Nervous chickens may offer lessons about mental illness in humans

Researchers have found a connection between genes that affect anxiety in chickens and human genes linked to bipolar disorder and schizophrenia.

Despite the compact size of the chicken genome — just a third the size of a human’s — the birds’ genes share surprising similarity to those of people.
Despite the compact size of the chicken genome — just a third the size of a human’s — the birds’ genes share surprising similarity to those of people.  (RUTH FREMSON / The New York Times)  

Despite all that neurotic clucking and scratching, domestic chickens are pretty unflappable. After all, we’ve bred them to be that way, preferring chill chicks to freaked-out fowl. But the behaviours of more anxious chickens could do more than ruffle a bunch of feathers: new research suggests that studying the genome of flustered birds could shed light on human mental disorders.

In a study published in the journal Genetics, evolutionary biologist Dominic Wright and his team looked at whether there’s a genetic connection between anxious behaviour in chickens, mice and humans. Despite the compact size of the chicken genome — it’s just a third of the size of a human’s — the birds’ genes share surprising similarity to those of people. There’s another reason chickens are so great for genetic research. Because there are both wild and domesticated chickens, researchers can observe their contrasting behaviours and easily pin them to genetic differences.

Wright bred wild red junglefowl chickens with their calmer cousins, white leghorn chickens, for the experiment. After eight generations, his team was able to run open field tests — experiments during which the birds were put in a brightly lit arena and assessed for how much time they spent cowering on the periphery instead of strutting through the room.

These behavioural tests helped the team identify brave and anxious birds, then narrow down areas of the genome related to variations in anxiety. They identified 10 candidate genes in the hypothalamus, an area of the brain which helps regulate anxiety.

Those genes were also found in a large data set of mice that had gone through the same types of experiments, which gave the team hope that they’d be found in anxious humans, too. But when it comes to humans, it’s harder to conduct standard tests for anxiety.

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“If you put a human in a novel arena with a bright light, you’d probably get remarkably similar responses,” said Wright with a laugh. “But kidnapping someone and putting them in a brightly lit room would probably be looked upon unfavourably.”

Instead of doing identical experiments on humans, the team did the next best thing. They compared genetic data from anxious chickens with data from humans with bipolar disorder, major depressive disorder and schizophrenia.

Wright was “quite shocked” to find that the genes that affected chicken anxiety tracked to conditions such as bipolar disorder and schizophrenia. Four of the genes tracked to similar genes within mice, and three were associated with schizophrenia or bipolar disorder in humans. The connection is perhaps not entirely surprising: more than 50 per cent of patients with diagnosed bipolar disorder also have a diagnosis of some kind of anxiety disorder. But the link with schizophrenia helps bring the mental illness, whose genetic links are only starting to be understood, into clearer focus for geneticists.

To Wright, the signals in both humans and mice mean that there’s more similarity between humans and animals than might meet the eye. “We always think of ourselves as being very unique,” he said, “but there seems to be a remarkable similarity in the system controlling anxiety in all different sorts of animals.”

Perhaps some mental disorders have an evolutionary basis in the same physical fear mechanisms that cause animals such as chickens to become alarmed in the presence of predators. Next, researchers hope to take the work a step further, establishing more concrete links between the genes and using the work to paint a better picture of how genes affect behaviour in all three animals.

Throwing chickens into terrifying situations in the name of human mental health seems harsh. But Wright, whose experiments were approved as ethical by a Swedish committee, says a better understanding of chicken anxiety could help chickens, too. He hopes to eventually see his study used to figure out how to breed fewer anxious chickens, making both scientific experiments and food production more humane.