Chemical compass model of avian magnetoreception

Approximately 50 species, including birds, mammals, reptiles, amphibians, fish, crustaceans and insects, are known to use the Earth's magnetic field for orientation and navigation. Birds in particular have been intensively studied, but the biophysical mechanisms that underlie the avian magnetic compass are still poorly understood. One proposal, based on magnetically sensitive free radical reactions, is gaining support despite the fact that no chemical reaction in vitro has been shown to respond to magnetic fields as weak as the Earth's ( approximately 50 muT) or to be sensitive to the direction of such a field. Here we use spectroscopic observation of a carotenoid-porphyrin-fullerene model system to demonstrate that the lifetime of a photochemically formed radical pair is changed by application of < or =50 microT magnetic fields, and to measure the anisotropic chemical response that is essential for its operation as a chemical compass sensor. These experiments establish the feasibility of chemical magnetoreception and give insight into the structural and dynamic design features required for optimal detection of the direction of the Earth's magnetic field.     

Clusters of iron-rich cells in the upper beak of pigeons are macrophages not magnetosensitive neurons

Understanding the molecular and cellular mechanisms that mediate magnetosensation in vertebrates is a formidable scientific problem. One hypothesis is that magnetic information is transduced into neuronal impulses by using a magnetite-based magnetoreceptor. Previous studies claim to have identified a magnetic sense system in the pigeon, common to avian species, which consists of magnetite-containing trigeminal afferents located at six specific loci in the rostral subepidermis of the beak. These studies have been widely accepted in the field and heavily relied upon by both behavioural biologists and physicists. Here we show that clusters of iron-rich cells in the rostro-medial upper beak of the pigeon Columbia livia are macrophages, not magnetosensitive neurons. Our systematic characterization of the pigeon upper beak identified iron-rich cells in the stratum laxum of the subepidermis, the basal region of the respiratory epithelium and the apex of feather follicles. Using a three-dimensional blueprint of the pigeon beak created by magnetic resonance imaging and computed tomography, we mapped the location of iron-rich cells, revealing unexpected variation in their distribution and number--an observation that is inconsistent with a role in magnetic sensation. Ultrastructure analysis of these cells, which are not unique to the beak, showed that their subcellular architecture includes ferritin-like granules, siderosomes, haemosiderin and filopodia, characteristics of iron-rich macrophages. Our conclusion that these cells are macrophages and not magnetosensitive neurons is supported by immunohistological studies showing co-localization with the antigen-presenting molecule major histocompatibility complex class II. Our work necessitates a renewed search for the true magnetite-dependent magnetoreceptor in birds.     

A physicochemical mechanism for magnetic field detection by migratory birds and homing pigeons

Migratory birds and homing pigeons can apparently obtain directional information from the Earth's magnetic field. The effect is difficult to detect, and discussion of the possible process of magnetic field detection by birds seems so far to have foundered on the simple fact that the orientational effect of the Earth's magnetic field on a single electron spin associated with a molecule of animal tissue would be of the order 10(-8) eV--almost certainly too small to be detectable biologically. Here I direct attention to a process which would overcome this basic problem, and which also seems to provide an explanation of all the main features of published data. It is a mechanism in principle only, however, and is discussed here in no more detail than is necessary to clarify the basic ideas and to provide a basis for further investigation.     

Cryptochrome mediates light-dependent magnetosensitivity in Drosophila

Although many animals use the Earth's magnetic field for orientation and navigation, the precise biophysical mechanisms underlying magnetic sensing have been elusive. One theoretical model proposes that geomagnetic fields are perceived by chemical reactions involving specialized photoreceptors. However, the specific photoreceptor involved in such magnetoreception has not been demonstrated conclusively in any animal. Here we show that the ultraviolet-A/blue-light photoreceptor cryptochrome (Cry) is necessary for light-dependent magnetosensitive responses in Drosophila melanogaster. In a binary-choice behavioural assay for magnetosensitivity, wild-type flies show significant naive and trained responses to a magnetic field under full-spectrum light ( approximately 300-700 nm) but do not respond to the field when wavelengths in the Cry-sensitive, ultraviolet-A/blue-light part of the spectrum (<420 nm) are blocked. Notably, Cry-deficient cry(0) and cry(b) flies do not show either naive or trained responses to a magnetic field under full-spectrum light. Moreover, Cry-dependent magnetosensitivity does not require a functioning circadian clock. Our work provides, to our knowledge, the first genetic evidence for a Cry-based magnetosensitive system in any animal.     

超顺磁磁铁矿磁接收器磁学模型

生物磁铁矿磁接收器理论模型包括单畴磁铁矿磁接收器模型和超顺磁磁铁矿磁接收器模型.蜜蜂体内存在典型的超顺磁磁铁矿颗粒.本文以蜜蜂为例,从磁学理论角度出发,定性的探讨了超顺磁磁铁矿磁接收器的磁学模型和工作机制.在外磁场作用下,每个超顺磁颗粒会受到力的作用,同时伴随着尺寸沿着一定方向的收缩和扩张.超顺磁颗粒把力以及扩张收缩作用传递给外面的生物膜及生物骨架(埋藏在神经系统中)从而产生相应的神经信号,而多个超顺磁颗粒磁接收系统的存在会放大和加强信号的产生.     

家鸽红细胞血型的初步研究

采用2种方法对家鸽的红细胞血型进行了初步研究．方法一：血清平板凝集试验．取家鸽的红细胞分别与家兔以及其它家鸽的血清进行混合，结果有些家鸽的红细胞与有些家兔的血清发生了凝集反应，而另一些则不发生；家鸽的不同个体之间也存在红细胞凝集现象．这表明家鸽的红细胞表面存在凝集原．方法二：异种动物免疫．将家鸽的红细胞注射到家兔体内，然后取家兔产生的免疫血清与该家鸽的红细胞混合，结果发生了凝集反应．这进一步表明家鸽的红细胞表面存在凝集原，即家鸽具有红细胞血型．     

单畴磁铁矿磁接收器磁学模型

很多生物可以利用地磁场辨别方向和方位,而生物磁铁矿被广泛发现存在于这些生物体中,研究者认为,生物磁铁矿与周围组织(包括神经组织)构成磁接收器,它在与外界磁场的相互作用中,将外界磁场信息转化成神经信息促使生物作出相应的反应;生物磁铁矿磁接收器理论包括单畴磁铁矿磁接收器模型和超顺磁磁铁矿磁接收器模型;趋磁细菌体内存在典型的单畴磁铁矿颗粒,本文中,以趋磁细菌为例,从磁学理论角度出发,定性的探讨了单畴磁铁矿磁接收器的磁学模型和工作机制:在外磁场中,外面包围着生物膜的单畴晶体会受到力的作用,单畴晶体把力转加给生物膜,再被生物膜中的机械感受器接收到,再转变为刺激信号,引起细胞相应的运动行为;或者是,磁铁矿粒子通过与生物膜的结合,把受到的力转变为打开或关闭离子通道,影响离子的流入,跨膜电势发生改变,从而产生刺激信号;多个单畴晶体及膜的存在会导致信号的增加与放大.     

鸽蛋人工孵化和仔鸽并窝的试验研究

研究了鸽蛋人工孵化和仔鸽并窝对产鸽生产性能的影响。试验结果表明:鸽蛋人工孵化可有效减少破蛋率,降低死胎率,出雏率提高12.2%(P<0.05)。同时,使产蛋周期缩短30 d,差异极显著(P<0.01);并窝3只的乳鸽体重增长与非并窝的乳鸽相似,但饲料报酬明提较高,重料比差异极显著(P<0.01);并窝4只的仔鸽饲料报酬高,但乳鸽增重较慢。说明一对亲鸽完全有可能同时哺喂3~4只仔鸽,但以每窝并至3只仔鸽较理想。     

Navigation: bat orientation using Earth's magnetic field

Bats famously orientate at night by echolocation, but this works over only a short range, and little is known about how they navigate over longer distances. Here we show that the homing behaviour of Eptesicus fuscus, known as the big brown bat, can be altered by artificially shifting the Earth's magnetic field, indicating that these bats rely on a magnetic compass to return to their home roost. This finding adds to the impressive array of sensory abilities possessed by this animal for navigation in the dark.     

Lateralization of magnetic compass orientation in a migratory bird

Lateralization of brain functions, once believed to be a human characteristic, has now been found to be widespread among vertebrates. In birds, asymmetries of visual functions are well studied, with each hemisphere being specialized for different tasks. Here we report lateralized functions of the birds' visual system associated with magnetoperception, resulting in an extreme asymmetry of sensing the direction of the magnetic field. We found that captive migrants tested in cages with the magnetic field as the only available orientation cue were well oriented in their appropriate migratory direction when using their right eye only, but failed to show a significant directional preference when using their left eye. This implies that magnetoreception for compass orientation, assumed to take place in the eyes alongside the visual processes, is strongly lateralized, with a marked dominance of the right eye/left brain hemisphere.     

蜜蜂体内的磁接收器

很多生物体内存在纳米磁铁矿颗粒,它们为体内的磁接收器奠定了生物物理基础,而磁接收器可以使这些生物能够利用磁场来辨别方位以及方向.蜜蜂腹部同样存在超顺磁磁铁矿颗粒,这些生物磁铁矿粒子尺寸的变化与铁沉积囊泡膜的相互抗拒作用以及与细胞骨架的相互作用组成一个完整的磁接收器系统,可以感觉磁场的变化并诱发神经信号的传递.     

True navigation and magnetic maps in spiny lobsters

Animals are capable of true navigation if, after displacement to a location where they have never been, they can determine their position relative to a goal without relying on familiar surroundings, cues that emanate from the destination, or information collected during the outward journey. So far, only a few animals, all vertebrates, have been shown to possess true navigation. Those few invertebrates that have been carefully studied return to target areas using path integration, landmark recognition, compass orientation and other mechanisms that cannot compensate for displacements into unfamiliar territory. Here we report, however, that the spiny lobster Panulirus argus oriented reliably towards a capture site when displaced 12-37 km to unfamiliar locations, even when deprived of all known orientation cues en route. Little is known about how lobsters and other animals determine position during true navigation. To test the hypothesis that lobsters derive positional information from the Earth's magnetic field, lobsters were exposed to fields replicating those that exist at specific locations in their environment. Lobsters tested in a field north of the capture site oriented themselves southwards, whereas those tested in a field south of the capture site oriented themselves northwards. These results imply that true navigation in spiny lobsters, and perhaps in other animals, is based on a magnetic map sense.     

无公害肉鸽饲养管理技术的研究

无公害肉鸽标准之一是生长健康,饲养过程中不使用药物添加剂及生长激素;合理使用兽药及其它化学药品,降低肉鸽制品的药物残留,保证肉的口感争品质。本文从鸽场的建造、饲养方式、饲料配制、保健沙、管理、疾病用药等方面对无公害内鸽的饲养管理技术进行了探讨。     

张九龄发明信鸽通讯考

中国何时出现信鸽通讯是学界至今未触及的问题。通过对中国野鸽、驯鸽、信鸽、传书鸽及海外舶鸽相关记载的详细考证，可以确认中国信鸽通讯是在公元702年以前由张九龄独自发明的。     

Transient aurora on Jupiter from injections of magnetospheric electrons

Energetic electrons and ions that are trapped in Earth's magnetosphere can suddenly be accelerated towards the planet. Some dynamic features of Earth's aurora (the northern and southern lights) are created by the fraction of these injected particles that travels along magnetic field lines and hits the upper atmosphere. Jupiter's aurora appears similar to Earth's in some respects; both appear as large ovals circling the poles and both show transient events. But the magnetospheres of Jupiter and Earth are so different---particularly in the way they are powered---that it is not known whether the magnetospheric drivers of Earth's aurora also cause them on Jupiter. Here we show a direct relationship between Earth-like injections of electrons in Jupiter's magnetosphere and a transient auroral feature in Jupiter's polar region. This relationship is remarkably similar to what happens at Earth, and therefore suggests that despite the large differences between planetary magnetospheres, some processes that generate aurorae are the same throughout the Solar System.     

家鸽桡神经和坐骨神经传入冲动在丘脑背外后核的会聚

在氨基甲酸乙酯麻醉的36只鸽上,记录和分析了丘脑背外后核对桡神经传入冲动发生反应的103个神经元的单位放电.神经元的诱发反应可分为六种类型.其中一部分单位还对刺激坐骨神经发生反应.不同前、后肢的同时传入可以在同一神经元上会聚并具有相互作用.丘脑背外后核的多种形式会聚可能是家鸽丘脑对四肢躯体感觉传入信息进行整合和加工的基础.     

Predation: Prey plumage adaptation against falcon attack

Several plumage types are found in feral pigeons (Columba livia), but one type imparts a clear survival advantage during attacks by the swiftest of all predators--the peregrine falcon (Falco peregrinus). Here we use quantitative field observations and experiments to demonstrate both the selective nature of the falcon's choice of prey and the effect of plumage coloration on the survival of feral pigeons. This plumage colour is an independently heritable trait that is likely to be an antipredator adaptation against high-speed attacks in open air space.     

Biological sensing of small field differences by magnetically sensitive chemical reactions

There is evidence that animals can detect small changes in the Earth's magnetic field by two distinct mechanisms, one using the mineral magnetite as the primary sensor and one using magnetically sensitive chemical reactions. Magnetite responds by physically twisting, or even reorienting the whole organism in the case of some bacteria, but the magnetic dipoles of individual molecules are too small to respond in the same way. Here we assess whether reactions whose rates are affected by the orientation of reactants in magnetic fields could form the basis of a biological compass. We use a general model, incorporating biological components and design criteria, to calculate realistic constraints for such a compass. This model compares a chemical signal produced owing to magnetic field effects with stochastic noise and with changes due to physiological temperature variation. Our analysis shows that a chemically based biological compass is feasible with its size, for any given detection limit, being dependent on the magnetic sensitivity of the rate constant of the chemical reaction.     

Solar wind dynamic pressure and electric field as the main factors controlling Saturn's aurorae

The interaction of the solar wind with Earth's magnetosphere gives rise to the bright polar aurorae and to geomagnetic storms, but the relation between the solar wind and the dynamics of the outer planets' magnetospheres is poorly understood. Jupiter's magnetospheric dynamics and aurorae are dominated by processes internal to the jovian system, whereas Saturn's magnetosphere has generally been considered to have both internal and solar-wind-driven processes. This hypothesis, however, is tentative because of limited simultaneous solar wind and magnetospheric measurements. Here we report solar wind measurements, immediately upstream of Saturn, over a one-month period. When combined with simultaneous ultraviolet imaging we find that, unlike Jupiter, Saturn's aurorae respond strongly to solar wind conditions. But in contrast to Earth, the main controlling factor appears to be solar wind dynamic pressure and electric field, with the orientation of the interplanetary magnetic field playing a much more limited role. Saturn's magnetosphere is, therefore, strongly driven by the solar wind, but the solar wind conditions that drive it differ from those that drive the Earth's magnetosphere.