Nitrogen-fixing symbioses, particularly in the form of root nodules, are major drivers in many terrestrial ecosystems. Remarkably, these evolutionary strategies are concentrated in one small branch of the plant tree of life, traditionally thought to be due to an underlying "predisposition" that enabled multiple subsequent origins of plant-microbe symbioses (increasingly genomic evidence is suggesting the possibility of a single origin followed by dozens of losses). Commonalities and differences among multiple origins of the nodule organ, assessed at multiple levels from genes to ecology, will be highly relevant to crop improvement in non-fixing lineages.
Given the presence of multiple evolutionary transitions, and high diversity across phylogenetic and phenotypic axes, this clade is an exemplar for elucidating the mechanisms behind symbiotic strategies. I am using previously developed approaches (below) and newly assembled trait and phylogenomic datasets to investigate the evolutionary context that led to global dominance and species richness of this clade. This research is supported by UF seed funding and a recently funded Department of Energy grant focused on massive phylogenomic approaches to elucidating and engineering symbioses.
Niche biology in the Saxifragales
The Saxifragales are an ancient, relatively isolated clade of angiosperms associated with the Rosids and Vitales, whose heterogeneous composition is one of the great surprises of plant molecular systematics. In comparison with other clades at this level, it is relatively modest in size but exhibits a vast diversity of habitats. For instance, in this group one finds desert succulents closely related to aquatic weeds, or forest dwellers near alpine cushion plants. I am using this clade as a test case for new ideas in integrating niche modeling and phylogenetics to examine historical habitat transitions.
Part of this work involves some methods development in the field of phyloclimatic modeling. Another important element is the use of collections; I have sequenced hundreds of specimens, including collections made over a century ago. This part of my work was funded as part of the first cohort of collections postdocs in the NSF PRFB program. Undergraduate students have played a major role in data collection for this project.
Deep hybridization in Heuchera
Heuchera has frequently been cited as a model for chloroplast capture, but recently developed sequencing technologies and coalescent methods have allowed me to return to this system with a high-resolution and probabilistically rigorous phylogenomic approach. This work has revealed deep phylogenetic incongruence involving Heuchera and two closely related genera, as well as numerous instances within the genus. I have also developed methods for ancestral reconstruction of niche space in order to evaluate how historical range dynamics during historical climatic cooling drove gene flow.