Nectar Yeasts in the Tall Larkspur Delphinium barbeyi (Ranunculaceae) and Effects on Components of Pollinator Foraging Behavior

Abstract

Microorganisms frequently colonize the nectar of angiosperm species. Though capable of altering a suite of traits important for pollinator attraction, few studies exist that test the degree to which they mediate pollinator foraging behavior. The objective of our study was to fill this gap by assessing the abundance and diversity of yeasts associated with the perennial larkspur Delphinium barbeyi (Ranunculaceae) and testing whether their presence affected components of pollinator foraging behavior. Yeasts frequently colonized D. barbeyi nectar, populating 54–77% of flowers examined depending on site. Though common, the yeast community was species-poor, represented by a single species, Metschnikowia reukaufii. Female-phase flowers of D. barbeyi were more likely to have higher densities of yeasts in comparison to male-phase flowers. Pollinators were likely vectors of yeasts, as virgin (unvisited) flowers rarely contained yeasts compared to flowers open to pollinator visitation, which were frequently colonized. Finally, pollinators responded positively to the presence of yeasts. Bombus foragers both visited and probed more flowers inoculated with yeasts in comparison to uninoculated controls. Taken together, our results suggest that variation in the occurrence and density of nectar-inhabiting yeasts have the potential to alter components of pollinator foraging behavior linked to pollen transfer and plant fitness.

Consequences of a nectar yeast for pollinator preference and performance

“…Recent studies have similarly detected evidence of bumblebee preference for yeasts (Herrera, Pozo & Medrano ; Schaeffer & Irwin ; Schaeffer et al . ); in the field, wild bumblebees removed significantly more nectar from Helleborus foetidus and Delphinium nuttallianum flowers that contained yeasts in comparison with controls. Preference for yeasts by bumblebees could result from a number of mechanisms, including alteration of the taste profile through changes in sugar or amino acid composition (Herrera, García & Pérez ; Peay, Belisle & Fukami ).…”

“…; Schaeffer & Irwin ; Schaeffer et al . ), highlight the significant role that NIMs may play in mediating pollinator behaviour, which, until recently, has largely been overlooked. Surprisingly, however, even though pollinators preferred flowers with yeast, neither yeast nor yeast metabolic activity within nectar affected microcolony performance, with nectar yeast treatments showing no benefits (or costs), even under pollen‐limited conditions.…”

Nectar‐inhabiting microorganisms influence nectar volatile composition and attractiveness to a generalist pollinator

“…For example, volatile compounds emitted by yeasts are attractive to insect vectors including Drosophila (Buser et al ., ). In nectar, microbial metabolism can influence sugar composition and concentration (Herrera et al ., ; Vannette et al ., ; Good et al ., ; Schaeffer et al ., , ), ethanol concentration, amino acid composition (Peay et al ., ) and other metabolic products that contribute to flavor and scent of nectar (Vannette & Fukami, ). Pollinators may respond innately or learn to associate such products with nectar availability or quality (Knauer & Schiestl, ).…”

Floral organs act as environmental filters and interact with pollinators to structure the yellow monkeyflower (Mimulus guttatus) floral microbiome

“…Flowers are multi‐purpose reproductive structures and microbial communities of flowers can have a large impact on plant fitness by directly affecting the survival and reproduction of the plant (e.g., Alexander & Antonovics, ), or through effects on pollination (Herrera, Pozo, & Medrano, ; Rering, Beck, Hall, McCartney, & Vannette, ; Schaeffer, Mei, Andicoechea, Manson, & Irwin, ; Schaeffer, Phillips, Duryea, Andicoechea, & Irwin, ; Vannette, Gauthier, & Fukami, ). Understanding microbial community assembly in flowers can highlight important, and underappreciated, ecological processes affecting floral evolution and plant‐pollinator interactions.…”