Comparative Morphology and Population Genomics of Naturally Co-Occurring North American Vitis Species

Leaf morphological variation in plants is can indicate genetic and environmental interaction. Through the study of leaf morphology, we can apply meaningful context to genetic regulation and development as well as glean insights into mechanisms of variation, such as recombination through intra- or interspecific gene flow. In turn, variation provides the necessary materials for natural selection to drive larger ecological and evolutionary processes such as local adaptation through natural selection, speciation, or ecological divergence. Economically important and ecologically pervasive North American Vitis species offer a unique opportunity to examine some of these evolutionary patterns. These species are long-lived, woody, ubiquitous members of eastern North American temperate forests, many with largely overlapping distributions. Interspecific hybridization is widely used in viticulture to produce more vigorous plants and is well documented in nature; however, the extent of gene flow among North American Vitis congeners within natural populations remains underexplored. This dissertation investigates patterns of morphological variation as well as genetic structure and differentiation in two closely related species, V. riparia and V. rupestris, and their co-occurring congeners. Vitis leaves are frequently used in evolutionary studies and cultivation practices, which make excellent characters for describing patterns of variation. First, leaf morphological variation within and among species and between individuals of V. riparia and V. rupestris were described, revealing a continuum of distinct leaf shapes within these levels of biological organization. Next, genotyping-by-sequencing (GBS) and digital leaf morphometrics were used to characterize Vitis individuals at seven field sites in the Midwest United States across the distributions of V. riparia and V. rupestris . Using GBS data, six genetic clusters were detected, with evidence for some genetically admixed individuals. This pattern of genetic differentiation is coherent with existing Vitaceae phylogenetic relationships and morphological species descriptions for six taxa. Leaf shape data analyzed using digital morphometric techniques largely support these species designations. Interestingly, there was preliminary observational evidence that V. rupestris leaf morphology exhibits a narrower range of variation when growing in sympatry with V. vulpina than when it occurs in allopatry. This pattern may be indicative of ecological competition occurring between these two Vitis species. These data support evidence for the role of species maintenance in the presence of interspecific gene flow and advocate for the examination of complex evolutionary histories through multiple means.