Consequences of a nectar yeast for pollinator preference and performance

• Published in: Functional ecology Vol. 31; no. 3; pp. 613 - 621
• Main Authors: Schaeffer, Robert N., Mei, Yu Zhu, Andicoechea, Jonathan, Manson, Jessamyn S., Irwin, Rebecca E.
• Format: Journal Article
• Language: English
• Published: London Wiley 01-03-2017; Wiley Subscription Services, Inc
• Subjects: Animal reproduction; Bees; Bombus impatiens; Breeding success; Colonization; Color; Egg laying; Eggs; Fitness; Flowers; Foraging behavior; Metschnikowia; Metschnikowia reukaufii; Microorganisms; Nectar; nectar yeasts; Plant-animal interactions; Pollen; pollinator preference; pollinator reproduction; Pollinators; Queenless; Reinforcement; Reproduction; Reproductive fitness; Viability; Workers (insect caste); Yeast; Yeasts
• ISSN: 0269-8463; 1365-2435
• DOI: 10.1111/1365-2435.12762

Summary
Pollinators utilize floral resources that vary in colour, scent and reward quality. Variation in such traits, including nectar rewards, in addition to cues associated with their quality, can influence pollinator foraging decisions with consequences for pollinator reproductive success. Nectar is commonly subject to colonization by micro‐organisms capable of affecting a suite of traits important for pollinator attraction and fitness; yet, links between microbial presence and changes in pollinator preference and performance remain few.
Here, we evaluated the effects of a nectar‐inhabiting micro‐organism on pollinator foraging behaviour and reproduction using the common eastern bumblebee Bombus impatiens and the cosmopolitan nectar yeast Metschnikowia reukaufii. Using a combination of choice and no‐choice behavioural and feeding assays, we manipulated the presence and viability of M. reukaufii in nectar and assessed bumblebee foraging and reproductive responses.
Bombus impatiens workers responded positively to the presence of yeasts. Foragers trained to associate yeast presence with flower colour visited a significantly greater proportion of flowers inoculated with yeast when subject to a colour discrimination test. Moreover, foragers naïve to nectar yeasts incorporated more yeast‐inoculated flowers into initial foraging bouts when presented with a novel floral array. In addition, bees spent significantly longer foraging on yeast‐inoculated flowers compared to yeast‐free flowers. However, when we manipulated yeast presence and viability in microcolonies of queenless workers, we found no effect of yeast on components of bumblebee reproduction, such as initiation of egg laying and number of eggs laid. This lack of an effect of yeast persisted even under conditions of pollen limitation.
Taken together, these results suggest that nectar yeasts can enhance floral signalling and alter pollinator foraging behaviour at individual flowers, though they may not directly affect pollinator performance. Thus, nectar yeasts may play a significant role in mediating pollinator foraging behaviour, with consequences for plant fitness and evolution of floral traits.
Lay Summary