帝王蝶依靠光感磁场辨别方向

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，爱好） 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. It's 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 (CRY), 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 Earth's 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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