Signatures of branched-chain fatty acids derived from a kidney reservoir confer stable chemical individuality on domestic cats.

Animals often rely on scent marks to communicate identity across time, yet how chemically dynamic signals remain individually informative is unresolved. Here, we show that domestic cats achieve durable chemical individuality through a reservoir-buffered system based on branched-chain fatty acids (BFAs). Using behavior-guided chemistry, we identify a structurally unusual repertoire of urinary BFAs whose compositional profiles are individually distinctive, stable within individuals, and relatively resistant to post-deposition drift. Cats discriminate donor-derived BFA compositions even when presented on a matched reconstructed urinary lipid background, showing that BFA composition carries discriminable donor-specific information. We trace these compounds to triacylglycerol-rich lipid droplets in the renal cortex, revealing a physiological reservoir that buffers short-term variation and supports repeatable urinary signatures. Comparative analyses across Felidae show that BFA-associated urinary and renal lipid signatures are broadly distributed but non-uniform and diversified in repertoire complexity and storage architecture. These findings identify an organ-level mechanism that stabilizes small-molecule chemical individuality in domestic cats and reveal a diversified reservoir-supported chemical substrate across felid lineages. VIDEO ABSTRACT.