What did the Current Biology study led by Professor Masao Miyazaki reveal about why domestic cats have unusually large numbers of lipid droplets in their kidneys, how 13 branched-chain fatty acids in urine create stable, individual-specific scent signatures detectable for at leas

The study proposes that cats’ unusually lipid-rich kidneys help preserve a durable chemical identity in urine. Thirteen semi-volatile branched-chain fatty acids (BFAs), present in individual-specific mixtures, appear to function as this scent “calling card”; the study identifies a strong candidate mechanism, not a final proof of every physiological step.

• Why the kidney droplets matter: BFAs were detected in kidney tissue but not in the other tissues examined, and BFA-containing neutral lipids occurred in lipid droplets in the renal cortex. The authors propose that the abundant droplets—long a feline anatomical mystery—store these lipids as a reservoir.

• A stable individual signature: Each cat had a markedly different combination and relative abundance of 13 BFAs, while its own profile remained comparatively stable across collection dates. Related cats had more-similar profiles, but still retained individual differences.

• Persistence after scent marking: Because these BFAs are semi-volatile and evaporate slowly, BFA profiles in urine-soaked samples held at 25°C remained comparatively stable for at least 24 hours—unlike many more volatile urinary odorants.

• Flehmen and recognition experiments: Cats showed the open-mouthed flehmen response more often to unfamiliar urine than to their own. The response waned with repeated exposure to the same sample and returned when urine from another individual was substituted. In a controlled exposure experiment, cats habituated to a sample increased sniffing when only the donor-derived BFA fraction was changed while other urinary lipids were controlled—evidence that they detect donor-specific BFA mixtures.