The “invisible hand” of floral scent in plant-pollinator interactions
Flowers are not merely objects of aesthetic beauty – they serve as engines of biological diversity, lynchpins of ecological stability and fonts of human ecosystem services from agriculture and floriculture to cosmetics.
Botanists have long been dazzled by the visual aspects of floral display (color, shape and pattern), whose importance to plant-pollinator interactions was appreciated before the birth of Darwin. In contrast, the chemical aspects of floral function, from the scents that guide pollinator attraction and learning to the composition of the nectars, resins and oils that reward their visits, somehow remain peripheral to the central bodies of ecological and evolutionary theory concerning pollination.
However, recent technological and conceptual advances have made it easier to analyze and manipulate floral chemistry, particularly floral scent, and a growing body of evidence points to more central roles for scent in mediating floral isolation, constancy, gene flow and defense. I will highlight several recent manipulative studies, in which visual signals were tracked and controlled, to illustrate the unexpected (“invisible”) roles played by scent in otherwise well-studied model systems.
Floral scent provides critical mechanisms that explain conditional reproductive isolation among sympatric Ipomopsis aggregata and I. tenuituba, balance floral defense and pollinator-mediated selection on floral form in Polemonium viscosum, and dictate the network structure of floral visitors to generalized pollinator hubs such as Cirsium arvense and Achillea millefolium.
In addition, I will explore our current knowledge of geographic variation in floral scent – the potential for local scent “dialects” – in the context of the Geographic Mosaic Theory of Coevolution, with reference to an ongoing study on the genus Oenothera.
Finally, I discuss the importance of scent to the convergent evolution of brood-site deception in dung- and carrion mimicking plants, by highlighting studies of dung mosses (Splachnaceae), a circumboreal lineage of bryophytes (common in Alberta!) that utilize unique combinations of sporophyte color and scent to attract diverse groups of flies as spore dispersal agents.
(The central importance of scent in obligate nursery pollination systems (yuccas and figs) will be addressed separately in the Colloquium on Mutualisms.)
Pollination is a topic that he’s been working on for many years. His first co-authored paper in Annals of Botany was The Impact of Biochemistry vs. Population Membership on Floral Scent Profiles in Colour Polymorphic Hesperis matronalis (2008). This has been followed by Extreme variation in floral characters and its consequences for pollinator attraction among populations of an Andean cactus (2009) and Extreme divergence in floral scent among woodland star species (Lithophragma spp.) pollinated by floral parasites
(2013). Most recently, he contributed to Novel adaptation to hawkmoth pollinators in Clarkia reduces efficiency, not attraction of diurnal visitors, in the special issue on Pollinator-Driven Speciation.
Elsewhere there’s Phenotypic selection to increase floral scent emission, but not flower size or colour in bee-pollinated Penstemon digitalis (New Phytologist) and Dosage-dependent impacts of a floral volatile on pollinators, larcenists and the potential for floral evolution in the alpine skypilot, Polemonium viscosum (The American Naturalist).
We’ll have more details on when and where the lecture is closer to the date. In the meantime you can catch up with recent research in pollination with our collection.