Each fall millions of monarch1 butterflies use a sophisticated navigation system to transverse（横断） 2,000 miles from breeding sites across the eastern United States to an overwintering habitat in specific groves2 of fir trees in central Mexico. Scientists at UMass Medical School and Worcester Polytechnic3 Institute have identified a new component4 of this complex system. They reported in Nature Communications that monarchs5 use a light-dependent inclination6（倾向，喜好） magnetic compass to help them orient southward during migration7. Taken as a whole, our study reveals another fascinating aspect of the monarch butterfly migratory8 behavior, said senior study author Steven Reppert, MD, the Higgins Family Professor of Neuroscience and distinguished9 professor of neurobiology at UMMS. Greater knowledge of the mechanisms10 underlying11 the fall migration may well aid in its preservation12, currently threatened by climate change and by the continuing loss of milkweed and overwintering habitats. A new vulnerability to now consider is the potential disruption of the magnetic compass in the monarchs by human-induced electromagnetic noise, which can also affect geomagnetic orientation13 in migratory birds.Co-author Robert Gegear, PhD, assistant professor of biology and biotechnology at WPI, explained, Our study shows that monarchs use a sophisticated magnetic inclination compass system for navigation similar to that used by much larger-brained migratory vertebrates such as birds and sea turtles.Monarchs use a time-compensated sun compass in their antenna14 to help them make their 2,000 mile migratory journey to overwintering sites. During the absence of daylight cues, such as under dense15 cloud cover, migrants have been, surprisingly, seen flying in the expected southerly direction. Its been hypothesized that monarchs use geomagnetic cues to help navigate16 when day light cues are unavailable to them during migration.Previous attempts by scientists to isolate17 use of an internal inclination compass in monarchs have yielded conflicting or unconvincing results. These studies, however, may not have accounted for the possibility that the magnetic compass was influenced by ultraviolet light that can penetrate18 cloud cover.Given the ability of monarch cryptochromes , a class of proteins that are sensitive to ultraviolet A/blue light, to restore a light-dependent magnetic response in CRY-deficient Drosophila, Reppert and colleagues suspected that monarchs also possessed19 a light-dependent magnetic compass.Using flight simulators equipped with artificial magnetic fields, Patrick Guerra, PhD, a postdoctoral fellow in the Reppert lab, examined monarch flight behavior under diffuse20 white light conditions. He found that tethered monarchs in the simulators oriented themselves in a southerly direction. Further tests in the simulator revealed that the butterflies used the inclination angle of Earths magnetic field to guide their movement. Reversing the direction of the inclination caused the monarchs to orient in the opposite direction, to the north instead of the south.
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1 monarch n.帝王，君主，最高统治者 参考例句： The monarchs role is purely ceremonial.君主纯粹是个礼仪职位。 I think myself happier now than the greatest monarch upon earth.我感觉这时比世界上什么帝王都快乐。
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