Data_Sheet_1_Nocturnal Bees Feed on Diurnal Leftovers and Pay the Price of Day – Night Lifestyle Transition.docx

Bees exemplify flights under bright sunlight. A few species across bee families have evolved nocturnality, displaying remarkable adaptations to overcome limitations of their daylight-suited apposition eyes. Phase inversion to nocturnality in a minority of bees that co-exist with diurnal bees provides a unique opportunity to study ecological benefits that mediate total temporal niche shifts. While floral traits and sensory modalities associated with the evolution of classical nocturnal pollination syndromes, e.g. by bats and moths, are well-studied, nocturnality in bees represents a poorly understood, recently invaded, extreme niche. To test the competitive release hypothesis, we examine how nocturnality shapes foraging by comparing pollen loads, nest pollen, and flower visitation of sympatric nocturnal and diurnal carpenter bees. We predicted that nocturnal bees primarily use night-blooming flowers, show little/no resource overlap with diurnal species and competitive release favors night-time pollen collection for provisioning. Contrarily, we found substantial resource overlap between nocturnal and diurnal bees. Flower opening times, floral longevity and plant abundance did not define nocturnal flower use. Smaller pollen loads on nocturnal foragers suggest subsistence on resource leftovers largely from diurnal flowers. Greater pollen types/diversity on nocturnal foragers indicate lower floral constancy compared to diurnal congenerics. Reduced activity during new moon compared to full moon suggests constraints to nocturnal foraging. Invasion and sustenance within the nocturnal niche is characterized by: (i) opportunistic foraging on residual resources as indicated by smaller pollen loads, extensive utilization of day-blooming flowers and substantial overlap with diurnal bees, (ii) generalization at two levels—between and within foraging trips as indicated by lower floral constancy, (iii) reduced foraging on darker nights, indicating visual constraints despite sensitive optics. This together with smaller populations and univoltine breeding in nocturnal compared to multivoltine diurnal counterparts suggest that nocturnality imposes substantial fitness costs. In conclusion, the evolution of nocturnality in bees is accompanied by resource generalization instead of specialization. Reduced floral constancy suggests differences in foraging strategies of nocturnal and diurnal bees which merits further investigation. The relative roles of competition, floral rewards and predators should be examined to fully understand the evolution and maintenance of nocturnality in bees.

蜜蜂是晴朗阳光下飞行的典型代表。在蜜蜂科中，少数物种进化出夜行性，并展现出惊人的适应性，以克服其日间适应的并列视觉器官的局限性。少数与日行性蜜蜂共存的蜜蜂向夜行性的转变，为研究调节总时间生态位转变的生态效益提供了独特的机会。虽然与蝙蝠和蛾等经典夜间授粉综合征（例如，蝙蝠和蛾的进化）相关的花卉特性和感官模式已被充分研究，但蜜蜂的夜行性却是一个理解不足、近期入侵的极端生态位。为了检验竞争释放假说，我们通过比较共栖的夜行性和日行性木蜂的传粉行为，如花粉负载、巢穴花粉和花朵访问，来研究夜行性如何塑造觅食行为。我们预测夜行性蜜蜂主要利用夜间开花的花朵，与日行性物种的资源重叠较小/无，竞争释放有利于夜间花粉收集以供繁殖。然而，我们发现夜行性和日行性蜜蜂之间存在实质性的资源重叠。花朵开放时间、花卉持久性和植物丰富度并没有定义夜行性花朵的使用。夜行性觅食者的花粉负载较小，表明主要依靠日行性花朵的剩余资源为生。夜行性觅食者上的花粉类型/多样性表明，与日行性同种相比，其花卉忠诚度较低。新月期间相对于满月期间的活动减少，表明夜行性觅食受到视觉限制，尽管其具有敏感的视觉系统。这与较小的种群数量和夜行性相对于多周期日行性同类的单周期繁殖一起表明，夜行性对蜜蜂的适应性产生了实质性的成本。总之，蜜蜂夜行性的进化伴随着资源泛化而非专业化。花卉忠诚度的降低表明夜行性和日行性蜜蜂的觅食策略存在差异，这值得进一步研究。应检查竞争、花卉奖励和捕食者的相对作用，以全面理解蜜蜂夜行性的演化和维持。