The geomagnetic field effects on animals: A review

The geomagnetic field (GMF) maintains the Earths long-term habitability for living organisms by preventing the radiation of solar wind and the oxygen and water ions escape. Understanding the biological effects of present, past and future changes of geomagnetic field is the main goal of biogeomagnetic research. As a nature element of Earth habitability environment, the role of geomagnetic field for all living organisms on the earth has recently attracted the attention of geophysicists and biologists. The intensity, declination and inclination of the GMF have provided reliable navigational reference information for animal orientation or migration. Many animals are able to perceive the geomagnetic field for orientation and navigation. Meanwhile, the presence of geomagnetic field is an essential environmental condition for the growth and development of living organisms on Earth. An increasing body of evidence suggests that once the GMF is weakened or deprived, it can cause a variety of negative biological responses. For example, long-term geomagnetic field shielding may lead to the emergence of abnormal embryonic development in Xenopus . Here we review the recent progresses made on the animals geomagnetic navigation and the biological effects of the geomagnetic field. Three major magnetoreception mechanisms and their corresponding evidences are discussed: (1) Electromagnetic induction, which hypothesizes the production of voltage across an electrical conductor moving through a static magnetic field, referring to elasmobranch fish (sharks, skates, and rays) in particular; (2) Magnetic-particle-based magnetoreception, which hypothesizes the intracellular biomineralized magnetic crystals act as compass needles; and (3) Radical-pair-based magnetoreception, which hypothesizes the quantum mechanics of electron spins could form the basis of a magnetic compass sense. Biological responses of animals in the weakened geomagnetic field and possible pathways to the biological effects are also discussed: Metal ions pathway, radical pair pathway and cytoskeleton pathway. The first two pathways are further extension of the animal magnetoreception mechanisms. The metal ions pathway hypothesizes a weak magnetic field causes the change of concentration/magnetic moment of metal ions in cells, which transiently activates the channel leading to cation influx and membrane depolarization. The radical pairs pathway hypothesizes the spin state of free electrons in radical pairs in cells depends on the change of the local magnetic field. For example, the changes of reactive oxygen species (ROS) in cells by hypomagnetic field exposure may induce the damage of mitochondrial membrane and apoptosis. The cytoskeleton pathway indicates the actin cytoskeleton probably as a mediator responds to the change of geomagnetic field. Although the cellular and molecular mechanisms of magnetic sense in animals still remain much unclear, the multidisciplinary collaborative approach involving geophysics, chemistry and biology will bring the exciting breakthrough times in this field.