Dissertation Research: Austral Biogeography: The Evolution of Subalpine Ourisia (Scrophulariaceae) in a Phylogenetic Context

University Of Texas At Austin, Austin TX

Investigators

Abstract

Summary (word count: 223) Ever since naturalist Joseph Dalton Hooker explored the southern continents over 150 years ago, biologists have been interested in understanding the current distributions of related organisms in southern South America, Australasia, and/or Africa. It has been argued that this austral biogeographic pattern is associated with the vicariant breakup of Gondwana that began over 80 million years ago, but a competing hypothesis suggests that the same pattern might have arisen more recently via long-distance dispersal. Fossil evidence and results from phylogenetic studies corroborate the vicariance paradigm for some woody forest groups, but few studies have focused on higher elevation herbaceous genera in southern regions. It has been suggested that these alpine herbs may not be relics of a widespread Gondwana flora, but rather the result of more recent events. Recentness is likely in alpine groups because these herbs occur in habitats that have existed only since the final Quaternary uplift of high-elevation mountains in New Zealand and South America. The subalpine, herbaceous genus Ourisia (Scrophulariaceae) comprises about 35 different species that are distributed throughout the South American Andes from Venezuela to Tierra del Fuego, the mountains of New Zealand, and high-elevation regions of Tasmania. We will reconstruct the evolutionary history of Ourisia using DNA sequence data and morphology to investigate vicariance and dispersal hypotheses as potential explanations for the austral biogeography of the genus. Significance (word count: 235) Our comprehensive phylogenetic study of Ourisia (Scrophulariaceae) presents a valuable opportunity to expand our understanding of the austral biogeographic pattern. Most biogeographic studies of plant groups that exhibit this southern distribution have focused on woody forest groups such as Nothofagus (Nothofagaceae), Araucaria (Araucariaceae), and closely related genera in Atherospermataceae. Although Gondwanan vicariance is a good model for these ancient groups, it may not apply to high-elevation herbaceous plants such as Ourisia that occupy habitats that are of more recent Quaternary origin. In addition to its biogeographical significance, our study will also allow us to examine some evolutionary patterns within Ourisia. Because Ourisia exhibits ample variation in floral morphology, chromosome number, habit, and vegetative characters, a comprehensive morphological study will provide new insights into character evolution in the genus. We will also examine radiation patterns of species in the mountains of New Zealand and South America, and discuss the general implications of areas where the phylogenetic pattern of Ourisia is congruent with current or historical barriers, geology, and climate. Our study will thus provide a reconstruction of the evolutionary history of Ourisia that we can use to: 1) provide a better understanding of the relationships of species within the genus, and between Ourisia and its closest relatives, 2) examine the biogeography of Ourisia and assess patterns of radiation within each geographical region, and 3) investigate evolution of chromosome number and morphological characters in the genus.