Isotopic homogeneity throughout the skin in small cetaceans

Abstract

Isotopic homogeneity within the skin suggests that the isotope ratios of a sample from a specific skin position can be considered representative of the ratios from the entire skin tissue in dolphins. This conclusion validates the results of previous stable isotope analyses in dolphins that used skin samples as representative of the whole skin tissue. Isotopic similarities or dissimilarities among tissues should be considered when analysing different tissues and comparing results from the same or different species.

Tracing gestation and lactation in free ranging gray whales using the stable isotopic composition of epidermis layers

“…The precise time period represented by each epidermal layer, however, it is not well known and could vary according to factors such as species and environmental conditions [ 14 ]. In addition, when intra-layer differences in δ 13 C and δ 15 N values were compared in stranded striped dolphins ( Stenella coeruleoalba ), bycaught common dolphins ( Delphinus delphis ) [ 17 ] and stranded gray whales ( Eschrichtius robustus ) [ 18 ], no significant differences were found, and authors assumed isotopic homogeneity within those species epidermis.…”

Evidence for dietary time series in layers of cetacean skin using stable carbon and nitrogen isotope ratios

“…However, while systematic in the differences among layers, the variability within a layer (across cores) was minimal and random. Furthermore, all but two of the ranges in δ 13 C and δ 15 N values within a layer were under 0.5‰, which was lower than the range of stable isotope ratios measured across 11 different skin positions in common and striped dolphins . Other causes of variability within a layer, including the two outlier layers with high variability, may be related to limitations in accuracy of cutting layers when sampling the skin.…”

“…Furthermore, all but two of the ranges in δ 13 C and δ 15 N values within a layer were under 0.5‰, which was lower than the range of stable isotope ratios measured across 11 different skin positions in common and striped dolphins. 39 Other causes of variability within a layer, including the two outlier layers with high variability, may be related to limitations in accuracy of cutting layers when sampling the skin. Increasing our sample size for each species would probably smooth out that variability.…”

“…However, key metabolic parameters allowing for precise interpretation of the temporal resolution of stable isotope results are often lacking, especially for metabolically active tissues. In addition, the variability of stable isotope ratios from different samples within a tissue is not well established, although existing studies indicate that replicate samples of muscle tissue from individual fish and zooplankton produced variability within a single individual of <0.2‰, and a recent study with common and striped dolphins showed there were no significant differences among stable isotope ratios across various locations on the skin . This variability is essential context to appropriately interpret differences in stable isotope ratios observed among tissues or individuals.…”

“…zooplankton produced variability within a single individual of <0.2‰, and a recent study with common and striped dolphins showed there were no significant differences among stable isotope ratios across various locations on the skin. [36][37][38][39] This variability is essential context to appropriately interpret differences in stable isotope ratios observed among tissues or individuals.…”