Shedding light on eDNA: neither natural levels of UV radiation nor the presence of a filter feeder affect eDNA-based detection of aquatic organisms

AbstractThe use of environmental DNA (eDNA) as a species detection tool is attracting attention from both scientific and applied fields, especially for detecting invasive or rare species. In order to use eDNA as an efficient and reliable tool, however, we need to understand its origin and state as well as factors affecting its degradation. Various biotic and abiotic environmental factors have been proposed to affect degradation of eDNA in aquatic environments and thus to influence detection rates of species. Here, we were interested in two of them, namely UV light, which can break down DNA, and the presence of filter feeders, which can remove DNA and DNA-bound particles. A few, mostly laboratory-based studies have found minor effects of UVB on the degradation of eDNA. Ultraviolet A radiation (UVA), however, has been neglected although it also causes DNA lesions and is 10- to 100-fold more prevalent than UVB when reaching the earth’s surface. Filter feeders are common in aquatic ecosystem, but their effects on eDNA has hitherto been ignored. We conducted a full-factorial aquatic mesocosm experiment under near-natural outdoor conditions manipulating UV radiation as well as the presence of Dreissena polymorpha, a strong filter feeder capable of filtering cells or organelles containing DNA. Surprisingly, we found that neither UV radiation nor the presence of the filter feeder affected eDNA-based detection rates of macroinvertebrates, even though the experiment took place in summer when UV radiation intensity and filtration activity is high for the chosen experimental site and conditions. These results, in combination with studies from marine or laboratory settings finding no effect of sunlight and its UV components on the detectability of eDNA, suggest that eDNA based species assessments could be relatively robust with respect to our two factors studied.

摘要 环境DNA（environmental DNA, eDNA）作为物种检测工具，正获得科研与应用领域的广泛关注，尤其适用于入侵或稀有物种的检测。然而，若要将eDNA开发为高效可靠的检测工具，亟需明晰其来源、存在状态以及影响其降解的各类因素。目前已有诸多生物与非生物环境因子被提出，可通过调控水生环境中eDNA的降解过程，进而干扰物种的检测成功率。本研究聚焦其中两类关键因子：一是可引发DNA链断裂的紫外线辐射，二是可清除DNA及结合DNA颗粒的滤食性动物（filter feeders）。既往相关研究多基于实验室环境，仅少数研究发现中波紫外线（UVB）对eDNA降解的影响较为微弱。而长波紫外线（UVA）尽管同样可造成DNA损伤，且到达地表后的辐射强度为UVB的10至100倍，却长期被学界忽视。滤食性动物在水生生态系统中分布广泛，但迄今为止其对eDNA的影响尚未得到关注。本研究在近乎自然的室外环境中开展了全因子设计的水生中型实验生态系统（mesocosm）实验，设置紫外线辐射与斑马贻贝（Dreissena polymorpha）的存在与否作为操控变量；该物种为强效滤食生物，可滤除携带DNA的细胞或细胞器。令人意外的是，尽管本实验于夏季开展，所选实验场地与环境条件下的紫外线辐射强度及滤食生物的滤食活性均处于较高水平，但我们并未发现紫外线辐射或滤食生物的存在对大型无脊椎动物的eDNA检测成功率产生任何影响。结合海洋环境或实验室环境下相关研究未发现日光及其紫外线组分对eDNA检测率的影响，本研究结果表明，基于eDNA的物种评估方法，针对本次研究的两类影响因子而言，具备相对较强的鲁棒性。