Data from: Do larger individuals cope with resource fluctuations better? An artificial selection approach

Size determines the rate at which organisms acquire and use resources but it is unclear what size should be favoured under unpredictable resource regimes. Some theories claim smaller organisms can grow faster following a resource pulse, whereas others argue larger species can accumulate more resources and maintain growth for longer periods between resource pulses. Testing these theories has relied on interspecific comparisons, which tend to confound body size with other life-history traits. As a more direct approach, we used 280 generations of artificial selection to evolve a 10-fold difference in mean body size between small- and large-selected phytoplankton lineages of the green microalga Dunaliella tertiolecta, while controlling for biotic and abiotic variables. We then quantified how body size affected the ability of this species to grow at nutrient-replete conditions and following periods of nitrogen or phosphorous deprivation. Overall, smaller cells showed slower growth, lower storage capacity and poorer recovery from phosphorous depletion, as predicted by the “fasting endurance hypothesis”. However, recovery from nitrogen limitation was independent of size – a finding unanticipated by current theories. Phytoplankton species are responsible for much of the global carbon fixation and projected trends of cell size decline could reduce primary productivity by lowering the ability of a cell to store resources.

体型决定了生物体获取与利用资源的速率，但在不可预测的资源供给格局下，何种体型更具选择优势仍未明确。部分理论提出，小型生物可在资源脉冲（resource pulse）事件发生后更快完成生长；另有理论则认为，大型物种能够积累更多资源，并在两次资源脉冲之间维持更长时间的生长状态。过往针对这些理论的验证多采用种间比较的方法，但这类手段往往会将体型与其他生活史特征的效应相混淆。为探索更直接的验证路径，本研究以绿微藻四列杜氏藻（Dunaliella tertiolecta）的浮游植物（phytoplankton）谱系为实验材料，通过280代人工选择，使小体型选育组与大体型选育组的平均体型产生10倍差异，同时严格控制生物与非生物变量的干扰。随后，我们量化了体型对该物种在营养充足条件下，以及经历氮或磷匮乏阶段后的生长能力的影响。总体而言，小型细胞的生长速率更低、资源存储能力更弱，且在磷匮乏后的恢复表现更差，这与“空腹耐力假说”（fasting endurance hypothesis）的预测结果一致。但氮匮乏后的细胞恢复能力与体型并无关联——这一发现超出了现有理论的预期范畴。浮游植物贡献了全球绝大多数的碳固定量，而预测中细胞体型持续下降的趋势，可能会通过降低细胞的资源存储能力削弱初级生产力。