Data from: Consequences of a nectar yeast for pollinator preference and performance

1. Pollinators utilize floral resources that vary in color, 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 microorganisms 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.

2. Here, we evaluated the effects of a nectar-inhabiting microorganism on pollinator foraging behavior and reproduction using the common eastern bumble bee Bombus impatiens and the cosmopolitan nectar yeast Metschnikowia reukaufii. Using a combination of choice and no-choice behavioral and feeding assays, we manipulated the presence and viability of M. reukaufii in nectar and assessed bumble bee foraging and reproductive responses.

3. Bombus impatiens workers responded positively to the presence of yeasts. Foragers trained to associate nectar presence with flower color visited a significantly greater proportion of flowers inoculated with yeasts when subject to a color 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 metabolic activity in microcolonies of queenless workers, we found no effect of yeast on components of bumble bee 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.

4. Taken together, these results suggest that nectar yeasts can enhance floral signaling as well as alter pollinator foraging behavior at individual flowers, though they may not directly affect pollinator performance. Thus, nectar yeasts may play a significant role in mediating pollinator foraging behavior, with consequences for plant fitness and evolution of floral traits.