Fins are relevant non-lethal surrogates for muscle to measure stable isotopes in amphibians

Stable isotope analyses (SIA) are now widely used in ecology research to quantify the trophic implications of a large range of ecological processes. Non-destructive sampling methods have been successfully developed for most vertebrates, but the validation of such methods is missing in amphibians. Filling this methodological gap is critical to reduce the significant lack of knowledge on the trophic ecology of this imperilled group. The relevance of tail fin as a surrogate for muscle, a tissue routinely used for SIA, was assessed in four amphibian species, including tadpoles and adult newts, by (1) testing the link between the isotope ratios of carbon and nitrogen in fin and muscle, and addressing the additional practical issues of (2) the effects of a topical anaesthetic on isotope ratios, and (3) the minimum quantities of fin needed for SIA to limit the severity of sampling. The isotope ratios were highly correlated between the two tissues in all four species. Equations were provided to predict muscle estimates from fin values for each species separately and grouped by their taxonomic order (anurans or urodeles), which represent a valuable solution for any other species. Topical anaesthetics had little influence on isotope ratios, and the surface of tail fin needed for SIA was small. We conclude that the tail fin of amphibians can be used as a non-lethal surrogate for muscle in SIA, and this offers promising prospects for research on the trophic ecology of amphibians, and potentially on their conservation.