Geomagnetic Guidance Mechanisms in Sea Turtles

海洋中的地磁引导机制海龟的远距离迁徙涉及动物界中一些最非凡的定向和导航壮举。刚孵化的海龟第一次进入海洋时，会立即建立走向公海的航线，并在游泳到看不见陆地的很长时间后坚定不移地保持这些航线。随着海龟的成熟，它们经常沿着复杂的迁徙路线穿越遥远的距离，有时跨越整个海洋盆地。年长的海龟在觅食地栖息，但会定期长途迁徙到特定的交配和筑巢地点，之后许多海龟会导航回到它们以前居住的相同觅食地点。海龟如何在看似毫无特色的广阔海洋中引导自己，一直是动物行为的一个永恒的谜团。尽管海龟和其他动物一样，在定向和导航方面利用多种线索，但越来越多的证据表明，地球磁场为海龟提供了一个重要的方向和位置信息来源，这些信息可以在不同的生活史阶段以不同的方式使用。作为刚孵化出来的海龟，海龟可能会首先使用地球的磁场作为方向信号，使它们在迁徙到海洋时保持头部。后来，在开阔的海洋中，区域磁场显然起到了导航标志的作用，在关键的地理边界处引发了游泳方向的变化，从而帮助小海龟保持在有利的海洋区域，并沿着迁徙路线前进。然而，在这个生活史阶段，海龟不会导航到特定的地理位置。相比之下，年龄较大的幼崽在沿海觅食地定居，最近的证据表明，它们获得了一张能够使它们导航到特定觅食地点的“磁性地图”。类似的导航能力可能可以解释成年海龟是如何找到筑巢海滩的。拟议的研究包括现场和实验室实验，旨在调查磁性线索在引导海龟在其生命的几个不同阶段所起的作用。这项工作有三个主要目标。首先，研究人员将进行一项关键的现场测试，以确定从佛罗里达州出生的海滩迁徙到几公里外的幼龟是否依赖磁罗盘方向来维持近海航向，这是根据广泛的实验室结果做出的假设。其次，研究人员将调查年轻的黑头海豚在跨洋迁徙过程中如何利用区域磁场作为公海航行标志。最后，将研究新发现的幼年绿海龟的磁图感觉，以期确定海龟如何利用磁场导航到用作觅食地点的沿海位置。更好地了解海龟在跨洋迁徙过程中如何引导自己，以及它们如何识别和重新定位对它们重要的特定地理位置，将有助于保护工作，使这些濒危物种免于灭绝。此外，这项工作的结果可能为与人类导航相关的可能的新方法提供见解。该项目将为一些本科生和研究生提供研究经验。

GEOMAGNETIC GUIDANCE MECHANISMS IN SEA TURTLESPI: Kenneth J. LohmannCo-PI: Catherine M. F. LohmannThe long-distance migrations of sea turtles involve some of the most extraordinary feats of orientation and navigation in the animal kingdom. Hatchling turtles entering the ocean for the first time immediately establish courses toward the open sea and steadfastly maintain them long after swimming beyond sight of land. As the turtles mature, they often follow complex migratory pathways across vast distances that sometimes span entire ocean basins. Older turtles take up residence in feeding grounds but periodically migrate long distances to particular mating and nesting sites, after which many navigate back to the same feeding sites that they inhabited previously. How sea turtles guide themselves across vast expanses of seemingly featureless ocean has remained an enduring mystery of animal behavior.Although sea turtles, like other animals, exploit multiple cues in orientation and navigation, growing evidence suggests that the Earth's magnetic field provides turtles with an important source of both directional and positional information that can be used in different ways at different life history stages. As hatchlings, turtles may first use the Earth's field as a directional cue that enables them to maintain headings as they migrate out to sea. Later, in the open ocean, regional magnetic fields apparently function as navigational markers that elicit changes in swimming direction at crucial geographic boundaries, thus helping young turtles remain within favorable oceanic regions and progress along the migratory route. Turtles at this life history stage, however, do not navigate to specific geographic locations. In contrast, older juveniles take up residence in coastal feeding grounds, and recent evidence suggests that they acquire a "magnetic map" that enables them to navigate to specific feeding sites. A similar navigational ability may explain how adult turtles locate nesting beaches.The proposed research consists of field and laboratory experiments designed to investigate the role that magnetic cues play in guiding sea turtles at several different stages of their lives. The work has three major objectives. First, the researchers will conduct a pivotal field test to determine whether hatchling turtles that have migrated a few kilometers away from their natal beaches in Florida rely on magnetic compass orientation to maintain offshore headings, as has been hypothesized on the basis of extensive laboratory results. Second, the researchers will investigate how young loggerheads exploit regional magnetic fields as open-sea navigational markers during their trans-oceanic migration. Finally, the newly discovered magnetic map sense of juvenile green turtles will be studied with a view toward determining how turtles exploit magnetic fields to navigate to coastal locations used as feeding sites. An improved understanding of how sea turtles guide themselves during transoceanic migrations, and how they recognize and relocate specific geographic locations of importance to them, will benefit conservation efforts to save these jeopardized species from extinction. In addition, the results of the work may provide insights into possible new methodologies relevant to human navigation. The project will provide research experience for a number of undergraduate and graduate students.