Data from: Parasite and host elemental content and parasite effects on host nutrient excretion and metabolic rate

Ecological stoichiometry uses the mass balance of elements to predict energy and elemental fluxes across different levels of ecological organization. A specific prediction of ecological stoichiometry is the growth rate hypothesis (GRH), which states that organisms with faster growth or reproductive rates will require higher phosphorus content for nucleic acid and protein synthesis. Although parasites are found ubiquitously throughout ecosystems, little is understood about how they affect nutrient imbalances in ecosystems. We (1) tested the GRH by determining the carbon (C), nitrogen (N), and phosphorus (P) content of parasitic trematodes and their intermediate host, the freshwater snail Elimia livescens, and (2) used this framework to determine the trematode effects on host nutrient excretion and metabolism. Snail and parasite tissues were analyzed for elemental content using a CHN analyzer and soluble reactive phosphorus (SRP) methods. Ammonium and SRP assays were used to estimate N and P excretion rates. A respirometer was used to calculate individual snail metabolism. Trematode tissues contained lower C:P and N:P (more P per unit C and N) than the snail tissues. Snail gonadal tissues more closely resembled the elemental content of parasite tissues, although P content was 13% higher in the gonad than the trematode tissues. Despite differences in elemental content, N and P excretion rates of snails were not affected by the presence of parasites. Parasitized snails maintained faster metabolic rates than nonparasitized snails. However, the species of parasite did not affect metabolic rate. Together, this elemental imbalance between parasite and host, and the altered metabolic rate of infected snails may lead to broader parasite effects in stream ecosystems.生态化学计量学（ecological stoichiometry）基于元素质量平衡原理，可预测不同生态组织层级间的能量与元素通量。该领域的一项具体预测为生长速率假说（growth rate hypothesis, GRH），其核心观点为：生长速率或繁殖速率更快的生物，其核酸与蛋白质合成过程需要更高的磷供给。尽管寄生虫在各类生态系统中广泛分布，但当前学界对其如何调控生态系统内养分失衡的机制仍知之甚少。本研究通过两项实验展开相关探究：（1）测定寄生吸虫及其中间宿主——淡水螺Elimia livescens的碳（C）、氮（N）、磷（P）含量，以此验证生长速率假说；（2）依托该实验框架，分析吸虫对宿主养分排泄与代谢状态的影响。研究采用碳氢氮元素分析仪（CHN analyzer）与可溶性反应磷（soluble reactive phosphorus, SRP）法，对螺与寄生虫组织的元素组成进行定量分析；通过铵态氮与SRP检测实验，估算宿主的氮、磷排泄速率；利用呼吸仪计算单只螺的个体代谢速率。实验结果表明，吸虫组织的碳磷比与氮磷比均低于螺组织（即单位碳、氮所对应的磷含量更高）。螺的生殖腺组织元素组成与寄生虫组织更为相似，尽管其磷含量较吸虫组织高出13%。尽管二者元素组成存在差异，但寄生虫的侵染并未对螺的氮、磷排泄速率产生显著影响。被寄生的螺维持了比未寄生个体更快的代谢速率，不过寄生虫的物种类型对宿主代谢速率无明显作用。综上，寄生虫与宿主间的元素失衡，以及受侵染螺的代谢速率改变，可能会对溪流生态系统产生更广泛的寄生虫介导生态效应。