Abstract
Isotopic signatures of carbon and nitrogen are widely used for analysis of the structure of food webs in aquatic ecosystems. The study of animals raises a number of methodological questions, including choice of representative tissues and organs for sampling as well as storage of the studied organisms. Furthermore, the impacts of preservation methods can be tissue-specific, age-specific, and even taxon-specific; thus, studies of these impacts on particular taxa are necessary. We focused on the C and N isotope composition of the common toad (Bufo bufo), one of the most widespread European anuran amphibians. We hypothesized that its different tissues and organs may vary in isotopic composition, and ethanol and freezing may have different effects on isotopic values. Our results showed that both “tissue” and “storage method” factors significantly affected the δ13C values of tadpoles and postmetamorphic juveniles, whereas only the “tissue” factor had a significant effect on the δ15N values. The two stages, tadpoles and postmetamorphs, should be analyzed separately despite the brief postmetamorphic period of the juveniles. The skin, legs, muscles, and tail in tadpoles and legs, muscles and heart in juveniles can be used for δ13C and δ15N analysis regardless of the method of storage. The results will serve for the optimization of future study designs in isotopic ecology.
Highlights
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The digestive tract of tadpoles was significantly depleted in 13 C relative to other organs and depleted in 15 N relative to the muscles and tail; the digestive tract of juveniles was significantly depleted in 13 C relative to the legs and enriched in 15 N relative to the skin (Figure 1A,B,D,E)
These differences in isotope compositions can most likely be caused by the remains of food or presence of parasites and symbionts in the digestive tract
Summary
The carbon 13 C/12 C ratio (usually expressed as δ13 C) allows tracing basal carbon sources [4,5], whereas 15 N/14 N ratio (δ15 N) increases as nitrogen passes from one consumer to another, indicating the trophic level of an animal in the trophic chain [6]. These phenomena make stable isotope analysis (SIA) a suitable tool for solving a wide range of questions in trophic ecology [7,8]
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