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The Ecology of Floral Signals in Penstemon digitalis
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Ecology and Genetics, Plant Ecology and Evolution.ORCID iD: 0000-0002-7383-3965
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, I combined field observations and lab experiments to explore the ecological significance of floral signals in a North American wildflower, Penstemon digitalis. More specifically, to determine the potential mechanisms driving selection on floral scent, I studied how scent mediates interactions with pollinators and antagonists by (1) observing spatiotemporal variation in scent emission (2), floral volatile ability to suppress microbes (3) the honest advertisement of nectar, and (4) if scent could aid pollinator learning by reinforcing visual signals.

Scent sampling of flower development, flower tissues, rewards and inflorescence day/night emission, revealed a complexity in floral scent composition and emission that could reflect several ecological functions. The floral bouquet of P. digitalis was strongest when flowers opened, primarily emitted from flower nectaries and was strongest during the day when pollinators are most active, suggesting a role in plant-pollinator interactions.

Because linalool was one of the few floral compounds found in nectar where microbe growth can degrade the pollinator reward, I studied its role in plant-microbe interactions. Bacteria strains isolated from floral and vegetative tissues were exposed to varying concentrations of nectar volatiles: linalool and methyl nicotinate. Linalool inhibited bacteria growth rate from all tissue origins whereas methyl nicotinate had little effect, suggesting that microbes could drive selection on linalool emission strength.   

To determine the extent that linalool could honestly signal nectar availability, linalool-nectar associations were measured for inflorescences and flowers. Linalool predicted inflorescence nectar availability but not flower, exposing a limit to its honesty. Pollinator Bombus impatiens could use linalool as a foraging signal at varying concentrations, suggesting linalool could be learned and used to choose the most rewarding plants.   

Measurement and comparison of signal-reward associations for both olfactory and visual signals/cues of P. digitalis displays found display size and linalool honest indicators of nectar. Lab behaviour experiments showed multiple signals correlated with reward could increase bumblebee foraging efficiency and promote learning, providing an explanation for why floral displays are complex and consist of multiple signals.   

Together my results show that an integrated approach is required to understand the mechanisms driving the evolution of the floral phenotype.  

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 46 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1421
Keyword [en]
Antimicrobial, Bombus impatiens learning, indirect signal, multimodal, nectar, protandry, signal-reward association, Volatile Organic Compounds (VOCs)
National Category
Natural Sciences
Research subject
Biology with specialization in Ecological Botany
Identifiers
URN: urn:nbn:se:uu:diva-302036ISBN: 978-91-554-9681-4 (print)OAI: oai:DiVA.org:uu-302036DiVA: diva2:956090
Public defence
2016-10-21, Lindahlsalen, Norbyvägen 18A, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2016-09-28 Created: 2016-08-29 Last updated: 2016-10-11
List of papers
1. Spatiotemporal floral scent variation of Penstemon digitalis
Open this publication in new window or tab >>Spatiotemporal floral scent variation of Penstemon digitalis
2015 (English)In: Journal of Chemical Ecology, ISSN 0098-0331, E-ISSN 1573-1561, Vol. 41, no 7, 641-650 p.Article in journal (Refereed) Published
Abstract [en]

Variability in floral volatile emissions can occur temporally through floral development, during diel cycles, as well as spatially within a flower. These spatiotemporal patterns are hypothesized to provide additional information to floral visitors, but they are rarely measured, and their attendant hypotheses are even more rarely tested. In Penstemon digitalis, a plant whose floral scent has been shown to be under strong phenotypic selection for seed fitness, we investigated spatiotemporal variation in floral scent by using dynamic headspace collection, respectively solid-phase microextraction, and analyzed the volatile samples by combined gas chromatography-mass spectrometry. Total volatile emission was greatest during flowering and peak pollinator activity hours, suggesting its importance in mediating ecological interactions. We also detected tissue and reward-specific compounds, consistent with the hypothesis that complexity in floral scent composition reflects several ecological functions. In particular, we found tissue-specific scents for the stigma, stamens, and staminode (a modified sterile stamen common to all Penstemons). Our findings emphasize the dynamic nature of floral scents and highlight a need for greater understanding of ecological and physiological mechanisms driving spatiotemporal patterns in scent production.

Keyword
Diel variation, Floral scent, Nectar scent, GC/MS, S-(+)-linalool, Pollen odor, Staminode
National Category
Ecology
Identifiers
urn:nbn:se:uu:diva-264677 (URN)10.1007/s10886-015-0599-1 (DOI)000361465800006 ()26133675 (PubMedID)
Funder
The Royal Swedish Academy of Sciences
Available from: 2015-10-16 Created: 2015-10-15 Last updated: 2017-12-01Bibliographically approved
2. Floral volatiles suppress Penstemon digitalis microorganisms
Open this publication in new window or tab >>Floral volatiles suppress Penstemon digitalis microorganisms
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-302041 (URN)
External cooperation:
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2016-09-07
3. Honest signalling of nectar scent depends on inflorescence not flower scale
Open this publication in new window or tab >>Honest signalling of nectar scent depends on inflorescence not flower scale
Show others...
(English)Manuscript (preprint) (Other academic)
Keyword
Pollination, plant-pollinator interactions, protandry, signal evolution, foraging
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-302038 (URN)
External cooperation:
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2016-08-29
4. Multimodal signal honesty in Penstemon digitalis enhances bumblebee foraging
Open this publication in new window or tab >>Multimodal signal honesty in Penstemon digitalis enhances bumblebee foraging
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(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-302043 (URN)
External cooperation:
Available from: 2016-08-29 Created: 2016-08-29 Last updated: 2016-09-09

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