by Yevgeny YESKOV, Dr. Sc. (Biol.), Russian State Agrarian Correspondence University
As experts tell us, the Earth had been exposed to electromagnetic impacts long before the origin of life on this planet - a fact that influenced the course of the evolution in general and also the present state of the biosphere in particular. Comprehensive studies in this field provided the foundation of a new area of research - electroecology. This field of modern science covers what experts call the biological effects of electromagnetic fields ( EEF ), protection from their impacts and studies of ways by which representatives of the flora and fauna (generally described as bioobjects) take advantage of EEF for spatial orientation and bonds. I, for one, have been lucky to be engaged in these studies for quite a number of years. My colleagues and I have been using the facilities of the Ryazan Radioacademy, the Research Institute of Apiculture, the Institute of Agricultural Research (in Pskov) and of the Russian State Agrarian Correspondence University for comprehensive studies of phenomena which are the subject of the present article.
What we describe by a general term of geomagnetic impact causes different effects on organisms of different levels of organization. To some it facilitates spatial orientation (we call this geomagnetotropism) and to others it helps improve the physiological status and helps maintain viability. For example, in studies of aerophilic (consuming air) water bacteria we identified species whose direction of migration is closely linked with the vector of the lines of force of the magnetic field of our planet (these are called magneto-toxic). These microorganisms, dwelling in fresh and salt water reservoirs, are usually localized at the border of the bottom silt layer. Being displaced by currents, they return to the original position, but not straight down to the ground, but at some angle. Our studies indicate that this angle depends on the geographical location of the water reservoir. In the Northern Hemisphere the trajectory of descent gravitates towards the Northern Magnetic Pole, and in the Southern Hemisphere it takes the opposite direction. At the equator both northward and southward deviations from the vertical have been observed. And in a homogeneous magnetic field of 240 A/m bacteria migrated in equal proportions in the opposite directions.
Having said that, what lies behind this "mode of behaviour" of the microorganisms? And it turns out that this "mechanism of orientation" in a magnetic field is "fuelled" by the presence of magnetite* in these bacteria. Thus the cytoplasm of Aquaspirillum bacteria, studied under an electron microscope, was found to have a chain (or two) possessing 10-15 electrodense magnetite inclusions; its length was 100 and width - 60 nm. Their localization remains unchanged all through the lifetime of the bacteria and even after their death - something which causes an interesting effect: such dead organisms, placed in the field of a permanent magnet, are drawn up
* Magnetite-black isometric mineral (FeFe 2 O 4 ) of the spinel group.- Ed.
along the lines of force, like iron filings. These findings were published for the first time in 1975 by the US scientist Professor R. Blackmore.
Earlier still, at the turn of the 20th century, geomagnetotropism was identified in plants. Experiments with maize conducted in 1969 at the Institute of Plant Selection, Seed-Growing and Agricultural Technology (Kishinev) revealed that if the germs in maize seeds are oriented to the south, they germinate sooner than the rest, mature more quickly and, finally, produce greater yields. A similar effect has been discovered in the seeds of coniferous plants (Lomonosov Moscow State University).
It would seem that the above results lead to the conclusion that the viability of seeds is in direct proportion to their magnetic susceptibility which influences the rate of germination and the subsequent plant growth. This, however, has not been supported by our experiments with wheat conducted in the late 1990s. We studied the "behavior" of wheat seeds suspended between the poles of a magnet with the induction of 1.5 T1. by the angle of turn. And we saw that seeds with a lower viability possessed the greatest magnetic response. In other words our findings call into question any direct links between these characteristics and the quality of seeds used for sowing. And the general conclusion is that our studies of geomagnetotropism in representatives of the flora are still at the initial stage.
Of considerable interest in this general context are observations by entomologists (Dr. Becker, USA, and our compatriot V. Chernyshev) over the behavior of different insects. Thus more sedentary species choose their body orientation along the lines of force of the Earth's magnetic field and some termite species even dig their underground passages along the magnetic meridian of the place. Ground beetles, for example, demonstrate unusual behaviour: in open spaces their movements are unpredictable, but in the conditions of poor visibility or in closed spaces, such as caves, their flight trajectories are always aimed at the Sun. And experts assume that this is because ground beetles rely on gravitational reference points in the process of their migrations.
In 1917 H. Parker and A. Hansen discovered the ability of fish to distinguish underwater objects by their electrical properties. For example, some American sheat-fish are able to find metal bars at a distance of several centimeters, and glass bars of the same size only by touch. Of considerable importance here is the contact area of the bars with water. If it is restricted to 5-6 cm 2 , the fish swim away, and if it measures 0.9-2.8 cm 2 , they approach and touch it, or simply ignore it in other cases.
What lies behind this rather unusual behaviour of sheat-fish? Experts point out that this is due to the effect of some microcurrents generated at the contact of metal with water (galvanic effect), and the response of the fish depends on current strength. If this is less than 0.99 mcA, sheat-fish swim towards the source and "bite" it, and if it is over 1.47 mcA - they swim away while showing no response in other cases.
In 1974 Dr. Bretshneider published an article in which he explained the aforesaid responses by an increased sensitivity to electric current of certain fish species. In some cases the muscle cell has been transformed into an electrical one, producing a specific organ sensory to external (electric) signals-the lateral line. Using electrophysiological methods, the scientists established that this organ of the common sheat-fish (Silurus glanis) responds to low-frequency sinusoidal oscillations (up to 25 Hz) at current density of 10 -10 A/mm 2 . This sensitivity makes it possible for fish of prey to locate their "targets" by electric signals generated by the movements of the body, tail, fins and other organs.
In the view of the Russian researcher A. Mironov (1948) the spatial orientation of fish during periodic migrations also involves what he called electroreceptors. Their "points of reference" could be telluric current of 90 mV/km with a drop gradient per length of the fish amounting to hundreds of a microvolt per centimeter, which is enough for registration by their electroreceptors.
Today, there is no established theory of geomagnetotropism, with experts amassing the facts and engaging in constant debates. This also covers the mechanism of orientation of migratory birds Hying over long distances. The species Numenius tahitensis, nesting in Alaska, winters in the Hawaii-more than 9,000 km away, and stormy petrels which spend the summer on the islands of Tristan da Cunha, cover a distance of over 10,000 km before they reach their permanent habitat.
The accuracy of birds migration demonstrates them having a reliable system of navigation which makes it possible for them to rely on astronomical points of reference, but only during the day and in clear weather. Some experts feel this is associated with the birds' perception of polarized light, while others attribute this to what they call an original gravitational-inertial concept*. And most ornithologists feel that migratory birds Hying over long distance rely on the induction gradient of the magnetic field of the Earth which varies from 25,000 nTl (on the equator) to 60,000 (at the poles). This explanation was originally suggested in the middle of the 19th century by member of the Russian Academy, Professor A. Middendorf. But even with some indirect evidence in favor of this theory, the physiological mechanism involved remains obscure. On the basis of various assumptions one can say that what we call the magnetoreception of
* See: G. Shvetsov, "Always on Track", Science in Russia, No. 3, 2000. - Ed .
birds and other animals rests on the presence in their bodies of large quantities of magnetite of biogenic nature which was first identified by Dr. J. Gold in 1978. So it turns out that the effect of the geomagnetic field of our planet upon the granules of magnetite is translated by the nervous system of animals by means of a multitude of what specialists call pro-prioreceptors (nerve endings in the muscular-joint apparatus). And it turns out that this process should be intensified in situations when an animal has to choose the direction of its movement.
This theory, however, has not been substantiated by our experiments with bees although they were also found to contain magnetite crystals. The picture was just the opposite - increased metabolism suppresses magnetic sensitivity, dampens the impact of natural magnetic disturbances and makes sensor systems used for spatial orientation less sensitive to them.
Now, let's take a look at how individual representatives of the fauna find their bearings in adverse circumstances and "communicate" with one another. It turns out that some fish species which are either nocturnal or dwelling in turbid water, possess high sensitivity to electric current which helps them in direction finding. The Nile pike, for example, responds to current changes of only 3 х 10 -15 А. This was reported in 1963 by the Russian biologist G. Lisman. His studies proved that the mechanism of electric direction finding of this fish is linked with a special body organ. It generates electric pulses of only 1.3 s in length at a frequency of some 300 Hz per second and with the amplitude of 4 V. Thanks to that the fish becomes a kind of a pulsed electric dipole.
This system of electrolocation differs in principle from echo location using reflected acoustic signals (like that of bats* or dolphins). Fish species possessing electrolocation can detect objects around them by means of a distorted configuration of the electric field. In homogeneous water media, and also when there are objects around with the same electric conductivity as water, lines of force around the fish are not distorted, and otherwise they are condensed. And if this object is a dielectric, the lines of force spread out around it. In this way, using receptors located near its head, the Nile pike can detect a glass stick some 0.2 mm in diameter. These findings were first reported by Dr. G. Lisman and Dr. K. Makhin in 1958.
Some interesting results were obtained in studies of "non-electric" fish (having no electric field generators) which were reported in 1985 by our compatriot Dr. B. Basov. As has been demonstrated in fish of these species generation of weak electric oscillations is linked with the movements, or locomotions (of the body, tail, fins, etc.). The amplitude of these oscillations at a distance of 10 cm amounts to 60+/-12 mcV for tench, 80+/-12 for bream and crucian, 170+/-15 for trout, 175+/-12 for pike and 200+/-10 mcV for
* See: V. Bolshakov, O. Orlov, "They Roost in Ural Caves", Science in Russia, No. 1, 2001 .- Ed.
burbot. These oscillations are attenuating pulses of different length, depending on the kind of fish.
The sensitivity to electric field differs appreciably in different aquatic organisms. Pike-perch, for example, responds to signals of 0.87 mV/cm, and to achieve the same response from a crucian this signal has to be from 5.5 to 16 mV/cm. Incidentally, the last characteristic is common for many kinds of fish which must be the reason why they cannot use electric signals they generate as a means of orientation and communication. As was demonstrated in 1982 by Dr. V. Protasov of the RAS Institute of Problems of Ecology and Evolution named after A. Severtsov, when bioelectric fields generated by shoals of fish are summed up and synchronized, there occurs their ordering (coordination) which makes it easier for fish to find their bearings. The scientist also assumed that the above change of the configuration of the summary electric field of a shoal of fish as a result of the interaction with the Earth's magnetic field can be "used" by the fish for navigation.
The author of the present article studied the uses of an electric field by swarms of bees for communication. While the main mass of bees remains in the beehive, "scouts" take off in search of food. Having found some, they come back and then the most interesting things begin to happen. The scout bees inform the hive of the direction and distance to the food by means of performing some stereotype movements (dances). Their bodies oscillate at a frequency of about 14 Hz, which corresponds to the frequency of the electric field generated by them themselves. An electric charge on the body of a "dancer" (which is tens of times greater than on "passive" bees) and oscillations of their bellies alter the strength of the surrounding electric field. Thanks to that "passive" bees can identify the "messengers" among all others and obtain information on where to fly for food.
The use by swarms of an electric field generated by "scout" bees has been proved experimentally. Say, a charged plastic model of a "dancer" attracts other bees, and not only the passive ones, but the "scouts" themselves, if the charge is strong enough. And an "uncharged" mechanical bee, imitating the movements of a "dancer", is simply ignored by the hive.
Now, what about other possible effects of electric fields upon different representatives of the fauna? Many insects sense approaching bad weather by increased atmospherics. Currents generated by these discharges are sensed by insects, stimulating them to escape into places sheltered from an approaching thunderstorm.
Summing it up, one can say that the functioning of organisms at all levels of organization is closely associated with the dynamics of electric processes which ensure the coordination of movements and of the whole set of responses to changes of the external and internal environment.
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