Fusani Leonida, Bertolucci Cristiano, Frigato Elena, Foà Augusto
Department of Life Sciences and Biotechnology, University of Ferrara, Via Luigi Borsari 46, 44121 Ferrara, Italy.
J Exp Biol. 2014 Mar 15;217(Pt 6):918-23. doi: 10.1242/jeb.096479.
Most passerine birds are nocturnal migrants. When kept in captivity during the migratory periods, these species show a migratory restlessness, or Zugunruhe. Recent studies on Sylvia warblers have shown that Zugunruhe is an excellent proxy of migratory disposition. Passerine birds can use the Earth's geomagnetic field as a compass to keep their course during their migratory flight. Among the candidate magnetoreceptive mechanisms are the cryptochromes, flavoproteins located in the retina that are supposed to perceive the magnetic field through a light-mediated process. Previous work has suggested that expression of Cryptochrome 1 (Cry1) is increased in migratory birds compared with non-migratory species. Here we tested the hypothesis that Cry1 expression depends on migratory status. Blackcaps Sylvia atricapilla were caught before fall migration and held in registration cages. When the birds were showing robust Zugunruhe, we applied a food deprivation protocol that simulates a long migratory flight. When the birds were refed after 2 days, their Zugunruhe decreased substantially, as is expected from birds that would interrupt migration for a refuelling stopover. We found that Cry1 expression was higher at night than during daytime in birds showing Zugunruhe, whereas in birds that underwent the fasting-and-refeeding protocol and reduced their levels of Zugunruhe, night Cry1 expression decreased to daytime levels. Our work shows that Cry1 expression is dependent on the presence of Zugunruhe and not on species-specific or seasonal factors, or on the birds being active versus inactive. These results support the hypothesis that cryptochromes underlie magnetoreceptive mechanisms in birds.
大多数雀形目鸟类是夜间迁徙的。在迁徙期间被圈养时，这些物种会表现出迁徙性不安，即迁徙躁动。最近对 Sylvia 莺的研究表明，迁徙躁动是迁徙倾向的一个很好的指标。雀形目鸟类可以利用地球的地磁场作为指南针，在迁徙飞行中保持路线。候选的磁感受机制包括隐花色素，它是位于视网膜中的黄素蛋白，被认为通过光介导的过程感知磁场。先前的研究表明，与非迁徙物种相比，迁徙鸟类中隐花色素 1（Cry1）的表达增加。在这里，我们测试了 Cry1 表达取决于迁徙状态的假设。在秋季迁徙前捕获黑顶林莺 Sylvia atricapilla，并将它们关在记录笼中。当鸟类表现出强烈的迁徙躁动时，我们采用了一种模拟长途迁徙飞行的食物剥夺方案。当鸟类在 2 天后重新进食时，它们的迁徙躁动大幅下降，这与因中途停留觅食而中断迁徙的鸟类预期情况相符。我们发现，表现出迁徙躁动的鸟类夜间 Cry1 表达高于白天，而在经历禁食和重新进食方案并降低迁徙躁动水平的鸟类中，夜间 Cry1 表达降至白天水平。我们的研究表明，Cry1 表达取决于迁徙躁动的存在，而不是物种特异性或季节性因素，也不是鸟类处于活跃或不活跃状态。这些结果支持了隐花色素是鸟类磁感受机制基础的假设。
