Preservation of stable isotope niche dynamics in squamate museum specimens

Natural history museums are invaluable resources for large-scale ecological and evolutionary studies, but certain ecological traits can be challenging to recover, particularly from fluid-preserved specimens. Stable isotope analysis is an elegant method for reconstructing the dietary niche over integrated timescales, and recovering this information from museum specimens can provide a critical axis of ecological information for studies of population dynamics through time and space. However, isotope ratios of tissues are known to be altered by extended contact with formalin and ethanol. Here, we assess whether intra- and interspecific variation in isotopic signature, which represent critical data used to assess metrics of niche diversity, can be reliably recovered following fluid preservation. We use a broad taxonomic distribution of squamates to compare niche metrics prior to and 8 weeks following a standard museum preservation process We could not recover intraindividual metrics of niche diversity but found that between-individual variation was not significantly altered, allowing for the reconstruction of community niche characteristics We present an example isotopic analysis from museum specimens representing generalist and specialist Thamnophis garter snake populations that aligns with empirical estimates of niche width We also present several additional analyses on tissue-specific effects, delipification and buffer storage, with useful insights for field collection and downstream analysis decisions.