Even though a male cichlid is one tough fish, he may be scared of his own reflection. A new study shows that squaring off to fight a mirror opponent can be worse than fighting a real foe.
Male cichlid fish readily attack other males as well as mirror images of themselves, posturing and lunging with the same aggression, says Julie K. Desjardins of Stanford University. Yet the reflection-fighting males show heightened activity in a part of the brain associated with fear and other negative reactions in vertebrates, she and Stanford colleague Russell Fernald have found.
Tangling with a real male doesn’t stir up that response, the researchers report in a Biology Letters study released online the week of May 11. Desjardins hesitates to equate whatever is going on in the fish brain with the human concept of “fear,” but she says the reaction to mirror images is indeed “negative.”
Earlier studies of fish and mirrors have suggested that fish just mistake their reflections for some impertinent, other fish that needs a good trouncing. The new paper gives the first indication of differential brain activity when fish meet mirrors, Desjardins says.
Scientists have a long tradition of studying animal reactions to mirrors as a way of trying to explore animal consciousness. Great apes, elephants, dolphins and magpies show evidence of recognizing themselves when gazing into mirrors, says Diana Reiss of Hunter College in New York City, who studies animal cognition. In experiments done so far, other animals, including monkeys and fish, don’t seem to get it.
The new study does not demonstrate mirror self-recognition in fish. “I want to be clear about that,” Reiss says. Yet the fish do perceive something different about their reflected opponent.
Desjardins and Fernald tested reactions to mirrors in males of an African cichlid species, Astatotilapia burtoni. Hormones as well as behavior looked similar regardless of whether the fish menaced a mirror image or a real male behind a clear partition. To see into the brain, researchers used two marker genes to compare activity in various brain regions. “It’s a kind of fishy MRI,” Desjardins says. What fired up more in the mirror fighters was the amygdala, a structure that’s involved in emotions in people.
Using this technique in a mirror study is certainly uncommon and possibly unprecedented, Desjardins says. Reiss adds, “It’s an interesting tool.”
Even with older approaches, though, a few studies have found that some animals without mirror recognition still perceive differences between reflections and reality, notes Joshua Plotnik of Emory University in Atlanta, who worked with Reiss in documenting mirror self-recognition in elephants. Work by other researchers shows differences in heart rates or in behaviors when monkeys encounter a reflection versus a real monkey, even though scientists have not shown self-recognition in monkeys.
As far as mirror self-recognition (or not), the new work “does not really change much,” says comparative psychologist Thomas Suddendorf of the University of Queensland in Brisbane, Australia.
What could change though, says Desjardins, is the current, widespread use of mirrors in experiments that probe behaviors unrelated to self-recognition. Researchers may want to show a fish or other creature another of the same size and species, for example. If animals are sensing that something is off about the mirror, “I think mirrors need to be used with caution,” Desjardin says.