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(American Journal of Botany. 2009;96:2087-2099.) doi: 10.3732/ajb.0900021 © 2009 Botanical Society of America, Inc.

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Evolutionary relationships, interisland biogeography, and molecular evolution in the Hawaiian violets (Viola: Violaceae)¹

² Department of Biology, Campbell University, Buies Creek, North Carolina 27506 USA ³ Laboratory of Vascular Plant Systematics and Evolution, Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701 USA ⁴ Department of Botany, University of Wisconsin, Madison, Wisconsin 53706 USA

ABSTRACT

The endemic Hawaiian flora offers remarkable opportunities to study the patterns of plant morphological and molecular evolution. The Hawaiian violets are a monophyletic lineage of nine taxa distributed across six main islands of the Hawaiian archipelago. To describe the evolutionary relationships, biogeography, and molecular evolution rates of the Hawaiian violets, we conducted a phylogenetic study using nuclear rDNA internal transcribed spacer sequences from specimens of each species. Parsimony, maximum likelihood (ML), and Bayesian inference reconstructions of island colonization and radiation strongly suggest that the Hawaiian violets first colonized the Maui Nui Complex, quickly radiated to Kaua’i and O’ahu, and recently dispersed to Hawai’i. The lineage consists of "wet" and "dry" clades restricted to distinct precipitation regimes. The ML and Bayesian inference reconstructions of shifts in habitat, habit, and leaf shape indicate that ecologically analogous taxa have undergone parallel evolution in leaf morphology and habit. This parallel evolution correlates with shifts to specialized habitats. Relative rate tests showed that woody and herbaceous sister species possess equal molecular evolution rates. The incongruity of molecular evolution rates in taxa on younger islands suggests that these rates may not be determined by growth form (or lifespan) alone, but may be influenced by complex dispersal events.

Key Words: adaptive radiation • biogeography • character evolution • dispersal • Hawaiian Islands ITS • relative rate • Viola • Violaceae

Received for publication 17 January 2009. Accepted for publication 26 June 2009.

FOOTNOTES

¹ S. Perlman and E. Misaki provided collection locations for violet populations on Moloka’i. M. Walsh and K. Brown assisted in collecting on Moloka’i, and The Nature Conservancy of Moloka’i provided collection permits for the Kamakou Preserve. S. Wyatt, H. Sanders, D. Luesse, V. Nadella, P. Pyle, R. Pyle, S. Aruch, L. Sack, M. Sporck, K. Tachibana, and C. O’Connell provided support with analyses and collections. M. Vis and E. Linton assisted with Bayesian analyses. This article benefited from the constructive comments of M. Vis and D. Drake. M. Clark, H. Oppenheimer, R. Gustafson, and the O’ahu Army Natural Resources Program provided images of Hawaiian violets. This work was supported by an Ohio University Baker award to H.B. and Ohio University Student Enhancement and Graduate Student Senate awards and an American Philosophical Society Lewis and Clark Grant for Exploration and Field Research award to J.C.H.

⁵ Author for correspondence (e-mail: havran{at}campbell.edu)

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