Brazilian Ants Diversity and the Local Geomagnetic Field: A Ferromagnetic Resonance Study

Ants have the ability of homing and some species can migrate or move over long distances (nomadic). The presence of magnetic particles as geomagnetic sensors is the most accepted hypothesis to explain ant orientation mechanisms. The room temperature Ferromagnetic Resonance (FMR) spectra of migratory, nomadic, arboreal, trap-jaw and fire ants, applied to 11 samples are presented. The spectra were studied taking into account two components: the low field (LF) with a maximum at g_max values higher than 8 and the high field (HF) at the g_eff=2.1 with a linewidth of about 900 Oe. This study tests the systematization plausibility of ant magnetic material characteristics based on absorption spectra area and the ratios between the peak-to-peak amplitude spectral components (LF/HF). The HF component predominates in the spectra of the migratory and one nomadic ant, while the LF is the dominant one in the arboreal and six fire ants studied. The Solenopsis absorption spectra area, proportional to the magnetic material amount, increases as the local magnetic field intensity increases, suggesting an adaptation of these ants to the magnetic environment characteristic.     

Use of a magnetic compass for Y-axis orientation in premetamorphic newts (Triturus boscai)

Experiments were carried out to investigate whether premetamorphic larvae of Boscas newt (Triturus boscai) are capable of using the geomagnetic field for Y-axis orientation (i.e., orientation toward and away from shore). Larvae were trained outdoor in two different training configurations, using one training tank aligned along the magnetic north–south axis, with shore facing north, and another training tank positioned with its length along the east–west axis, with shore located west. After training, premetamorphic newts were tested in an outdoor circular arena surrounded by a pair of orthogonally aligned cube-surface coils used to alter the alignment of the Earths magnetic field. Each newt was tested only once, in one of four magnetic field alignments: ambient magnetic field (i.e., magnetic north at North), and three altered fields (magnetic north rotated to East, West, South). Distributions of magnetic bearings from tested larvae indicated that they oriented bimodally along the magnetic direction of the trained Y-axis. These findings demonstrate that T. boscai larvae are sensitive to the geomagnetic field and can use it for orienting along a learned Y-axis. This study is the first to provide evidence of Y-axis orientation, accomplished by a magnetic compass, in larval urodeles.     

Shifted magnetic fields lead to deflected and axial orientation of migrating robins,Erithacus rubecula,at sunset

The migratory orientation of the robin was tested in shifted magnetic fields during the twilight period after sunset, under clear skies and under simulated total overcast. The horizontal direction of the geomagnetic field was shifted 90° to the right or left in relation to the local magnetic field, without changing either the intensity of the field or its angle of inclination. Experiments were conducted during both spring and autumn, with robins captured as passage migrants at the Falsterbo and Ottenby bird observatories in southern Sweden as test subjects. Generally, the orientation of robins was affected by magnetic shifts compared to controls tested in the natural geomagnetic field. Autumn birds from the two capture sites differed in their responses, probably because of different migratory dispositions and body conditions. The robins most often changed their orientation to maintain their typical axis of migration relative to the shifted magnetic fields. However, preferred directions in relation to the shifted magnetic fields were frequently reverse from normal, or axial rather than unimodal. These results disagree with suggested mechanisms for orientation by visual sunset cues and with the proposed basis of magnetic orientation. They do, however, demonstrate that the geomagnetic field is involved in the sunset orientation of robins, probably in combination with additional visual or non-visual cues that contribute to establish magnetic polarity.     

Avian orientation: effects of cue-conflict experiments with young migratory songbirds in the high Arctic

The migratory orientation of juvenile white-crowned sparrows, Zonotrichia leucophrys gambelli, was investigated by orientation cage experiments in manipulated magnetic fields performed during the evening twilight period in northwestern Canada in autumn. We did the experiments under natural clear skies in three magnetic treatments: (1) in the local geomagnetic field; (2) in a deflected magnetic field (mN shifted −90°); and (3) after exposure to a deflected magnetic field (mN −90°) for 1 h before the cage experiment performed in the local geomagnetic field at dusk. Subjects showed a mean orientation towards geographical east in the local geomagnetic field, north of the expected migratory direction towards southeast. The sparrows responded consistently to the shifted magnetic field, demonstrating the use of a magnetic compass during their first autumn migration. Birds exposed to a cue conflict for 1 h on the same day before the experiment, and tested in the local geomagnetic field at sunset, showed the same northerly orientation as birds exposed to a shifted magnetic field during the experiment. This result indicates that information transfer occurred between magnetic and celestial cues. Thus, the birds' orientation shifted relative to available sunset and geomagnetic cues during the experimental hour. The mean orientation of birds exposed to deflected magnetic fields prior to and during testing was recorded up to two more times in the local geomagnetic field under natural clear and overcast skies before release, resulting in scattered mean orientations.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

Bats Respond to Very Weak Magnetic Fields

How animals, including mammals, can respond to and utilize the direction and intensity of the Earth’s magnetic field for orientation and navigation is contentious. In this study, we experimentally tested whether the Chinese Noctule, Nyctalus plancyi (Vespertilionidae) can sense magnetic field strengths that were even lower than those of the present-day geomagnetic field. Such field strengths occurred during geomagnetic excursions or polarity reversals and thus may have played an important role in the evolution of a magnetic sense. We found that in a present-day local geomagnetic field, the bats showed a clear preference for positioning themselves at the magnetic north. As the field intensity decreased to only 1/5^th of the natural intensity (i.e., 10 μT; the lowest field strength tested here), the bats still responded by positioning themselves at the magnetic north. When the field polarity was artificially reversed, the bats still preferred the new magnetic north, even at the lowest field strength tested (10 μT), despite the fact that the artificial field orientation was opposite to the natural geomagnetic field (P<0.05). Hence, N. plancyi is able to detect the direction of a magnetic field even at 1/5th of the present-day field strength. This high sensitivity to magnetic fields may explain how magnetic orientation could have evolved in bats even as the Earth’s magnetic field strength varied and the polarity reversed tens of times over the past fifty million years.     

Orientation by magnetic field in leaf-cutter ants, Atta colombica (Hymenoptera: Formicidae)

Leaf‐cutter ants (Atta colombica) use trail following to travel between foraging sites and the home nest. However, this combination of pheromone and visual cues is likely to be complemented by a directional reference system such as a compass, used not only when foraging but also during colony formation, where foraging trails degrade or where ants become displaced. One candidate system is the magnetic polarity compass. We tested the orientation of leaf‐cutter ants under a magnetic field of reversed‐polarity, with the prediction that the ants would show 180° deflection compared with control ants in an unchanged geomagnetic field. When the sun's disc was unobstructed by clouds, orientation was the same as that of control ants, implying that magnetic cues were not used to orient. However, when the sky was overcast, ants in the experimental treatment significantly shifted their mean orientation both in comparison with controls and reversed‐polarity ants under the sun. Although a total reversal in orientation was not induced, the results demonstrate that Atta respond to magnetic reversal in the absence of sunlight cues, and suggest a role for magnetic cues in determining direction during orientation.     

Magnetic Compass Orientation in Larval Iberian Green Frogs, Pelophylax Perezi

Experiments were carried out to investigate whether Iberian green frog tadpoles Pelophylax perezi (formerly Rana perezi) are able of using the geomagnetic field for y‐axis orientation (i.e. orientation toward and away from shore). Tadpoles were trained outdoor for 5 d, in two different training configurations: (i) a training tank aligned along the magnetic north–south axis, with shore facing south, and (ii) a training tank aligned along the magnetic east–west axis, with shore located east, and similar to the shore–deep water axis (‘y‐axis’) found in their home stream, which flows from south to north. After training, tadpoles were individually tested for magnetic orientation in a water‐filled circular outdoor arena surrounded by a pair of orthogonally aligned cube‐surface‐coils used to alter the alignment of the earth's magnetic field. Tadpoles held in the east–west training tank oriented towards shore, indicating that they were able to distinguish between the shoreward and waterward direction along the y‐axis. Tadpoles trained in the tank that was aligned along the north–south axis showed bimodal magnetic compass orientation along the shore–deep water magnetic axis. These findings provide evidence for the use of magnetic compass cues for y‐axis orientation by P. perezi tadpoles.     

Variability of morphometric indices of cleaving embryos in two anuran amphibians under modified magnetic conditions

We studied the effects of modified magnetic fields, such as reduced geomagnetic field or only its horizontal component, strengthened vertical component, or periodic alteration of horizontal component polarity, on two-, four-, and eight-cell embryos of Bufo viridis and Rana macrocnemis. Modified magnetic conditions did not affect the first or second cleavage furrow geometry. The strengthened vertical component of geomagnetic field alone decreased the frequency of two-cell embryos with the second furrow, which was not closed on the animal pole. Modified magnetic conditions more distinctly affected the vertical sizes of animal and vegetal blastomeres of eight-cell toad embryos due, apparently, to displacement of the third cleavage plane towards the animal or vegetal pole. The response of frog embryos to modified magnetic conditions was much less pronounced.     

The horizontal magnetic dance of the honeybee is compatible with a single-domain ferromagnetic magnetoreceptor

Although honeybees are able to sense the geomagnetic field, very little is known about the method in which they are able to detect it. The recent discovery of biochemically precipitated magnetite (Fe₃O₄) in bees, however, suggests the possibility that they might use a simple compass organelle for magnetoreception. If so, their orientation accuracy ought to be related to the accuracy of the compass, e.g. it should be poor in weak background fields and enhanced in strong fields. When dancing to the magnetic directions on a horizontal honeycomb, bees clearly show this type of alignment behavior. A least-squares fit between the expected alignment of a compass and this horizontal dance data is consistent with this hypothesis, and implies that the receptors have magnetic moments of 5 × 10^?13 emu, or magnetite volumes near 10^?15 cm³. Additional considerations suggests that these crystals are slightly sub-spherical and single-domain in size, held symmetrically in their receptors, and have a magnetic orientation energy of approximately to 6 kT in the geomagneticfield. A model of a magnetite-based magnetoreceptor consistent with these constraints is discussed.     

Orientation of Dunnocks (Prunella modularis) at Sunset

To find out the relative importance of the geomagnetic and solar cues for the orientation at the time of sunset, dunnocks were tested outdoors during the spring migration periods of 1982 and 1983. Experimental magnetic fields were produced by Helmholtz coils. In the various magnetic conditions, the following results were obtained:

• 1 In the local geomagnetic field, the dunnocks oriented in a seasonally appropriate northerly direction.
• 2 In a magnetic field the north of which was shifted 120° clock-wise to ESE, the birds showed a corresponding shift in their orientation.
• 3 In a vertical magnetic field without meaningful directional information, birds previously tested in either the local geomagnetic field or the shifted magnetic field now displayed axially bimodal orientation, with the axes of the two groups differing.

These findings indicate that for migratory dunnocks, the magnetic field plays a dominant role in determining their orientation at the time of sunset, and that magnetic information may affect the dunnocks' response to other directional, presumably solar cues as well.     

Magnetic compass orientation in the Eastern red-spotted newt (Notophthalmus viridescens)

Summary Laboratory tests were carried out to examine the orientation behavior of adult Eastern red-spotted newts (Notophthalmus viridescens) to earth-strength magnetic fields. Groups of 30 to 40 newts were housed in water-filled, all-glass aquaria with an artificial shoreline at one end. The aquaria were located in a greenhouse or outdoors adjacent to the laboratory building, and aligned on either the magnetic north-south or east-west axis. Tests were carried out in an enclosed indoor arena. Newts were tested in four horizontal alignments of the magnetic field: the ambient magnetic field (magnetic north at North) and three altered fields (magnetic north rotated to East, South or West). Data were analyzed after pooling the magnetic bearings from all four conditions in such a way as to retain the component of the newts' orientation that was a consistent response to the magnetic field. Elevation of training tank water temperature was used to increase the newts' motivation to orient in the direction of shore. Newts exposed to a training tank water temperature of 33–34 °C just prior to testing exhibited consistent unimodal magnetic compass orientation. The direction of orientation was altered predictably by changing training tank alignment and location relative to the laboratory building. The results provide the first evidence of a strong, replicable magnetic compass response in a terrestrial vertebrate under controlled laboratory conditions. Further, the present study demonstrates that the Eastern newt is able to learn a directional response relative to the earth's magnetic field.     

Integrated use of moon and magnetic compasses by the heart-and-dart moth,Agrotis exclamationis

Use of the moon as a compass during migration appears difficult due to the complexity of the moon's change in azimuth during the lunar month. These apparent difficulties would be eased if the moon's position were calibrated at intervals against a constant reference source, such as the geomagnetic field. Yet, until now, no animal has been shown to integrate moon and magnetic compasses for orientation. In this study, light-traps were used on 15 nights during a lunar month to obtain samples of heart-and-dart moths, Agrotis exclamationis, characterized by a preference to fly ‘toward’ (i.e.±90°) the moon's azimuth. The compass orientation of each sample was then tested in normal and reversed geomagnetic fields, out of sight of the moon. Compass orientation relative to the ambient magnetic field coincided with the compass bearing of the moon at the time of capture. Directional preference changed during the lunar month in a way that tracked the change in the moon's azimuth. It is concluded that moths use the geomagnetic field to calibrate a moon compass.     

Magnetic Alignment in Carps: Evidence from the Czech Christmas Fish Market

While magnetoreception in birds has been studied intensively, the literature on magnetoreception in bony fish, and particularly in non-migratory fish, is quite scarce. We examined alignment of common carps (Cyprinus carpio) at traditional Christmas sale in the Czech Republic. The sample comprised measurements of the directional bearings in 14,537 individual fish, distributed among 80 large circular plastic tubs, at 25 localities in the Czech Republic, during 817 sampling sessions, on seven subsequent days in December 2011. We found that carps displayed a statistically highly significant spontaneous preference to align their bodies along the North-South axis. In the absence of any other common orientation cues which could explain this directional preference, we attribute the alignment of the fish to the geomagnetic field lines. It is apparent that the display of magnetic alignment is a simple experimental paradigm of great heuristic potential.     

Behavioural responses of European silver eels(Anguilla anguilla) to the geomagnetic field

Magnetic orientation of European silver eels(Anguilla anguilla) was tested in an octagonal tank. Orientation was determined from photo-registrations of eel positions in tests performed alternately in the natural magnetic field and a field with the horizontal component rotated 180°. Tests were performed in LD 11 : 13. At a daytime light intensity of 100 lux the fish were diurnally active, while at 0.10 lux crepuscular or nocturnal activity dominated. The eels probably differed in preferred orientation, largely depending on the clockwise or anti-clockwise swimming of some of the animals. Therefore there was no preferred direction common to all eels. The orientation of single eels differed, however, significantly between the two magnetic fields, suggesting that the eels responded to the geomagnetic field.     

Light effects on the multicellular magnetotactic prokaryote ‘<Emphasis Type="Italic">Candidatus</Emphasis> Magnetoglobus multicellularis’ are cancelled by radiofrequency fields: the involvement of radical pair mechanisms

‘Candidatus Magnetoglobus multicellularis’ is the most studied multicellular magnetotactic prokaryote. It presents a light-dependent photokinesis: green light decreases the translation velocity whereas red light increases it, in comparison to blue and white light. The present article shows that radio-frequency electromagnetic fields cancel the light effect on photokinesis. The frequency to cancel the light effect corresponds to the Zeeman resonance frequency (DC magnetic field of 4 Oe and radio-frequency of 11.5 MHz), indicating the involvement of a radical pair mechanism. An analysis of the orientation angle relative to the magnetic field direction shows that radio-frequency electromagnetic fields disturb the swimming orientation when the microorganisms are illuminated with red light. The analysis also shows that at low magnetic fields (1.6 Oe) the swimming orientation angles are well scattered around the magnetic field direction, showing that magnetotaxis is not efficiently in the swimming orientation to the geomagnetic field. The results do not support cryptochrome as being the responsible chromophore for the radical pair mechanism and perhaps two different chromophores are necessary to explain the radio-frequency effects.     

Testing Magnetic Orientation in a Solitary Subterranean Rodent Ctenomys talarum (Rodentia: Octodontidae)

To test for the hypothesis that Ctenomys talarum can use the earth's magnetic field for spatial orientation, we carried out field and laboratory experiments to analyse if C. talarum burrows present any geomagnetic orientation in their natural habitat, if C. talarum show any spontaneous directional preference when starting to excavate their burrows and if this subterranean rodent is capable to use the earth's magnetic field to orient towards a goal in a complex maze. No correlation between the burrowing direction and the earth's magnetic field was found. We could not find any evidence for any spontaneous directional preference when starting to excavate the burrows in C. talarum. The change of the horizontal vector of the geomagnetic field did not affect the ability of this rodent to orient towards a goal in an artificial labyrinth. Explanations for these results and other possible mechanisms of orientation that could be used by C. talarum are discussed.     

Learned magnetic compass orientation by the Siberian hamster, Phodopus sungorus

Magnetic orientation in mammals has been demonstrated convincingly in only two genera of subterranean mole-rats (Spalax and Cryptomys sp.) by examining the directional placement of nests in radially symmetrical indoor arenas. Mole-rats show a spontaneous directional preference to place their nests to the south or southeast of magnetic north. Using a similar nest-building assay, we show that laboratory-raised Siberian hamsters also use directional information from the magnetic field to position their nests. In contrast to mole-rats, however, the directional preference for nest position shown by Siberian hamsters appears to be learned. Hamsters were housed in rectangular cages aligned along perpendicular axes before testing. When subsequently tested in a radially symmetric arena, the hamsters positioned their nests in a bimodal distribution that coincided with the magnetic direction of the long axis of the holding cages. We also present results from an earlier set of experiments in which hamsters showed consistent orientation only in the ambient magnetic field, and not in experimentally rotated magnetic fields. The conditions under which these earlier experiments were carried out suggest that holding conditions prior to testing and the presence of nonmagnetic cues may influence the expression of magnetic orientation in the Siberian hamster. Failure to consider these and other factors may help to explain why previous attempts to demonstrate magnetic orientation in a number of rodent species have failed or, when positive results have been obtained, have been difficult to replicate. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.     

The response of European Daphnia magna Straus and Australian Daphnia carinata King to changes in geomagnetic field

This study investigates the effects of lifelong exposure to reversed geomagnetic and zero geomagnetic fields (the latter means absence of geomagnetic field) on the life history of Daphnia carinata King from Australia and Daphnia magna Straus from Europe. Considerable deviation in the geomagnetic field from the usual strength, leads to a decrease in daphnia size and life span. Reduced brood sizes and increased body length of neonates are observed in D. magna exposed to unusual magnetic background. The most apparent effects are induced by zero geomagnetic field in both species of Daphnia. A delay in the first reproduction in zero geomagnetic field is observed only in D. magna. No adaptive maternal effects to reversed geomagnetic field are found in a line of D. magna maintained in these magnetic conditions for eight generations. Integrally, the responses of D. magna to unusual geomagnetic conditions are more extensive than that in D. carinata. We suggest that the mechanism of the effects of geomagnetic field reversal on Daphnia may be related to differences in the pattern of distribution of the particles that have a magnetic moment, or to moving charged organic molecules owing to a change in combined outcome and orientation of the geomagnetic field and Earth's gravitational field. The possibility of modulation of self-oscillating processes with changes in geomagnetic field is also discussed.     

Power lines and the geomagnetic field

The metric of prime interest in power line epidemiological studies has been AC magnetic intensity. To consider also possible geomagnetic involvement, the orientation of a long straight power line is examined relative to a uniform geomagnetic field (GMF) with dip angle α. An expression is derived for the component of the total GMF that is parallel, at an elevation β, to the circuital magnetic field that surrounds the line. This component is a function of the angles α and β, the total geomagnetic intensity B_T, and the angle θ between the axis of the power line and magnetic north. Plotting these geomagnetic parameters for known leukemia residences allows one to test for possible ion cyclotron resonance or other GMF interactions. This approach, in principle, is an easy addition to existing or planned studies, because residential access is not required to obtain local values for α, β, θ, and B_T. We recommend including these parameters in the design of epidemiological studies examining power line fields and childhood leukemia. © 1995 Wiley-Liss, Inc.     

The role of skylight polarization in the orientation of a day-migrating bird species

To assess the role of skylight polarization in the orientation system of a day-migrating bird, Yellow-faced Honeyeaters (Lichenostomus chrysops, Meliphagidae) were tested in funnel cages for their directional preferences. In control tests in the natural local geomagnetic field under the clear natural sky, they preferred their normal migratory course. Manipulations of the e-vector by depolarizing the skylight or rotating the axis of polarization failed to affect the orientation as long as the natural geomagnetic field was present. When deprived of magnetic information, the birds continued in their normal migratory direction as long as they had access to information from the natural sky, or when either the sun or polarized light was available. However, when sun was hidden by clouds, depolarizers caused disorientation. — These findings indicate that polarized skylight can be used for orientation when no other known cues are available. However in the hierarchy of cues of this species, the polarization pattern clearly ranks lower than information from the geomagnetic field.