Dolphins meet their friends by tasting their urine, according to a new study. By taking sips of the other dolphins’ urine, they demonstrated a type of social acceptance that begins with an exchange of whistles that are unique to certain individuals — much like human names.
Scientists have long known that dolphins identify with what are known as signature whistles, which are different for each dolphin, and that they address one another by mimicking such whistles. However, the researchers weren’t sure whether this copying showed that dolphins associate distinctive whistles with individual identity or with a more general concept like “friend.”
Recently, scientists have found that bottlenose dolphins not only recognize names, but also replicate that recognition with another sense: taste.
By sampling each other’s urine and recognizing the source, the dolphins demonstrated that they could 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 discovered that dolphins perform this type of identification through urine tasting while studying whether the animals really call each other by name when they copy whistles. The scientists conducted what they called a cross-modal study, in which experiments test whether an animal can recognize an object or another animal based on multiple signals received from different senses.
Scientists have previously conducted such experiments on a variety of animals, including fish and animals monkeys. However, most animals’ communication systems lack sounds that are recognizable as labels for individuals, such as dolphins’ distinctive whistles, the researchers wrote.
However, finding a second sense in dolphins that could be tested under laboratory conditions has been a challenge. Testing the visual range or echolocation of dolphins “would involve moving giant monitor lizards or even the dolphins themselves, which is impossible,” said the study’s lead author Jason Bruck, a biologist at Stephen F. Austin State University in Texas. But dolphins have been known to swim through other dolphins’ plumes of urine with their mouths open, and they may do so to obtain social information, “like a dog sniffs a fire hydrant,” Bruck told Live Science.
“But dolphins would have to do that with taste, not smell,” he added, since whales lack the olfactory bulb.
A question of identity
Researchers found that dolphins spent about three times as long collecting urine from unfamiliar dolphins than from familiar ones. This indicated that the animals could identify known conspecifics based on taste.
To test the persistence of the identification across all senses, the researchers paired recordings of distinctive whistles with urine from dolphins: in some of the pairings, the urine came from the whistler, while in others it was produced by another dolphin. The scientists then introduced dolphins to the sound of a whistle and the taste of a urine sample.
When the pee matched the whistle, listening dolphins lingered closer to the playback speakers. This indicated that the animals recognized the consistency of the signals perceived by two senses – taste and hearing – and that both taste and sound came from the same dolphin.
These findings mean whistles to dolphins represent the dolphin’s specific identity in the minds of other dolphins, including the taste of those dolphins’ urine.
“We now know that when a dolphin produces that signature whistle, they’re really referring to the dolphin they’re copying,” Bruck said. “They use these whistles the same way we use names.”
Future studies could explore the mechanisms behind this newfound dolphin ability, Bruck said. Taste-driven identification in dolphins can be driven by lipid recognition; If so, dolphin research may uncover a lipid-sensitive taste bud that’s larger and more robust than the human variant, making it easier to study. Such a discovery could inform research on human obesity, Bruck said.
In principle, these results could open up new avenues of dolphin research, Bruck added. “Transmission of social information from dolphin to dolphin [is] as easy as [using] an underwater speaker” and could offer insights into “how dolphins perceive each other as individuals,” he said.
The results were published in the journal on May 18 scientific advances.
Original article on Live Science.
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