In honor of World Snake Day, which is today, here's what happens when you put a bunch of snakes on a plane...for science.
Most animals perceive the weightlessness of microgravity as if they were falling upside down. If you drop a cat from a great height, for example, it will roll over to attempt to land on its feet. This is called the "righting response." In microgravity, this leads to repeated rolling-over.
Scientists have interpreted the repeated rolling-over as a repetitive righting response, since the animal never gets any feedback that the action was successfully executed. This behavioral pattern is common and has been observed for various mammals, frogs, and turtles in microgravity.
But other herptiles (reptiles and amphibians) have very different responses to microgravity. Some snakes aggressively attack their own bodies; caecilians (which resemble snakes, but are amphibians) tend to become immobile and lose muscle tension; certain tree-frogs engage in diving behaviors.
That tree frogs think that they're diving makes a great deal of sense. Caecilians may become limp simply because these animals, which live out their lives in the ground like earthworms, never have the possibility of falling, and thus never develop strong righting responses.
But why would snakes attack their own bodies? That's where things get really interesting. Could it be that the self-directed aggression was the result of a loss of proprioception? Perhaps in microgravity, a snake can't recognize its own body as part of its own self.
In this study, the researchers loaded a bunch of snakes onto a Vomit Comet. These are planes that fly in parabolas: as the plane moves over the top of the curve, everything inside is temporarily weightless. At the bottom of the curve, it the pull of gravity actually feels a bit stronger.
Here's a video of one snake, Elaphe obsoleta, in microgravity. In the first parabola, the snake eventually knotted its tail and ceased all other body movements. In the second parabola the snake knotted its whole body and once again ceased moving while in microgravity. This posture was held through the next parabola and in the intervening time between the parabolas.
While the researchers didn't observe the self-attack behaviors seen previously, the knotting behavior that they did observe in many of their snakes still reflects a basic loss of proprioception. When snakes become stressed out, they sometimes bunch together in a group in order to relax. Which, in a way, is exactly what that airborne snake did in microgravity.
In the absence of gravity, it appears as if snakes have a difficulty distinguishing self from non-self. The snake managed to relax, but only because it didn't realize that it was working to relax its own self! At least, that's the hypothesis.
The authors say that given the variation seen among the various species that have been subjected to weightlessness, "one must be cautious in selecting species as model organisms for orbital space flight experiments. Clearly, not all animals react the same to microgravity even when they have similar morphology, ecology, and evolutionary history."