Bernáth Balázs, Gál József, Horváth Gábor
Department of Biological Physics, Eötvös University, H-1117 Budapest, Pázmány sétány 1, Hungary.
J Exp Biol. 2004 Feb;207(Pt 5):755-65. doi: 10.1242/jeb.00810.
Using 180 degrees field-of-view imaging polarimetry, we measured the reflection-polarization patterns of two artificial surfaces (water-dummies) in the red, green and blue spectral ranges under clear and partly cloudy skies at different solar elevations. The dummies consisted of a horizontal glass pane with a matt black or matt light grey cloth underneath, imitating a dark or bright water body, respectively. Assuming that polarotactic water insects interpret a surface as representing water if the degree of linear polarization of reflected light is higher than a threshold and the deviation of the direction of polarization from the horizontal is lower than a threshold, we calculated the proportion, P, of the artificial surfaces detected polarotactically as water. We found that at sunrise and sunset P is maximal for both water-dummies and their reflection-polarizational characteristics are most similar. From this, we conclude that polarotactic water detection is easiest at low solar elevations, because the risk that a polarotactic insect will be unable to recognize the surface of a dark or bright water body is minimal. This partly explains why many aquatic insect species usually fly en masse at dusk. The daily change in the reflection-polarization pattern of water surfaces is an important visual ecological factor that may contribute to the preference of the twilight period for habitat searching by polarotactic water insects. Air temperature at sunrise is generally low, so dusk is the optimal period for polarotactic aquatic insects to seek new habitats.
利用180度视野成像偏振测量法，我们在不同太阳高度的晴朗和部分多云天空条件下，测量了两种人造表面（水模型）在红、绿、蓝光谱范围内的反射偏振模式。这些模型由一块水平玻璃板组成，玻璃板下方分别铺有哑光黑色或哑光浅灰色布料，分别模拟黑暗或明亮的水体。假设趋偏振水昆虫在反射光的线性偏振度高于阈值且偏振方向与水平方向的偏差低于阈值时，会将一个表面视为水体，我们计算了被趋偏振检测为水体的人造表面的比例P。我们发现，在日出和日落时，两种水模型的P值最大，且它们的反射偏振特性最为相似。由此，我们得出结论，在低太阳高度下，趋偏振水检测最为容易，因为趋偏振昆虫无法识别黑暗或明亮水体表面的风险最小。这部分解释了为什么许多水生昆虫物种通常在黄昏时成群飞行。水面反射偏振模式的每日变化是一个重要的视觉生态因素，可能导致趋偏振水昆虫在黄昏时期更倾向于寻找栖息地。日出时的气温通常较低，所以黄昏是趋偏振水生昆虫寻找新栖息地的最佳时期。
