Data from: Validating the incorporation of 13C and 15N in a shorebird that consumes an isotopically distinct chemosymbiotic bivalve

The wealth of field studies using stable isotopes to make inferences about animal diets require controlled validation experiments to make proper interpretations. Despite several pleas in the literature for such experiments, validation studies are still lagging behind, notably in consumers dwelling in chemosynthesis-based ecosystems. In this paper we present such a validation experiment for the incorporation of 13C and 15N in the blood plasma of a medium-sized shorebird, the red knot (Calidris canutus canutus), consuming a chemosymbiotic lucinid bivalve (Loripes lucinalis). Because this bivalve forms a symbiosis with chemoautotrophic sulphide-oxidizing bacteria living inside its gill, the bivalve is isotopically distinct from ‘normal’ bivalves whose food has a photosynthetic basis. Here we experimentally tested the hypothesis that isotope discrimination and incorporation dynamics are different when consuming such chemosynthesis-based prey. The experiment showed that neither the isotopic discrimination factor, nor isotopic turnover time, differed between birds consuming the chemosymbiotic lucinid and a control group consuming a photosynthesis-based bivalve. This was true for 13C as well as for 15N. However, in both groups the 15N discrimination factor was much higher than expected, which probably had to do with the birds losing body mass over the course of the experiment.

大量利用稳定同位素（stable isotopes）推断动物食性的野外研究，均需开展对照验证实验以保障结果解读的科学性与准确性。尽管学界已有多篇文献呼吁开展此类实验，但相关验证研究的推进仍较为迟缓，在以化能合成生态系统（chemosynthesis-based ecosystems）为栖息生境的消费者类群中，这一问题尤为突出。本文针对以化能共生满月蛤科双壳类（Loripes lucinalis）为食的中型滨鸟——红腹滨鹬（Calidris canutus canutus），开展了一项验证实验，用以探究其血浆（blood plasma）中13C与15N的同位素同化过程。由于该双壳类与其鳃内的化能自养硫化物氧化细菌（chemoautotrophic sulphide-oxidizing bacteria）形成共生关系，其同位素特征与食物基础为光合作用的“常规”双壳类存在显著差异。本实验旨在验证如下假说：当取食此类基于化能合成的猎物时，动物的同位素分馏（isotopic discrimination）与同化动力学特征存在差异。实验结果显示，取食化能共生满月蛤的滨鸟与取食光合来源双壳类的对照组个体相比，其13C与15N的同位素分馏因子及同位素周转时间（isotopic turnover time）均无显著差异。这一结论同样适用于13C与15N两种同位素。然而，两组实验个体的15N分馏因子均远高于预期值，这大概率与实验期间实验鸟体质量下降有关。