Seasonal reproductive state determines gene expression in the hypothalamus of a latitudinal migratory songbird during the spring and autumn migration.

We investigated gonadal effects on hypothalamic transcription of genes in sham-operated and castrated redheaded buntings photostimulated into spring and autumn migratory states. RNA-Seq results showed testes-dependent differences between spring and autumn migratory states. In particular, differentially expressed genes enriched G-protein-coupled receptor and calcium-ion signaling pathways during spring and autumn states, respectively. qPCR assay showed attenuated gabra5, ttr, thra and thrb expressions, suggesting reduced GABA and thyroid hormone effects on photo-sexual response in spring. In spring castrates, reduced npy, tac1 and nrcam and increased ank3 expression suggested testicular effects on the appetite, prolactin release and neuronal functions, whereas in autumn castrates, reduced rasgrp1, grm5 and grin1, and increased mras expression suggested testicular effects on the ras, G-protein and glutamate signaling pathways. Castration-induced reciprocal switching of pomc and pdyn expressions suggested effects on the overall homeostasis in both seasons. These results demonstrate transcriptome-wide changes, with season-dependent roles of testes in songbird migration.

Navigating at night: fundamental limits on the sensitivity of radical pair magnetoreception under dim light.

Night-migratory songbirds appear to sense the direction of the Earth's magnetic field via radical pair intermediates formed photochemically in cryptochrome flavoproteins contained in photoreceptor cells in their retinas. It is an open question whether this light-dependent mechanism could be sufficiently sensitive given the low-light levels experienced by nocturnal migrants. The scarcity of available photons results in significant uncertainty in the signal generated by the magnetoreceptors distributed around the retina. Here we use results from Information Theory to obtain a lower bound estimate of the precision with which a bird could orient itself using only geomagnetic cues. Our approach bypasses the current lack of knowledge about magnetic signal transduction and processing in vivo by computing the best-case compass precision under conditions where photons are in short supply. We use this method to assess the performance of three plausible cryptochrome-derived flavin-containing radical pairs as potential magnetoreceptors.

The Earth's Magnetic Field and Visual Landmarks Steer Migratory Flight Behavior in the Nocturnal Australian Bogong Moth.

Like many birds [1], numerous species of nocturnal moths undertake spectacular long-distance migrations at night [2]. Each spring, billions of Bogong moths (Agrotis infusa) escape hot conditions in different regions of southeast Australia by making a highly directed migration of over 1,000 km to a limited number of cool caves in the Australian Alps, historically used for aestivating over the summer [3, 4]. How moths determine the direction of inherited migratory trajectories at night and locate their destination (i.e., navigate) is currently unknown [5-7]. Here we show that Bogong moths can sense the Earth's magnetic field and use it in conjunction with visual landmarks to steer migratory flight behavior. By tethering migrating moths in an outdoor flight simulator [8], we found that their flight direction turned predictably when dominant visual landmarks and a natural Earth-strength magnetic field were turned together, but that the moths became disoriented within a few minutes when these cues were set in conflict. We thus conclude that Bogong moths, like nocturnally migrating birds [9], can use a magnetic sense. Our results represent the first reliable demonstration of the use of the Earth's magnetic field to steer flight behavior in a nocturnal migratory insect.

Double-Cone Localization and Seasonal Expression Pattern Suggest a Role in Magnetoreception for European Robin Cryptochrome 4.

Birds seem to use a light-dependent, radical-pair-based magnetic compass. In vertebrates, cryptochromes are the only class of proteins that form radical pairs upon photo-excitation. Therefore, they are currently the only candidate proteins for light-dependent magnetoreception. Cryptochrome 4 (Cry4) is particularly interesting because it has only been found in vertebrates that use a magnetic compass. However, its structure and localization within the retina has remained unknown. Here, we sequenced night-migratory European robin (Erithacus rubecula) Cry4 from the retina and predicted the currently unresolved structure of the erCry4 protein, which suggests that erCry4 should bind Flavin. We also found that Cry1a, Cry1b, and Cry2 mRNA display robust circadian oscillation patterns, whereas Cry4 shows only a weak circadian oscillation. When we compared the relative mRNA expression levels of the cryptochromes during the spring and autumn migratory seasons relative to the non-migratory seasons in European robins and domestic chickens (Gallus gallus), the Cry4 mRNA expression level in European robin retinae, but not in chicken retinae, is significantly higher during the migratory season compared to the non-migratory seasons. Cry4 protein is specifically expressed in the outer segments of the double cones and long-wavelength single cones in European robins and chickens. A localization of Cry4 in double cones seems to be ideal for light-dependent magnetoreception. Considering all of the data presented here, especially including its localization within the European robin retina, its likely binding of Flavin, and its increased expression during the migratory season in the migratory bird but not in chicken, Cry4 could be the magnetoreceptive protein.

Biological effects of the hypomagnetic field: An analytical review of experiments and theories.

During interplanetary flights in the near future, a human organism will be exposed to prolonged periods of a hypomagnetic field that is 10,000 times weaker than that of Earth's. Attenuation of the geomagnetic field occurs in buildings with steel walls and in buildings with steel reinforcement. It cannot be ruled out also that a zero magnetic field might be interesting in biomedical studies and therapy. Further research in the area of hypomagnetic field effects, as shown in this article, is capable of shedding light on a fundamental problem in biophysics-the problem of primary magnetoreception. This review contains, currently, the most extensive bibliography on the biological effects of hypomagnetic field. This includes both a review of known experimental results and the putative mechanisms of magnetoreception and their explanatory power with respect to the hypomagnetic field effects. We show that the measured correlations of the HMF effect with HMF magnitude and inhomogeneity and type and duration of exposure are statistically absent. This suggests that there is no general biophysical MF target similar for different organisms. This also suggests that magnetoreception is not necessarily associated with evolutionary developed specific magnetoreceptors in migrating animals and magnetotactic bacteria. Independently, there is nonspecific magnetoreception that is common for all organisms, manifests itself in very different biological observables as mostly random reactions, and is a result of MF interaction with magnetic moments at a physical level-moments that are present everywhere in macromolecules and proteins and can sometimes transfer the magnetic signal at the level of downstream biochemical events. The corresponding universal mechanism of magnetoreception that has been given further theoretical analysis allows one to determine the parameters of magnetic moments involved in magnetoreception-their gyromagnetic ratio and thermal relaxation time-and so to better understand the nature of MF targets in organisms.

The quantum needle of the avian magnetic compass.

Migratory birds have a light-dependent magnetic compass, the mechanism of which is thought to involve radical pairs formed photochemically in cryptochrome proteins in the retina. Theoretical descriptions of this compass have thus far been unable to account for the high precision with which birds are able to detect the direction of the Earth's magnetic field. Here we use coherent spin dynamics simulations to explore the behavior of realistic models of cryptochrome-based radical pairs. We show that when the spin coherence persists for longer than a few microseconds, the output of the sensor contains a sharp feature, referred to as a spike. The spike arises from avoided crossings of the quantum mechanical spin energy-levels of radicals formed in cryptochromes. Such a feature could deliver a heading precision sufficient to explain the navigational behavior of migratory birds in the wild. Our results (i) afford new insights into radical pair magnetoreception, (ii) suggest ways in which the performance of the compass could have been optimized by evolution, (iii) may provide the beginnings of an explanation for the magnetic disorientation of migratory birds exposed to anthropogenic electromagnetic noise, and (iv) suggest that radical pair magnetoreception may be more of a quantum biology phenomenon than previously realized.

Changes in brain peptides associated with reproduction and energy homeostasis in photosensitive and photorefractory migratory redheaded buntings.

Present study examined the expression of brain peptides associated with the reproduction and energy homeostasis (GnRH/GnIH, NPY/VIP), and assessed their possible functional association in the photosensitive (non-breeding, pre-breeding), photostimulated (breeding) and photorefractory (post-breeding) migratory redheaded buntings (Emberiza bruniceps), using double-labeled immunohistochemistry. Particularly, we measured immunoreactive (-ir) cell numbers, per cent cell area and cell optical density (OD) in the preoptic area (GnRH-I), midbrain (GnRH-II), paraventricular nucleus (GnIH), dorsomedial hypothalamus, DMH and infundibular complex, INc (NPY and VIP), and lateral septal organ (VIP) of buntings kept under natural photoperiods at the wintering latitude (26°55'N). There was a significant seasonal difference in GnRH-I, not GnRH-II, with reduced -ir cells in the photosensitive and photorefractory buntings, and notably with increased cell OD between the refractory and non-breeding states with no increase in testis size. Also, increased cell OD of GnIH neurons in non-breeding state indicated its role in the maintenance of small testes during the post-refractory period. Overall, seasonal changes in GnRH-I and GnIH were found consistent with their suggested roles in reproductive regulation of absolute photorefractory birds. Further, there was a significant seasonal change in cell OD of NPY neurons in DMH, not the INc. In contrast, VIP immunoreactivity was seasonally altered, with a significantly higher VIP-ir cells in breeding than the pre-breeding state. Finally, close proximity between perikarya with fibres suggested functional interactions between the GnRH and GnIH, and NPY and VIP. Thus, seasonal plasticity of brain peptides is perhaps the part of neural regulation of seasonal reproduction and associated energy homeostasis in migratory songbirds.

Genetic analysis of circadian responses to low frequency electromagnetic fields in Drosophila melanogaster.

The blue-light sensitive photoreceptor cryptochrome (CRY) may act as a magneto-receptor through formation of radical pairs involving a triad of tryptophans. Previous genetic analyses of behavioral responses of Drosophila to electromagnetic fields using conditioning, circadian and geotaxis assays have lent some support to the radical pair model (RPM). Here, we describe a new method that generates consistent and reliable circadian responses to electromagnetic fields that differ substantially from those already reported. We used the Schuderer apparatus to isolate Drosophila from local environmental variables, and observe extremely low frequency (3 to 50 Hz) field-induced changes in two locomotor phenotypes, circadian period and activity levels. These field-induced phenotypes are CRY- and blue-light dependent, and are correlated with enhanced CRY stability. Mutational analysis of the terminal tryptophan of the triad hypothesised to be indispensable to the electron transfer required by the RPM reveals that this residue is not necessary for field responses. We observe that deletion of the CRY C-terminus dramatically attenuates the EMF-induced period changes, whereas the N-terminus underlies the hyperactivity. Most strikingly, an isolated CRY C-terminus that does not encode the Tryptophan triad nor the FAD binding domain is nevertheless able to mediate a modest EMF-induced period change. Finally, we observe that hCRY2, but not hCRY1, transformants can detect EMFs, suggesting that hCRY2 is blue light-responsive. In contrast, when we examined circadian molecular cycles in wild-type mouse suprachiasmatic nuclei slices under blue light, there was no field effect. Our results are therefore not consistent with the classical Trp triad-mediated RPM and suggest that CRYs act as blue-light/EMF sensors depending on trans-acting factors that are present in particular cellular environments.

Acoustic and foraging behavior of a Baird's beaked whale, Berardius bairdii, exposed to simulated sonar.

Beaked whales are hypothesized to be particularly sensitive to anthropogenic noise, based on previous strandings and limited experimental and observational data. However, few species have been studied in detail. We describe the underwater behavior of a Baird's beaked whale (Berardius bairdii) from the first deployment of a multi-sensor acoustic tag on this species. The animal exhibited shallow (23 ± 15 m max depth), intermediate (324 ± 49 m), and deep (1138 ± 243 m) dives. Echolocation clicks were produced with a mean inter-click interval of approximately 300 ms and peak frequency of 25 kHz. Two deep dives included presumed foraging behavior, with echolocation pulsed sounds (presumed prey capture attempts) associated with increased maneuvering, and sustained inverted swimming during the bottom phase of the dive. A controlled exposure to simulated mid-frequency active sonar (3.5-4 kHz) was conducted 4 hours after tag deployment, and within 3 minutes of exposure onset, the tagged whale increased swim speed and body movement, and continued to show unusual dive behavior for each of its next three dives, one of each type. These are the first data on the acoustic foraging behavior in this largest beaked whale species, and the first experimental demonstration of a response to simulated sonar.

Magnetic orientation of garden warblers (Sylvia borin) under 1.4 MHz radiofrequency magnetic field.

We report on the experiments on orientation of a migratory songbird, the garden warbler (Sylvia borin), during the autumn migration period on the Courish Spit, Eastern Baltics. Birds in experimental cages, deprived of visual information, showed the seasonally appropriate direction of intended flight with respect to the magnetic meridian. Weak radiofrequency (RF) magnetic field (190 nT at 1.4 MHz) disrupted this orientation ability. These results may be considered as an independent replication of earlier experiments, performed by the group of R. and W. Wiltschko with European robins (Erithacus rubecula). Confirmed outstanding sensitivity of the birds' magnetic compass to RF fields in the lower megahertz range demands for a revision of one of the mainstream theories of magnetoreception, the radical-pair model of birds' magnetic compass.

Photoperiodic induction of pre-migratory phenotype in a migratory songbird: identification of metabolic proteins in flight muscles.

Migratory birds need to undergo physiological changes during their preparation for migration. The current study characterized those changes in photoperiodic migratory black-headed buntings (Emberiza melanocephala), which initiate their northward spring migration in response to increasing day lengths. We measured differences in body mass, testis size and triglycerides levels in buntings between groups exposed to short (8 h light:16 h darkness, 8L:16D; SD) and long (16L:8D; LD) days, and identified proteins that showed significant differences between SD and LD in the flight muscle. To confirm that photostimulated changes were linked with migration, similar measurements were done on photoperiodic non-migratory Indian weaverbirds (Ploceus philippinus), which share the habitat with buntings for almost half-a-year. Buntings were fattened and gained weight and had elevated serum triglyceride levels and recrudesced testes under LD, but not SD. The SDS-polyacrylamide gel electrophoresis revealed differences between SD and LD conditions in the flight muscle protein profiles of buntings, but not of weaverbirds. Two-dimensional gel electrophoresis of flight muscle of bunting separated three proteins, of which two were upregulated under LD condition. Mass spectroscopic analysis and a protein database search identified them as the fatty acid binding protein (FABP), myoglobin and creatine kinase (CK). Further semi-quantitative and quantitative PCR assays revealed that FABP and myoglobin transcript levels in buntings, but not in weaverbirds, were upregulated under LD condition. However, there was no difference in CK mRNA levels between SD and LD in both the species. High FABP is perhaps linked with increased energy demands and high myoglobin with intense physical activity during migration. A difference in the CK protein, but not in mRNA levels between SD and LD may possibly indicate its photoperiodic regulation at the translational level.

Quantum coherence and entanglement in the avian compass.

The radical-pair mechanism is one of two distinct mechanisms used to explain the navigation of birds in geomagnetic fields, however little research has been done to explore the role of quantum entanglement in this mechanism. In this paper we study the lifetime of radical-pair entanglement corresponding to the magnitude and direction of magnetic fields to show that the entanglement lasts long enough in birds to be used for navigation. We also find that the birds appear to not be able to orient themselves directly based on radical-pair entanglement due to a lack of orientation sensitivity of the entanglement in the geomagnetic field. To explore the entanglement mechanism further, we propose a model in which the hyperfine interactions are replaced by local magnetic fields of similar strength. The entanglement of the radical pair in this model lasts longer and displays an angular sensitivity in weak magnetic fields, both of which are not present in previous models.

[Migration of rodents in the Eastern Urals Radioactive Trace zone (radiobiological aspect)].

We investigated migrations of mouse-like rodents in the Eastern Urals Radioactive Trace (EURT) zone using the method of small mammal group marking by tetracycline (additionally to the data of radionuclide self-marking). The originality of small mammals' population in the EURT zone is defined by a configuration of radioactively polluted area and features of animals' migrations. The tetracycline label is detected in the dentine of upper incisors fluorescing in UV light. A high migration activity of rodents is observed both in the EURT zone and adjacent areas. When migrating, rodents used the certain ways of moving. Our new data allowed us to conclude that the EURT zone, as well as any other areas, is inhabited by a population with a constantly changing set of individuals, i.e. a flowing population. It is the convincing evidence of the absence of any isolation. Migrations of small mammals in the narrow and extended EURT zone (1) considerably decrease the probability that certain adaptive changes may be fixed and inherited in a series of generations; (2) are the base of transmission of radio-induced effects in adjacent areas. The fact of a flowing population should be taken into account in a wide spectrum of investigations when analyzing the remote consequences of chronic radiation influence.

A new type of radical-pair-based model for magnetoreception.

Certain migratory birds can sense the Earth's magnetic field. The nature of this process is not yet properly understood. Here we offer a simple explanation according to which birds literally see the local magnetic field through the impact of a physical rather than a chemical signature of the radical pair: a transient, long-lived electric dipole moment. Based on this premise, our picture can explain recent surprising experimental data indicating long lifetimes for the radical pair. Moreover, there is a clear evolutionary path toward this field-sensing mechanism: it is an enhancement of a weak effect that may be present in many species.

Robins have a magnetic compass in both eyes.

Arising from W. Wiltschko et al. 419, 467-470 (2002); Wiltschko et al. replyThe magnetic compass of migratory birds is embedded in the visual system and it has been reported by Wiltschko et al. that European Robins, Erithacus rubecula, cannot show magnetic compass orientation using their left eye only. This has led to the notion that the magnetic compass should be located only in the right eye of birds. However, a complete right lateralization of the magnetic compass would be very surprising, and functional neuroanatomical data have questioned this notion. Here we show that the results of Wiltschko et al. could not be independently confirmed using double-blind protocols. European Robins can perform magnetic compass orientation with both eyes open, with the left eye open only, and with the right eye open only. No clear lateralization is observed.

[The adaptive strategy of rodent populations living in conditions of radioactive and chemical environmental pollution].

The comparative analysis of demographic, morphological and physiological processes in mouselike rodents in pollution zones (90Sr + 90Y, 137Cs) on East-Ural radioactive track (EURT) and (Cu + Cd + Pb + Zn + SO2) on a site near copper-smelting factory is carried out. The direct (not mediated) defeat of animals by an irradiation leads to inherited adaptation (density preservation, tolerance increase to pollution, migration decrease and so forth). The mediated defeat of animals at pollution by metals influences animals as a result of degradation of a vegetative cover, reducing a forage reserve, shelters and reproduction places. Population is decreasing, migration is increasing. Hence, population reacts onto direct defeat of animals or on inhabitancy locuses degradation, id est unspecifically, without dependence from the physical and chemical nature of pollution.

Avian magnetite-based magnetoreception: a physiologist's perspective.

It is now well established that animals use the Earth's magnetic field to perform long-distance migration and other navigational tasks. However, the transduction mechanisms that allow the conversion of magnetic field variations into an electric signal by specialized sensory cells remain largely unknown. Among the species that have been shown to sense Earth-strength magnetic fields, birds have been a model of choice since behavioural tests show that their direction-finding abilities are strongly influenced by magnetic fields. Magnetite, a ferromagnetic mineral, has been found in a wide range of organisms, from bacteria to vertebrates. In birds, both superparamagnetic (SPM) and single-domain magnetite have been found to be associated with the trigeminal nerve. Electrophysiological recordings from cells in the trigeminal ganglion have shown an increase in action potential firing in response to magnetic field changes. More recently, histological evidence has demonstrated the presence of SPM magnetite in the subcutis of the pigeon's upper beak. The aims of the present review are to review the evidence for a magnetite-based mechanism in birds and to introduce physiological concepts in order to refine the proposed models.

Animal cryptochromes mediate magnetoreception by an unconventional photochemical mechanism.

Understanding the biophysical basis of animal magnetoreception has been one of the greatest challenges in sensory biology. Recently it was discovered that the light-dependent magnetic sense of Drosophila melanogaster is mediated by the ultraviolet (UV)-A/blue light photoreceptor cryptochrome (Cry). Here we show, using a transgenic approach, that the photoreceptive, Drosophila-like type 1 Cry and the transcriptionally repressive, vertebrate-like type 2 Cry of the monarch butterfly (Danaus plexippus) can both function in the magnetoreception system of Drosophila and require UV-A/blue light (wavelength below 420 nm) to do so. The lack of magnetic responses for both Cry types at wavelengths above 420 nm does not fit the widely held view that tryptophan triad-generated radical pairs mediate the ability of Cry to sense a magnetic field. We bolster this assessment by using a mutant form of Drosophila and monarch type 1 Cry and confirm that the tryptophan triad pathway is not crucial in magnetic transduction. Together, these results suggest that animal Crys mediate light-dependent magnetoreception through an unconventional photochemical mechanism. This work emphasizes the utility of Drosophila transgenesis for elucidating the precise mechanisms of Cry-mediated magnetosensitivity in insects and also in vertebrates such as migrating birds.

Biophysics of magnetic orientation: strengthening the interface between theory and experimental design.

The first demonstrations of magnetic effects on the behaviour of migratory birds and homing pigeons in laboratory and field experiments, respectively, provided evidence for the longstanding hypothesis that animals such as birds that migrate and home over long distances would benefit from possession of a magnetic sense. Subsequent identification of at least two plausible biophysical mechanisms for magnetoreception in animals, one based on biogenic magnetite and another on radical-pair biochemical reactions, led to major efforts over recent decades to test predictions of the two models, as well as efforts to understand the ultrastructure and function of the possible magnetoreceptor cells. Unfortunately, progress in understanding the magnetic sense has been challenged by: (i) the availability of a relatively small number of techniques for analysing behavioural responses to magnetic fields by animals; (ii) difficulty in achieving reproducible results using the techniques; and (iii) difficulty in development and implementation of new techniques that might bring greater experimental power. As a consequence, laboratory and field techniques used to study the magnetic sense today remain substantially unchanged, despite the huge developments in technology and instrumentation since the techniques were developed in the 1950s. New methods developed for behavioural study of the magnetic sense over the last 30 years include the use of laboratory conditioning techniques and tracking devices based on transmission of radio signals to and from satellites. Here we consider methodological developments in the study of the magnetic sense and present suggestions for increasing the reproducibility and ease of interpretation of experimental studies. We recommend that future experiments invest more effort in automating control of experiments and data capture, control of stimulation and full blinding of experiments in the rare cases where automation is impossible. We also propose new experiments to confirm whether or not animals can detect magnetic fields using the radical-pair effect together with an alternate hypothesis that may explain the dependence on light of responses by animals to magnetic field stimuli.