The staminal column in Solanum pollination: important in attraction, essential as a landing platform

Abstract

The staminal column-corolla association in solanums constitutes a floral pattern that is distinctive, and generalized across a number of genera and families – characterized as ‘solanum-type’ flowers. We conducted experiments in natural populations of Solanum xanti in California, USA, to test the structure-function of the solanum staminal column and corolla. We excised the corolla of some flowers, the stamens of others, and painted stamens of others to assay pollinator response to changes in visible and UV patterns. Acrylic-painted staminal columns were yellow like the original anther color or concolorous with the corollas, and reflected light in the UV range instead of absorbing it. The flowers with stamens excised or with paint-altered UV patterns showed significantly lower fruit set, including those painted yellow. Experimental flowers with staminal columns only, i.e. with excised corollas, set fruit at the same rate as control flowers. Thus, the bee pollinators visit experimentally-altered flowers; they do not simply avoid aberrant flowers. While the combination of stamens and corolla are undoubtedly important visual attractants, our experiments support the underappreciated, and essential, role of the staminal column as a scaffold for the common, but distinctive, ‘buzz’ pollinators of solanums.

Keywords:

• Anther structure-function
• buzz pollination
• corolla function
• floral UV patterns
• Solanum

Acknowledgements

Discussions with Herbert Baker and Irene Baker regarding anthers, and in particular his generous encouragement (in 1979) to watch for the ‘solanum-flower syndrome’ in Australia, were significant inspirations, as were the many seminal papers on buzz pollination by Steve Buchmann and co-authors, particularly, Jim Cane. Furthermore, conversations and advice from several colleagues at the Univ. of California-Davis (i.e. Grady Webster, Barbara Webster, Charles Rick, June McCaskill, Robbin Thorp, Lynn Gillespie and Maureen Stanton and her lab group) were very helpful. The UC Davis Center for Plant Diversity provided facilities, office space, collegiality and field site recommendations. C. Eugene Jones and Dylan Burge generously provided field-collected seeds, and Ellen Dean and Daniel McNair supplied rooted cuttings of S. xanti. Gene Jones was also an early inspiration for GJA for plant reproductive biology studies. Tom Eisner, pioneer in UV studies, initially took photos to document color patterns in the UV range of the spectrum. Meghan Moriarty, Matt Opel, Clinton Morse, and Adam Histen helped grow plants in the Univ. of Connecticut greenhouses. Nathaniel Mione helped prepare Figures 1–6. Karen Anderson and Amy Swanson were field assistants, and lab aid was provided by Cassandra Swanson, Vivian Swanson, Clara Gabriel-Anderson and Henry Gabriel-Anderson. Thanks to David Taylor and two anonymous reviewers for comments on the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Support from Ecology and Evolutionary Biology at the University of Connecticut and the AFRF is much appreciated.