Snakes can distinguish themselves from others using their sense of smell – 04/14/2024 – Science

Say the words animal self-recognition and most scientists will think of chimpanzees, crows and elephants.

For the first time, researchers — using an innovative approach to the mirror test — have found evidence that “garter snakes,” the English name for a genus (Thamnophis) of common snakes from the Northern Hemisphere, can distinguish themselves from others, using not vision, but smell.

“Reptiles are massively understudied,” said Noam Miller, a comparative psychologist at Wilfrid Laurier University in Ontario, Canada, and author of the paper, published in the journal Proceedings of the Royal Society B. “There’s a bias out there that they’re boring animals. , not very cognitive, and that’s completely wrong. That’s one of the reasons we were very interested in studying them and showing the complex cognitive things they can do.”

A traditional sign of animal cognition has generally been the mirror test, Miller said, or whether an animal can learn to recognize itself in a reflective surface, a trait thought to be a proxy for more sophisticated intelligence. Used by primate researchers in the 1970s, the test usually involves marking an animal with paint somewhere visible only in the mirror and waiting to see if it investigates the change.

Similar tests have been done on a variety of species since then: elephants (passed), pandas (failed), roosters (passed) and even fish like the cleaner wrasse (passed).

But the mirror test is aimed at animals that are primarily visual. Many species — like snakes — rely primarily on their sense of smell, Miller said. In 2017, researchers developed an olfactory version of the test for dogs. (They passed.)

Two different species of snakes were tested in the new study. In one corner: garter snakes from eastern North America, insect and fish predators with a surprisingly complex social life. On the other, African ball pythons, constrictor snakes that catch their prey in ambushes.

Snakes, like humans, have oils on their skin that leave a scent trail. The team rubbed makeup remover pads along the undersides of the two species to collect scent samples, some of which were adulterated with olive oil.

They placed the pads on the ends of long, narrow boxes and offered the animals several choices: between their own scent and pure olive oil; its own odor modified with olive oil; and the modified or unmodified odors of other snakes of the same species.

The team measured the snakes’ interest by assessing how long they stuck out their tongues to smell the air — longer indicated sustained interest, he said. Ball pythons showed no apparent distinction. But garter snakes focused on their own adulterated scent and ignored variations in other snakes’ scents.

“Essentially, it seems that if others smell strange, they don’t care,” Miller said. “If they smell funny, that’s something they need to investigate.”

Recent research has found that eastern garter snakes are remarkably social, gathering in large groups to hibernate in the winter and forming networks — complete with “friends” — during their active season.

As a more gregarious species, they may be more attuned to the need to distinguish themselves from others. A possible explanation of how self-recognition works is the ability to recognize the difference between one’s self and one’s non-self, according to Miller. “That then links it to social behaviors.”

It’s difficult to say, however, whether the ball pythons’ failure to pass the test is due to a lack of skill or a lack of interest, he added. Ongoing laboratory research suggests that ball pythons, although more solitary, are socially complex.

But with more than 5,000 species of living snakes inhabiting a variety of different environments, he added, the family as a whole offers a wide range of opportunities to discover which ecologies and behaviors might lead animals to actively distinguish themselves.

Future tests could focus on arboreal species or on vipers like rattlesnakes, which recent research has suggested prefer to shelter with relatives and be less stressed around other snakes. However, the rattlesnake is also “more difficult to work with in a lab full of college students,” Miller said.

“In many ways, I think their experimental paradigm is more powerful than the mirror tests,” said Rulon Clark, a biologist at San Diego State University who has researched snake social behavior and was not involved in the study. “A highly reflective mirror surface doesn’t have many ecological analogues. But finding and understanding the importance of chemical clues left by you and your congeners is probably a profoundly important aspect of the natural history of these animals.”

“Our research links how snakes experience themselves with how they experience the world around them,” said Morgan Skinner, a biologist at Wilfrid Laurier University and author of the study. “It also demonstrates that when you can do this effectively in an experiment, you can find cognitive capabilities that some might find surprising.

“Little is known about the social structures of snakes and other reptiles,” Miller said. “And if we want to understand the fundamental building blocks of social structure, we need to study a broader range of species, rather than just rats and pigeons all the time.”