Bainbridge, Susan J. , Baldwin, Bruce G. .
Self-incompatability, pollen limitation, and endangerment in the Hawaiian silversword alliance (Compositae) on Kaua`i.
Strong self-incompatibility in the Hawaiian silversword alliance is highly unusual for angiosperms of remote oceanic islands and makes these plants especially vulnerable to severe pollen limitation from pollinator loss, loss of S-allele diversity, or both. In wet forests of Kaua`i, lack of recruitment of the locally common tree Dubautia knudsenii subsp. knudsenii and extreme rarity of the shrub or small tree D. kalalauensis led us to study whether pollen limitation impacts these taxa and, if so, why. Controlled crosses in each taxon between plants of the same or different stands and controlled self-pollinations were conducted over consecutive years (2007 and 2008) and stands were surveyed for any naturally recruited seedlings or juveniles. Results of these hand pollinations in comparison with levels of natural seed set of the same plants indicated that D. knudsenii subsp. knudsenii was completely pollen limited, with no natural seed set detected. Extensive seed set and germination of vigorous seedlings from within- and between-stand hand-crosses of D. knudsenii subsp. knudsenii indicated that lack of pollinator service and not loss of S-allele diversity (or other genetic factors) was responsible for lack of natural seed set. Absence of any observed visitation by potential pollinators, discovery of only one juvenile plant across both studied stands, and unusual floral characteristics (including minimal pollen production) of D. knudsenii subsp. knudsenii raise concern that the taxon may have lost its pollinator and be biologically extinct despite still being locally common. In contrast, results from the sympatric D. kalalauensis indicate minimal pollen limitation, substantial recruitment, and extensive visitation by potential pollinators, with active destruction of entire plants by feral goats and, apparently, by invasive Passiflora mollissima. Preliminary results from other taxa of Dubautia from Kaua`i reinforce the above finding that different factors can be most important as causes of rarity or endangerment of closely related taxa sharing the same environment.
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1 - University of California, Berkeley, Jepson Herbarium, 1001 Valley Life Sciences Building #2465, Berkeley, CA, 94720-2465, USA
2 - University of California, Berkeley, Jepson Herbarium and Department of Integrative Biology, 1001 Valley Life Sciences Building #2465, Berkeley, CA, 94720-2465, USA
Presentation Type: Oral Paper:Papers for Topics
Location: 551A/Convention Center
Date: Wednesday, August 4th, 2010
Time: 10:45 AM