Evolutionary relationships in Afro-Malagasy Schefflera (Araliaceae) based on nuclear and plastid markers

Abstract

EVOLUTIONARY RELATIONSHIPS IN AFRO-MALAGASY SCHEFFLERA (ARALIACEAE) BASED ON NUCLEAR AND PLASTID MARKERS By Morgan Robert Gostel, M.S. Biology A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science at Virginia Commonwealth University. Virginia Commonwealth University, 2010. Thesis Director: Dr. Gregory M. Plunkett, Affiliate Research Professor, Department of Biology and Director, Cullman Program for Molecular Systematics, The New York Botanical Garden Thesis Co-Director: Dr. Rodney J. Dyer, Associate Professor, Department of Biology The genus Schefflera is the largest in Araliaceae, with approximately 900 species. Recent studies have shown that Schefflera is polyphyletic and represents no fewer than five distinct clades, each corresponding to a specific geographic region including Asia, continental Africa and Madagascar, Melanesia, the Neotropics, and a small clade distributed throughout several islands in the insular Pacific Ocean. The Afro-Malagasy clade contains nearly 50 species distributed throughout tropical, sub-Saharan Africa, Madagascar, the Comoros, and the Seychelles islands. Previous studies have suggested that this group is monophyletic, identifying two smaller subclades within Afro-Malagasy Schefflera corresponding roughly to informal groups identified as “Meiopanax” and “Sciodaphyllum” on the basis of morphology. Using sequence data from nuclear rDNA spacers and plastid markers derived from 32 of the 48 currently circumscribed species of Afro-Malagasy Schefflera, this study tested the monophyly of Afro-Malagasy Schefflera and of each of its two proposed subclades. Trees based on this molecular data were used to examine patterns of morphological evolution and biogeography among species in the clade. Results support the monophyly of Afro-Malagasy Schefflera and both subclades, which correspond closely to “Meiopanax” and “Sciodaphyllum” which are herein referred to as Neocussonia and Astropanax, respectively. Additional interspecific relationships were examined, which provides evidence for hybridization among several species. Schefflera myriantha, the most widely distributed species of Afro-Malagasy Schefflera, is paraphyletic with respect to two other species, S. humblotiana and S. monophylla. Many morphological features historically used to distinguish species of Afro-Malagasy Schefflera appear to be evolutionarily labile, with a history of gains and losses (e.g., reduction in leaflet number, which occurs independently in both subclades). Biogeographic analyses suggest an African ancestry for the entire Afro-Malagasy Schefflera clade, and for both subclades, with two independent divergence events to Madagascar.