November 11th, 2012 by James Ayre
Crocodiles and alligators have some of the most acutely sensitive skin in the animal kingdom, new research has found. Though their thick bumpy armored looking skin is immediately recognizable, it may not be obvious at first that so much of their predatory super-awareness derives from the structure of their skin and its exceptional sensitivity.
Their highly-developed sense of touch is based on and concentrated in the pigmented armor looking domes that are all over their body. For alligators, this sensory awareness is concentrated around their jaws and skull.
In new research, it has been found that these spots are essentially a concentrated bundle of touch sensors that are even more sensitive to vibration and pressure than human fingertips are.
“We didn’t expect these spots to be so sensitive because the animals are so heavily armored,” said Duncan Leitch, the graduate student who performed the studies under the supervision of Ken Catania, Stevenson Professor of Biological Sciences at Vanderbilt.
These spots have long been noted by researchers, and over the years a variety of different theories about their possible function have been put forward, ranging from electroreception to oil glands that keep their skin healthy.
But back in 2002, it was noted by a researcher at the University of Maryland that alligators in an absolutely darkened aquarium “turned to face the location of single droplets of water even when their hearing was disrupted by white noise.” The researcher concluded that it was the sensor spots on their faces that “allowed them to detect the tiny ripples that the droplets produced.”
“This intriguing finding inspired us to look further,” Catania said. “For a variety of reasons, including the way that the spots are distributed around their body, we thought that the ISOs (integumentary sensor organs) might be more than water ripple sensors.”
So the researchers then began a thorough investigation of the neural connections to the ISOs, in American alligators and also Nile crocodiles.
The researchers discovered that the ISOs are connected to the brain via the trigeminal ganglia, which is the nerve bundle that gives sensory awareness to the jaw and face in humans. The researchers also largely ruled out the alternative theories for the function of the ISOs. The anatomical studies didn’t find any evidence of pores that would be able to release cleansing oils. And the nerve bundles in the ISOs were unresponsive when exposed to electric fields or changes in salinity.
“I didn’t test for sensitivity to magnetic fields, but we don’t think this is likely either,” said Leitch. “In animals that can detect magnetic fields the sensors are located inside the body, not on the surface.”
“What he did find is a diverse collection of ‘mechanoreceptors:’ nerves that respond to pressure and vibration. Some are specially tuned to vibrations in the 20-35 Hertz range, just right for detecting tiny water ripples. Others respond to levels of pressure that are too faint for the human fingertip to detect.”
The researchers concluded that the crocodilian’s touch system is unique and very highly-developed. The system allows a rich awareness of their watery environment, and any potential prey in the area. And it also helps them to determine the exact location and structure of the prey that they are in contact with, leading to very fast and accurate attacks.
It is also helpful for the manipulation of non-food objects in their jaws, such as when carrying their young. And may be necessary for female alligators and crocodiles, as part of their parental behavior includes “delicately” breaking open their eggs when they are ready to hatch. And transporting their young within their jaws to keep them out of the reach of predators. These are the same jaws that can close with the force of more than 2,000 psi, so their highly developed awareness may even be a necessity to avoid injuring their young.
The new research was just published in the November 8th issue of the Journal of Experimental Biology.
Source: Vanderbilt University
Image Credits: Catania Lab
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