Some fish can recognize their own faces in photos and mirrors, an ability usually attributed to humans and other animals considered particularly brainy, such as chimpanzees, scientists report. Finding the ability in fish suggests that self-awareness may be far more widespread among animals than scientists once thought.

“It is believed widely that the animals that have larger brains will be more intelligent than animals of the small brain,” such as fish, says animal sociologist Masanori Kohda of Osaka Metropolitan University in Japan. It may be time to rethink that assumption, Kohda says.
Kohda’s previous research showed that bluestreak cleaner wrasses can pass the mirror test, a controversial cognitive assessment that purportedly reveals self-awareness, or the ability to be the object of one’s own thoughts. The test involves exposing an animal to a mirror and then surreptitiously putting a mark on the animal’s face or body to see if they will notice it on their reflection and try to touch it on their body. Previously only a handful of large-brained species, including chimpanzees and other great apes, dolphins, elephants and magpies, have passed the test.

In a new study, cleaner fish that passed the mirror test were then able to distinguish their own faces from those of other cleaner fish in still photographs. This suggests that the fish identify themselves the same way humans are thought to — by forming a mental image of one’s face, Kohda and colleagues report February 6 in the Proceedings of the National Academy of Sciences.

“I think it’s truly remarkable that they can do this,” says primatologist Frans de Waal of Emory University in Atlanta who was not involved in the research. “I think it’s an incredible study.”

De Waal is quick to point out that failing the mirror test should not be considered evidence of a lack of self-awareness. Still, scientists have struggled to understand why some species that are known to have complex cognitive abilities, such as monkeys and ravens, have not passed. Researchers have also questioned whether the test is appropriate for species like dogs that rely more on scent, or like pigs that may not care enough about a mark on their bodies to try to touch it.

The mixed results in other animals make it all the more astonishing that a small fish can pass. In their first mirror test studies, published in 2019 and 2022, Kohda’s team exposed wild-caught cleaner fish in separate tanks to mirrors for a week. The researchers then injected brown dye just beneath the scales on the fish’s throats, making a mark that resembles the parasites these fish eat off the skin of larger fish in the wild. When the marked fish saw themselves in a mirror, they began striking their throats on rocks or sand in the bottom of the tank, apparently trying to scrape off the marks.

In the new study, 10 fish that passed the mirror test were then shown a photo of their own face and a photo of an unfamiliar cleaner fish face. All the fish acted aggressively toward the unfamiliar photo, as if it were a stranger, but were not aggressive toward the photo of their own face.

When another eight fish that had spent a week with a mirror but had not previously been marked were shown a photo of their own face with a brown mark on the throat, six of them began scraping their throats just like the fish that passed the mirror test. But they did not scrape when shown a photo of another fish with a mark.
Animals that recognize their reflection in the mirror most likely first learn to identify themselves by seeing that the movement of the animal in the mirror matches their own movement, researchers think. Because the cleaner fish were also able to recognize their own faces in still images, they, and possibly other animals that have passed the mirror test, may be able to identify themselves by developing a mental image of their own face that they can compare to what they see in the mirror or photos, the authors say.

“I think it’s a great next step,” says comparative cognitive psychologist Jennifer Vonk of Oakland University in Rochester, Mich., who wasn’t involved in the study. But she would like to see more research before drawing conclusions about what’s being represented in the mind of a nonverbal being like a fish. “As with most other studies, it still leaves some room for further follow-up.”

Kohda’s lab has more experiments planned to continue to probe what’s going on in the brain of the cleaner fish, and to try the new photo-recognition method on another popular research fish, the three-spined stickleback (Gasterosteus aculeatus).

Animal behaviorist Jonathan Balcombe, author of the book What a Fish Knows, is already convinced, describing the new study as “robust and quite brilliant.” People shouldn’t be surprised that fish could be self-aware given that they have already been shown to have complex behavior including tool use, planning and collaboration, Balcombe says. “It’s time we stopped thinking of fishes as somehow lesser members of the vertebrate pantheon.”

Fritillaria plants should be simple to spot.

The usually bright green plants often stand alone amid the jumbled scree that tops the Himalayan and Hengduan mountains in southwestern China — easy pickings for traditional Chinese medicine herbalists, who’ve ground the bulbs of wild Fritillaria into a popular cough-treating powder for more than 2,000 years. The demand for bulbs is intense, since about 3,500 of them are needed to produce just one kilogram of the powder, worth about $480.

But some Fritillaria are remarkably difficult to find, with living leaves and stems that are barely distinguishable from the gray or brown rocky background. Surprisingly, this plant camouflage seems to have evolved in response to people. Fritillaria delavayi from regions that experience greater harvesting pressure are more camouflaged than those from less harvested areas, researchers report November 20 in Current Biology.

The new study “is quite convincing,” says Julien Renoult, an evolutionary biologist at the French National Centre for Scientific Research in Montpellier who wasn’t involved in the study. “It’s a nice first step toward demonstrating that humans seem to be driving the very rapid evolution of camouflage in this species.”
Camouflaged plants are rare, but not unheard of, says Yang Niu, a botanist at the Kunming Institute of Botany in China, who studies cryptic coloration in plants. In wide open areas with little cover, like mountaintops, blending in can help plants avoid hungry herbivores (SN: 4/29/14). But after five years of studying camouflage in Fritillaria, Niu found few bite marks on leaves, and he did not spot any animals munching on the plants. “They don’t seem to have natural enemies,” he says.

So Niu, his colleague Hang Sun and sensory ecologist Martin Stevens of the University of Exeter in England decided to see if humans might be driving the evolution of the plants’ camouflage. If so, the more heavily harvested a particular slope, the more camouflaged the plants that live there should be.

In an ideal world, to measure harvesting pressure “you’d have exact measures of exactly how many plants had been collected for hundreds of years” at multiple sites, Stevens says. “But that data is practically nonexistent.”

Luckily, at seven study sites, local herbalists had noted the total weight of bulbs harvested each year from 2014 to 2019. These records provided a measure of contemporary harvesting pressure. To estimate further back in time, the researchers assessed ease of harvesting by recording how long it took to dig up bulbs at six of those sites, plus an additional one. On some slopes, bulbs are easily dug up, but in others they can be buried under stacks of rocks. “Intuitively, areas where it’s easier to harvest should have experienced more harvesting pressure” over time, Stevens says.

Both measures revealed a striking pattern: The more harvested, or harvestable, a site, the better the color of a plant matched its background, as measured by a spectrometer. “The degree of correlation was really, really convincing for both metrics we used,” Stevens says.
Human eyes also had a harder time spotting camouflaged plants in an online experiment, suggesting that the camouflage actually works.

Hiding in plain sight may present some challenges for the plant. Pollinators might have a harder time finding camouflaged plants, and the gray and brown coloration could impair photosynthetic activity. Still, despite those potential costs, these F. delavayi show just how adaptable plants can be, Steven says. “The appearance of plants is much more malleable than we might have expected.”