WHEN a crayfish sheds its protective exoskeleton, it becomes temporarily vulnerable to attack by predators. Now there is evidence that this leads to behaviour that resembles anxiety, and that this can be relieved using the same anti-anxiety drugs that humans take.
鈥淭hey worry, they have an apprehension state that makes them avoid potentially dangerous areas. It鈥檚 kind of like a primitive anxiety,鈥� says Pascal Fossat at the University of Bordeaux in France.
Fossat and his colleagues collected crayfish from swamps near Bordeaux and stored them in聽individual tanks that mimicked their natural habitat.
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When the crayfish began to moult, the researchers placed them in a maze that had two dark sections and two lit sections, and recorded their behaviour.
Over the following two days, the crayfish showed a strong preference for hiding in the dark regions. If they did encounter the lit sections, they retreated into the dark in 80 per cent of cases.
For comparison, when the crayfish weren鈥檛 moulting they typically spent about 30 per cent聽of their time in the light.
鈥淭hey鈥檙e very weak when they remove the old exoskeleton, and the new one is totally soft until they eat the old one to get back the聽minerals that make the new exoskeleton stronger,鈥� says Fossat. 鈥淭hey鈥檙e vulnerable, so they have to hide.鈥�
The team also took crayfish that weren鈥檛 moulting and injected them with an ecdysteroid 鈥� a class of hormone that controls moulting, produced by many animals with an exoskeleton. They found that the crayfish exhibited the same anxiety-like behaviour, avoiding light and retreating to the dark.
To explore whether it was possible to suppress this behaviour, Fossat and his colleagues took the animals they had treated with the ecdysteroid and injected them with anti-anxiety drugs developed for use in humans. The crayfish returned聽to spending about one-third of their time in the light.
鈥淭hey didn鈥檛 have the apprehension from before,鈥� says Fossat ().
Robert Elwood at Queen鈥檚 University Belfast in the UK says it聽is surprising that anti-anxiety drugs designed for human use also work on invertebrates, given that they last shared a common ancestor with us hundreds of millions of years ago. 鈥淚 was taken aback [by] that,鈥� he says.
Fossat suspects crayfish may be聽capable of other primitive emotions 鈥� although it is a difficult subject to investigate because crayfish are biologically so different from humans.
Elwood says the animals may be聽acting on basic physiological mechanisms that humans have interpreted as feelings. But he says that new research is helping us understand the range of emotions invertebrates may experience.
鈥淲e鈥檝e spent a lot of time worried about animal welfare, asking whether they are in stress or pain,鈥� he says. 鈥淣ow we鈥檙e beginning to turn that over and聽ask if we can say when an animal is happy or gleeful.鈥�
