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EVOLUTION OF THE HAWAIIAN VIOLETS ( VIOLA )

EVOLUTION OF THE HAWAIIAN VIOLETS ( VIOLA ). HARVEY E. BALLARD, JR. Department of Environmental and Plant Biology, and Molecular and Cellular Biology Program, Ohio University. EVOLUTION OF THE HAWAIIAN VIOLAS. Evolutionary relationships of Hawaiian violets

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EVOLUTION OF THE HAWAIIAN VIOLETS ( VIOLA )

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  1. EVOLUTIONOF THE HAWAIIAN VIOLETS (VIOLA) HARVEY E. BALLARD, JR. Department of Environmental and Plant Biology, and Molecular and Cellular Biology Program, Ohio University

  2. EVOLUTION OF THE HAWAIIAN VIOLAS • Evolutionary relationships of Hawaiian violets • Relationships among Hawaiians, Diversification and Inter-Island Dispersal • Adaptive Radiation • Biogeographic Source and Mechanism

  3. GROWTH HABITS OF HAWAIIAN VIOLAS treelet/tall shrub (V. tracheliifolia) erect shrub (V. chamissoniana, V. robusta, V. oahuensis, V. waialenalenae) creeping herb/subshrub (V. kauaensis, V. maviensis)

  4. QUESTIONS ABOUT HAWAIIAN VIOLAS What does DNA data reveal about the origin and relationships of the Hawaiian violets that morphology cannot? Does the evolutionary pattern of the Hawaiian violets conform to the “progression rule”?

  5. QUESTIONS ABOUT HAWAIIAN VIOLAS What typical features of an “adaptive radiation” are demonstrated by Hawaiian violets? How did the ancestral seed get from the Arctic to Kauai?

  6. EVOLUTION OF THE HAWAIIAN VIOLAS • Evolutionary relationships of Hawaiian violets • Relationships among Hawaiians, Diversification and Inter-Island Dispersal • Adaptive Radiation • Biogeographic Source and Mechanism

  7. PHYLOGENETIC TREE FROM DNA SEQUENCE DATA FOR GENUS VIOLA WORLDWIDE • Hawaiians not basal w/Latin Americans • Hawaiians form a “natural” group • Nearest relative is Viola langsdorffii

  8. PREVIOUSLY HYPOTHESIZED RELATIVES OF THE HAWAIIAN VIOLAS Viola kauaensis Viola rubella Viola tracheliifolia Viola waialenalenae Viola stipularis

  9. NEW DNA EVIDENCE--ARCTIC TUNDRA BOG VIOLET, VIOLA LANGSDORFFII, IS NEAREST RELATIVE TO THE HAWAIIAN VIOLAS!! • Northern Pacific rather than Latin American origin for Hawaiians • Herbaceous rather than woody ancestry • Wetland origin

  10. EVOLUTION OF THE HAWAIIAN VIOLAS • Evolutionary relationships of Hawaiian violets • Relationships among Hawaiians, Diversification and Inter-Island Dispersal • Adaptive Radiation • Biogeographic Source and Mechanism

  11. PHYLOGENETIC TREE FROM DNA SEQUENCE DATA FOR HAWAIIAN AND RELATED VIOLAS • Branch lengths shorter in Hawaiian violets than others in related groups • Short basal branches in Hawaiiansabrupt diversification

  12. PHYLOGENETIC TREE SHOWING ISLAND DISTRIBUTIONS AND HABITATS OF HAWAIIAN VIOLAS • Basal species diversified on Kauai • Arctic bog violet yielded first dry-land, then wet-land plants • Dispersal/diversifi-cation west to east

  13. INFERRED SEQUENCE OF SPECIATION AND DISPERSAL EVENTS IN HAWAIIAN VIOLA

  14. EVOLUTION OF THE HAWAIIAN VIOLAS • Evolutionary relationships of Hawaiian violets • Relationships among Hawaiians, Diversification and Inter-Island Dispersal • Adaptive Radiation • Biogeographic Source and Mechanism

  15. CANONICAL VARIATES ANALYSIS OF HAWAIIAN VIOLA TAXA USING LEAF CHARACTERS

  16. PRINCIPAL COMPONENTS ANALYSIS OF LEAF CHARACTERS SHOWING HABITAT ASSOCIATIONS

  17. PHYLOGENETIC TREE HABITATS AND GROWTH FORMS OF HAWAIIAN VIOLAS • Growth form not linked to evolutionary relationship • Rather, growth form commonly linked to habitat

  18. PHYLOGENETIC TREE SHOWING LEAF TRAITS OF HAWAIIAN VIOLAS • Leaf morphology not linked to evolutionary relationship • Like growth form, it is linked to habitat • Leaf anatomy similar (not shown)

  19. EVOLUTION OF THE HAWAIIAN VIOLAS • Evolutionary relationships of Hawaiian violets • Relationships among Hawaiians, Diversification and Inter-Island Dispersal • Adaptive Radiation • Biogeographic Source and Mechanism

  20. SOURCE AREAS FOR WINTERING HAWAIIAN BIRDS

  21. SUMMARY • Hawaiian Viola is monophyletic (a “natural group”, recently derived • Biogeographic origin is Arctic/Boreal • Woody growth and inflorescences are convergent traits evolved under tropical oceanic conditions • Initial colonization on Kaui <3.2 million years ago • Dispersal eastward, conforming to “chain rule”

  22. SUMMARY • Diversification proceeded along an environmental gradient, from wet to dry (forest/cliff) and mesic habitats • Growth habit and leaf morphology (and anatomy) tied closely to habitat, presumably due to strong environmental selection; led to distinctive “ecomorphic syndromes” in each habitatadaptive radiation!

  23. FUTURE RESEARCH • Population genetic studies using highly variable molecular markers • Ecological characterization of microhabitats and habitat types • Investigation of potential hybridization in three taxon pairs • Studies on taxonomic variation in V. maviensis, V. kauaensis and V. chamissoniana-tracheliifolia

  24. ANSWERS TO QUESTIONS ABOUT HAWAIIAN VIOLAS What does DNA data reveal about the origin and relationships of the Hawaiian violets that morphology cannot? Latin American violet groups are not the nearest relatives; the Hawaiians are most closely related to an Arctic tundra bog violet, Viola langsdorffii.

  25. ANSWERS TO QUESTIONS ABOUT HAWAIIAN VIOLAS Does the evolutionary pattern of the Hawaiian violets conform to the “progression rule”? Yes, all the most primitive violet groups grow on the oldest island, Kauai (or can be interpreted to arise there first). Dispersal/diversification proceeded to younger islands further east.

  26. ANSWERS TO QUESTIONS ABOUT HAWAIIAN VIOLAS • What typical features of “adaptive radiation” are demonstrated by Hawaiian violets? • Morphology not reflective of evolutionary relationships—convergence in same habitats • Growth form & leaf morphology linked to environment (“adaptive”) • Woody island species from an herbaceous ancestor

  27. ANSWERS TO QUESTIONS ABOUT HAWAIIAN VIOLAS • How did the ancestral seed get from the Arctic to Kauai? • Probably by birds, either in mud on their feet or in their digestive tract.

  28. REFERENCES • Ballard, H. E., Jr., K. J. Sytsma, and R. R. Kowal. 1999. Shrinking the violets: Phylogenetic relationships of infrageneric groups in Viola (Violaceae) based on Internal Transcribed Spacer DNA Sequences. Systematic Botany 23:439-458. • Ballard, H. E., Jr. and K. J. Sytsma. 2000. Evolution and biogeography of the woody Hawaiian violets (Viola, Violaceae): Arctic origins, herbaceous ancestry and bird dispersal. Evolution 54:1521-1532. • Carlquist, S. 1992. Hawaii: A natural history. Lawai, Kauai: Pacific Tropical Botanical Garden. • Givnish, T. J. 1998. Adaptive plant evolution on islands: Classical patterns, molecular data, new insights. • Skottsberg, C. 1940. Observations on Hawaiian violets. Gothenburg. Botaniska Tradgard. Medelanden 13:451-528.

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