Autotomy
Why does the tail of a lizard move even after it is cut off from the body?
Ashwin Nair, Srikrishnapuram, Kerala
The voluntary shedding of an appendage from the body of an animal in response to mechanical and/or visual stimulation is termed “Autotomy.” An example is lizard-tail autotomy. A portion of the spinal cord at the proximal end of the lizard tail is the control centre for the movement of the shed tail. This small portion of the spinal cord assumes control over the signal transmission to perform the movements of the cut-off tail when the tail is no longer connected to the lizard 's brain. Recent discovery reveals that the tail motion is an elaborate repetitive motion, a stock of diverse and extremely intricate arrhythmic movements with an acrobatic flips up to 3 cm in height ,and these series of movements would slow down .
This complex outburst activity is achieved through multiple networks of neurons in the tail's spinal cord. Two active, independent neural circuits regulate the movements following autotomy. The first has regularly repeated rhythmic signals persisting throughout the duration of tail movements, whereas the alternative is possibly sensitive to the external or internal feedback. However the activation of additional neural pathway is still a mystery. The explanations put forth by scientists were random firing until fatigued, the pathway is sensitive to environmental input and muscle proprioceptors. Sensors present on the surface of the tail relies on the feedback from the environment and based on the information the tail may jump, pivot or travel in a certain direction as evidenced from electromyography. This wiggling stays active for 30 minutes, even after lizards abandon their tails.
This behaviour is essential for the lizard to escape from predators as they focus on the shed tail's motion while the lizard stays still or gets away. Sometimes the lizard comes back and eat the dropped tail, which is a rich source of fat so that they could recoup some of the lost energy.
Azhwar Raghunath
This week’s question
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Corrections and Clarifications
Name missed out inadvertently: The question - “ >Why does the tail of a lizard move even after it is cut off from the body? ” (Question Corner, S&T page, April 11, 2016) - had been answered by Azhwar Raghunath.
