Anxious crayfish, anxious people: Surprising similarities

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Anxious crayfish, anxious people: Surprising similarities

Crayfish, aka crawfish, crawdad, mud-bug

 Face-to-face photo of a curious crayfish exploring vegetation 

Whether you call me crayfish or crawfish, crawdad or mud-bug, you and I share more qualities than you think. Like you, when we get stressed, we get anxious. And then we become more cautious.

But when we take a drug that you humans use to treat anxiety, that anxious behavior returns to normal. In both of us, the process seems to be governed by serotonin, a neurotransmitter that’s working in the brain you’re using to understand these words.

So the next time you’re tempted to throw me and my extended family into a pot of boiling water, please consider my anxiety…

I know this for a fact:

We crawfish are freshwater crustaceans, closely related to lobsters. Sick of being treated as mud-loving creepy-crawlies, we have a new idol: Daniel Cattaert, of the National Center for Scientific Research (CNRS) in Talence, France. He’s just published an article showing some startling similarities between crayfish, rodents and yes, those Homo sapiens who adopt titles like M.D. and strategic content supervisor.

I sing Cattaert’s praises because he put some of my brethren in a cross-shaped maze, turned on the electric current, watched their behavior, and wrote an article in a fancy science journal named, can you guess, “Science”?

And he didn’t boil us alive. He says he never eats crayfish.

If you’re wondering about the point of the “shock the mud-bug” shenanigans, Cattaert says it grew from a desire to understand how information from the senses affects behavior.

That’s why he put us in this container shaped like a plus sign, where two arms are brightly lit, and the other two are dark.

Unstressed Crayfish

An unstressed crayfish explores the aquatic dark/light plus-shaped maze, entering both dark and light areas.
Video courtesy Pascal Fossat

Stressed Crayfish

A stressed crayfish avoids light areas of the maze.
Video courtesy Pascal Fossat

Stressed crayfish treated with anxiety drug

A stressed crayfish that was injected with a benzodiazepine drug that reduces anxiety in people explores the entire maze.
Video courtesy Pascal Fossat

We crayfish are nocturnal, so we feel a lot safer in the dark arm, but we still like to know what’s around us. So we started to explore when Cattaert dumped us into his curious container. (I’m not saying curiosity killed the crawdad, but Chris Columbus wasn’t the only one who wanted to know what was on the other side!)

And so we clambered about the maze. Before we entered a lighted arm, we stopped to think about it. And unless we were stressed, we entered it.

This Cattaert fellow was obsessed with stress. He says it has broad effects on animals.

Close-up photo of the tested crayfish highlighting the crustacean's claws and legs.
A crayfish enters a light arm in the plus-shaped maze.
Image courtesy Jean-Paul Delbecque

In our watery world, stress can mean a bigdaddy crawdaddy is trying to lord it over us. For his experiment, Cattaert needed a more consistent source of stress.

The CNRS is HQ for French science, and you don’t get hired for being a dumbo, so he jolted the water with a low-level electric current for 30 minutes.

That would have set our teeth on edge — if we had them.

Anyway, after the current was switched off, the poor crayfish was suddenly afraid of the light.

You could call it “anxiety” — a type of fear that occurs even when a source of stress (like that itty-bitty electric shock) is absent. Cattaert and his colleagues called it “anxiety-like behavior.”

  Even when we were stressed, we did visit the border of the light area, but we retreated and did not enter. “If it’s not stressed, it stops but eventually may enter the lighted half,” Cattaert says. This behavior, he adds, is very similar to rodents in a maze that contains areas without walls, which they consider dangerous. “Before they enter a risky compartment, they will stop; it’s like they are thinking, as if they are making a decision.”

How come? you ask

Getting back to us shellfish: Once Cattaert had shocked us, the next thing you know, he was injecting us with benzodiazepine, an anti-anxiety drug sometimes sold as Librium. He figured what was good for anxious attorneys was good for an aquatic crustacean.

I, personally, was skeptical, but it worked! “After we stressed them and injected them with benzodiazepine, the animals went into all the arms of the maze,” says Cattaert. “Before, they tended to avoid the risky environment, now they have no more apprehension.”

Two men empty a tub of live crayfish into a boiling pot of water while a third man stirs the pot with a wooden paddle.
Anxious much? These crawdads take their last bath.

Cattaert and his collaborators also found that we crayfish had high levels of serotonin, a common neurotransmitter, in our neural apparatus. To prove that serotonin was causing the behavior change, Cattaert injected us with serotonin, and again saw what he calls “anxiety-like behavior. They refused to enter the light half.”

Again, it was the anti-anxiety med to the rescue. “When we injected those crayfish with benzodiazepine, that restored the exploratory behavior,” he told me.

Got to wonder

I bet you humans are surprised to learn that a wallop of serotonin, which helps you enjoy Beethoven and Beyoncé, can cause anxiety in your distant relations in the bayou.

Anxious crayfish? Is that possible?

Maybe. We crustaceans split off from the ancestors of the vertebrates (vultures, sharks and people) hundreds of million years ago, and yet we both share a mechanism that causes anxiety.

Finding a trait in two arms of an evolutionary tree does not prove it originated in a common ancestor — the trait could have evolved twice, through convergent evolution. But Cattaert says the genes for some neurotransmitter receptors are so similar in mammals and crayfish that it’s almost certain that those chemical communication systems arose once — in the common ancestor.

Meaning that ancient and long-lost relative suffered anxiety.

But don’t waste pity on our anxious ancestors. Cattaert argues that anxiety may cause an animal to become cautious, and that improves survival. “This system developed very early during evolution. As soon animals faced danger, they had to adapt. Otherwise when they faced the problem the next time, they would be killed.”

– David (Crawdaddy) Tenenbaum

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Kevin Barrett, project assistant; Terry Devitt, editor; S.V. Medaris, designer/illustrator; David J. Tenenbaum, feature writer

Bibliography

  1. Anxiety-like behavior in crayfish is controlled by serotonin, Pascal Fossat et al, Science, 12 June 2014.
  2. Do lobsters and other invertebrates feel pain? New research has some answers.
  3. A Brief History of Crawfish Farming in Louisiana
  4. One-fifth of invertebrate species at risk of extinction, study shows.