Dipartimento di Biologia ed Evoluzione, Università di Ferrara, Ferrara 44121, Italy.
J Exp Biol. 2012 Sep 15;215(Pt 18):3200-6. doi: 10.1242/jeb.074419. Epub 2012 Jun 12.
The present study first examined whether ruin lizards, Podarcis sicula, are able to orientate using plane-polarized light produced by an LCD screen. Ruin lizards were trained and tested indoors, inside a hexagonal Morris water maze positioned under an LCD screen producing white polarized light with a single E-vector, which provided an axial cue. White polarized light did not include wavelengths in the UV. Lizards orientated correctly either when tested with E-vector parallel to the training axis or after 90 deg rotation of the E-vector direction, thus validating the apparatus. Further experiments examined whether there is a preferential region of the light spectrum to perceive the E-vector direction of polarized light. For this purpose, lizards reaching learning criteria under white polarized light were subdivided into four experimental groups. Each group was tested for orientation under a different spectrum of plane-polarized light (red, green, cyan and blue) with equalized photon flux density. Lizards tested under blue polarized light orientated correctly, whereas lizards tested under red polarized light were completely disoriented. Green polarized light was barely discernible by lizards, and thus insufficient for a correct functioning of their compass. When exposed to cyan polarized light, lizard orientation performances were optimal, indistinguishable from lizards detecting blue polarized light. Overall, the present results demonstrate that perception of linear polarization in the blue is necessary - and sufficient - for a proper functioning of the sky polarization compass of ruin lizards. This may be adaptively important, as detection of polarized light in the blue improves functioning of the polarization compass under cloudy skies, i.e. when the alternative celestial compass based on detection of the sun disk is rendered useless because the sun is obscured by clouds.
本研究首先考察了穴居蝾螈（Podarcis sicula）是否能够利用液晶显示屏产生的平面偏振光进行定向。穴居蝾螈在室内、一个位于液晶显示屏下方的六边形 Morris 水迷宫中接受训练和测试，该显示屏产生具有单一 E-矢量的白色偏振光，提供轴向提示。白色偏振光不包括紫外线波长。当 E-矢量与训练轴平行或 E-矢量方向旋转 90 度时，蜥蜴能够正确定向，从而验证了该设备的有效性。进一步的实验研究了蜥蜴感知偏振光 E-矢量方向的光光谱是否存在偏好区域。为此，在白色偏振光下达到学习标准的蜥蜴被分为四个实验组。每组在不同光谱的平面偏振光（红、绿、蓝和青）下进行定向测试，其光子通量密度相等。在蓝色偏振光下测试的蜥蜴能够正确定向，而在红色偏振光下测试的蜥蜴则完全迷失方向。绿色偏振光几乎无法被蜥蜴察觉，因此不足以使其罗盘正常工作。当暴露在青色偏振光下时，蜥蜴的定向表现最佳，与检测蓝色偏振光的蜥蜴无异。总体而言，本研究结果表明，对蓝线偏振的感知是穴居蝾螈天空偏振罗盘正常运作的必要条件，也是充分条件。这可能在适应上具有重要意义，因为在阴天（即基于太阳盘检测的替代天体罗盘因云层遮挡太阳而无法使用时）检测蓝线偏振光可以改善偏振罗盘的功能。
