The crocodilian sense of touch is concentrated in a series of small, pigmented domes that dot their skin all over their body. In alligators, the spots are concentrated around their face and jaws.
This is a small alligator floating with just its eyes above the water.
Credit: Mike Todd, Vanderbilt University
A new study, published in the Nov. 8 issue of the Journal of Experimental Biology, has discovered that these spots contain a concentrated collection of touch sensors that make them even more sensitive to pressure and vibration than human fingertips.
"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.
Scientists who have studied crocodiles and alligators have taken note of these spots, which they have labeled "integumentary sensor organs" or ISOs.
Over the years they have advanced a variety of different hypotheses about their possible function. These include: source of oily secretions that keep the animals clean; detection of electric fields; detection of magnetic fields; detection of water salinity; and, detection of pressure and vibrations.
In 2002, a biologist at the University of Maryland reported that alligators in a darkened aquarium turned to face the location of single droplets of water even when their hearing was disrupted by white noise. She concluded that the sensor spots on their faces 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 might be more than water ripple sensors."
As a result, Leitch began a detailed investigation of the ISOs and their neural connections in both American alligators and Nile crocodiles.
Leitch found that these sensory spots are connected to the brain through the trigeminal ganglia, the nerve bundle that provides sensation to the face and jaw in humans.
In addition, his studies ruled out most of the alternative hypothesis for the ISOs function. For example, his anatomical studies didn't find pores that could release cleansing oil. Similarly, he found that the nerves in the ISOs didn't react to electric fields or, when submerged in water, to 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, he explained, 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.
Their analysis led the scientists to conclude that the crocodilian's touch system is exceptional, allowing them to not only detect water movements created by swimming prey, but also to determine the location of prey through direct contact for a rapid and direct strike and to discriminate and manipulate objects in their jaws.
Their finding that the most heavily wired ISOs are located in the mouth near the teeth suggests that the touch sensors help the animals identify the objects that they catch in their jaws. The sensors also appear to provide the sensitivity that female alligators and crocodiles need to delicately break open their eggs when they are ready to hatch and to protect their hatchlings by carrying them in their jaws, the same jaws that can clamp down on prey with a force of more than 2,000 psi.
This research was supported by National Science Foundation grant #0844743 and by a Vanderbilt University Discover Grant.
David F Salisbury | Vanderbilt University
Rainbow colors reveal cell history: Uncovering β-cell heterogeneity
22.09.2017 | DFG-Forschungszentrum für Regenerative Therapien TU Dresden
The pyrenoid is a carbon-fixing liquid droplet
22.09.2017 | Max-Planck-Institut für Biochemie
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
For the first time, physicists have successfully imaged spiral magnetic ordering in a multiferroic material. These materials are considered highly promising candidates for future data storage media. The researchers were able to prove their findings using unique quantum sensors that were developed at Basel University and that can analyze electromagnetic fields on the nanometer scale. The results – obtained by scientists from the University of Basel’s Department of Physics, the Swiss Nanoscience Institute, the University of Montpellier and several laboratories from University Paris-Saclay – were recently published in the journal Nature.
Multiferroics are materials that simultaneously react to electric and magnetic fields. These two properties are rarely found together, and their combined...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
22.09.2017 | Life Sciences
22.09.2017 | Medical Engineering
22.09.2017 | Physics and Astronomy