Metabarcoding of sample preservative versus morphometric identification of macroinvertebrates to assess stream impacts from forest harvesting

Aquatic macroinvertebrate communities are often used to assess the ecological integrity of streams. However, conventional methods to assess macroinvertebrate communities are usually costly and time-consuming. Here we compare stream macroinvertebrate community metrics based on conventional morphometrics vs. non-destructive DNA metabarcoding from storage ethanol to assess forest management impacts on headwater streams in an intensively managed forest watershed in eastern Canada. The two approaches demonstrated substantial congruence in the detection of taxa (81% and 69% at the family and genus level, respectively) and in the characterization of community composition and richness. However, DNA metabarcoding from preservative ethanol identified significantly less genera (3.3 on average) and families (2.0) than conventional morphometrics. Taxa missed by metabarcoding from ethanol were typically low in proportional mass or poorly represented in the CO1 reference database. This led to some differences in the explanatory variables identified as being related to macroinvertebrate metrics, which could have implications on conclusions and management actions that might result therefrom. For example, the negative relationships between reach variables associated with forest management intensity and richness identified based on morphometrics were weaker based on metabarcoding. Discriminatory power was greater when data at the genus level were used. The congruence between functional feeding group results derived from morphometric (based on relative abundance) vs. metabarcoding (based on relative frequency and read abundance) identifications was group specific (r = 0.16-0.63), but low overall. We conclude that DNA metabarcoding of storage ethanol provides a promising approach for generating biomonitoring data, but that its full deployment in biomonitoring projects requires developing more complete reference libraries and enhancing the sensitivity for detecting taxa with low sample biomass.水生大型无脊椎动物群落（aquatic macroinvertebrate communities）常被用于评估溪流的生态完整性。然而，传统的大型无脊椎动物群落评估方法往往成本高昂且耗时漫长。本研究针对加拿大东部一处集约经营森林流域内的源头溪流，对比了基于传统形态计量学与基于保存乙醇的非破坏性DNA宏条形码（DNA metabarcoding）的溪流大型无脊椎动物群落指标，以此评估森林经营活动对源头溪流的影响。两种方法在类群检出（科级与属级水平分别为81%与69%）以及群落组成与丰富度表征上均表现出较高的一致性。然而，基于保存乙醇的DNA宏条形码检测到的属（平均3.3个）与科（平均2.0个）的数量均显著少于传统形态计量学方法。未被DNA宏条形码检出的类群通常生物量占比较低，或在CO1参考数据库（CO1 reference database）中代表性不足。这导致被识别为与大型无脊椎动物群落指标相关的解释变量存在一定差异，进而可能影响由此得出的研究结论与后续管理措施。例如，基于形态计量学识别出的、与森林经营强度相关的河段变量与群落丰富度之间的负相关关系，在DNA宏条形码分析中表现得更弱。使用属级数据时的判别能力更强。基于形态计量学（基于相对多度）与DNA宏条形码（基于相对频率与读段丰度）得到的功能摄食类群结果的一致性因类群而异（r=0.16~0.63），但整体偏低。本研究认为，基于保存乙醇的DNA宏条形码技术为生成生物监测数据提供了极具潜力的途径，但其在生物监测项目中的全面应用仍需构建更为完整的参考数据库，并提升对低生物量样本类群的检测灵敏度。