How close are you to your friends? Most of us could probably pick our besties out by sight or sound, and if you’re especially close maybe you could even sniff them out – but that’s about the limit. Right?
Not if you’re a dolphin, it turns out, as a study published this week in the journal Science Advances has revealed that the marine mammals recognize friends and relatives in a way even more intimate: by tasting them.
Specifically, by tasting their urine.
“Dolphins explored urine samples for longer if they came from known animals or when they were presented together with the dolphin’s unique and distinctive signature whistle,” reported Professor Vincent Janik, Director of the Scottish Oceans Institute and lead author of the study.
Together with colleagues Jason Bruck and Sam Walmsley, he presented bottlenose dolphins with various pees from their comrades at three facilities in Bermuda and Hawaii to see how they reacted, which is frankly the kind of thing that gets non-scientists banned from the premises.
“This shows not only that they can tell animals apart by taste,” he explained, “but also that they recognize animals across their senses, hinting at a complex representation of familiar animals in a dolphin’s brain.”
To be fair, “taste” is a bit of a misnomer – dolphins can’t actually taste very much. They have no olfactory bulb, an underdeveloped olfactory nerve, and a nose entirely separate from their mouth and esophagus, so they don’t have a sense of smell at all – and as anybody who’s had a nasty cold recently will know, this can often result in everything tasting like cardboard.
But dolphins likely don’t even get that level of cardboardy zing: “Dolphins are unlikely to recognize an individually different composition of components in the urine of conspecifics using basic mammalian taste sensors,” the paper explains, “because they experienced a loss of taste receptor genes responsible for the perception of four of the five basic tastes in mammals.”
Instead, Janik explained, the cetaceans are likely relying on “unusual sensory cells on their tongue that are probably involved in this detection of individual tastes of other animals.” Together with the prominence of certain brain areas associated with chemoreception through taste, the paper explains that dolphins likely can detect taste “through the facial or trigeminal nerves despite the loss of the olfactory and vomeronasal cranial nerves.”
Tasting the urine of your acquaintances might seem a teensy bit overly friendly from a human perspective – but to a dolphin, it makes perfect sense, the authors write.
“The use of taste is highly beneficial in the open ocean because urine plumes will persist for a while after an animal has left,” they note. “By recognizing who caused a plume, dolphins would be alerted to the recent presence of that individual even if it had not signaled its presence vocally.”
And if you’re wondering how they’d get to know what their friends… um, taste like... well: “Genital inspection in which there is rostrum [beak] to genital contact is relatively common in dolphin social interactions,” the paper notes, “and provides a good opportunity to learn the taste of a conspecific’s urine.”
While the practice may be a bit novel, the results are yet more evidence of dolphins’ big-brained mental prowess. Dolphins are known to remember each other’s “names” for over 20 years, and the researchers think this newly discovered talent may provide a way for the animals to check up on their pals’ physical and emotional states.
“Given the recognition skills revealed in our study, we think that it is likely that dolphins can also extract other information from urine, such as reproductive state, or use pheromones to influence each other’s behavior,” the paper explains.
“In combination with […] previous studies, our results show that dolphins form persistent modality-independent representations that have learned labels just as in human concept formation,” the authors conclude. “The resulting concepts of conspecifics may be used in mental operations such as planning, mental time travel, or the simulation of social scenarios.”