Data from: The choice of universal primers and the characteristics of the species mixture determines when DNA metabarcoding can be quantitative.

DNA metabarcoding is a technique used to survey biodiversity in many ecological settings, but there are doubts about whether it can provide quantitative results, i.e. the proportions of each species in the mixture as opposed to a species list. While there are several experimental studies that report quantitative metabarcoding results, there are a similar number that fail to do so. Here we provide the rationale to understand under what circumstances the technique can be quantitative. Basically, we simulate a mixture of DNA of S species with a defined initial abundance distribution. In the simulated PCR, each species increases its concentration following a certain amplification efficiency. The final DNA concentration will reflect the initial one when the efficiency is similar for all species; otherwise, the initial and final DNA concentrations would be poorly related. Although there are many known factors that modulate amplification efficiency, we focused on the number of primer-template mismatches, arguably the most important one. We used 15 common primers pairs targeting the mitochondrial COI region and the mitogenomes of ca. 1200 insect species. The results showed that some primers pairs produced quantitative results under most circumstances, whereas some other primers failed to do so. Many species, and a high diversity within the mixture, helped the metabarcoding to be quantitative. In conclusion, depending on the primer pair used in the PCR amplification and on the characteristics of the mixture analysed (i.e., high species richness, low evenness), DNA metabarcoding can provide a quantitative estimate of the relative abundances of different species.DNA宏条形码（DNA metabarcoding）是一种可在诸多生态场景中用于调查生物多样性的技术，但学界对其能否提供定量结果——即能否获取混合样本中各物种的占比而非仅物种名录——尚存疑虑。尽管已有多项实验研究报道了定量的宏条形码结果，但同样有数量相当的研究未能实现这一目标。本文旨在阐明该技术可实现定量结果的适用情境。 本研究首先模拟了包含S个物种的DNA混合样本，其初始丰度分布已明确设定。在模拟的聚合酶链式反应（Polymerase Chain Reaction, PCR）过程中，各物种的DNA浓度会随特定的扩增效率增长。若所有物种的扩增效率趋于一致，则最终DNA浓度可准确反映初始丰度；反之，初始与最终DNA浓度之间将无显著相关性。尽管已知有诸多因素可调控扩增效率，但本研究聚焦于引物-模板错配数量，这通常被认为是最为关键的影响因素。我们使用了15对靶向线粒体细胞色素C氧化酶亚基I（COI）区域的通用引物，以及约1200种昆虫的线粒体基因组（mitogenome）数据。 结果显示，部分引物对在多数情境下可产出定量结果，而另有部分引物对则无法实现这一点。混合样本中包含的物种数量越多、群落多样性越高，越有助于宏条形码技术实现定量分析。综上，根据聚合酶链式反应所用的引物对以及所分析混合样本的特征（即高物种丰富度、低均匀度），DNA宏条形码技术可对不同物种的相对丰度作出定量估算。