Data from: Isotopic turnover rates and diet-tissue discrimination depend on feeding habits of freshwater snails

Estimates of animal diets and trophic structure using stable isotope analysis are strongly affected by diet-tissue discrimination and tissue turnover rates, yet these factors are often unknown for consumers because they must be measured using controlled-feeding studies. Furthermore, these parameters may be influenced by diet quality, growth, and other factors. We measured the effect of dietary protein content on diet-tissue discrimination and tissue turnover in three freshwater snail species. We fed lettuce to individually housed snails (n = 450 per species) for ten weeks, then half were switched to a high-protein diet. Isotopic values of muscle and gonad tissue were assessed at 48 and 80 days post-diet change. Snail discrimination factors varied by diet (low-protein > high-protein) and usually differed among species for both N and C, although species had similar carbon discrimination when fed the low-protein diet. Carbon turnover rates were similar among species for a given tissue type, but nitrogen turnover varied more among species. In addition, diet affected growth of species differently; some species grew larger on high-protein (H. trivolvis) while others grew larger on low-protein diet (Lymnaea spp.). These differences among species in growth influenced turnover rates, which were faster in the species with the highest growth rate following the diet switch from low to high-protein. Thus, growth is one of the main processes that affects tissue turnover, but growth and feeding preference did not affect diet-tissue discrimination, which was greater on low-protein than high-protein diets for all species regardless of growth performance. These results suggest that diet might influence two key parameters of stable isotope analysis differently.

利用稳定同位素分析（Stable Isotope Analysis）评估动物日粮与营养结构的结果，会受到饮食-组织分馏系数（diet-tissue discrimination）与组织周转速率（tissue turnover rates）的显著影响，但这些参数往往难以通过消费者物种直接获取，需通过控制饲喂实验进行测定。此外，这些参数还可能受日粮质量、生长状况及其他因素的调控。
本研究针对3种淡水螺类，探究了日粮蛋白质含量对其饮食-组织分馏系数与组织周转速率的影响。
研究人员将单独饲养的螺类（每个物种450个个体）以生菜饲喂10周，随后将其中一半个体转换为高蛋白日粮。分别在日粮转换后的第48天与第80天，检测其肌肉与性腺组织的同位素值。
结果显示，螺类的分馏系数随日粮类型发生变化（低蛋白日粮组＞高蛋白日粮组），且氮与碳的分馏系数在不同物种间通常存在差异，但在饲喂低蛋白日粮时，各物种的碳分馏系数较为相近。
对于特定组织类型而言，不同物种间的碳周转速率较为相似，但氮周转速率在物种间的差异更为显著。
此外，日粮对不同螺类物种的生长影响存在差异：部分物种在高蛋白日粮下体型更大（如*H. trivolvis*），而另一些物种则在低蛋白日粮下生长更佳（如*Lymnaea* spp.）。
不同物种间的生长差异会影响组织周转速率：在从低蛋白日粮转换为高蛋白日粮后，生长速率最快的物种其组织周转速率也更快。
由此可见，生长是影响组织周转速率的核心过程之一，但生长与采食偏好并不会对饮食-组织分馏系数产生影响；无论生长表现如何，所有物种在低蛋白日粮下的分馏系数均高于高蛋白日粮组。
本研究结果表明，日粮可能会以不同方式影响稳定同位素分析的两个关键参数。