Anxiety research: Even crayfish get stressed, scientists show
Steve Connor is the Science Editor of The Independent and i. He has won many awards for his journalism, including five-times winner of the prestigious British science writers’ award; the David Perlman Award of the American Geophysical Union; four times highly commended as specialist journalist of the year in the UK Press Awards; UK health journalist of the year and a special merit award of the European School of Oncology for his investigations into the tobacco industry. He has a degree in zoology from the University of Oxford and has a special interest in genetics and medical science, human evolution and origins, climate change and the environment.
Thursday 12 June 2014
Anxiety is not only felt by the followers of the England football team, it can also be found in the lowly crayfish, a small lobster-like creature that appears to be capable of fearing the future just like a soccer fan, a study has found.
For the first time scientists have found unequivocal signs that the state of anxiety normally associated with higher forms of life such as humans, mammals and other animals with a backbone is also shared with a spineless species with a worrying disposition.
An experiment has shown that the freshwater crayfish can be induced into a state of deep anxiety that can only be alleviated by the same kind of tranquilisers used to treat people afflicted by a similar condition, scientists said.
The study revealed that the crayfish emotion is governed by the same chemical transmitters in its nervous system that are involved in controlling anxiety in humans, which is why anxious crayfish respond to benzodiazepine, a tranquiliser used to treat anxiety in people, scientists said
“Anxiety is different from fear, which is something that even the simplest animals show. Anxiety is a kind of fear of the fear, and animals who experience it will display adaptive behaviour to minimise the threat,” said Daniel Cattaert, a neuroscientist at the University of Bordeaux in France.
“Acute anxiety can be beneficial. After an animal has faced a bad experience then if it adapts its behaviour to minimise the risk in the future, then this can be beneficial for the animal. People thought this only occurs in animals with complex nervous systems, but we have found it in crayfish,” Dr Cattaert said.
The study, published in the journal Science, involved subjecting crayfish to a series of mild electric shocks which understandably made them nervous and so prone to flicking their tails as an escape response.
They also changed their behaviour when compared to crayfish that had not been treated with electric shocks. Instead of exploring the well-lit parts of their tank, the anxious crayfish kept almost entirely to the darker corners as light made them fearful.
“This adaptation in the stressed crayfish lasts for about an hour after being subjected to about 20 minutes of stress. A naïve crayfish will readily explore the well-lit arms of the cross-shaped tank but the stressed crayfish are clearly anxious about doing this,” Dr Cattaert said.
“There is clear decision making involved. They may start to enter the lit areas of the tank but then they stop and go back to the dark areas,” he said.
When the stressed crayfish were treated with chlordiazepoxide, a potent benzodiazepine, they overcame their anxiety and readily explored the well-lit areas of the tank, showing no abnormal aversion to light, he added.
Injecting the neurotransmitter serotonin into unstressed crayfish, however, caused them to behave as if they had undergone the electric-shock treatment. Serotonin also plays a key role in governing the stress response in humans, suggesting that there is a common origin of anxiety in crayfish and people, the researchers said.
“Our results demonstrate that crayfish exhibit a form of anxiety similar to that described in vertebrates, suggesting the conservation of several underlying mechanisms during evolution,” they said in the study published in Science.
Dr Cattaert did not want to go as far as to suggest that crayfish are showing some kind of conscious behaviour, or even that they feel pain in the same way that mammals feel pain.
“It doesn’t mean that the emotions are the same, although we have found that the mechanism that has been developed in vertebrates [animals with backbones] is also present in crayfish. But I wouldn’t say that this changes totally our view of crayfish,” he said.
“Crayfish forget things pretty rapidly and if you don’t have a long memory you have no sense of consciousness.”
Animal emotions: Do beasts feel burdened?
Emotions are seen as something unique to humans. However, we can often see “emotions” in other animals, although not all scientists agree on whether they are exactly analogous to what people feel.
Fear An aversion to an imminent threat is almost universal in the animal kingdom. Rodents have been shown to fear the smell of a predator, such as cat’s urine, and birds in a nest will lie low when the silhouette of a hawk flies overhead.
Love Bonding and attachment are also both universal, but love is a subjective state. Some animals, such as swans, will form long-term mating bonds that last for much of their lives.
Sadness Any dog owner will attest to the ability of a pet to show signs of depression or sadness. Some wild animals, such as elephants and chimpanzees, have been shown to mourn their dead.
Happiness Social mammals are particularly good at displays of affection and “happiness”. Young wolves, which live in a pack, will clearly show signs of being content and “happy”.
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