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，往往会偏离原本一致的、类群特异性的多元素化学计量比。这类元素浓度变异可产生显著的生态效应，但其背后的生理机制仍未明确。我们在不同生物能量学条件下，测试了个体生长稀释（somatic growth dilution, SGD）对多种元素浓度的影响。当个体快速生长导致生物量相对于某一特定元素的积累不成比例增加时，便会发生个体生长稀释效应。个体生长稀释可对多种生物体内的元素产生显著影响，但目前尚无通用框架来整合不同研究的结果并评估其整体重要性。我们基于元素积累模型推导了触发个体生长稀释效应的通用条件。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该模型进行参数化，以此比较个体生长稀释对3种水生无脊椎动物类群内15种元素（非必需金属、必需微量元素、大量营养素）的影响效应。针对所有受试类群，我们发现个体生长稀释：(1) 在符合自然实际的生长与摄食速率范围内，对全部15种元素均会产生一定程度的影响；(2) 对外排（排泄）速率较低的元素影响最为显著，包括部分非必需金属（如MeHg、Po）、必需微量元素与大量营养素（如N、Fe）。因此，在自然条件下，个体生长稀释可对多种元素的浓度产生显著影响。本研究结果为预测动物元素组成的变异提供了通用框架。