Experimental Observations on the decay of Environmental DNA from Bighead and Silver Carp-Data

Interest in the field of environmental DNA (eDNA) is growing rapidly and eDNA surveys are becoming an important consideration for aquatic resource managers dealing with invasive species. However, in order for eDNA monitoring to mature as a research and management tool, there are several critical knowledge gaps that must be filled. One such gap is the fate of eDNA materials in the aquatic environment. Understanding the environmental factors that influence the decay of eDNA and how these factors impact detection probabilities over time and space could have significant implications for eDNA survey design and data interpretation. Here we experimentally explore eDNA decay in waste materials and reproductive cells obtained from captive stocks of the invasive bigheaded carps, Hypophthalmichthys nobilis and H. molitrix, as well as the influence of differing levels of water turbulence, temperature, microbial load, and pH on rates of eDNA decay. We found that the decay patterns of eDNA associated with both H. nobilis biological waste and H. molitrix milt significantly fit monophasic exponential decay curves. Secondly, we observed that the highest temperature we tested resulted in decay half-life as much as 5.5X more rapid than the lowest temperature we tested. When we suppressed microbial loads in eDNA samples, we observed that overall losses of eDNA were reduced by about 2.5X. When we amended eDNA samples with pond water the half-life of eDNA was reduced by about 2.25X, despite relatively little apparent increase in the overall microbial load, indicating the microbial sources, not only loads, might play a critical role in eDNA degradation. A shift in pH from 6.5 to 8.0 in the samples resulted in a 1.6X reduction in eDNA half-life. Water turbulence in our study had no apparent effect on eDNA decay. When we combined different temperature, pH, and microbial load treatments to create a rapid decay conditions and a slow decay conditions, and tracked eDNA decay over 91 days, we observed a 5.0X greater loss of eDNA by Day 5 under rapid decay conditions than under slow decay conditions. At the end of the trials, the differences in eDNA loss between the rapid decay and baseline and slow decay conditions were 0.1X and 3.3X, respectively. Our results strongly demonstrate the potential for environmental factors to influence eDNA fate, and thus the interpretation of eDNA survey results.

环境DNA（environmental DNA，简称eDNA）领域的研究热度与日俱增，针对入侵物种开展水生资源管理的从业者，也愈发重视eDNA调查工作。然而，若要让eDNA监测发展为成熟的科研与管理工具，仍有若干关键认知空白亟待填补。其中一项空白便是eDNA物质在水生环境中的归趋。解析影响eDNA降解的环境因子，以及这些因子如何随时间与空间变化影响检测成功率，对eDNA调查方案设计与数据解读均具有重要意义。本研究通过实验手段，探究了入侵性大头鲤（Hypophthalmichthys nobilis与H. molitrix）人工繁育种群的排泄物及生殖细胞中的eDNA降解情况，同时分析了不同水平的水流扰动、温度、微生物负载与pH值对eDNA降解速率的影响。研究发现，鳙排泄物与鲢精液中的eDNA降解模式均显著符合单指数衰减曲线。其次，本研究观测到，实验设置的最高温度组中，eDNA降解半衰期较最低温度组快达5.5倍。当我们抑制eDNA样本中的微生物负载时，eDNA的总降解量降低了约2.5倍。当我们向eDNA样本中添加池塘水后，尽管样本整体微生物负载仅出现小幅上升，但eDNA半衰期缩短了约2.25倍，这表明微生物来源而非仅微生物负载量，可能在eDNA降解中发挥关键作用。将样本pH值从6.5调整至8.0，可使eDNA半衰期缩短1.6倍。本研究中，水流扰动对eDNA降解未表现出显著影响。当我们通过组合不同温度、pH值与微生物负载处理，分别构建快速降解与慢速降解环境，并对eDNA降解过程进行长达91天的跟踪观测后发现，在第5天时，快速降解组的eDNA损失量较慢速降解组高出5.0倍。实验结束时，快速降解组、基线组与慢速降解组的eDNA损失量差异分别为0.1倍与3.3倍。本研究结果充分证实，环境因子可显著影响eDNA的归趋，进而对eDNA调查结果的解读产生重要作用。