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.     

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.     

Light-Dependent Shift in Bullfrog Tadpole Magnetic Compass Orientation: Evidence for a Common Magnetoreception Mechanism in Anuran and Urodele Amphibians

Previous studies have demonstrated the presence of a light‐dependent magnetic compass in a urodele amphibian, the eastern red‐spotted newt Notophthalmus viridescens, mediated by extraocular photoreceptors located in or near the pineal organ. Newts tested under long‐wavelength (≥500 nm) light exhibited a 90° shift in the direction of orientation relative to newts tested under full spectrum (white) or short‐wavelength light. Here we report that bullfrog tadpoles Rana catesbeiana (an anuran amphibian) exhibit a 90° shift in the direction of magnetic compass orientation under long‐wavelength (≥500 nm) light similar to that observed in newts, suggesting that a common light‐dependent mechanism mediates these responses. These findings suggest that a light‐dependent magnetic compass may have been the ancestral state in this group of vertebrates.     

Behavioral titration of a magnetic map coordinate

Spatial variation in the inclination of the geomagnetic field has been implicated in the map component of homing by eastern red-spotted newts Notophthalmus viridescens. Here we show that when newts are exposed to small changes in magnetic inclination, the most dramatic effects on homing orientation occur at values close to the 'home value', as predicted by the magnetic map hypothesis (Phillips 1996). Newts reverse the direction of homing orientation over a range of inclination of 0.5 degrees spanning the home value, providing further evidence that magnetic inclination or one of its components (i.e., vertical or horizontal intensity) is used to derive map information.     

Use of a Magnetic Compass for Nocturnal Homing Orientation in the Palmate Newt, Lissotriton helveticus

Previous studies have shown that migrating palmate newts (Lissotriton helveticus) can rely on acoustic cues for orientation to breeding ponds. Nonetheless, although acoustic cues are reliable over relatively short distances, they are unlikely to account for the long‐distance homing demonstrated in several other species of newts. Most individuals of L. helveticus migrate only a few hundred meters (Diego‐Rasilla, F. J. & Luengo, R. M. 2007: Acoustic orientation in the palmate newt, Lissotriton helveticus. Behav. Ecol. Sociobiol. 61, 1329—1335), raising the possibility that this species may only utilize short‐distance cues (Joly, P. & Miaud, C. 1993: How does a newt find its pond? The role of chemical cues in migrating newts (Triturus alpestris). Ethol. Ecol. Evol. 5, 447—455; Russell, A. P., Bauer, A. M. & Johnson, M. K. 2005: Migration of amphibians and reptiles: an overview of patterns and orientation mechanisms in relation to life history strategies. In: Migration of Organisms (Elewa, M. T., ed). Springer‐Verlag, Berlin Heidelberg, pp. 151—203; Sinsch, U. 2006: Orientation and navigation in Amphibia. Mar. Freshw. Behav. Phy. 39, 65—71). Therefore, experiments were carried out to investigate the use of the geomagnetic field in the nocturnal homing orientation of L. helveticus. Tests were carried out at night in an outdoor circular arena, under total overcast sky that prevented access to celestial compass cues. Individual newts were tested in one of four symmetrical alignments of an earth‐strength magnetic field. We studied the orientation behaviour of newts from two breeding ponds located 9.05 km west‐southwest and 19 km east‐northeast of the testing site. The distribution of magnetic bearings from both groups of newts exhibited significant orientation in the homeward direction. These findings indicate that palmate newts are capable of long‐distance homing and are able to orient in the homeward direction at night using the magnetic compass as the sole source of directional (i.e., compass) information.     

Magnetic Orientation in the Savannah Sparrow

Although magnetic compass orientation has been reported in a number of invertebrate and vertebrate taxa, including about a dozen migratory bird species, magnetic orientation capabilities in animals remain somewhat controversial. We have hand-raised a large number of Savannah sparrows (Passerculus sandwichensis) to study the ontogeny of orientation behavior. Young birds with a variety of early experience with visual and magnetic orientation cues have been tested for magnetic orientation during their first autumn migration. Here we present data from 80 hand-raised sparrows, each tested several times in both normal and shifted magnetic fields. Birds reared indoors with no experience with visual orientation cues showed axial north-south orientation that shifted by almost exactly the magnitude of 90° clockwise and counterclockwise shifts in the direction of magnetic north. Other groups of birds with varying early experience with visual orientation cues showed different preferred orientation directions, but all groups shifted orientation direction in response to shifts in the magnetic field. The data thus demonstrate a robust magnetic orientation ability in this species.     

Spontaneous preferences for magnetic compass direction in the American red-spotted newt, <Emphasis Type="Italic">Notophthalmus viridescens</Emphasis> (Salamandridae,Urodela)

In addition to other sensory modalities, migratory vertebrates are able to use the earths’ magnetic field for orientation and navigation. The magnetic cue may also serve as a reference for other orientation mechanisms. In this study, significant evidence is shown that, even in darkness, newts (Notophthalmus viridescens, Salamandridae) spontaneously align according to the natural or to the deviated earth’s magnetic field lines, thereby demonstrating a magnetic compass sensitivity. All newts preferred compass directions close to east or west or chose the E/W axially and hence sought to maintain a specific angle or axis relative to the magnetic field vector. Such an active alignment is considered an essential precondition for magnetic orientation. When the horizontal magnetic vector was experimentally compensated, animals became disoriented. We infer that the animals have either learned the preferred magnetic direction/axis individually or that these choices are innate and could even be seasonally different as in migrating birds. It is still an unanswered question as to how and where the physical and physiological mechanisms of magnetic transduction and reception take place. The visual system and other light-dependent (radical pairs) mechanisms alone are often claimed to be in function, but this must now be reconsidered given the results from animals when deprived of light. The results may therefore point to putative receptor mechanisms involving magnetite elements in specialized magneto-receptors.     

Magnetic Compass Orientation in the European Eel

European eel migrate from freshwater or coastal habitats throughout Europe to their spawning grounds in the Sargasso Sea. However, their route (∼ 6000 km) and orientation mechanisms are unknown. Several attempts have been made to prove the existence of magnetoreception in Anguilla sp., but none of these studies have demonstrated magnetic compass orientation in earth-strength magnetic field intensities. We tested eels in four altered magnetic field conditions where magnetic North was set at geographic North, South, East, or West. Eels oriented in a manner that was related to the tank in which they were housed before the test. At lower temperature (under 12°C), their orientation relative to magnetic North corresponded to the direction of their displacement from the holding tank. At higher temperatures (12–17°C), eels showed bimodal orientation along an axis perpendicular to the axis of their displacement. These temperature-related shifts in orientation may be linked to the changes in behavior that occur between the warm season (during which eels are foraging) and the colder fall and winter (during which eels undertake their migrations). These observations support the conclusion that 1. eels have a magnetic compass, and 2. they use this sense to orient in a direction that they have registered moments before they are displaced. The adaptive advantage of having a magnetic compass and learning the direction in which they have been displaced becomes clear when set in the context of the eel’s seaward migration. For example, if their migration is halted or blocked, as it is the case when environmental conditions become unfavorable or when they encounter a barrier, eels would be able to resume their movements along their old bearing when conditions become favorable again or when they pass by the barrier.     

Celestial orientation in the marbled newt (Triturus marmoratus)

Orientation toward breeding ponds plays an important role in the seasonal movements of amphibians. In this study, adult marbled newts were tested in a circular arena to determine sensory cues used to locate breeding ponds. Animals were collected from a temporary pond situated in northern Spain, taken to the experimental site 340 m distant, and tested for orientation under a variety of conditions (i.e., orientation under a clear night sky, orientation under an overcast night sky, and orientation under a clear night sky in the presence of an altered geomagnetic field). These investigations have demonstrated that the marbled newt is able to orient using celestial cues. Animals chose a compass course in the direction of their breeding pond only when celestial cues were available. Conversely, the ambient geomagnetic field does not seem to be relevant to orientation of marbled newts since they were unable to orient themselves using the ambient geomagnetic field in the absence of celestial cues. Electronic Publication     

Effects of Ultraviolet Radiation on Locomotion and Orientation in Roughskin Newts (Taricha granulosa)

Environmental changes, including those associated with the atmosphere may significantly affect individual animals and ultimately populations. Ultraviolet (UV) radiation, perhaps increasing due to stratospheric ozone depletion, has been linked to mortality in a number of organisms, including amphibians. The eggs and larvae of certain amphibian species hatch at significantly lower rates when exposed to ambient ultraviolet light. Yet little is known about the sublethal effects of UV radiation. For example, UV radiation may affect specific behaviors of an animal that could alter its ability to survive. To examine if UV radiation affects amphibian behavior, we used roughskin newts ( Taricha granulosa ) as a model. Newts were exposed to low-level doses of UV in the laboratory and then tested in the field to examine if UV-exposed and control (no UV) newts differed in orientation towards water or in locomotor activity levels. UV-exposed and control newts both exhibited a significant orientation towards water in field tests but there was no significant difference in orientation between treatments. However, UV-exposed newts were significantly more active than control newts. Our results suggest that exposure to short-term low levels of UV radiation alters certain behaviors. Environmentally induced changes in behavior may have significant ecological and evolutionary consequences.     

You Can Get There from Here: Responses to Simulated Magnetic Equator Crossing by the Bobolink (Dolichonyx oryzivorus)

The avian magnetic compass works as an inclination compass. Instead of using the polarity of the magnetic field to determine direction, birds use the inclination of the dip angle. Consequently, transequatorial migrants have to reverse their response to the magnetic compass after crossing the magnetic equator. When confronted with an artificial magnetic field that reverses the vertical component of the magnetic field, migrants such as the bobolink reverse their headings relative to magnetic north even in the presence of visual cues such as stellar patterns. Bobolinks, which breed in temperate North America and winter in temperate South America, were tested in a planetarium under fixed star patterns in a series of magnetic fields incremented each night from the natural field in the northern hemisphere through an artificial horizontal field to an artificial southern hemisphere magnetic field. The birds maintained a constant heading throughout the experiment and did not reverse direction after the simulated crossing of the magnetic equator as previous experiments predicted. In nature, this response would have meant continuation of their migration flight across the equator and into the opposite hemisphere. The switch from “equatorward” orientation to “poleward” orientation is probably triggered by experience with a horizontal magnetic field and/or visual cues. The ability to maintain an accurate heading while crossing the magnetic equator may be based on the use of visual cues such as the stars.     

Use of an Inclination Compass during Migratory Orientation by the Bobolink (Dolichonyx oryzivorus)

Adult bobolinks were tested in a planetarium under patterns of nonrotating artificial stars to determine the influence of natural and modified magnetic fields on their migratory orientation. The modified magnetic field was of the same total intensity as the natural field, but the vertical vector was reversed, causing the resulting total vector to point up and north (compared to the natural northern hemisphere vector pointing down and north). When exposed to the artificial magnetic field, the birds reversed their preferred headings relative to the stellar and geographic references. This response is consistent with the use of an inclination compass. Although 60 % of the individuals reversed their headings the first night, some individuals took up to 5 nights (mean = 2.1 nights).     

Two different types of light-dependent responses to magnetic fields in birds

A model of magnetoreception proposes that the avian magnetic compass is based on a radical pair mechanism, with photon absorption leading to the formation of radical pairs. Analyzing the predicted light dependency by testing migratory birds under monochromatic lights, we found that the responses of birds change with increasing intensity. The analysis of the orientation of European robins under 502 nm turquoise light revealed two types of responses depending on light intensity: under a quantal flux of 8.10(15) quanta m(-2) s(-1), the birds showed normal migratory orientation in spring as well as in autumn, relying on their inclination compass. Under brighter light of 54.10(15) quanta m(-2) s(-1), however, they showed a "fixed" tendency toward north that did not undergo the seasonal change and proved to be based on magnetic polarity, not involving the inclination compass. When birds were exposed to a weak oscillating field, which specifically interferes with radical pair processes, the inclination compass response was disrupted, whereas the response to magnetic polarity remained unaffected. These findings indicate that the normal inclination compass used for migratory orientation is based on a radical-pair mechanism, whereas the fixed direction represents a novel type of light-dependent orientation based on a mechanism of a different nature.     

Innate preference for magnetic compass direction in the Alpine newt, <Emphasis Type="Italic">Triturus alpestris</Emphasis> (Salamandridae,Urodela)?

Magnetic compass orientation was first discovered for migrating/homing birds in which all individuals of a population or species prefer a predictable magnetic direction during a particular migratory situation. If all other sensory cues are absent, the Earth’s magnetic field may serve as a reference for other orientation mechanisms. It will be demonstrated that alpine newts (Triturus alpestris, Salamandridae) spontaneously align according to the natural or the deviated magnetic field lines of the Earth. They are able to do this in the dark and by apparently seeking to maintain a specific angle with respect to the magnetic field vector. When the horizontal component of the magnetic vector was eliminated, animals became disoriented, and orientation became random. We infer that the animals observed had learned to prefer a particular magnetic direction following environmental/geographical cues. Alternatively, the magnetic directional alignments are innate as, e.g. in migrating birds, but these may be modified/altered according to season, age, hormonal status, and environmental factors such as “landmarks”, light-, sound-, or olfactory cues. Numerous observations of the aligning showed that the preference for a certain magnetic compass direction/axis was not only individual but also specific for the population-subgroups tested. Specimens roughly preferred magnetic directions close to east or west. However, the larvae were able to learn to align to obviously attractive hiding spots (tubes) that were provided in a direction that deviated with respect to the first magnetic preference. The new conditioned alignments were, again, referred to magnetically by the animals and remained stable, even if the hiding tubes were absent. Animals preferred that direction until, eventually, a new directional cue became attractive.     

Rapid Learning of Magnetic Compass Direction by C57BL/6 Mice in a 4-Armed ‘Plus’ Water Maze

Magnetoreception has been demonstrated in all five vertebrate classes. In rodents, nest building experiments have shown the use of magnetic cues by two families of molerats, Siberian hamsters and C57BL/6 mice. However, assays widely used to study rodent spatial cognition (e.g. water maze, radial arm maze) have failed to provide evidence for the use of magnetic cues. Here we show that C57BL/6 mice can learn the magnetic direction of a submerged platform in a 4-armed (plus) water maze. Naïve mice were given two brief training trials. In each trial, a mouse was confined to one arm of the maze with the submerged platform at the outer end in a predetermined alignment relative to magnetic north. Between trials, the training arm and magnetic field were rotated by 180^° so that the mouse had to swim in the same magnetic direction to reach the submerged platform. The directional preference of each mouse was tested once in one of four magnetic field alignments by releasing it at the center of the maze with access to all four arms. Equal numbers of responses were obtained from mice tested in the four symmetrical magnetic field alignments. Findings show that two training trials are sufficient for mice to learn the magnetic direction of the submerged platform in a plus water maze. The success of these experiments may be explained by: (1) absence of alternative directional cues (2), rotation of magnetic field alignment, and (3) electromagnetic shielding to minimize radio frequency interference that has been shown to interfere with magnetic compass orientation of birds. These findings confirm that mice have a well-developed magnetic compass, and give further impetus to the question of whether epigeic rodents (e.g., mice and rats) have a photoreceptor-based magnetic compass similar to that found in amphibians and migratory birds.     

Magnetic compass orientation by larval Drosophila melanogaster

We report evidence for magnetic compass orientation by larval Drosophila melanogaster. Groups of larvae were exposed from the time of hatching to directional ultraviolet (365 nm) light emanating from one of four magnetic directions. Larvae were then tested individually on a circular agar plate under diffuse light in one of four magnetic field alignments. The larvae exhibited magnetic compass orientation in a direction opposite that of the light source in training. Evidence for a well-developed magnetic compass in a larval insect that moves over distances of at most a few tens of centimeters has important implications for understanding the adaptive significance of orientation mechanisms like the magnetic compass. Moreover, the development of an assay for studying magnetic compass orientation in larval D. melanogaster will make it possible to use a wide range of molecular genetic techniques to investigate the neurophysiological, biophysical, and molecular mechanisms underlying the magnetic compass.     

Bird navigation: what type of information does the magnetite-based receptor provide?

Previous experiments have shown that a short, strong magnetic pulse caused migratory birds to change their headings from their normal migratory direction to an easterly direction in both spring and autumn. In order to analyse the nature of this pulse effect, we subjected migratory Australian silvereyes, Zosterops lateralis, to a magnetic pulse and tested their subsequent response under different magnetic conditions. In the local geomagnetic field, the birds preferred easterly headings as before, and when the horizontal component of the magnetic field was shifted 90 degrees anticlockwise, they altered their headings accordingly northwards. In a field with the vertical component inverted, the birds reversed their headings to westwards, indicating that their directional orientation was controlled by the normal inclination compass. These findings show that although the pulse strongly affects the magnetite particles, it leaves the functional mechanism of the magnetic compass intact. Thus, magnetite-based receptors seem to mediate magnetic 'map'-information used to determine position, and when affected by a pulse, they provide birds with false positional information that causes them to change their course.     

Magnetic information calibrates celestial cues during migration

Migratory birds use celestial and geomagnetic directional information to orient on their way between breeding and wintering areas. Cue-conflict experiments involving these two orientation cue systems have shown that directional information can be transferred from one system to the other by calibration. We designed experiments with four species of North American songbirds to: (1) examine whether these species calibrate orientation information from one system to the other; and (2) determine whether there are species-specific differences in calibration. Migratory orientation was recorded with two different techniques, cage tests and free-flight release tests, during autumn migration. Cage tests at dusk in the local geomagnetic field revealed species-specific differences: red-eyed vireo, Vireo olivaceus, and northern waterthrush, Seiurus noveboracensis, selected seasonally appropriate southerly directions whereas indigo bunting, Passerina cyanea, and grey catbird, Dumetella carolinensis, oriented towards the sunset direction. When tested in deflected magnetic fields, vireos and waterthrushes responded by shifting their orientation according to the deflection of the magnetic field, but buntings and catbirds failed to show any response to the treatment. In release tests, all four species showed that they had recalibrated their star compass on the basis of the magnetic field they had just experienced in the cage tests. Since release tests were done in the local geomagnetic field it seems clear that once the migratory direction is determined, most likely during the twilight period, the birds use their recalibrated star compass for orientation at departure. Copyright 2000 The Association for the Study of Animal Behaviour.     

Orientation responses of American eels, Anguilla rostrata, to varying magnetic fields

1. The locations of freshwater yellow eels in an eight-chambered octagonal behavior tank were videotaped during six-day intervals while the animals were being subjected to normal and experimental magnetic fields. 2. The earth's magnetic field (0.5 g) was utilized for two control periods at the start and completion of each run for each animal. 3. During each run, the sequence of applied magnetic fields was +1.0, 0.0, -0.5 and -1.0 g, each being applied for a period of 24 hr. 4. Under the influence of the earth's magnetic field, the eels showed a preference for a northeast direction (27.01%). During the second control period (i.e. after being subjected to variations in the magnetic field), the animals showed a dual preference for north and northwest directions (23.02% and 25.9%, respectively). 5. In a 0.0 g field, the eels preferred the north chamber (24.43%) and the vestibule of the behavior tank (19.46%); a preference for north was also obtained with a field of +1.0 g (25.95%). 6. The preferred direction with the -0.5 and -1.0 g fields was southeast (20.93 and 26.71%, respectively).