Short- and Long-Term Effects of Fixation and Preservation on Stable Isotope Values (δ13C, δ15N, δ34S) of Fluid-Preserved Museum Specimens
Short- and Long-Term Effects of Fixation and Preservation on Stable Isotope Values (δ13C, δ15N, δ34S) of Fluid-Preserved Museum Specimens
复制标题
固定和保存对博物馆液体标本稳定同位素值（δ13C、δ15N、δ34S）的短期和长期影响
作者：
Melanie S. Edwards;T. F. Turner;Z. Sharp
摘要 由于对福尔马林固定效果的担忧，很大程度上排除了在稳定同位素研究中使用液体保存的博物馆标本。我们试图通过检查成对的新鲜冷冻鱼组织样本和经过自然历史博物馆采用的固定和保存程序的组织之间同位素特征的差异，来确定福尔马林引起的碳、氮和硫同位素值变化的幅度、方向和原因。研究了几个因素作为福尔马林引起的变化的预测因素：（1）福尔马林固定和乙醇保存的持续时间； (2)福尔马林和乙醇提取脂质； (3)不同厂家福尔马林制剂同位素含量差异。福尔马林固定导致样品和处理中 δ13C 值下降（所有处理中保存的组织平均下降 1.1‰，SD = 0.8）。消耗的程度取决于用于固定的福尔马林的同位素组成，而不取决于固定或提取脂质的持续时间。所有样品的 δ15N 值均得到富集，且幅度与福尔马林品牌和所有其他研究因素无关（所有处理平均增加 0.5‰，SD = 0.3）。在任何测试条件下，δ34S 值均未系统地受到福尔马林的影响。与生态系统研究感兴趣的自然分馏过程预期的变化相比，福尔马林引起的鱼类组织碳、氮和硫同位素值的变化很小。因此，自然历史博物馆保存的标本为量化水生生态系统中营养循环和食物网的历史变化提供了潜在的重要的干扰前材料来源。
Abstract Concerns about the effects of formalin fixation have largely precluded the use of fluid-preserved museum specimens in stable isotope studies. We sought to determine the magnitude, direction, and causes of formalin-induced change in isotopic values of carbon, nitrogen, and sulfur by examining differences in isotopic signatures between paired fresh-frozen fish tissue samples and tissues subjected to fixation and preservation procedures employed in natural history museums. Several factors were investigated as predictors of formalin-induced change: (1) duration of formalin fixation and ethanol preservation; (2) lipid extraction by formalin and ethanol; and (3) differences in isotopic content among formalin preparations from different manufacturers. Formalin fixation caused a decrease in the δ13C-values across samples and treatments (mean decrease in preserved tissues of 1.1‰ for all treatments, SD = 0.8). The magnitude of depletion depended on the isotopic composition of formalin used for fixation, but not duration of fixation or extraction of lipids. δ15N-values were enriched for all samples and magnitude was independent of brand of formalin and all other factors studied (mean increase of 0.5‰ for all treatments, SD = 0.3). δ34S-values were not systematically affected by formalin under any conditions of the tests. Formalin-induced changes in carbon, nitrogen, and sulfur isotope values of fish tissue were small compared to changes expected from natural fractionation processes that are of interest in ecosystem studies. Thus, specimens held by natural history museums offer a potentially important source of predisturbance material for quantifying historical change in nutrient cycles and food webs in aquatic ecosystems.