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.

传粉昆虫会利用色彩、气味与回报质量各不相同的花卉资源。此类性状（包括花蜜回报）以及与其质量相关的信号的差异，会影响传粉昆虫的觅食决策，进而对传粉昆虫的繁殖成功率产生影响。花蜜通常会被微生物定植，这些微生物能够改变一系列对传粉昆虫吸引度和适合度至关重要的性状；然而，目前关于微生物存在与传粉昆虫偏好性、行为表现变化之间的关联研究仍较为匮乏。

本研究以普通东部熊蜂（Bombus impatiens）和广布性花蜜酵母梅奇尼科夫氏酵母（Metschnikowia reukaufii）为研究对象，评估了一种花蜜栖息微生物对传粉昆虫觅食行为与繁殖的影响。本研究结合选择与非选择行为学及饲喂实验，操控了花蜜中梅奇尼科夫氏酵母的存在与否与活性状态，并评估了熊蜂的觅食与繁殖响应。

东部熊蜂的工蜂对酵母的存在表现出正向响应。经过训练将酵母存在与花色建立关联的觅食蜂，在花色辨别测试中，会显著更高比例地造访接种了酵母的花卉。此外，未接触过花蜜酵母的觅食蜂，在面对全新的花卉组合时，会将更多接种了酵母的花卉纳入其初始觅食行程中。相较于无酵母的花卉，熊蜂在接种了酵母的花卉上的觅食时长显著更长。然而，当我们在无蜂王的工蜂微蜂群中操控酵母的存在与活性时，并未发现酵母对熊蜂繁殖相关指标（如产卵起始与产卵量）存在影响。即便在花粉限制的条件下，酵母的这种无影响效应依然存在。

综合来看，本研究结果表明，花蜜酵母可增强花卉的信号传递，并改变传粉昆虫在单朵花卉上的觅食行为，尽管它们可能不会直接影响传粉昆虫的行为表现。因此，花蜜酵母可能在调控传粉昆虫觅食行为方面发挥重要作用，并进而对植物适合度以及花卉性状的演化产生影响。