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

Abstract

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.

Feasibility of using non‐lethally obtained fin tissue to determine δ 13 C and δ 15 N of Gymnocypris fish in the Lake Langcuo of Tibetan plateau, China

“…Post et al, 2007). Further to this, similar studies with high C:N ratios in fin and muscle went on to lipid normalise both tissues (Bélouard et al, 2019). However, in this experiment, the C:N values of the two kinds of fish are almost lower than 3.5, and the lipid content of the two kinds of fish is low, so there is no need to degrease.…”

Intra-Body Variations of Stable Isotope Ratios (δ13C, δ15N) and Influence of Storage Methods in Aquatic and Post-Aquatic Stages of the Common Toad, Bufo bufo

“…Importantly, non-lethal sampling of tissues for stable isotope analysis (small pieces of fins for larvae or fingers for adults) is possible and preferable for large-sized specimens of amphibians [30,54] because this group of vertebrates is recognized to be declining since the second half of 20th century [67]. However, when sampling small-sized larvae or juveniles it is difficult to adhere to this guidance.…”

“…The studied specimens were sacrificed by immersion in ethyl 3-aminobenzoate methanesulfonate (Sigma-Aldrich). This anesthetic does not have significant influence on isotope ratios of tissues [30]. Half of the caught specimens were placed in a freezer and stored at −18 • C, other half of the samples were fixed in 96% ethanol (hereafter the factor is referred to as "storage method").…”

“…Indeed, a significant variation in the isotopic composition of carbon (δ 13 C) and nitrogen (δ 15 N) within one organism was shown for a number of invertebrates and vertebrates, including diplopods [18], orthopterans [19], aphids [20], fishes [21], reptiles [22,23], birds [24] and mammals [25][26][27]. However, we know little about such differences between tissues in amphibian [28][29][30], which play an important role in trophic webs of both aquatic (in larval stage) and terrestrial (as adults) ecosystems.…”

Supplementary material 1 from: Belouard N, Petit EJ, Cucherousset J, Paillisson J-M (2024) Variation of the stable isotope niches of native amphibians in ponds invaded by the red swamp crayfish. NeoBiota 93: 245-262. https://doi.org/10.3897/neobiota.93.120477

“…Overall, red swamp crayfish were found in 12 of 18 ponds and amphibians in 9 to 16 ponds depending on species (Table 1). The fin of amphibians was sampled using a biopsy punch (one to two 2.5-or 3-mm-diameter samples per amphibian, see details in Belouard et al (2019b)) and individuals were immediately released. Crayfish were euthanised by freezing during the field campaign.…”