Physicists learn about electrostatics, the laws governing stationary charges. Then they learn about electrodynamics, the laws governing moving charges. Biologists are finding that life utilizes both systems of laws at all scales, from within the cell to tissues, organs, and entire organisms. Here are some recent discoveries in the emerging science of bioelectricity.
How does that tick jump from its twig onto your clothing as you walk through brush? The answer, says Current Biology, is by hopping on an electrostatic bullet train. A cow or other host animal walking through the bushes carries a net static charge. The tick, regardless of its own charge polarity, is “pulled by these electric fields across air gaps of several body lengths.”
Images in the paper show that a rabbit or cow literally glows with an electric field as it walks through vegetation. “Live ticks are passively attracted by the electric fields of their hosts,” the scientists found through experiment and measurement. It may not be good news for us, but the discovery suggests ways to fight back.
We also find that this electrostatic interaction is not significantly influenced by the polarity of the electric field, revealing that the mechanism of attraction relies upon induction of an electrical polarization within the tick, as opposed to a static charge on its surface. These findings open a new dimension to our understanding of how ticks, and possibly many other terrestrial organisms, find and attach to their hosts or vectors. Furthermore, this discovery may inspire novel solutions for mitigating the notable and often devastating economic, social, and public health impacts of ticks on humans and livestock. [Emphasis added.]
Electromagnetic induction was one of the major discoveries made by the devout scientist Michael Faraday in 1831 (published independently in America the following year by another devout scientist, Joseph Henry). Yet here we see a tiny arachnid making use of electromagnetic induction. We can’t blame the tick for this trick. It doesn’t intentionally carry disease germs. It’s just taking advantage of a transportation system to hitchhike around, the way a cocklebur does when its Velcro-like seeds latch onto the fur of a passing cow. Pretty clever, actually.
Roundworms also know about this trick. In another paper in Current Biology, scientists wondered why dauers [larvae] of the common roundworm C. elegans come equipped with electrical sensors. The answer: “electroreception helps these microscopic worms to attach themselves to insects for transportation.” Leave it to scientists to design clever experiments to test and measure this trick! They charged bumblebees up to 724 thousand volts per meter!
The electric field strength (200 kV/m) required to induce leaping behavior in C. elegans far exceeds the upper limit of those seen in aquatic animals. It is also worth noting that air is a good electrical insulator compared with the aquatic environment, which makes it possible for terrestrial animals to carry significantly more electrostatic charges. Thus, it is highly possible that dauers can electrostatically interact with other animals in nature. To directly test this theory, the authors used bumblebees that are known to be highly electrostatically charged in the wild. These bumblebees were artificially charged by rubbing them against a Canadian goldenrod flower. Further experiments confirmed that the charge of bumblebees obtained in the lab was comparable to those observed in the wild. When the charged bumblebees were put close to the nictating dauers, leaping behavior was detected (Figure 1A). The electric field strength calculated was about 724 kV/m, exceeding the 200 kV/m leaping threshold. Strikingly, as many as 80 dauers were able to leap at the same time (Figure 1B). The leaping distance between dauers and bumblebees was about five times the dauer body length, which is also biologically meaningful.
Plant Electrodynamics in the Venus Flytrap
The involvement of electricity in the well-known traps of Dionaea muscipula, the Venus flytrap, are becoming increasingly appreciated. Researchers at Linköping University in Sweden speak of the flow of electrical signals in these amazing plants — and probably to some extent in all plants.
Most people know that the nervous system in humans and other animals sends electric impulses. But do plants also have electrical signals even though they lack a nervous system? Yes, plants have electrical signals that are generated in response to touch and stress factors, such as wounds caused by herbivores and attacks on their roots. As opposed to animals, who can move out of the way, plants must cope with stress factors where they grow.
For a plant studied by Darwin, it’s remarkable how much remains unknown about electrical propagation in the Venus flytrap. How can a plant, without neurons, conduct electricity? This team found some new things.
Electrical signalling in living organisms is based on a difference in voltage between the inside of cells and the outside environment. This difference in voltage is created when ions, i.e. electrically charged atoms, are moved between the inside and the outside of the cell. When a signal is triggered — for instance by mechanical stimulation in the form of bending a sensory hair — ions flow very fast through the cell membrane. The rapid change in voltage gives rise to an impulse that is propagated.
Their results, published in Science Advances, add to knowledge about plant electrophysiology. They carefully observed the “action potentials” of the traps, and how the signal is propagated in the leaf. Using 30 delicate electrodes arranged in a “neurogrid” attached to the inside of the trap, the team found that the action potential (AP) spreads first, followed by a calcium ion wave. It begins at the trigger hair, as expected, but then propagates radially outward at 2 cm/s across both lobes of the trap without a particular direction.
Biologists have long known that the trigger hairs must be touched twice within thirty seconds for the trap to close. This trick allows the traps to ignore non-living stimuli, but how that threshold is encoded is not clear. Did I hear codes?
In addition, any combination of hair stimulations induces faster AP propagation during the second stimulation, indicating that the excitability information must be encoded across the entire trap, rather than coupled with the stimulated hair alone. The nature of this information encoding remains unclear.
This is the first time that biologists have applied methods of measuring electrical transmission in plants that have normally been performed on animals, such as on rodent brains. The authors are excited about the possibilities of learning more about plant electricity. What about Darwinism? They apparently have no need of that hypothesis.
More on Microbes
More findings about intercellular electricity in bacteria have come forth. In May, Phys.org published the “First experimental confirmation that some microbes are powered by electricity.” In “electrosynthesis,” bacteria can make alcohol using carbon dioxide and electricity, but how they do it has been unclear. The new research in Germany was “able to confirm experimentally for the first time that the bacteria use electrons from hydrogen and can produce more chemical substances than previously known.” A report on this research at ChemEurope.com says it may lead to harnessing bacteria to make useful chemicals for industry. Feed the microbes hydrogen and watch them run their power plants.
A month earlier, Duke University reported that a “previously unknown intracellular electricity may power biology.” Specifically, that article says that electric fields may underlie the formation of biological condensates that bring interacting molecules together. Read about condensates in my earlier article here.
The future of bioelectricity looks bright. Here, an unexpected series of discoveries opened the door to new ways of looking at biological processes. And with it, as in previous revelations, biologists are finding codes, communication of information, and exquisite engineering.