Ciliates in shallow alpine lakes are exposed to high levels of incident solar ultraviolet radiation (UVR). We observed the presence of specific sunscreen compounds, the mycosporine-like amino acids (MAAs), in several populations of Bursaridium, a relatively large ciliate species found in such lakes. The populations from 3 highly UV transparent lakes revealed the presence of 7 MAAs (MG, SH, PR, PI, AS, US, and PE) in total concentrations of 3.6–52.4 10⁻⁵ μg μg⁻¹ dry weight (DW) per individual, whereas in one glacially turbid and less UV transparent lake, no MAAs were detected in the Bursaridium population. The MAAs in the ciliates generally reflected the composition and relative amounts of the lakes’ seston MAAs, assuming that the ciliates fed on MAA-rich plankton. We experimentally found that naturally acquired MAAs prevented ciliate mortality under simulated UVR and photosynthetically active radiation (PAR) conditions. We further tested the dietary regulation of the MAAs-content in the ciliates under artificial UVR and PAR exposure and found an increase in MAAs concentrations in all treatments. Our assumption was that several stress factors other than irradiation were involved in the synthesis or up-regulation of MAAs.

浅高山湖泊的纤毛虫暴露于高水平的入射太阳紫外线辐射（UVR）中。我们观察到特定防晒化合物的存在下，菌胞素样氨基酸（马斯），在几个群体Bursaridium，相对大的纤毛虫物种在这种湖泊找到。从3个高度的UV透明湖泊种群揭示7马斯（MG，SH，PR，PI，AS，美国，和PE）中总浓度3.6-52.4 10的存在^-5微克微克^-1每干重（DW）个体，而在一个冰川混浊和更少的UV透明色淀，不进行马斯在检测到的Bursaridium人口。假定纤毛虫以富含MAA的浮游生物为食，纤毛虫的MAA通常反映了湖泊的湖泊MAA的组成和相对含量。我们通过实验发现，自然获得的MAA可以在模拟的UVR和光合有效辐射（PAR）条件下防止纤毛虫死亡。我们进一步测试了在人工UVR和PAR暴露下纤毛虫中MAAs含量的饮食调节，发现所有处理中MAAs浓度均增加。我们的假设是MAA的合成或上调涉及辐射以外的几种应激因素。