EVOLUTION OF THE HAWAIIAN VIOLETS VIOLA

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EVOLUTIONOF THE HAWAIIAN VIOLETS (VIOLA)

• HARVEY E. BALLARD, JR.
• Department of Environmental and Plant Biology,
  and
• Molecular and Cellular Biology Program, Ohio
  University

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EVOLUTION OF THE HAWAIIAN VIOLAS

• Evolutionary relationships of Hawaiian violets
• Relationships among Hawaiians, Diversification
  and Inter-Island Dispersal
• Adaptive Radiation
• Biogeographic Source and Mechanism

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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)
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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?
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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?
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EVOLUTION OF THE HAWAIIAN VIOLAS

• Evolutionary relationships of Hawaiian violets
• Relationships among Hawaiians, Diversification
  and Inter-Island Dispersal
• Adaptive Radiation
• Biogeographic Source and Mechanism

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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

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

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EVOLUTION OF THE HAWAIIAN VIOLAS

• Evolutionary relationships of Hawaiian violets
• Relationships among Hawaiians, Diversification
  and Inter-Island Dispersal
• Adaptive Radiation
• Biogeographic Source and Mechanism

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• 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

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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

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INFERRED SEQUENCE OF SPECIATION AND DISPERSAL
EVENTS IN HAWAIIAN VIOLA
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EVOLUTION OF THE HAWAIIAN VIOLAS

• Evolutionary relationships of Hawaiian violets
• Relationships among Hawaiians, Diversification
  and Inter-Island Dispersal
• Adaptive Radiation
• Biogeographic Source and Mechanism

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CANONICAL VARIATES ANALYSIS OF HAWAIIAN VIOLA
TAXA USING LEAF CHARACTERS
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PRINCIPAL COMPONENTS ANALYSIS OF LEAF CHARACTERS
SHOWING HABITAT ASSOCIATIONS
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PHYLOGENETIC TREE HABITATS AND GROWTH FORMS OF
HAWAIIAN VIOLAS

• Growth form not linked to evolutionary
  relationship
• Rather, growth form commonly linked to habitat

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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)

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EVOLUTION OF THE HAWAIIAN VIOLAS

• Evolutionary relationships of Hawaiian violets
• Relationships among Hawaiians, Diversification
  and Inter-Island Dispersal
• Adaptive Radiation
• Biogeographic Source and Mechanism

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SOURCE AREAS FOR WINTERING HAWAIIAN BIRDS
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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 lt3.2 million years
  ago
• Dispersal eastward, conforming to chain rule

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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!

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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

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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.
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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.
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ANSWERS TO QUESTIONS ABOUT HAWAIIAN VIOLAS

• What typical features of adaptive radiation are
  demonstrated by Hawaiian violets?
• Morphology not reflective of evolutionary
  relationshipsconvergence in same habitats
• Growth form leaf morphology linked to
  environment (adaptive)
• Woody island species from an herbaceous ancestor

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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.

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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 23439-458.
• 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
  541521-1532.
• 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 13451-528.