Crawfish, Like Humans, Are Anxious Worrywarts

As the first invertebrates ever found to demonstrate anxiety, crawfish might help reveal the evolutionary origins of that stressful state of mind

"Get away from me, get away from me!" - an anxious crawfish freaking out. Photo: John Cancalosi/National Geographic Society/Corbis License Type:Rights Managed (RM)

Millions of people are regularly plagued by anxiety, or the tendency to worry about and anticipate future problems. A wealth of studies shows that this type of stress can have particularly detrimental impacts on people’s well-being and health. Anxiety manifests in some animals, too, including zebrafish and rodents. But until now, researchers assumed that vertebrates were the only worrywarts among the world’s diverse life forms.

Crawfish, however, have just added a little invertebrate diversity to the pool of stress-prone animals. According to new research published by a team of French scientists in Science, those delectable freshwater crustaceans experience anxiety, too. 

The researchers determined this by subjecting captive crustaceans to a few experiments conducted in a cross-shaped aquarium. Two branches of the tank were well lit, while the other two were kept dark. Crawfish are curious creatures and are quick to explore their surroundings, but they also prefer to scuttle around in the safety of the dark. Still, the crawfish were bold: when left to their own devices, they explored the entire tank, including the well-lit arms (though they spent a bit more time in the dark).

After establishing the crustaceans’ normal behavior patterns in this cross-shaped tank, the team cranked things up a notch. They exposed the animals to mild “repetitive electrical fields” that caused the crawfish to rapidly retreat (a motion called “tail-flips”).

Clearly, the crawfish did not like this. Even after the unpleasant stimulus was removed, the emotionally scarred crawfish largely refused to emerge from their dark dens or to further explore their surroundings. They remained in this traumatized state for up to an hour and a half. “The stress-induced behavioral adaptation of crayfish was sustainable, which is another criterion of anxiety,” the team points out.

The team’s scientific curiosity was still not satisfied, however. To get at the neurological basis of the anxiety-like behavior, they injected non-stressed crawfish with 5HT—a chemical receptor that the researchers found in elevated concentrations in the stressed crawfish’s brains—to see if the anxiety could be chemically transferred. Indeed, it was; those stress-injected crawfish behaved just like their electrified friends, avoiding the light at all cost.

Finally, the team gave the crawfish a break. They exposed both 5HT-injected and electric field-exposed crawfish to chlordiazepoxide, a sedative used to treat anxiety in humans. That drug worked on both groups of the stressed crawfish, too. They quickly returned to their normal behaviors after being exposed to that soothing chemical, and were largely unfazed by new stressors the researchers threw their way. 

Crawfish, the team thinks, could serve as excellent study subjects for future anxiety research, as well as for exploring the evolutionary origins of more sophisticated (read: more distressing) forms of anxiety that occur in humans.

While the finding will likely open many research doors, it also means that some crawfish will face stressors involved with trips to the neurology lab in addition to those that come with a boiling cauldron of Cajun spices, corn and potatoes (mmmm delicious). Unfortunately for the crustaceans, crawfish’s status as invertebrates means that many of the ethical protections their rodent counterparts enjoy are not extended to them. 

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