Biology Department, Duke University, Durham, NC 27708, USA
Biology Department, University of North Carolina, Chapel Hill, NC 27599, USA.
J Exp Biol. 2020 Sep 23;223(Pt 18):jeb164921. doi: 10.1242/jeb.164921.
Diverse organisms use Earth's magnetic field as a cue in orientation and navigation. Nevertheless, eliciting magnetic orientation responses reliably, either in laboratory or natural settings, is often difficult. Many species appear to preferentially exploit non-magnetic cues if they are available, suggesting that the magnetic sense often serves as a redundant or 'backup' source of information. This raises an interesting paradox: Earth's magnetic field appears to be more pervasive and reliable than almost any other navigational cue. Why then do animals not rely almost exclusively on the geomagnetic field, while ignoring or downplaying other cues? Here, we explore a possible explanation: that the magnetic sense of animals is 'noisy', in that the magnetic signal is small relative to thermal and receptor noise. Magnetic receptors are thus unable to instantaneously acquire magnetic information that is highly precise or accurate. We speculate that extensive time-averaging and/or other higher-order neural processing of magnetic information is required, rendering the magnetic sense inefficient relative to alternative cues that can be detected faster and with less effort. This interpretation is consistent with experimental results suggesting a long time course for magnetic compass and map responses in some animals. Despite possible limitations, magnetoreception may be maintained by natural selection because the geomagnetic field is sometimes the only source of directional and/or positional information available.
不同的生物利用地球磁场作为导向和导航的线索。然而，无论是在实验室还是自然环境中，可靠地引发磁导向反应往往都很困难。如果有可用的非磁线索，许多物种似乎更倾向于利用这些线索，这表明磁感觉通常是冗余的或“备用”信息源。这就提出了一个有趣的悖论：地球磁场似乎比几乎任何其他导航线索都更加普遍和可靠。那么，为什么动物不几乎完全依赖地磁场，而忽略或淡化其他线索呢？在这里，我们探讨一种可能的解释：动物的磁感觉是“嘈杂”的，因为相对于热噪声和受体噪声，磁信号很小。因此，磁受体无法即时获取高度精确或准确的磁信息。我们推测，需要对磁信息进行广泛的时间平均和/或其他更高阶的神经处理，从而使磁感觉相对于其他可以更快、更省力地检测到的替代线索效率降低。这种解释与实验结果一致，表明在某些动物中，磁罗盘和地图反应的时间过程较长。尽管存在可能的限制，但磁受体可能是通过自然选择来维持的，因为地磁场有时是唯一可用的方向和/或位置信息源。
