Dissertation Research: Evolution of Growth Form and Phytochemical Consequences in Adenia (Passifloraceae)

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Is it possible that a plant's growth form predicts plant chemistry? We investigate the association between evolutionary changes in growth form and shifts in plant chemistry with this research. The genus Adenia (Passifloraceae) provides an ideal group to research this and related questions. With ca. 90 species, species in this group have diversified into trees, succulent shrubs, tuberous herbs, tuberous vines, caudiciforms, fibrous rooted vines, and lianas, as well as variants on these basic forms. In addition to this remarkable growth form radiation, the chemistry is varied and appears to play an important role in the plants' interactions with Acraea caterpillars and various Chyrsomelidae which use Adenia as a host. By constructing a molecular phylogenetic hypothesis of the relationships of species in Adenia, we hope to test the monophyly of the group and determine where Adenia fits within the Passifloraceae family. During the second phase of the research, we investigate the development and evolution of stem anatomy as it relates to growth form. We test the hypotheses that the ancestral growth form is a vine (implying that the trees, shrubs, and herbs are derived from vines) and that the succulence observed in the trees and shrubs is a result of paedomorphic processes. Ultimately, we map leaf cyanogenesis and leaf tannin content on the phylogeny to test hypotheses developed from allocation theory and apparency theory. We believe that cyanogenesis will be highest in vines whereas tannins will be most concentrated in other more "apparent" growth forms. Furthermore, we predict that changes in stem anatomy will correlate with changes in chemistry. Species of Adenia are distributed throughout the Old-World tropics. Hearn has traveled to South and Eastern Africa to make field collections and observations of the Adenia there. This fall and winter, 2001, he will travel to Madagascar to research the 20 Adenia endemics found there. This DDIG support provides the funding to carry out both the Malagasy research, the anatomy research, and parts of the molecular and chemistry research.