Systematics and biogeography of the Pandanaceae with a population genetics approach to the "Pandanus tectorius problem."

Abstract

This research investigates the systematics and biogeography of the Pandanaceae, an angiosperm family in the monocot order Pandanales. In the first stage of this research, I tested relationships among the genera of the Pandanaceae and subgenera of the genus Pandanus in a time-calibrated molecular phylogenetic framework. The phylogeny reconstruction was then used to infer the biogeographic history of the family and the evolution of key traits related to dispersal and population establishment. In the second phase of this research, I investigated the origins, membership, population dynamics, and dispersal pathways of the widespread ocean-dispersed "Pandanus tectorius complex." The impetus for this study stems from the fact that there has been considerable taxonomic debate as to the delimitation of species, and relationships between taxa were poorly understood impeding research on the group. Further, although ocean-dispersal is one of three main modes of transport for colonizing organisms to reach islands, there have been few systems studied thus far to explore biogeographic patterns among ocean-dispersed angiosperms. The P. tectorius complex represents a useful system to this end due to its widespread distribution, aspects of its dispersal biology, and the morphological diversity represented within the group which suggests an atypical degree of diversity for an ocean-dispersed angiosperm lineage. Results include the first well supported molecular phylogeny of the Pandanaceae. The family likely originated in the Late Cretaceous in Laurasia and subsequently spread across the paleotropics through the actions of long-distance-dispersal. Berries are the ancestral fruit condition while aerenchyma-containing drupes capable of floatation evolved in the common ancestor of Martellidendron, Benstonea, and Pandanus. The P. tectorius complex has its origins in coastal eastern Queensland Australia within the past five million years. Pandanus tectorius is part of an adaptive radiation of species in Australia, each of which inhabits a specific habitat. The P. tectorius complex has subsequently spread throughout the tropical Indo-Pacific. Limitations to migration between geographic regions and the establishment of inland populations away from coastal areas have resulted in substantial population substructure. In some cases, isolated populations have evolved into unique species.