The influence of lipid-extraction and long-term DMSO preservation on carbon (δ13C) and nitrogen (δ15N) isotope values in cetacean skin

Abstract

Stable isotope analysis (SIA) has rapidly become a useful tool to study the ecology of wild animal populations, especially for elusive, wide-ranging predators like marine mammals. The development of projectile biopsy techniques resulted in the collection of thousands of cetacean tissue samples that were archived in a dimethyl sulfoxide (DMSO) solution for long-term, multidecadal preservation. Here we examine the influence of DMSO preservation on carbon (δ13C) and nitrogen (δ15N) values by comparing a set of paired delphinid skin samples stored frozen without preservative and in DMSO for up to 22 yr. Treatment of paired frozen and DMSO-preserved skin in a 2:1 chloroform:methanol solution yielded similar δ13C and δ15N values, revealing that DMSO and lipid contamination have similar isotopic effects on skin, and that these effects can be removed using routine lipid-extraction methods. Further, amino acid concentrations in DMSO-preserved and frozen skin tissue were similar, providing independent evidence of minimal protein alteration due to preservation. Access to a rich archive of skin samples preserved in DMSO will expand our ability to examine temporal and spatial variability in the isotope values of cetaceans, which will aid our understanding of how their ecology has been influenced by historical changes in environmental conditions.