Viljanen Martta L M, Nevala Noora E, Calais-Granö Cecilia L, Lindström K Magnus W, Donner Kristian
Department of Biosciences, University of Helsinki, 00014 Helsinki, Finland
Department of Biosciences, University of Helsinki, 00014 Helsinki, Finland.
J Exp Biol. 2017 Aug 1;220(Pt 15):2798-2808. doi: 10.1242/jeb.155101. Epub 2017 May 17.
The eyes of two glacial-relict populations of opossum shrimp inhabiting the different photic environments of a deep, dark-brown freshwater lake and a variably lit bay of the Baltic Sea differ in their susceptibility to functional depression from strong light exposures. The lake population is much more vulnerable than the sea population. We hypothesized that the difference reflects physiological adaptation mechanisms operating on long time scales rather than genetically fixed differences between the populations. To test this, we studied how acclimation to ultra-slowly increased illumination (on time scales of several weeks to months) affected the resilience of the eyes to bright-light exposures. Light responses of whole eyes were measured by electroretinography, the visual-pigment content of single rhabdoms by microspectrophotometry and the structural integrity of photoreceptor cells by electron microscopy (EM). Slow acclimation mitigated and even abolished the depression of photoresponsiveness caused by strong light exposures, making a dramatic difference especially in the lake animals. Still, acclimation in the sea animals was faster and the EM studies suggested intrinsic differences in the dynamics of microvillar membrane cycling. In conclusion, we report a novel form of physiological adaptation to general light levels, effective on the time scale of seasonal changes. It explains part but not all of the differences in light tolerance between the lake and sea populations.
两种负鼠虾的冰川遗迹种群，分别栖息于一个深棕色淡水湖的不同光照环境以及波罗的海一个光照变化的海湾中，它们的眼睛对强光照射导致的功能衰退的易感性有所不同。湖泊种群比海洋种群更易受影响。我们推测，这种差异反映了在长时间尺度上起作用的生理适应机制，而非种群之间的基因固定差异。为了验证这一点，我们研究了对超缓慢增加的光照（在数周至数月的时间尺度上）的适应如何影响眼睛对强光照射的恢复能力。通过视网膜电图测量整个眼睛的光反应，用显微分光光度法测量单个视杆的视觉色素含量，并用电子显微镜（EM）观察光感受器细胞的结构完整性。缓慢适应减轻甚至消除了强光照射引起的光反应抑制，这在湖泊动物中表现得尤为明显。不过，海洋动物的适应速度更快，并且电子显微镜研究表明微绒毛膜循环动力学存在内在差异。总之，我们报告了一种对一般光照水平的新型生理适应形式，在季节变化的时间尺度上有效。它解释了湖泊和海洋种群之间部分而非全部的耐光性差异。
