Phylogenetics of Acanthaceae: A nested approach to resolving relationships of Acanthaceae and their closest relatives

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Dr. Lucinda McDade of the Philadelphia Academy of Natural Sciences and Dr. Thomas Daniel at the California Academy of Sciences are conducting a collaborative study to resolve phylogenetic relationships at several levels within the diverse (4,000 species), largely tropical plant family Acanthaceae and between these plants and their closest relatives in the order Lamiales (mints and relatives). The primary source of data will be DNA sequences from chloroplast and nuclear genes; in addition, morphological information (including pollen) and chromosome counts will also be acquired whenever possible. The work to be accomplished has four goals; these were chosen to test hypotheses regarding relationships, to interpret morphological evolution, to contribute toward understanding the evolution of pollinator relationships in Acanthaceae, and to provide data for continued studies of molecular evolution. Goal 1 is to identify the closest living relatives of Acanthaceae. Goal 2 is to establish the precise phylogenetic placement of the black mangrove genus Avicennia. These plants have been shown by previous work to be closely related to Acanthaceae. Goals 3 and 4 are to clarify relationships within two sublineages of Acanthaceae, Acantheae and Justicieae. Taxon sampling and data gathering strategies will complement existing and on-going projects, with field work in Madagascar providing critical new samples along with material from Africa and South America from colleagues there. Regions of DNA to be sequenced were determined by the level of relationships to be resolved: higher level work (goals 1 and 2) requires sequences from relatively slowly evolving loci, whereas work within Acanthaceae (goals 3 and 4) requires sequences from gene regions that are evolving more rapidly. The species richness, extreme morphological diversity, and nearly worldwide distribution of Acanthaceae mean that achieving the goals of this project will have impact beyond systematics. In the context of phylogenetic relationships, derived characters can be sorted from primitive characters to clarify both the pattern of morphological evolution and suggest testable ideas about process. Plants interact with environments as morphological beings and thus morphology is key to understanding ecological and evolutionary processes. For example, by interpreting morphological evolution, the stage is set for studies of the evolution of pollinator relationships. Acanthaceae have been thought of as Gondwanan in origin, but it is clear that biogeographic history has been much more complicated than simple vicariance. The research proposed will point to groups of tractable size with which to address historical biogeography. Finally, it is clear that there are fascinating problems of molecular evolution in this group. The non-coding DNA regions for which sequences are available are not evolving in a clock-like fashion throughout the group. Adding sequences for protein-coding genes (part of the work to be accomplished during this project) will not only provide better resolution of phylogenetic relationships but will also advance knowledge of the relationship between morphological and molecular diversity.