AFP, published on Wednesday, May 18, 2022 at 10:57 p.m.
Dolphins can recognize conspecifics they have already crossed paths with by the taste of their urine, in addition to their whistle, according to a study published Wednesday in the journal Science Advances.
“Dolphins are the first vertebrates for which we have demonstrated social recognition through taste alone,” Jason Bruck, lead author of the study, told AFP. They “keep their mouths open and taste urine from familiar individuals longer” than from unfamiliar individuals, he explained.
This work, carried out by observing the reactions of eight bottlenose dolphins (tursiops truncatus) in captivity, sheds light on a question that scientists have been asking for a long time, namely whether animals can categorize members of their species as “friends”, like humans.
“In the ocean, it is difficult to find others, and hearing or smelling a familiar individual via taste is an important indicator” to be able to locate it, explains the study.
Especially since urine has the advantage of persisting for a long time in water, even after the animal has left.
Much like dogs sniff each other when they pass each other, inspecting the genitals of other individuals is a common practice among dolphins. This gives them the opportunity to taste each other’s urine.
To find out if dolphins recognize their peers this way, scientists first trained other dolphins to voluntarily provide their urine, thanks to food rewards. Samples were collected in syringes.
The researchers then compared the reaction of the eight dolphins (two females and six males) when samples of either water or urine were poured into their tanks. As a result, the animals spent twice as long analyzing urine as water.
In a second step, urine samples from familiar dolphins, and others from unknown dolphins, were tested: the individuals then spent three times more time tasting the known samples than foreign ones.
Finally, the scientists added sound through speakers. Dolphins have the particularity of each having a unique whistle, which they develop when young.
When pouring the urine, whistles of the correct dolphin that provided the sample, or of a completely different and therefore mismatched dolphin, were played.
When the whistle matched the individual to which the urine belonged, the dolphins spent more time near the loudspeakers, showing that this combination generated greater interest.
According to the study authors, it is “likely that dolphins can derive other information from urine, such as reproductive status”.
And it could be useful, in the future, to study how marine pollution affects the ability of dolphins to recognize their conspecifics. “It could be that this prevents males from identifying females capable of reproduction,” said Jason Bruck.