Data from: Multielement stoichiometry in aquatic invertebrates: when growth dilution matters

Element concentrations in organisms can be variable, often causing deviations from otherwise consistent, taxon-specific multielement stoichiometries. Such variation can have considerable ecological consequences, yet physiological mechanisms remain unclear. We tested the influence of somatic growth dilution (SGD) on multiple element concentrations under different bioenergetic conditions. SGD occurs when rapid individual growth causes a disproportional gain in biomass relative to gain of a specific element. SGD can strongly affect elements in various organisms, but we lack a general framework to unify results across studies and assess its overall importance. We derived the general conditions that trigger SGD from an element accumulation model. We parameterized the model with bioenergetic and element-specific rates summarized from the literature to compare SGD effects on 15 elements (nonessential metals, essential trace elements, macronutrients) in three aquatic invertebrate taxa. For all taxa, we found that SGD: (1) occurs to some degree for all 15 elements over realistic ranges of growth and ingestion rates, and (2) has the greatest effect on elements with low efflux (excretion) rates, including certain nonessential metals (e.g., MeHg, Po), essential trace elements and macronutrients (e.g., N, Fe). Thus, SGD can strongly affect concentrations of a spectrum of elements under natural conditions. These results provide a framework for predicting variation in elemental composition of animals.生物体内的元素浓度存在波动，这往往会偏离原本一致的类群特异性多元素化学计量比。这类波动可能带来显著的生态效应，但其背后的生理机制仍不明晰。我们在不同生物能量学条件下，检测了个体生长稀释（somatic growth dilution, SGD）对多种元素浓度的影响。当个体快速生长使得生物量的增长相对于某一特定元素的增长不成比例时，便会发生个体生长稀释现象。个体生长稀释可对多种生物体内的元素产生显著影响，但目前尚无统一的研究框架来整合不同研究的结果并评估其整体重要性。我们通过元素积累模型推导了触发个体生长稀释的通用条件。我们利用从文献中汇总的生物能量学参数与元素特异性速率对模型进行参数化，以此比较个体生长稀释对三类水生无脊椎动物类群中15种元素（非必需金属、必需微量元素、大量营养素）的影响。针对所有受试类群，我们发现个体生长稀释具备以下特征：(1) 在符合实际情况的生长与摄食速率范围内，15种元素均会出现不同程度的个体生长稀释效应；(2) 对外排（排泄）速率较低的元素影响最为显著，这类元素包括部分非必需金属（如甲基汞（MeHg）、钋（Po））、必需微量元素以及大量营养素（如氮（N）、铁（Fe））。因此，在自然条件下，个体生长稀释可对一系列元素的浓度产生显著影响。本研究结果可为预测动物元素组成的波动提供理论框架。