Yi-Hsin Erica Tsai

Research Interests

My research examines how communities change through space and time. Through examples from the fossil record and molecular phylogeography we know that species respond individually to climate change; however, they often are constrained by the same ecological or geographical barriers so that similar species associations may reassemble in new spaces. I am interested in how closely associated species, such as hosts and parasites, respond to climate drivers and change their distributions with relation to one another. My dissertation work focuses on reconstructing the past colonization history of a parasitic plant, Epifagus virginiana, with relation to the migration history of its host tree, Fagus grandifolia. In my future research I would like to further explore these interests in comparative phylogeography, landscape genetics, and symbiotic interactions.

Comparative phylogeography

Ecological, evolutionary, and spatial processes have shaped the present day distribution and population structure of species. Considering multiple species histories together allows us to understand the cohesiveness of a community and gives a spatial and temporal view of interspecies associations. In my dissertation I investigate the invasion biology of a parasitic plant and consider the effects of host density, host population structure, and concurrent host range shifts. Paleo-pollen and molecular phylogeographic data on the host provides hypotheses of how these host effects may have controlled the spread of this parasite and dictated its migration routes. These hypotheses are rigorously tested using multiple analytical techniques such as Bayesian coalescent methods and assignment tests. From this work I see the necessity of improving these methods and developing novel approaches to analyzing multiple species datasets. For example, I know how difficult and critical it is to define good hypotheses. I would like to explore the utility of using niche modeling to generate reasonable hypotheses of glacial refugia and migration routes which phylogeographic datasets can test.

Landscape genetics

Phylogeographic studies often focus on the phylogenetic or population genetic components of a dataset and neglect the corresponding spatial information. We can more effectively incorporate the geographic data into our analyses of population history by borrowing tools from landscape ecology and including spatially explicit GIS-based analyses into our studies. I’ve taken this approach with my host-parasite dataset by performing Monmonier’s analyses, landscape interpolations, and spatially explicit assignment tests. Furthermore, I’ve developed a web-based tool, PhyloGeoViz, that visualizes phylogeographic information on a map to encourage consideration of geography in analyses. One of the next steps would be to explore the effects of specific environmental variables on the genetic landscape through use of quantitative GIS models. The interface between geography and population biology promises to provide new more powerful analytical tools, and I would like to expand my research in this area.

Symbiotic interactions

Interspecies interactions shape the evolutionary trajectories of all actors, but how do those members become associated in the first place? Comparative phylogeography and landscape genetics can infer whether the geographic associations between species are long-lived or fleeting. The historical connections between species provide important context in understanding what evolutionary and ecological processes are in operation. Furthermore, knowledge of the population structures of multiple community members is necessary to predict the coevolutionary dynamics in the system. For example, I study the fine scale population structure and patch dynamics of a host-parasite pair to characterize processes of local adaptation and density effects. I have studied primarily host-parasite interactions, but I am interested in many types of interspecies interactions such as endosymbionts, mutualists, and plant-pollinator dynamics. In particular, I have an interest in disease ecology and pathogen population dynamics. Emerging diseases coupled with invasive species provide an interesting system where we can apply knowledge of the past invasion history to forecast community changes in order to shape conservation, crop protection, and management strategies.