Investigating habitat shift in Symphyotrichum subg. Virgulus: A three-way integration of morphology, ecological niche, and phylogenomics

The radiation of species in a changing environment can be understood by investigating morphological evolution through time. Accomplishing the three-way overlay of phylogenetic, ecological, and morphological relationships among species allows the investigation of the radiation process and particularly disentangling phylogenetic niche conservatism (PNC) and rapid, convergent change, which often co-occur in clades in a complex matrix. Here, we investigated morphological and ecological disparification in Symphyotrichum subg. Virgulus ( Symphyotrichum , Asteraceae) from a comparative perspective by integrating 13 morphometric characters, 36 environmental predictor variables capturing aspects of climate, soil, land cover, and topography, and a well-resolved phylogeny. Species were significantly different across morphological and environmental axes; both Pagel’s λ and Blomberg’s K revealed a lack of phylogenetic signal in overall morphological and environmental space, although individual morphologies and niche attributes often showed strong signal. We further evaluated the distinct habitat shifts by clustering quantitative niche descriptors into categorical habitat classifications. We found independent evolution of most of the examined morphological traits and environmental variables, and a complex and possibly discordant relationship of morphological aspects with niche shift and evolutionary history. Morphological evolution was more strongly shaped by habitat than phylogeny. Moreover, we found evidence for multiple major habitats shifts during the climatic volatility of the Pleistocene epoch, yet other species radiated in the ancestral habitat, possibly explaining discordant morphology-environment relationships.