Evaluating the Molecular Potential and Interpretability of DNA in Historical Spirit Collection Media.

Advancements in historical genomics increasingly leverage museum collections to study past ecosystems, species interactions and biodiversity. Formalin-fixed, ethanol-preserved specimens, once thought inaccessible to molecular analyses due to DNA degradation, are emerging as valuable genomic resources. If recoverable and reliably attributable, DNA within preservation media could provide a non-destructive alternative to conventional tissue sampling, with the potential to expand molecular access to valuable or irreplaceable specimens. We tested whether preservation media contains recoverable DNA suitable for taxonomic inference. We coupled passive adsorption and active filtration of specimen media with hot alkaline lysis DNA extraction followed by metabarcoding and shotgun metagenomics. DNA was recoverable across samples, including 41 of 61 (~67%) targets in a composite sample. However, detections were dominated by non-target taxa, indicating that preservation media retain a layered mixture of specimen-derived DNA and broader collection-level background. Detection success tracked with preservation chemistry (near-neutral pH and low residual formaldehyde) rather than specimen age. Method choice influenced detections: active filtration increased target detections but admitted more background; passive capture was sparser but more selective; shotgun sequencing retrieved broader vertebrate signals, including reptiles, but was heavily enriched for non-targets. Because both target and non-target taxa were often abundant, read-abundance cut-offs were unreliable for attribution. Spirit-media DNA is therefore best interpreted as a collection-level signal and a screening tool to identify jars with molecular potential (e.g., taxa of conservation or biosecurity interest), rather than as a definitive non-destructive proxy for specimen identity. Prioritising chemically favourable jars and implementing rigorous contamination controls should improve signal interpretability and help unlock the value of preservation media for historical genomics.