Lohmann K, Lohmann C
J Exp Biol. 1994 May;190(1):1-8. doi: 10.1242/jeb.190.1.1.
During their natal migration, hatchling loggerhead sea turtles (Caretta caretta L.) establish courses towards the open ocean and maintain them after swimming beyond sight of land. Laboratory experiments have demonstrated that swimming hatchlings can orient using the earth's magnetic field. For the magnetic compass to function in guiding the offshore migration, however, hatchlings must inherit or acquire a magnetic directional preference that reliably leads them towards the open sea. On land, hatchlings find the ocean using light cues associated with the seaward horizon. To determine whether turtles might acquire a preference for a specific magnetic direction on the basis of such cues, we studied the magnetic orientation of turtles initially exposed to light from either magnetic east or west. Hatchlings that had been exposed to light in the east subsequently oriented eastward when tested in darkness, whereas those that had been exposed to light in the west swam westward. Reversing the magnetic field resulted in a corresponding shift in orientation, indicating that the turtles were orienting to the ambient magnetic field. These results demonstrate that light cues can set the preferred direction of magnetic orientation by loggerhead hatchlings. We therefore hypothesize that hatchlings initially establish a seaward course using visual cues available on or near land, then maintain the course using magnetic cues as they migrate into the open sea.
在出生后的洄游过程中，蠵龟（Caretta caretta L.）幼龟会朝着开阔海洋确定路线，并在游出陆地视野范围后保持该路线。实验室实验表明，正在游动的幼龟能够利用地球磁场进行定向。然而，要使磁罗盘在引导近海洄游中发挥作用，幼龟必须遗传或获得一种可靠地引导它们前往公海的磁方向偏好。在陆地上，幼龟利用与向海地平线相关的光线线索找到海洋。为了确定海龟是否可能基于此类线索获得对特定磁方向的偏好，我们研究了最初暴露于磁东或磁西光线的海龟的磁定向。在黑暗中测试时，最初暴露于东方光线的幼龟随后向东定向，而那些最初暴露于西方光线的幼龟则向西游动。反转磁场会导致定向相应改变，这表明海龟是根据周围磁场进行定向的。这些结果表明，光线线索可以设定蠵龟幼龟磁定向的偏好方向。因此，我们假设幼龟最初利用陆地或陆地附近可用的视觉线索确定向海路线，然后在它们洄游到公海时利用磁线索保持该路线。
