- to hundred-fold disparity in tree diversity at small spatial scales observed between temperate and tropical forests (Fischer 1960, Schemske 2009). In our recent publications, we have found differences in the foliar metabolome among congeneric species to be far greater than sources of within-species variation due to leaf ontogeny, light environment, and precipitation season (Sedio et al. 2017 Ecology). In comparing the metabolomes of tree communities in Maryland and Panama, we observed a profound difference in the chemical diversity of a temperate and a tropical forest, driven by striking differences in secondary metabolites among congeneric species in a handful of species-rich tropical tree genera (Sedio et al. 2018 Ecology). These results suggest that the chemical defenses reflected in plant metabolomes play a fundamental role in plant ecology and evolution. Furthermore, they illustrate the emerging power of metabolomics to shed light on basic questions in community ecology (Sedio 2017 New Phytologist).
Ongoing work: Chemical ecology at the regional scale. In May 2018 we began collecting leaf samples from ca. 500 tree species from the Barro Colorado Nature Monument in Panama. Over the next three years, we aim to analyze secondary metabolites in as many as 2000 tree species in Panama in a network of 1-ha forest dynamics plots established by Rick Condit (Field Museum, ForestGEO) and Jim Dalling (University of Illinois). Our goal is to understand how secondary metabolites affect survival, growth, and recruitment by distinguishing seedlings and saplings from their neighbors, and the strength of such chemical niche differences may vary with precipitation, elevation, and species richness at the regional scale within Panama. If you are interested in joining this project as a postdoc based at the Smithsonian Tropical Research Institute in Panama, please contact Brian (sediob at utexas dot edu) or Joe Wright (wrightj at si dot edu).
Ongoing work: Chemical ecology at the continental and global scale. With support from the National Science Foundation and through collaborations with the PIs of forest dynamics plots in the Forest Global Earth Observatory (ForestGEO) network coordinated by the Smithsonian Institution, we are planning to examine the importance of species differences in secondary metabolites for neighborhood effects on survival, growth, and recruitment in forest dynamics plots spanning a range of variation in climate and latitude, from subarctic boreal forest to tropical rain forest.
Plant-microbe interactions
Ongoing work: We study the communities of microbial endophytes that occur within the leaves of trees in four ForestGEO plots in collaboration with researchers at the SmithsonianTropical Research Institute, Wilfred Laurier University, the University of Michigan, and UC Santa Cruz. These four forests comprise a Canadian boreal forest (Scotty Creek, Northwest Territories, Nicola Day and Jenn Baltzer), an eastern U.S. deciduous forest (University of Michigan 'Big Woods' plot, Tim James and Chris Dick), a mediterranean-climate forest in California (UC Santa Cruz, Greg Gilbert), and a tropical moist forest (Barro Colorado Island, Panama, Jordan Kueneman). Our goal is to relate the host use patterns of fungal and bacterial endophytes to differences in secondary chemistry among potential host plant species, as well as plant phylogeny and community diversity.
Chemical evolution
Ongoing work: We are exploring the comparative metabolomics and genomics of tree species from Panama. Our goal is to understand chemical evolution and its contribution to diversification in trees by testing basic predictions derived from the hypothesis that species-rich tree genera represent adaptive radiations, the diversification of which is driven by the evolution of defensive secondary metabolites. This work is led by University of Texas at Austin Stengl-Wyer Postdoctoral Fellow Dr. Guillaume Dury. PhD student Christian López is investigating the relationships between climate, geography, phylogeny, and secondary metabolites in ferns and lycophytes.
Trait evolution and biogeography
The biogeographic history of taxa has the potential to greatly influence our understanding of evolutionary and even ecological processes often thought to occur at finer spatiotemporal scales. In a particularly striking example, we examined the community structure of the Psychotria of BCI, Panama in light of their geographic history, and found that nearly 50% of the variation in hydraulic traits and habitats was associated with the region of the Neotropics in which each species originated prior to dispersing to central Panama (Sedio et al. 2013). Furthermore, we developed phylogenetic models of climatic niche evolution for 253 species of Psychotria by measuring climatic data for over 20,000 georeferenced herbarium specimens from the Missouri Botanical Garden, most of which had been authoritatively identified by Rubiaceae specialist and collaborator Charlotte Taylor. Accounting for the geographic origins of branches in this larger Psychotria phylogeny substantially improves the fit of phylogenetic models of climatic niche evolution in the clade (Sedio et al. 2013). In combination, these results suggest that even very local-scale niche differences and their prevalence in the community may be strongly influenced by historical migration rather than in situ trait evolution. This conclusion therefore challenges the utility of the local community as a unit for understanding diversity by extending the mechanisms responsible for observed niche differences to biogeographic scales of time and space.
