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Patterns and Mechanisms of Evolution of Island Plants

Baldwin, Bruce G. [1].

Adaptive radiation of shrubby tarweeds (Deinandra) in the California Islands parallels evolution of the closely related Hawaiian silversword alliance (Compositae-Madiinae).

Phylogenetic analyses of nuclear rDNA transcribed spacers (ETS and ITS) and cytogenetic studies of interspecific hybrids uphold Carlquist,s hypothesis that shrubby tarweeds (Deinandra) of Guadalupe Island, Mexico are an example of in situ radiation in the endemic flora of the California Islands, where occurrence of autochthonous plant diversification has been uncertain. Based on rDNA evidence, the three Guadalupe Island endemics (D. frutescens, D. greeneana subsp. greeneana, and D. palmeri) constitute a monophyletic group that arose after evolution of various annual, mainland Californian lineages of Deinandra. High interfertility, normal meiosis in F1 hybrids, and lack of rDNA divergence of the three endemics are consistent with recent, rapid diversification of the Guadalupe Island lineage, especially in light of reduced interfertility (to complete intersterility), meiotic irregularities in F1 hybrids, and considerable rDNA divergence between other, mostly mainland taxa of Deinandra. Morphological differences of putative ecological importance and somewhat displaced flowering times between the completely interfertile and sympatric D. greeneana subsp. greeneana and D. palmeri indicate extrinsic barriers to gene flow and a probable role for ecological divergence in diversification on Guadalupe Island. Evidence for monophyly, rapid diversification, and ecological evolution of the endemic tarweeds of Guadalupe Island supports Carlquist,s suggestion of limited adaptive radiation of the group, in parallel with another oceanic-island tarweed lineage, the Hawaiian silversword alliance (Argyroxiphium, Dubautia, Wilkesia). Both groups are probable exceptions to Baker,s Rule that stem from herbaceous, self-incompatible ancestors in western North America and each has evidently undergone within-island diversification without evolution of major sterility barriers among lineages. Although of limited diversity compared to the silversword alliance, the Guadalupe Island deinandras are exceptional as well-supported examples of neo-endemism in the woody flora of the California Islands.


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1 - University of California, Berkeley, Jepson Herbarium and Department of Integrative Biology, 1001 Valley Life Sciences Bldg. #2465, Berkeley, California, 94720, USA

Keywords:
Asteraceae
islands
speciation.

Presentation Type: Symposium or Colloquium Presentation
Session: 42-5
Location: Salon J - Austin Grand Ballroom/Hilton
Date: Wednesday, August 17th, 2005
Time: 10:15 AM
Abstract ID:144


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