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Evidence for a light-dependent magnetic compass. a and b Orientation of newts trained under full-spectrum light, and tested alternately in the same experiments a under full-spectrum light or b under 400 or 450 nm light. c and d Orientation of newts trained under full-spectrum light, and tested alternately in the same experiments c under full-spectrum light, or d under 500, 550 or 600 nm light. e and f Orientation of newts trained under full-spectrum light, and tested alternately in the same experiments (e) under full-spectrum light, or f under 475 nm light. g and h Orientation of newts trained under long-wavelength light (wavelengths > 500 nm), and tested alternately in the same experiments (g) under full-spectrum light, or h under long-wavelength (> 500 nm) light. Shore directions are at the top of each diagram. Light intensities in tests carried out under 400, 450, 475, 500, 550, and 600 nm light were 12.3–12.6 log quanta/cm²/s. (From Phillips and Borland. Nature 359:142–144, Phillips and Borland 1992b. With kind permission of Springer Nature)
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Sensitivity to the earth’s magnetic field is the least understood of the major sensory systems, despite being virtually ubiquitous in animals and of widespread interest to investigators in a wide range of fields from behavioral ecology to quantum physics. Although research on the use of magnetic cues by migratory birds, fish, and sea turtles is mor...
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Citations
... For humans, the magnetic compass is the most mysterious, as we do not possess it naturally; at least, we have no conscious perception of the magnetic field (Chernetsov et al., 2021). Nevertheless, the magnetic compass has been demonstrated in animals by numerous behavioral experiments (Naisbett-Jones and Lohmann, 2022;Phillips and Diego-Rasilla, 2022;Wiltschko, 2005, 2019). Animals can use two variants of the magnetic compass: the 'polar compass', which is based on the polarity of the horizontal component of Earth's magnetic field (i.e. ...
... Hypothesis 1 is unlikely: it is difficult to imagine that the magnetic compass is only available over narrow time intervals during the day, considering the stable conditions (magnetic field, light spectrum and luminous flux, temperature, and humidity) in our laboratory. We also know that other amphibians can orient by the magnetic field at different times of the day (Phillips and Diego-Rasilla, 2022). ...
... Frogs in our experiments oriented exactly during the day, and they were not demotivated by irregular disturbances of similar amplitude. Although in nature, short-wavelength light grows stronger in the spectrum with decreasing solar elevation, from daylight to nautical twilight (Spitschan et al., 2016), no part of the light spectrum disappears as a result of changes in their proportion (by factors and not orders); moreover, it is suggested that shortwavelength light is necessary for the correct functioning of the magnetic compass, according to the studies on tadpoles and newts (Phillips and Diego-Rasilla, 2022). ...
Animals can use two variants of the magnetic compass: “polar compass” or “inclination compass”. Among vertebrates the compass type has been identified for the salmon, mole rats, birds, turtles, and urodeles. However, no experiments have been conducted to determine the compass variant in anurans. To elucidate this, we performed a series of field and laboratory experiments on males of the European common frog during the spawning season. In the field experiments in a large circular arena we identified the direction of stereotypic migration axis on a total of 581 frogs caught during migration from river to ponds or in a breeding pond. We also found that motivation of the frogs varied throughout the day, likely to avoid deadly night freezes, which are common in spring. The laboratory experiments were conducted on a total of 450 frogs in a T-maze placed in a three-axis Merritt coil system. The maze arms were positioned parallel to the natural migration axis inferred on the basis of magnetic field. Both vertical and horizontal components of the magnetic field were altered, and frogs were additionally tested in a vertical magnetic field. We conclude that European common frogs possess inclination magnetic compass, as do newts, birds, and sea turtles, and potentially use it during the spring migration. The vertical magnetic field confuses the frogs, apparently due to the inability to choose a direction. Notably, diurnal variation in motivation of the frogs was identical to that in nature, indicating the presence of internal rhythms controlling this process.
... Mechanisms or processes leading to the ability to return to the same spawning location year after year are still poorly unknown. Several studies show that amphibians are able to use a magnetic compass for orientation and navigation to the breeding ponds (Phillips et al., 1995;Diego-Rasilla, 2003;Diego-Rasilla et al., 2005, 2008, Sinsch, 2006, Phillips et al., 2022Landler, 2022). The use of the geomagnetic field would be essential in situations where other positioning sources (maps) and directional cues (compasses), such as olfactory signals (and celestial cues are unavailable (Joly & Miaud, 1993;Diego-Rasilla et al., 2005). ...
El campo magnético de la Tierra (EMF) es una de las fuentes de información direccional más uniformes y accesibles que los animales pueden usar en los movimientos de comportamiento. El presente estudio tuvo como objetivo determinar la capacidad de Rhinella arenarum para percibir los campos electromagnéticos. Para evaluar la influencia de los campos electromagnéticos en los anuros in situ, recolectamos cuarenta y cuatro especímenes adultos de R. arenarum durante la temporada de reproducción. Registramos el movimiento de cada sapo desde el centro hasta la periferia de un arenero circular utilizando una cámara de visión nocturna. Repetimos el experimento después de cinco minutos, con un campo magnético inducido adicional (IMF), que fue creado empleando dos bobinas de aire Helmholtz. Los movimientos de los sapos bajo la presencia de EMF y IMF fueron significativamente diferentes. Concluimos que R. arenarum podría usar el EMF como mecanismo de navegación y sistema de ubicación, para viajar largas distancias hasta los estanques de desove año tras año.
... Studies on amphibian responses to climate change have shown variability in phenological shifts across species and populations, with both earlier spring breeding 18,[24][25][26][27][28] and delays in seasonal migrations 29,30 . This means that the direction, timing, and strength of these changes can depend on specific environmental conditions experienced at the local scale, along with other important factors such as endogenous rhythms 19,[31][32][33][34] . Shifts in amphibian phenology often have negative consequences for their fitness, as phenological mismatch can alter habitat availability and predator-prey dynamics, and consequently compromise community stability 9,14,17,25,35 . ...
In the last century, a plethora of species have shown rapid phenological changes in response to climate change. Among animals, amphibians exhibit some of the greatest responses since their activity strongly depends on temperature and rainfall regimes. These shifts in phenology can have negative consequences for amphibian fitness. Thus, understanding phenological changes in amphibians is pivotal to design conservation actions to mitigate climate change effects. We used data on Common Spadefoot Toad (Pelobates fuscus) reproductive migration to wetlands over a period of 8 years in Italy to (i) identify the factors related to breeding migrations, (ii) assess potential phenological shifts in the breeding period, and (iii) determine which climatic factors are related to the observed phenological shifts. Our results showed that toads migrate to spawning sites preferably in early spring, on rainy days with temperatures of 9–14 °C, and with high humidity. Furthermore, despite an increase in average temperature across the study period, we observed a delay in the start of breeding migrations of 12.4 days over 8 years. This counterintuitive pattern was the result of a succession of hot and dry years that occurred in the study area, highlighting that for ephemeral pond breeders, precipitation could have a larger impact than temperature on phenology. Our results belie the strong presumption that climate change will shift amphibian phenology toward an earlier breeding migration and underline the importance of closely investigating the environmental factors related to species phenology.
... In both embryos and adult amphibians, orientating behaviour depends on the integration of a redundant-multisensory system, including acoustic, magnetic, mechanical, olfactory and visual cues (Landler, 2022). Interestingly, amphibians, including Xenopus tadpoles (Leutch, 1990), display light-dependent magnetic compass orientation (Phillips et al., 2010;Phillips and Diego-Rasilla, 2022). In the present study, we challenged Xenopus embryos to a condition in which the light and magnetic field cues had a controlled direction and diverged by 90 • . ...
... What is more interesting, the test revealed a dose-dependent change in the orienting response of DLZ-treated animals. Independently from the specific mechanisms involved, which are likely complex and may include photoreceptors in the retina (Phillips and Diego-Rasilla, 2022), it is clear that DLZ may alter the orienting capacity of the animals, again a survival-threatening consequence. Effects on vision are not exclusive to Xenopus embryos but are also reported in humans. ...
Benzodiazepines, psychotropic drugs, are among the most frequently found pharmaceuticals in aquatic matrices. An increasing number of studies are reporting their harmful effects on adults' behaviour and physiology, while little information is available regarding developing organisms exposed since early stages. Improper activation of GABA receptors during embryonic development is likely to induce relevant consequences on the morphogenesis and, at later stages, on behaviour. This study investigated the negative effects of three increasing concentrations of delorazepam on Xenopus laevis retinal and skeletal muscle morphogenesis. Morphological and ultrastructural investigations were correlated with gene expression, while Raman spectroscopy highlighted the main biochemical components affected. Conventional phototactic response and orientation in the magnetic field were assessed as indicators of proper interaction between sensory organs and the nervous system. Results confirm the profound impact of delorazepam on development and return an alarming picture of the amphibians’ survival potentialities in a benzodiazepine-contaminated environment.
... An active area of research, two leading mechanisms are under investigation: one hypothesis concerns magnetically sensitive radical pairs formed by photoexcitation of cryptochrome proteins within the organism's retina (Schulten et al. 1978;Ritz and Schulten 2000;Wiltschko and Wiltschko 2014;Hore and Mouritsen 2016), whereas a magnetite-based hypothesis involves detection of GMF-induced movements of single-domain biogenic magnetite particles (Fe 3 O 4 ) contained within an organism's tissues (Kirschvink and Gould 1981;Kirschvink et al. 2001;Winklhofer and Kirschvink 2010). The "magnetite-particle" and "cryptochrome" mechanisms apparently exist within a wide range of animals (e.g., Wiltschko and Wiltschko 1995;Phillips and Diego-Rasilla 2022) and have been associated with the "map" and "compass" functions of their navigational systems, respectively (e.g., Wiltschko and Wiltschko 2007). ...
... Elements of the avian "map", however, are more obscure and controversial than those of the avian compass. The proposed avian magnetic "map" is commonly associated with global N-S gradients in GMF inclination and intensity ( Fig. 1c) (Walcott 1978;Dennis et al. 2007;Wiltschko et al. 2010;Wiltschko and Wiltschko 2015;Lohmann et al. 2022;Phillips and Diego-Rasilla 2022). The bicoordinate olfactory "map" hypothesis also comprises gradients in putative ratios of atmospheric trace odors (Papi 1989;Wallraff 2013). ...
... Core-field N-S intensity gradients over 10 s of km ( Fig. 1c) are orders of magnitude less than the GMF's total intensity, and local gradients in the crustal field are often large enough to locally obscure them (Lednor 1982;Walcott 1991;Phillips and Diego-Rasilla 2022). Total intensity profiles in Fig. 5 show that the core field's N-S gradient at 700 m can be discerned only over distances of at least 50 to 100 km, whereas the E-W gradient is virtually imperceptible. ...
The geomagnetic field (GMF) is a worldwide source of compass cues used by animals and humans alike. The inclination of GMF flux lines also provides information on geomagnetic latitude. A long-disputed question, however, is whether horizontal gradients in GMF intensity, in combination with changes in inclination, provide bicoordinate “map” information. Multiple sources contribute to the total GMF, the largest of which is the core field. The ubiquitous crustal field is much less intense, but in both land and marine settings is strong enough at low altitudes (< 700 m; sea level) to mask the core field’s weak N–S intensity gradient (~ 3–5 nT/km) over 10 s to 100 s of km. Non-orthogonal geomagnetic gradients, the lack of consistent E–W gradients, and the local masking of core-field intensity gradients by the crustal field, therefore, are grounds for rejection of the bicoordinate geomagnetic “map” hypothesis. In addition, the alternative infrasound direction-finding hypothesis is briefly reviewed. The GMF’s diurnal variation has long been suggested as a possible Zeitgeber (timekeeper) for circadian rhythms and could explain the GMF’s non-compass role in the avian navigational system. Requirements for detection of this weaker diurnal signal (~ 20–50 nT) might explain the magnetic alignment of resting and grazing animals.
Background:
Human electromagnetic hypersensitivity (EHS) or electrosensitivity (ES) symptoms in response to anthropogenic electromagnetic fields (EMFs) at levels below current international safety standards are generally considered to be nocebo effects by conventional medical science. In the wider field of magnetoreception in biology, our understanding of mechanisms and processes of magnetic field (MF) interactions is more advanced.
Methods:
We consulted a range of publication databases to identify the key advances in understanding of magnetoreception across the wide animal kingdom of life.
Results:
We examined primary MF/EMF sensing and subsequent coupling to the nervous system and the brain. Magnetite particles in our brains and other tissues can transduce MFs/EMFs, including at microwave frequencies. The radical pair mechanism (RPM) is accepted as the main basis of the magnetic compass in birds and other species, acting via cryptochrome protein molecules in the eye. In some cases, extraordinary sensitivity is observed, several thousand times below that of the geomagnetic field. Bird compass disorientation by radio frequency (RF) EMFs is known.
Conclusions:
Interdisciplinary research has established that all forms of life can respond to MFs. Research shows that human cryptochromes exhibit magnetosensitivity. Most existing provocation studies have failed to confirm EHS as an environmental illness. We attribute this to a fundamental lack of understanding of the mechanisms and processes involved, which have resulted in the design of inappropriate and inadequate tests. We conclude that future research into EHS needs a quantum mechanistic approach on the basis of existing biological knowledge of the magnetosensitivity of living organisms.
Inspired by the way sea turtles rely on the Earth’s magnetic field for navigation and locomotion, a novel magnetic soft robotic turtle with programmable magnetization has been developed and investigated to achieve biomimetic locomotion patterns such as straight-line swimming and turning swimming. The soft robotic turtle (12.50 mm in length and 0.24 g in weight) is integrated with an Ecoflex-based torso and four magnetically programmed acrylic elastomer VHB-based limbs containing samarium-iron–nitrogen particles, and was able to carry a load more than twice its own weight. Similar to the limb locomotion characteristics of sea turtles, the magnetic torque causes the four limbs to mimic sinusoidal bending deformation under the influence of an external magnetic field, so that the turtle swims continuously forward. Significantly, when the bending deformation magnitudes of its left and right limbs differ, the soft robotic turtle switches from straight-line to turning swimming at 6.334 rad/s. Furthermore, the tracking swimming activities of the soft robotic turtle along specific planned paths, such as square-shaped, S-shaped, and double U-shaped maze, is anticipated to be utilized for special detection and targeted drug delivery, among other applications owing to its superior remote directional control ability.
Studies of learned magnetic compass orientation by C57 BL/6 mice were carried out to determine if responses to magnetic cues were disrupted by exposure to a very low-level (1–2 nT) 1.46 MHz radio frequency field. Findings show that exposure to the same intensity of the 1.46 MHz RF in training and testing (1.0 to 1.2 nT) had no effect on magnetic compass orientation. However, exposure to a slightly higher intensity of RF in training (1.3 to 2.1 nT) eliminated magnetic compass orientation either because the stronger intensity was above a critical threshold for disruption of the underlying magnetoreception mechanism, or because the difference in the RF intensities in training and testing resulted in qualitatively different patterns of magnetic input (‘magnetic modulation patterns’). Importantly, although similar effects of RF on magnetic compass orientation have been reported in other organisms, sensitivity to such low intensities of RF fields cannot be explained by current models of the mechanisms of magnetoreception in terrestrial organisms. Consequently, future research to determine if the findings from C57 BL/6 reported here are replicable is of the first importance.
