Dissertation Research: The Role of Hybridization in the Evolution of Argyranthemum in Macaronesia

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9902276Jansen and Goertzen Oceanic islands are ideal natural laboratories for studying evolutionary processes. Their isolation, environmental variability, and easily determined ages have aided biologists ever since Darwin in unraveling the forces behind evolutionary change. Our understanding of natural hybridization, a potentially major force in plant and animal evolution, has been advanced considerably by studies of species in the Hawaiian and Juan Fernandez islands in particular. Under the direction of Dr. Robert K. Jansen at the University of Texas at Austin, graduate student Leslie Goertzen is studying the role of hybridization in the evolution of the plant genus Argyranthemum (family Asteraceae). This group of 24 species found only in the Macaronesian archipelagos (Canaries, Madeira, and Salvage islands) is a spectacular example of adaptive radiation throughout the islands' elevational zones and has many characteristics which make it a model system for addressing evolutionary questions. This study will examine evidence for ancient introgression in the genus as well as the dynamics and consequences of contemporary species contact. A phylogenetic framework for these island plants will be constructed using variable nuclear DNA sequences, and a statistical comparison between these data and maternally inherited chloroplast DNA will be performed. Preliminary data suggest significant incongruence between the two data sets for several species pairs, raising the possibility of introgressive hybridization during the evolution of these lineages. Specific cases of contemporary hybridization will be examined by screeningnatural and hybrid populations for species-specific nuclear and chloroplast genetic markers. This will allow the direction and extent of interspecific gene flow, if any, to be determined. Potential hybrids of species from different elevational zones are of special interest, for understanding factors causing shifts into new habitats. In addition, the analyses will provide data of relevance to conservation efforts for several rare species and contribute to the understanding of a theoretical process which threatens many organisms in isolated conditions, extinction via hybridization.