Bumblebees’ food preferences are jointly shaped by rapid valuation of nectar sugar concentration and viscosity

Animals are often assumed to follow a strategy of energy maximisation, and therefore should evaluate feeding options based on energy intake rates. Contrastingly, rhesus macaque’s learned food preferences are based on sensory properties, e.g. sweetness and resistance, regardless of energy differences. Here, we show that nectar sugar concentration (sweetness) and nectar viscosity (resistance) drive preferences of bumblebees, classical models for economic and foraging decision-making. Using a tasteless/odourless biopolymer (tylose), we created feeding options that differed in sweetness and resistance, properties that affect energy intake rate and can be immediately sensed. When energy intake rates were similar, bumblebees developed preferences based on sweetness and resistance. When energy intake rates were different but sweetness and resistance were balanced against each other, bees developed no preferences. Decision dynamics during training indicated that bumblebees simultaneously evaluated sweetness and resistance to make decisions quickly (in seconds). These results indicate that bumblebees’ food preferences are jointly affected by the immediate sensation of nectar sweetness and resistance as positively and negatively reinforcing properties, respectively, irrespective of energy intake rate. From these findings we propose that subjective valuations of sensory food properties should be considered as constraints in models of foraging behaviour.

学界通常认为动物遵循能量最大化策略，因此应基于能量摄入率评估取食选择。与之形成对比的是，恒河猴(rhesus macaque)习得的食物偏好基于感官属性（如甜度与阻力），不受能量差异的影响。本研究表明，花蜜糖浓度（甜度）与花蜜黏度（阻力）会驱动熊蜂(bumblebees)的取食偏好——熊蜂是经济与觅食决策研究的经典模式生物。我们使用无味道、无气味的生物聚合物(tylose)构建了取食选择范式，其甜度与阻力存在差异，这两种属性既会影响能量摄入率，又可被动物即时感知。当能量摄入率相近时，熊蜂会基于甜度与阻力形成取食偏好；当能量摄入率存在差异但甜度与阻力属性相互抵消时，熊蜂则不会形成明确的取食偏好。训练过程中的决策动力学特征表明，熊蜂会同时评估甜度与阻力，从而在数秒内快速做出决策。上述结果表明，熊蜂的食物偏好分别受花蜜甜度的正向强化与花蜜阻力的负向强化的即时感官影响，且与能量摄入率无关。基于上述发现，我们提出：在觅食行为模型中，应将食物感官属性的主观估值视为约束条件之一。