DISSERTATION RESEARCH: Investigating the main contributors to plant speciation in a rapidly diverging lineage in western North America

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Studies of the process of speciation, or the splitting of one species into two, have most often taken the approach of intensive study of a single species or species pair, and have therefore focused on the primary driver of divergence of that one event. If instead, we take a longer-time, evolutionary view of speciation, examined through the lens of evolutionary relationships and the traits that are important for recognizing and defining species, we have the opportunity to investigate the relative contributions of the properties of a species at both the level of recent speciation events and back through the evolutionary history of the group. This implies that we can confidently identify and describe species. Molecular, morphological, ecological, and/or geographic variation often serve as evidence of boundaries between one species and another, however, when used alone, these characteristics are not always capable of differentiating species. This study will contribute significantly to empirical tests of the theory and methodologies of species delimitation, and will bridge the gap between theoretical, empirical, and applied sciences. By working towards definitions of species that reflect their evolutionary histories, this project will contribute to the discovery, conservation, and management of biodiversity in western North America. Finally, this research will directly impact the training and academic development of the co-PI through the learning of new laboratory, field, and analytical techniques, as well as the mentoring and training of undergraduates. This project aims to identify the macroevolutionary signatures of speciation via the identification of species criteria, the robust delimitation of species, and the evaluation of the contribution of individual species criteria across a phylogeny, to begin to construct a broad picture of speciation in the mountains of western North America. To accomplish this objective, this project entails 1) the collection of extensive species criterion data (i.e., molecular, morphological, ecological, geographic, and cytological data, 2) the application of rigorous species delimitation methods (using multiple individual criteria and an integrated data approach) focused on poorly resolved nodes in a genus-wide phylogeny, and 3) the examination of the relative contributions of individual species criteria through comparative phylogenetic analyses of the rate of trait evolution through time. Several western North American species complexes from the diverse perennial clade of the paintbrushes (Castilleja, Orobanchaceae) are the model system for approaching these questions, and were selected for their contrasting variation in morphological, ecological, and cytological characteristics.