Trade‐offs between reducing complex terminology and producing accurate interpretations from environmental DNA: Comment on “Environmental DNA: What's behind the term?” by Pawlowski et al., (2020)

Abstract

In a recent paper, "Environmental DNA: What's behind the term? Clarifying the terminology and recommendations for its future use in biomonitoring," Pawlowski et al. argue that the term eDNA should be used to refer to the pool of DNA isolated from environmental samples, as opposed to only extra-organismal DNA from macro-organisms. We agree with this view. However, we are concerned that their proposed two-level terminology specifying sampling environment and targeted taxa is overly simplistic and might hinder rather than improve clear communication about environmental DNA and its use in biomonitoring. This terminology is based on categories that are often difficult to assign and uninformative, and it overlooks a fundamental distinction within eDNA: the type of DNA (organismal or extra-organismal) from which ecological interpretations are derived.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Environmental versus extra‐organismal DNA

“…We are very pleased that our opinion paper "Environmental DNA: What's behind the term?" (Pawlowski et al, 2020) stimulated a lively discussion and we are grateful for the comments on proposed terminology (Rodriguez-Ezpeleta et al, 2021). The clarity of scientific terms is essential for both fundamental and applied research and any debate on this issue is very important, especially in the early days of a new field.…”

“…We think that targeting extra-organismal DNA corresponds to such complementary information and this information can be included in the description of the study. As correctly emphasized by Rodriguez-Ezpeleta et al (2021), the ecological interpretation of extraorganismal DNA data must consider many factors specific to this type of DNA. Nevertheless, in practice such a distinction at best concerns only those organisms over a certain size.…”

“…Nevertheless, in practice such a distinction at best concerns only those organisms over a certain size. As shown in figure 1 of Rodriguez-Ezpeleta et al (2021), there is overlap over at least six orders of magnitude in size between intra-and extra-organismal DNA, and even they conclude that "it is currently impractical to separate and independently analyse organismal and extra-organismal DNA. "…”

Plant-animal interactions in the era of environmental DNA (eDNA) – a review

“…In effect, practitioners may sample different sources of eDNA (cellular, extracellular, extra-organismal, etc.) (Stewart, 2019;Rodriguez-Ezpeleta et al, 2021), which may lead to different PAI interpretations. For example, pollen and spores (extra organismal DNA) are more or less ubiquitous in the atmosphere, travel long distances (through wind or water), and contain adaptations to remain in dormant stages for long periods of time.…”

“…Given the need for conservation-friendly sampling without harming any organism (including nontarget taxa), collecting eDNA samples from soil, water, air, and even from the surface of an organism offers a completely non-invasive method (Valentin et al, 2020), preventing the scarification or sacrifice of organisms. These non-invasive eDNA samples have cetainly advanced our ability to accurately detect the presence/absence of species Rodriguez-Ezpeleta et al, 2021), and are highly cost and time efficient (Qu & Stewart 2019). Indeed, they have even outperformed conventional methods of biodiversity sampling in several comparisons (McElroy et al 2020;Fediajevaite et al 2021).…”