Department of Entomology and Nematology, University of California, Davis, One Shields Avenue, Davis, California, 95616, USA.
Ecology. 2018 Oct;99(10):2187-2195. doi: 10.1002/ecy.2475. Epub 2018 Aug 30.
Phenological shifts have been observed in a wide range of taxa, but the fitness consequences of these shifts are largely unknown, and we often lack experimental studies to assess their population-level and evolutionary consequences. Here, we describe an experimental study to determine the fitness consequences of phenological shifts in blue orchard bee (Osmia lignaria) emergence, compare the measured seasonal fitness landscape with observed phenology in the unmanipulated population, and assess seasonal variation in key factors related to reproduction, foraging, and brood parasitism that were expected to affect the shape of the fitness landscape. By tracking individually marked females, we were able to estimate the lifetime fitness impacts of phenological advances and delays. We also measured parasitism risk, floral resource use, and nesting behavior to understand how each varies seasonally, and their combined effects on realized fitness. Survival to nesting decreased non-monotonically throughout the season, with a 20.4% decline in survival rates between the first and second cohorts. The total reproductive output per maternal bee was 14.9% higher in the second cohort compared to the first, and 161% higher in the second cohort compared to the third. Combining seasonal patterns in survival and reproductive output, experimentally advanced females showed 30.6% higher fitness than bees released at the historic peak. In contrast, the nesting phenology of unmanipulated bees showed nearly equal numbers of nesting attempts in the first two cohorts. Both increased resource availability and reduced parasitism risk favored earlier emergence. These results are consistent with a population experiencing directional selection for earlier emergence, adaptive bet-hedging, or developmental constraints. Our study offers insight into the fitness consequences of phenological shifts, the mechanisms affecting the fitness consequences of phenological shifts in a community context, and the potential for adaptive responses to climate change.
物候转变在广泛的分类群中都有观察到，但这些转变对适应性的影响在很大程度上是未知的，我们通常缺乏实验研究来评估其对种群和进化的影响。在这里，我们描述了一项实验研究，以确定蓝果园蜜蜂（Osmia lignaria）出蜂期物候转变的适应代价，将测量的季节性适应景观与未受干扰种群中的观察到的物候进行比较，并评估与繁殖、觅食和巢寄生有关的关键因素的季节性变化，这些因素预计会影响适应景观的形状。通过跟踪单独标记的雌性，我们能够估计出蜂期提前和延迟对终生适应的影响。我们还测量了寄生风险、花卉资源利用和筑巢行为，以了解它们如何随季节变化，以及它们对实现适应的综合影响。整个季节的存活到筑巢呈非单调下降，第一批和第二批蜂群之间的存活率下降了 20.4%。与第一批相比，第二批母蜂的总繁殖输出增加了 14.9%，与第三批相比增加了 161%。将季节性存活和繁殖输出模式结合起来，实验提前的雌蜂表现出比在历史高峰期释放的蜜蜂高 30.6%的适应度。相比之下，未受干扰的蜜蜂的筑巢物候在头两个蜂群中几乎有相同数量的筑巢尝试。资源可用性的增加和寄生风险的降低都有利于提前出蜂。这些结果与一个经历了提前出蜂的定向选择、适应的套期保值或发育限制的种群一致。我们的研究提供了对物候转变适应代价的深入了解，以及在群落背景下影响物候转变适应代价的机制，以及对气候变化的适应潜力。
