Steiner, Kim E. , Cruz, Boni C. .
Floral and pollinator divergence in a specialized South African orchid.
Recent studies have illustrated the importance of flowering phenology, habitat specificity and pollinator niche in the adaptive radiation of plants. The purpose of this study was to examine the role that these factors have played in the divergence of two closely related orchid species. Pterygodium catholicum secretes floral oil and is pollinated by a single species of oil-collecting bee, viz. Rediviva peringueyi (Melittidae). Its flowering time, however, exceeds the activity period of its pollinator by more than a month. A closely related species, P. acutifolium, also secretes floral oil, but flowers later and overlaps with the end of the P. catholicum flowering period. It is visited by a different oil-collecting bee, viz. R. gigas. We used a combination of scent, molecular sequence, pollination, and phenological data to examine variability within and between these two morphologically similar orchid species. We found that late-flowering populations of P. catholicum have a scent profile more similar to P. acutifolium than to early-flowering P. catholicum populations. We also found that the flowers of late-flowering P. catholicum plants appeared more similar in color to P. acutifolium flowers than to the flowers of early-flowering P. catholicum plants. Furthermore, late-flowering P. catholicum and P. acutifolium plants occur on low nutrient soils supporting fynbos vegetation, whereas early-flowering P. catholicum plants generally occur on richer clay soils that support renosterveld vegetation. Despite the similarity in floral color, scent, and soil type, the sequence data from the late-flowering ecotype of P. catholicum is more similar to that of the early-flowering ecotype than to P. acutifolium. We conclude that P. catholicum has two different pollination ecotypes, an early-flowering ecotype that is pollinated by R. peringueyi and a late-flowering ecotype that is pollinated by R. gigas. The possible pathways involved in the evolution of these ecotypes will be discussed.
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1 - California Academy of Sciences, Department of Botany, 875 Howard Street, San Francisco, California, 94103-3009, USA
2 - California Academy of Sciences, Department of Botany, 875 Howard St., San Francisco, CA, 94103-3009, USA
Presentation Type: Oral Paper:Papers for Topics
Location: Lake Ontario/Hilton
Date: Tuesday, July 10th, 2007
Time: 4:00 PM