A new study recently revealed that for bottlenose dolphins, it's the urine's taste and signature whistle that enable them to recognize their friends at a distance,
The study's first author Jason Bruck, from the Stephen F. Austine State University in Texas, said dolphins keep their mouths open "and simple urine longer from familiar individuals than unfamiliar ones, a ScienceAlert report specified.
Bruck added this is important since dolphins are the first vertebrates ever observed to have social recognition solely through taste.
The researchers, which included the University of St. Andrews' Sam Walmsley and Vincent Janik, wrote that taste could be very beneficial in the open ocean since urine plumes stay for a while after an animal leaves.
This then alerts dolphins to the particular animal's recent presence even if it had not vocally signaled its presence.
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A baby bottlenose dolphin swims beside his mother at the Hakkeijima Sea Paradise aquarium in Yokohama, suburban Tokyo.
Signature Whistles
Bottlenose dolphins, which use signature whistles to address specific individuals selectively, and can recall these for more than two decades, were an interesting test case.
To examine, the authors of the study published in Science Advances presented eight dolphins with urine samples from both familiar and unfamiliar individuals, discovering they spent around thrice as long sampling urine from those they knew.
Furthermore, genital inspection, in which a dolphin uses its jaw to touch another individual's genitals, is typical in their social interactions, offering a good opportunity to learn the taste of urine of others.
The dolphins were trained to provide urine samples on demand in exchange for food for this study's purpose. Essentially, dolphins don't have olfactory bulbs, leaving the researchers sure it was taste, instead of smell, at play.
Urine Paired with Whistles
For the second part of the study, the authors paired urine samples with recordings of signature whistles played through underwater speakers, corresponding either to the same dolphin that provides the pee sample or a mismatched specimen.
The study investigators observed that the dolphins stayed near the speaker longer when the vocalizations matched the urine samples, possibly specifying that the two congruent lines of evidence spurred more interest.
Bruck said it is not every day that scientists discover evidence of "noun-like use of signals" in a non-human vocal system, "and that's pretty exciting."
The first author also said that dolphins have rich social worlds. It may be equally beneficial for a dolphin to recognize alliance members as it is for them to identify probable opponents.
Link to Obesity
A similar ZBT News report indicated that the research team suggested that lipids were possibly responsible for individual chemical signatures.
They wrote, given the recognition skills revealed in their research, they think that it is possible that dolphins can extract other information from urine, as well, "such as reproductive state, or use pheromones to influence each other's behavior."
In an unexpected twist, the study could have substances for human obesity, the same gene that enables dolphins to determine lipids in urine also exists in humans, where it helps them know when they have had enough to eat.
Examining the gene in dolphins could enhance insight into how it's working in people. The work could have other implications, as well.
For instance, human-caused pollution such as oil spills or other chemical runoffs may restrict the ability of the dolphins to signal to one another, therefore doing even more harm than previously thought, explained Bruck.
Related information about how dolphins communicate is shown on PBS NewsHour's YouTube video below:
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