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Eye model used for the calculation of visual modulation patterns. Rays 1 and 2 enter through an infinitesimal hole at O and are projected onto a spherical retina. The receptor molecules are assumed to be oriented normal to the retina surface (directions z 1 and z 2 ), thus forming different angles with the direction of the magnetic field vector.
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A large variety of animals has the ability to sense the geomagnetic field and utilize it as a source of directional (compass) information. It is not known by which biophysical mechanism this magnetoreception is achieved. We investigate the possibility that magnetoreception involves radical-pair processes that are governed by anisotropic hyperfine c...
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... one needs to specify how such a process interacts with the visual pathway. For the purpose of illustration we assume that the radical-pair process affects the sensitivity of the light receptors in the eye. This modulation of sensitivity will result in a response pattern that varies over the hemisphere of the eye. We model the eye as displayed in Fig. 5 as a pinhole camera with an infinitesimal opening at O. The retina is assumed to be a perfect sphere with the light receptors oriented normal to the sphere (c.f. z 1 and z 2 in Fig. 5). The eye is assumed to be cyclopean, i.e., in the center of the head. The direction of the central line connecting O and O, henceforth, will be referred ...
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... receptors in the eye. This modulation of sensitivity will result in a response pattern that varies over the hemisphere of the eye. We model the eye as displayed in Fig. 5 as a pinhole camera with an infinitesimal opening at O. The retina is assumed to be a perfect sphere with the light receptors oriented normal to the sphere (c.f. z 1 and z 2 in Fig. 5). The eye is assumed to be cyclopean, i.e., in the center of the head. The direction of the central line connecting O and O, henceforth, will be referred to as the viewing or head ...
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... during head movement. If the bird flies parallel to the geomagnetic field vector and moves its head up, the disk will follow its eyes, however, with a reduced angular velocity. The angular velocity depends on the eye-lens geometry. In our model, the disk moves with half the angular velocity of the eye, as can be readily explained on the basis of Fig. 5: the angular change of ray 1 is half that of z 1 , since angle (1, O, C) is half the angle (1, O, C). If the bird turns its head up and down it will "see" a disk-like feature that follows its head movement and is only in the center of FIGURE 6 Visual modulation patterns through the geomagnetic field (0.5 G) for a bird looking into ...
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... of FIGURE 6 Visual modulation patterns through the geomagnetic field (0.5 G) for a bird looking into different directions at angles 0°, 30°, 60°, 90°, 120°, 150°, and 180° with the magnetic field vector. The patterns have been evaluated assuming radical-pair receptors with anisotropic hyperfine couplings arranged in the eye model depicted in Fig. 5. The schematic illustrations next to the modulation patterns indicate the corresponding direction into which a bird would be flying at Urbana-Champaign (geomagnetic field inclination of ...
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... patterns through the geomagnetic field (0.5 G) for a bird flying parallel to the horizon at Urbana-Champaign (geomagnetic field inclination of 68°) and looking toward N, NE, E, SE, S, SW, W, and NW. The patterns have been evaluated assuming radical-pair receptors with anisotropic hyperfine couplings arranged in the eye model depicted in Fig. 5. ring-like feature is more prominent than the disk. A bird that is used to seeing the disk moving around might first be disoriented at higher fields until it becomes familiar with the new pattern. Familiarity with the new pattern would not prevent the bird from orienting with the familiar pattern generated by the geomagnetic field. A ...
Citations
... Among these abilities, many animals, like birds, fish, and insects use a magnetic compass for orientation during their long and often seasondependent journeys [8][9][10][11]. Despite extensive research, the precise mechanisms of how animals sense the geomagnetic field are still unknown while different theories have been proposed [3,[12][13][14][15][16][17][18][19]. A promising hypothesis regarding how animals can navigate using the geomagnetic field was proposed by Schulten et al. in 1978, who suggested that the magnetic compass could rely on quantum mechanically entangled electrons [12]. ...
... An external magnetic field (e.g., the geomagnetic field) may influence the interconversion between these states of the RP and consequently modulate the yield of a potential spin-dependent RP reaction product once it reaches thermal equilibrium. Changing the direction of the magnetic field affects the RP dynamics, thereby leading to different reaction product yields that may be neuronally processed [13,14,18,20,21]. ...
Marine fish migrate long distances up to hundreds or even thousands of kilometers for various reasons that include seasonal dependencies, feeding, or reproduction. The ability to perceive the geomagnetic field, called magnetoreception, is one of the many mechanisms allowing some fish to navigate reliably in the aquatic realm. While it is believed that the photoreceptor protein cryptochrome 4 (Cry4) is the key component for the radical pair-based magnetoreception mechanism in night migratory songbirds, the Cry4 mechanism in fish is still largely unexplored. The present study aims to investigate properties of the fish Cry4 protein in order to understand the potential involvement in a radical pair-based magnetoreception. Specifically, a computationally reconstructed atomistic model of Cry4 from the Atlantic herring (Clupea harengus) was studied employing classical molecular dynamics (MD) and quantum mechanics/molecular mechanics (QM/MM) methods to investigate internal electron transfers and the radical pair formation. The QM/MM simulations reveal that electron transfers occur similarly to those found experimentally and computationally in Cry4 from European robin (Erithacus rubecula). It is therefore plausible that the investigated Atlantic herring Cry4 has the physical and chemical properties to form radical pairs that in turn could provide fish with a radical pair-based magnetic field compass sensor.
... At the forefront of explanatory models stands the radical pair mechanism (RPM), first introduced by Ref. [1]. Central to this mechanism is the involvement of Cryptochrome (CRY) in the retinas of animals' eyes, forming a quantum compass used by migrating birds [2][3][4][5][6]. In addition, the RPM not only provides a model for avian navigation but also extends its scope to include a broader range of cellular phenomena [7]. ...
Cellular magnetic field effects are assumed to base on coherent singlet-triplet interconversion of radical pairs that are sensitive to applied radiofrequency (RF) and weak magnetic fields (WEMFs), known as radical pair mechanism (RPM). As a leading model, the RPM explains how quantum effects can influence biochemical and cellular signalling. Consequently, radical pairs generate reactive oxygen species (ROS) that link the RPM to redox processes, such as the response to hypoxia and the circadian clock. Therapeutic nuclear magnetic resonance (tNMR) occupies a unique position in the RPM paradigm because of the used frequencies, which are far below the range of 0.1–100 MHz postulated for the RPM to occur. Nonetheless, tNMR was shown to induce RPM like effects, such as increased extracellular H2O2 levels and altered cellular bioenergetics. In this study we compared the impact of tNMR and intermittent hypoxia on the circadian clock, as well as the role of superoxide in tNMR induced ROS partitioning. We show that both, tNMR and intermittent hypoxia, exert on/off effects on cellular clocks that are dependent on the time of application (day versus night). In addition, our data provide further evidence that superoxide plays a central role in magnetic signal transduction. tNMR used in combination with scavengers, such as Vitamin C, led to strong ROS product redistributions. This discovery might represent the first indication of radical triads in biological systems.
... Such dependence suggested the necessity of photostimulation for the magnetoreceptor to function. In the early 2000s, a hypothesis of light-dependent magnetoreception in cryptochromes in the retina of birds based on the known effect of the magnetic field on the spin state of electrons in radicals was proposed [Ritz et al., 2000]. ...
The review presents contemporary data on the influence of the geomagnetic field and its variations on insect behavior. The most probable mechanisms of magnetoreception in different species are discussed. The prospects for studying insect electroreceptors as magnetodetectors are considered. Special attention is paid to studies investigating the impact of geomagnetic storms on insects. Differences in primary magnetoreception mechanisms are considered a potential cause for divergences in the reactions of different insect species to geomagnetic disturbances.
... MFE on flavin-based radical pair system is of great interest to a number of researchers, especially because cryptochrome, a blue-light photoreceptor protein, plays a pivotal role in animal magnetoreception [134][135][136]. Cryptochromes (Crys) are thought to govern avian magnetoreception., which help the migratory birds to detect the direction of Earth's magnetic field for the purpose of navigation. ...
... Birds were found to orient preferentially in short-wavelength light (below 600nm) and moreover used an inclination compass which could detect the angle of the earth's magnetic field but was not responsive to the northsouth direction. Quantum physical principles suggested that such a 'chemical magnetoreceptor' must undergo a reaction mechanism that generates radical pairs (Ritz and Schulten et al., 2000;Hore and Mouritsen, 2016). As a consequence, cryptochrome, which is localized in the bird's retina, was suggested as a possible avian magnetoreceptor. ...
Cryptochromes are widely dispersed flavoprotein photoreceptors that regulate numerous developmental responses to light in plants, as well as to stress and entrainment of the circadian clock in animals and humans. All cryptochromes are closely related to an ancient family of light-absorbing flavoenzymes known as photolyases, which use light as an energy source for DNA repair but themselves have no light sensing role. Here we review the means by which plant cryptochromes acquired a light sensing function. This transition involved subtle changes within the flavin binding pocket which gave rise to a visual photocycle consisting of light-inducible and dark-reversible flavin redox state transitions. In this photocycle, light first triggers flavin reduction from an initial dark-adapted resting state (FADox). The reduced state is the biologically active or ‘lit’ state, correlating with biological activity. Subsequently, the photoreduced flavin reoxidises back to the dark adapted or ‘resting’ state. Because the rate of reoxidation determines the lifetime of the signaling state, it significantly modulates biological activity. As a consequence of this redox photocycle Crys respond to both the wavelength and the intensity of light, but are in addition regulated by factors such as temperature, oxygen concentration, and cellular metabolites that alter rates of flavin reoxidation even independently of light. Mechanistically, flavin reduction is correlated with conformational change in the protein, which is thought to mediate biological activity through interaction with biological signaling partners. In addition, a second, entirely independent signaling mechanism arises from the cryptochrome photocycle in the form of reactive oxygen species (ROS). These are synthesized during flavin reoxidation, are known mediators of biotic and abiotic stress responses, and have been linked to Cry biological activity in plants and animals. Additional special properties arising from the cryptochrome photocycle include responsivity to electromagnetic fields and their applications in optogenetics. Finally, innovations in methodology such as the use of Nitrogen Vacancy (NV) diamond centers to follow cryptochrome magnetic field sensitivity in vivo are discussed, as well as the potential for a whole new technology of ‘magneto-genetics’ for future applications in synthetic biology and medicine.
... Increasing evidence suggests that a light-induced radicalpair based mechanism in cryptochrome (Cry) proteins forms the basis for magnetoreception in night-migratory songbirds [13][14][15]. Cry are blue light photoreceptors, usually discussed in the context of circadian rhythm regulation. They are the only known photoreceptor molecules in the bird's eye with the potential to form long-lived, magnetically sensitive, radical-pairs (transient reaction intermediates comprising two radicals with unpaired electrons) [14][15][16]. ...
Migratory birds possess remarkable accuracy in orientation and navigation, which involves various compass systems including the magnetic compass. Identifying the primary magnetosensor remains a fundamental open question. Cryptochromes (Cry) have been shown to be magnetically sensitive, and Cry4a from a migratory songbird seems to show enhanced magnetic sensitivity in vitro compared to Cry4a from resident species. We investigate Cry and their potential involvement in magnetoreception in a phylogenetic framework, integrating molecular evolutionary analyses with protein dynamics modelling. Our analysis is based on 363 bird genomes and identifies different selection regimes in passerines. We show that Cry4a is characterized by strong positive selection and high variability, typical characteristics of sensor proteins. We identify key sites that are likely to have facilitated the evolution of an optimized sensory protein for night-time orientation in songbirds. Additionally, we show that Cry4 was lost in hummingbirds, parrots and Tyranni (Suboscines), and thus identified a gene deletion, which might facilitate testing the function of Cry4a in birds. In contrast, the other avian Cry (Cry1 and Cry2) were highly conserved across all species, indicating basal, non-sensory functions. Our results support a specialization or functional differentiation of Cry4 in songbirds which could be magnetosensation.
... However, biological RP reactions must satisfy specific physical and chemical requirements to accomplish magnetic sensing (Timmel et al., 1998;Player and Hore, 2019). The flavoprotein cryptochrome has been proposed to be a biological magnetic receptor (Ritz et al., 2000), where a RP is initialized by either photoexcitation or during the redox cycle of the flavin cofactor (Maeda et al., 2008;Hogben et al., 2009;Hore and Mouritsen, 2016). Other protein systems have been suggested to sense weak magnetic fields (Jones, 2016). ...
... Following the RP-based magnetoreception theory (Schulten and Wolynes, 1978;Timmel et al., 1998;Ritz et al., 2000;Procopio and Ritz, 2016), we have calculated the singlet (ϕ T S ) H 2 O 2 and triplet (ϕ T T ) O 2 ...
... The RP distance can affect spin relaxation and thus magnetic sensing in the radicals, whereas the problems with spin relaxation can be essentially removed by a radical scavenger by the quantum Zeno effect (Kattnig, 2017). Using the RP theory avian magnetoreception (Ritz et al., 2000), simulations have been performed to quantify ROS products that are dictated by coherent dynamics of singlet and triplet RP spin states . We have determined singlet and triplet product yields, and thus relative distributions of O 2 •− and H 2 O 2 as a function of the static magnetic field strength. ...
Biological magnetic field sensing that gives rise to physiological responses is of considerable importance in quantum biology. The radical pair mechanism (RPM) is a fundamental quantum process that can explain some of the observed biological magnetic effects. In magnetically sensitive radical pair (RP) reactions, coherent spin dynamics between singlet and triplet pairs are modulated by weak magnetic fields. The resulting singlet and triplet reaction products lead to distinct biological signaling channels and cellular outcomes. A prevalent RP in biology is between flavin semiquinone and superoxide (O2 •−) in the biological activation of molecular oxygen. This RP can result in a partitioning of reactive oxygen species (ROS) products to form either O2 •− or hydrogen peroxide (H2O2). Here, we examine magnetic sensing of recombinant human electron transfer flavoenzyme (ETF) reoxidation by selectively measuring O2 •− and H2O2 product distributions. ROS partitioning was observed between two static magnetic fields at 20 nT and 50 μT, with a 13% decrease in H2O2 singlet products and a 10% increase in O2 •− triplet products relative to 50 µT. RPM product yields were calculated for a realistic flavin/superoxide RP across the range of static magnetic fields, in agreement with experimental results. For a triplet born RP, the RPM also predicts about three times more O2 •− than H2O2, with experimental results exhibiting about four time more O2 •− produced by ETF. The method presented here illustrates the potential of a novel magnetic flavoprotein biological sensor that is directly linked to mitochondria bioenergetics and can be used as a target to study cell physiology.
... (2) Numerous studies demonstrate a wavelength-dependent effect of light on magnetic compass orientation in tadpoles of Alytes obstricans, Pelophylax perezi, R. temporaria and Lithobates catesbeianus (Diego-Rasilla and Luengo, 2020;Diego-Rasilla et al., 2010, 2013Freake and Phillips, 2005). This is important evidence in favor of the inclination compass as, in theory, the lightdependent chemical compass is inclinational (Ritz et al., 2000), but not crucial proof, as only the horizontal component was varied in these experiments. (3) Experiments using a circular arena during spawning migration of B. bufo and experiments using a T-maze parallel to the migration axis for P. ridibundus stimulated to spawn. ...
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.
... The extant literature exemplifies the rich dividends that are being yielded from such cross-disciplinary ventures. Data reveal that the ability of birds to migrate across great distances is underpinned by magnetically sensitive cryptochrome proteins in the avian eye used to detect the Earth's geomagnetic field, where radical pair formation is thought to induce signaling that acts as a biological compass (Ritz et al., 2000;Xu et al., 2021;Tonelli et al., 2023). Interestingly other migratory animals, including fish, can also detect magnetic fields to navigate their environment (Naisbett-Jones and Lohmann, 2022). ...
Quantum biology studies span multiple disciplines including physics, engineering, and biology with the goal of understanding the quantum underpinnings of living systems. Recent findings have brought wide attention to the role of quantum mechanisms in the function and regulation of biological processes. Moreover, a number of activities have been integral in building a vibrant quantum biology community. Due to the inherent interdisciplinary nature of the field, it is a challenge for quantum biology researchers to integrate and advance findings across the physical and biological disciplines. Here we outline achievable approaches to developing a shared platform—including the establishment of standardized manipulation tools and sensors, and a common scientific lexicon. Building a shared community framework is also crucial for fostering robust interdisciplinary collaborations, enhancing knowledge sharing, and diversifying participation in quantum biology. A unified approach promises not only to deepen our understanding of biological systems at a quantum level but also to accelerate the frontiers of medical and technological innovations.
... Though the OMF effect has been experimentally demonstrated by several research groups, its biophysical origin as well as its possible role in migration ecology remain not quite clear. Indeed, it finds a qualitative explanation in the model of the light-dependent magnetic compass of birds, based on cryptochrome molecules in the eyes (Ritz et al. 2000), due to the electron paramagnetic resonance in photoexcited radical-pairs (Timmel and Hore 1996;Ritz et al. 2004;Hore and Mouritsen 2016). However, the predictions of this model are in considerable quantitative disagreement with the experimental results. ...
... Natural radio frequency electromagnetic noise might also have the potential to disturb magnetic orientation behavior, specifically solar RF and atmospheric RF electromagnetic noise (Bianco et al. 2019;Granger et al. 2022). Some researchers hold on the idea that the sensitivity to OMF is related to the mechanism of magnetoreception itself (Ritz et al. 2000, but see Kavokin 2009), others suggest that there may be an additional sensory system aimed at the detection of the environmental magnetic noise (Kirschvink 2014;Bojarinova et al. 2023). We would like to stress that our experimental results do not allow us to make a choice among different models of the OMF effect. ...
Weak oscillating magnetic fields (OMF) in the radiofrequency range are known to disrupt the orientation of birds. However, until now, it has not been experimentally verified that the sensitivity to OMF is a characteristic feature specifically of the magnetic compass and OMF does not influence the celestial compass system as well. Here we studied if OMF affected the star compass of a long-distance migrant, the Garden Warbler. The birds were tested under the natural starry sky under two different conditions: in the natural magnetic field (NMF) and in radiofrequency OMF with the amplitude 20nT and frequency 1.41 MHz (matching the Larmor frequency of a freestanding electron spin in the local NMF of 50,400 nT). This amplitude is about ten times higher than the sensitivity threshold to OMF shown for this species in previous studies. Our experimental results clearly demonstrated that OMF did not influence the celestial (star) compass system: with access to the starry sky garden warblers showed migratory orientation appropriate for autumn migratory season both in the NMF and in the OMF. Thus, the OMF effect is pertinent to the magnetic compass system, not to the avian orientation in general.
