This past weekend, I was searching around the interwebz looking for something interesting to write about for Monday Pets. Lately, Monday Pets has been somewhat cat- and dog-heavy, so I was looking for something a bit different. I asked on twitter if there were any requests or recommendations. Friend of the blog Dave Munger responded: "What about snakes?"
What about snakes indeed? There are many parallels between myself and Indiana Jones, but one big one is that we both hate snakes. Another similarity is whenever I travel by plane, I leave a series of red dashes to mark my path. We both look awesome in a fedora and leather jacket. Also, we both crave adventure.
I never really thought about snakes as pets, but it is true that plenty of people have pet snakes. There was even a pet snake named Slimey in my Kindergarten classroom.
So I went to my trusty old Pubmed and began looking for something on cognition in snakes. And I kept looking. And looking. There are TONS of studies out there that used snakes as stimuli to investigate fear in humans, monkeys, chipmunks, squirrels, and so forth. But not too many studies about the snakes themselves, at least with respect to cognition. But I did find a few. And one of them just sang out to me. I knew it had to be blogged.
The abstract starts like this: "In the present study, we exposed 53 animals from 23 different species of amphibians and reptiles to microgravity." (Here, we shall only focus on the snakes.) A study about subjecting snakes to zero gravity situations? I'm in. Did they take the snakes to the International Space Station? Nope. So how you do you subject a snake to weightlessness?
Ready for it?
So the researchers loaded up all the animals onto the plane, a Falcon 20. Actually, they split the animals into three groups, and so they conducted three separate flights. Each animal was placed into a closed terrarium, each with its own video camera. Each flight included four parabolas, each lasting 23-24 seconds. When the plane reaches the vertex of the parabola, the animals in the plane (as well as, of course, the people) are briefly subjected to weightlessness.
Why were they interested in the behavior of snakes in microgravity? Well, first of all it is REALLY COOL. Some animals had already been subjected to microgravity in prior research, and most perceive the weightlessness of microgravity as if they were falling upside down. If you drop a cat upside down from a height, 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. This is interpreted as a repetitive righting response, since the animal never gets any feedback that the action was successfully executed. This behavioral pattern has been observed for various mammals, frogs, and turtles in microgravity.
But different responses to microgravity had been seen in various reptile and amphibian species. 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 engage in diving behaviors makes sense. There is no good explanation for way caecilians become limp, but one possibility is that these animals which tend to live in the ground like earthworms never have the possibility of falling, and thus never develop strong righting responses. One interesting hypothesis that caught my eyes, regarding the snakes, was that the aggressive behavior was the result of a loss of proprioception. This meant that the snake did not recognize its own body as part of its own self.
So what happened to the snakes in this experiment?
None of them aggressively attacked their own bodies, so they failed to replicate previous results. Interestingly, however, many of the snakes knotted themselves, and upon doing so seemed to relax. This is different from the expected repetitive righting response.
Here's a video from the supplemental materials 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 hyper-g states between the parabolas.
Although the knotting behavior is different from the self-attack behaviors seen previously, both reflect a basic loss of proprioception. That is, in the absence of gravity, these snakes have difficulty distinguishing self from non-self. The fact that they calmed down upon knotting themselves suggests that the tactile (touch) information takes precedence over vestibular (balance and orientation) information. So, that's pretty cool. One would think that proprioception - having awareness of the body's place in the environment - is pretty crucial to survival, so I'm surprised that it is so easily lost under situations of weightlessness. Why might be the case? I'm not sure and I don't see any speculations in this paper.
Why is this research important? The authors say that given the variation seen among the various species (the other species showed different responses than did the snakes), "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." Okay, I buy that. We can't just go about subjecting humans over and over again to microgravity (they didn't name it the Vomit Comet by accident). So I guess it's pretty important to find a good model organism on which to investigate the effects of weightlessness.
Plus, you know, any excuse to include Samuel L. Jackson in your research...
Wassersug, R., Roberts, L., Gimian, J., Hughes, E., Saunders, R., Devison, D., Woodbury, J., & O'Reilly, J. (2005). The behavioral responses of amphibians and reptiles to microgravity on parabolic flights Zoology, 108 (2), 107-120. DOI: 10.1016/j.zool.2005.03.001