Crayfish suffer from stress and anxiety in the same way humans do
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Football fans, stage performers and worried parents aren't the only ones to get anxious - the emotion can also be found in the primitive crayfish.
These small lobster-like creatures feel stress in the same way humans do, and can be similarly calmed down using drugs, a study has shown.
This is the first time that clear signs of anxiety, normally associated with more complex forms of life, has been observed in a spineless species.
Football fans, stage performers and worried parents aren't the only ones to get anxious - the emotion can also be found in the primitive crayfish. These small lobster-like creatures feel stress and can be calmed down when given a drug used to treat anxiety, a study has shown
Anxiety, the researchers explain, is different from fear, which is an emotion that even the simplest animals show.
In the experiment, French scientists exploited the fact that the crustaceans are more comfortable in darker water.
After giving crayfish a series of mild electric shocks, they placed the creatures in an aquarium 'maze' containing both well-lit, and darkened tunnels.
Although non-stressed crayfish preferred the dark arms, they also explored the lit regions. But crayfish given the electric shocks hardly entered the lit arms of the aquarium at all.
After giving crayfish a series of mild electric shocks, they placed the creatures in an aquarium 'maze' containing both well-lit and darkened arms. Although non-stressed crayfish preferred the dark arms, they also explored the lit regions (pictured)
Crayfish responded positively to chlordiazepoxide, a drug used to treat anxiety in humans
The stressed animals' light avoidance was linked to boosted levels of the brain chemical serotonin, which also has a big effect on mood in humans.
Merely injecting crayfish with the neurotransmitter was enough to make them anxious, the researchers discovered.
They also found that the creatures responded positively to chlordiazepoxide (CDZ), a drug used to treat anxiety in humans.
Treated crustaceans lost their nerves and were happier to explore the bright parts of the aquarium.
The team, led by Dr Daniel Cattaert, from the University of Bordeaux, wrote in the journal Science: 'Analyses of this ancestral behaviour in a simple model reveal a new route to understanding anxiety and may alter our conceptions of the emotional status of invertebrates.
'[Our results] emphasise the ability of an invertebrate to exhibit a state that is similar to a mammalian emotion.'
The study follows a number of scientific papers that suggest crustaceans can also feel pain.
The seafood industry may need to rethink how it treats these creatures, some experts claim.
However, Dr Cattaert did not want to go as far as to suggest crayfish are showing some kind of conscious behaviour, or even that they feel pain in the same way as mammals.
Crustaceans are currently not considered sentient by organisations such as the European Food Safety Authority, and there are no regulations concerning their treatment.
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For years, scientists have told us the bond between a pet and its owner goes no further than their need for food and security.
But new research suggests what dog owners knew all along - that they do in fact experience feelings of love and affection.
Scientists at Emory University in Atlanta, Georgia, discovered a part of the brain associated with positive emotions, was similar in dogs and humans.
The team trained more than a dozen dogs to cope with noisy magnetic resonance imaging (MRI) scanners, enabling them to sit still within a scanner to get clear images of their brains without sedating them.
Gregory Berns, a neuroscientist who initially worked with a dog trainer to teach Callie, a nine-month-old rescue dog, and McKenzie, a three-year-old collie, to lie in a MRI machine, said: 'We can really begin to understand what a dog is thinking rather than infer it from their behaviour.'
Using hand signals to indicate the dogs were about to receive a food treat, Berns and his team showed that the caudate nucleus, a part of the brain associated with positive emotions, was similar in dogs and humans.
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