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

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.