Systematics Section / ASPT
Whittall, Justen B. , Hodges, Scott .
Darwin’s Race Revisited: Pollinator Shifts Drive Increasingly Long Nectar Spurs During Adaptive Radiation in the Columbines.
IN 1862, Darwin predicted the existence of a hawkmoth with an exceptionally long proboscis based on the long-spurred flowers of the Malagasy orchid Angraecum sesquipedale. In doing so, he proposed that a coevolutionary 'race' was responsible for increasing the lengths of both the moth's tongue and the plant's nectar spur. Forty years later, the discovery of a long-tongued hawkmoth (Xanthopan morgani ssp. praedicta) validated Darwin's prediction, yet his model for the evolution of long-spurred flowers has remained controversial. An alternative to the coevolutionary race hypothesis is a pollinator shift model which postulates that the evolutionary fit of tongue and spurs is one-sided; that spurs evolve to fit the pollinator's already established tongue length. Here, using a species-level AFLP phylogeny of the North American columbine adaptive radiation (Aquilegia), we show that nectar spur lengths have indeed evolved in an increasing fashion, but that they have done so through a predictable pattern of pollinator shifts. We find significant directionality in pollinator shifts from bumblebee to hummingbird pollination and from hummingbird to hawkmoth pollination, but no reversals. Associated with this directionality is an evolutionary trend toward increasing spur lengths when shifting between discrete pollination syndromes and also within pollination syndromes. Our results support the pollinator shift model to explain the evolution of long spurs and highlight the one-sided-ness of floral adaptations to pre-existing pollinator morphologies during the columbine adaptive radiation.[c.e.:srb]
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1 - University of California Davis, Section of Evolution & Ecology, One Shields Avenue, Davis, California, 95616, USA
2 - University of California Santa Barbara, Department of Ecology Evolution And Marine Biology, Santa Barbara, California, 93106-9610, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 144/Performing Arts Center
Date: Monday, July 31st, 2006
Time: 5:00 PM