Dolphins get to know their friends by tasting their pee, according to a new study. By taking sips of urine from each other, the dolphins demonstrated a type of social recognition that begins with an exchange of whistles unique to specific individuals – much like human names.
Scientists have long known that dolphins identify each other using so-called signature whistles that are different for each dolphin and that they address each other by mimicking such whistles. But the researchers were unsure whether this copy showed that the dolphins associated the signature whistles with individual identity or with a more general concept such as “friend”.
Recently, scientists have learned that bottlenose dolphins not only demonstrate name recognition, but also replicate that recognition with another sense: taste.
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By tasting each other’s urine and recognizing the source, dolphins have shown that they can track dolphin identities using two types of sensory input. This means the animals could create and store a mental concept of other dolphins, according to the new study.
Researchers have found that dolphins perform this type of identification by pee tasting while investigating whether the animals really call each other by name when copying whistles. The scientists conducted what is called a cross-modal study, in which experiments test whether an animal can recognize an object or another animal through multiple signals received from different senses.
Scientists have already used such experiments on a wide range of animals, including fish and monkeys. But most animals’ communication systems lack recognizable sounds as labels for individuals, such as the characteristic whistles of dolphins, the researchers wrote.
However, finding a second sense in dolphins that could be tested under laboratory conditions was difficult. Testing dolphin sight or echolocation “would involve moving giant monitors or even the dolphins themselves, which is impossible,” said study lead author Jason Bruck, a biologist at the Stephen F. Austin State University in Texas. But dolphins have been known to swim through other dolphins’ urine plumes, mouth agape, and they may do so for social information “like a dog sniffing out a fire hydrant,” Bruck told Live Science. .
“Except dolphins should do this with taste, not smell,” because cetaceans lack olfactory bulbs, he added.
A question of identity
The researchers found that dolphins spent about three times longer collecting urine from unfamiliar dolphins than from familiar dolphins. This suggested that the animals could identify known mates by taste.
To test the persistence of identification across the senses, the researchers matched recordings of signature whistles with dolphin urine: in some pairings, the urine came from the whistler, while in others it was produced by a different dolphin. The scientists then introduced the dolphins to the sound of a whistle and the taste of a urine sample.
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When the pee matched the whistle, the listening dolphins lingered closer to the playback speakers. This indicated that the animals recognized the consistency of signals perceived by the two senses – taste and hearing – and that taste and sound came from the same dolphin.
These findings mean that for dolphins, the whistles represent the dolphin’s specific identity in the minds of other dolphins, including the taste of that dolphin’s pee.
“We now know that when a dolphin makes that signature whistle, it’s really referring to that dolphin it’s copying,” Bruck said. “They use these whistles the same way we use names.”
Future studies could investigate the mechanisms behind this newly discovered dolphin ability, Bruck said. Dolphin taste identification may be driven by lipid recognition; if so, research on dolphins may reveal a lipid-sensitive taste bud that is larger and more robust than the human variety and therefore easier to study. Such a finding could inform research on obesity in humans, Bruck said.
More fundamentally, these findings could open up new avenues of dolphin research, Bruck added. “Transmitting social information from dolphin to dolphin [is] as easy as [using] an underwater speaker” and could offer insight into “how dolphins view themselves as individuals,” he said.
The results were published on May 18 in the journal Scientists progress.
Original article on Live Science.