Dolphins can identify their friends by taste, study shows for the first time

We humans rely on a range of cues to recognize our friends, such as their smiles, their voices, or the way they walk. Biologists have known for decades that dolphins form close friendships and that cetaceans recognize their friends by their unique whistles. Now, new surprising research suggests bottlenose dolphins use their sense of taste to distinguish their friends’ urine from unrelated dolphins.

Study leader Jason Bruck, a marine biologist at Stephen F. Austin State University in Texas, had no intention of testing whether bottlenose dolphins could identify each other through their urine. His original goal was to test whether dolphins use their signature whistles in the same way that humans rely on names. But to do that, he needed a second way dolphins could identify each other. (Read more about how dolphins respond to their “names.”)

To find out if dolphins could associate a whistle with a specific dolphin, Bruck turned to an unlikely substance: urine. A scientist had previously seen wild dolphins swim purposefully through plumes of urine, leading Bruck to suspect they were collecting information from them.

“It was a bull’s eye,” says Bruck, whose study was published this week in the journal scientific progress. “And I didn’t expect it to work, to be honest.”

In experiments with captive dolphins, the team found that dolphins paid more attention to their friends’ urine and whistles, suggesting they knew the animals that released them, he says.

The findings are the first robust evidence that an animal identifies other members of its species using taste. They also show that by using at least two clues to identify individuals, dolphins have a complex understanding of their family and friends, just like humans do.

“I was shocked, just shocked,” says Bruck. “I had a big grin on my face, like, Oh my God, this worked.”

Enthusiastic participants

In 2016 and 2017, Bruck and colleagues observed several bottlenose dolphins at dolphin interaction facilities in Bermuda and Hawaii, which also maintain a breeding consortium for the species. At these Dolphin Quest sites, dolphins live in lagoons fed by natural seawater, which mimics their environment in the wild.

The researchers’ first step was to see if dolphins could detect urine in the seawater. Over the course of evolution, bottlenose dolphins have lost their sense of smell, but have retained a strong sense of taste.

In vast pools of temporarily separated dolphins, the scientists poured water with ice into the water and then watched how each animal reacted. Curious dolphins exploring the ice water were good candidates for the experiment. Next, the team had to test whether the animals’ responses to ice water and urine varied and whether they reacted differently to known than to unfamiliar urine. (Read why dolphins have the longest memory in the animal kingdom.)

The team knew which dolphins knew each other based on who had lived together for at least five years. So the researchers poured about 20 milliliters of both known and unknown dolphin urine into the pool, one after the other, in the order determined by the toss of the coin.

The dolphins spent about three times longer examining the known urine than the unknown urine, with a few individuals sampling the known substance for more than 20 seconds. The cetaceans paid little attention to the unfamiliar urine, taking it only for the same amount of time they had ice water.

“The dolphins were very, very eager to participate,” says Bruck, who added that they were not rewarded with food. “Usually dolphins are bored with my experiments. We took advantage of something that is part of the world of dolphins.”

Cetacean Expectations

The latest test examined whether dolphins had a paired understanding of other dolphins’ signals, in other words, whether a person’s whistle and urine were connected in their minds.

To do this, Bruck did what behavioral ecologists call a “expectation violation” experiment: showing animals something that’s not right and seeing how they react. In humans, this would be like seeing your best friend’s face but hearing a different voice. (Learn how dolphins have bold and shy personalities like us.)

For this latest experiment, Bruck tested different urine-whistle combinations on 10 dolphins, five of which were the same animals in the previous experiments.

When exposed to an incorrect combination of urine and whistle, the dolphins didn’t pay too much attention — perhaps a useful innovation for the wild, where the mammals would be inundated with mismatched whistles and urine, he says.

But when a dolphin encountered the correct urine whistle pair, the animal explored the area for an average of 10 seconds longer than the mismatched pair. Two individuals lingered for more than 40 seconds — the compelling evidence the team needed to recognize their friends.

A taste of success

“It’s very difficult to show that a concept exists in the mind of an animal, so these kinds of experiments to answer that question are very interesting and useful,” said Bruno Díaz López, chief biologist at Spain-based Bottlenose Dolphin Research. Institute, which was not involved in the study.

López, who would like to see similar studies tried in the wild, adds, “it’s a good approach and a good first step” to understand the role taste could play in dolphin recognition. (How dolphins use tools, teamwork, and trickery to get their dinner.)

“This really deepens our understanding of how dolphins monitor each other, which we know is very important to them,” said Laela Sayigh, a marine biologist at the Woods Hole Oceanographic Institute in Massachusetts, who was also not involved in the study. used to be.

“It opens doors to other kinds of questions about what all they could learn” from urine traces, she says.

As for Bruck, he would like to investigate what biological mechanism the dolphins use to taste urine.

A promising possibility is lipids in the urine, which can be detected with a physical “aerial” on their taste buds. It’s especially urgent, he adds, because it’s not known what impact man-made pollution has on the dolphins’ taste-based abilities.

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