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An exception to Darwin's syndrome: floral position, protogyny, and insect visitation in Besseya bullii (Scrophulariaceae)
McKone, Mark J. Ostertag, Rebecca Rauscher, Jason T. Heiser, David A. Russell, F. Leland
McKone, Mark J.
Ostertag, Rebecca
Rauscher, Jason T.
Heiser, David A.
Russell, F. Leland
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1995
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Besseya bullii,Pollination,Protogyny Halictidae,Foraging behavior
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An exception to Darwin's Syndrome: Floral position, protogyny, and insect visitation in Besseya bullii (Scrophulariaceae)
Mark J. McKone, Rebecca Ostertag, Jason T. Rauscher, David A. Heiser and F. Leland Russell
Oecologia
Vol. 101, No. 1 (1995), pp. 68-74
Published by: Springer in cooperation with International Association for Ecology
Abstract
Darwin pointed out that plants with vertical
inflorescences are likely to be outcrossed if the inflorescence
is acropetalous (flowers from the bottom up),
the flowers are protandrous (pollen is dispersed before
stigmas are receptive), and pollinators move upward
on the inflorescence. This syndrome is common in
species pollinated by bees and flies, and very few exceptions
are known. We investigated flowering phenology
and pollinator behavior in Besseya bullii (Scrophulariaceae)
and found that it did not fit Darwin's syndrome.
The vertical inflorescence was acropetalous but the
flowers were distinctly protogynous, so flowers with
newly receptive stigmas appeared on the inflorescence
above those with dehiscing anthers. A number of small
insects visited B. bullii; bees in the family Halictidae
(Augochlorella striata and Dialictus spp.) were most
common. When insects moved between gender phases
within inflorescences, they moved up more often than
down (61% versus 39% of observations, respectively)
but this difference was only marginally significant. Most
visits were to male-phase flowers only, and this preference
was more pronounced for pollen-foraging insects
than for nectar-foraging insects. B. bullii was self-compatible,
so its flowering characteristics potentially could
result in considerable self-pollination. However, an
average of 38% of the lowermost flowers opened before any pollen was available on the same inflorescence;
these "solo females" had a high probability of outcrossing
(though fruit set was relatively low in the bottom
portion of the inflorescence). Upper flowers may
also be outcrossed because downward insect movement
was not uncommon. Therefore protogyny in B. bullii
may not necessarily lead to more selfing than would
protandry.
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Full text is not available due to publisher's copyright restrictions. Find this article in JSTOR: http://www.jstor.org/stable/4220854
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Oecologia (1995) 101:68-74
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0029-8549