[JAC: In lieu of “readers’ wildlife” today, we have “Mayer’s wildlife”: His disquisition on snake locomotion. Be sure to keep those photos coming in, and don’t worry if you haven’t seen yours yet, as I have them all.]
by Greg Mayer
Matthew sends the following tweet of a tiger snake making its way along a wire fence.
— Wildlife Land Trust (@wlt_au) February 14, 2018
At first glance, two things struck me at about this, aside from its generalized coolness. The form of locomotion is a typical one for snakes called lateral undulation, in which waves of muscular contraction alternate down the sides of the body. You can see the snake is pushing first on one side of the wire, then the other, in waves down the body. This is not unusual for snakes. And there are many arboreal snakes (vine snakes, parrot snakes, etc.) that habitually move along very narrow surfaces, such as vines and branches. The novelty here to me is the length of the narrow surface– most vine snakes frequently encounter crosswise vines and branches, so they don’t move for any great distance in a perfectly straight line along a narrow surface, as this snake is doing.
Other climbers show a fabulous ability to throw their trunk into multiple, regular, and controlled bends of very short radius. The African file snakes (Mehelya) apparently can travel along telephone wires with alternate half-loops hanging respectively over the left and right sides of the wire.
The second thing that struck me was that a tiger snake is not a vine snake of any sort– they’re terrestrial. So, climbing along wires is not where I would expect to see them. But that’s book knowledge, and perhaps Australian readers can enlighten us from experience.
On reflection, I was also struck by this being an example of what Gans called “excessive construction”– the ability of structures (and in this case also behaviors) to be successfully used in circumstances that were not part of the historical evolutionary development of the structure. Gans thought, and I agree, that such circumstances can be the basis for adaptation (i.e. heritable changes in the structure/behavior) to the new circumstances. Again from Biomechanics (p. 14-15):
Gans provides a much more insightful view here of how functions change, and how new adaptations arise, than did Gould and Vrba in their largely unnecessary coining of the word and concept “exaptation“.
Gans, C. 1974 (1980). Biomechanics: An Approach to Vertebrate Biology. University of Michigan Press, Ann Arbor.
Gans, C. 1979. Momentarily excessive construction as the basis for protoadaptation. Evolution 33:227-233.
Gould, S.J. and E.S. Vrba. 1982. Exaptation- a missing term in the science of form. Paleobiology 8:4-15. pdf