Current status and topical issues on the use of eDNA-based targeted detection of rare animal species

Animal detection through DNA present in environmental samples (eDNA) is a valuable tool for detecting rare species, that are difficult to observe and monitor. eDNA-based tools are underpinned by molecular evolutionary principles, key to devising tools to efficiently single out a targeted species from an environmental sample. Here, we present a comprehensive review of the use of eDNA-based methods for the detection of targeted animal species, such as rare, endangered, or invasive species, through the analysis of 549 publications (2008-2022). Aquatic ecosystems have been the most surveyed, in particular, freshwaters (74 %), and to a less extent marine (14 %) and terrestrial systems (10 %). Vertebrates, in particular, fish (38 %), and endangered species, have been the focus of most of these studies, and Cytb and COI are the most employed markers. Among invertebrates, assays have been mainly designed for Mollusca and Crustacea species (21 %), in particular, to target invasive species, and COI the most employed marker. Targeted molecular approaches, in particular qPCR, have been the most adopted (75 %), while eDNA metabarcoding has been rarely used to target single or few species (approx. 6 %). However, less attention has been given in these studies to the effects of environmental factors on the amount of shed DNA, the differential amount of shed DNA among species, or the sensitivity of the markers developed, which may impact the design of the assays, particularly to warrant the required detection level and avoid false negatives and positives. The accuracy of the assays will also depend on the availability of genetic data and vouchered tissue or DNA samples from closely related species to assess both marker and primers' specificity. In addition, eDNA-based assays developed for a particular species may have to be refined for use in a new geographic area taking into account site-specific populations, as well as any intraspecific variation.

Environmental DNA as an emerging tool in botanical research

Over the past quarter century, environmental DNA (eDNA) has been ascendant as a tool to detect, measure, and monitor biodiversity (species and communities), as a means of elucidating biological interaction networks, and as a window into understanding past patterns of biodiversity. However, only recently has the potential of eDNA been realized in the botanical world. Here we synthesize the state of eDNA applications in botanical systems with emphases on aquatic, ancient, contemporary sediment, and airborne systems, and focusing on both single-species approaches and multispecies community metabarcoding. Further, we describe how abiotic and biotic factors, taxonomic resolution, primer choice, spatiotemporal scales, and relative abundance influence the utilization and interpretation of airborne eDNA results. Lastly, we explore several areas and opportunities for further development of eDNA tools for plants, advancing our knowledge and understanding of the efficacy, utility, and cost-effectiveness, and ultimately facilitating increased adoption of eDNA analyses in botanical systems.

A molecular survey based on eDNA to assess the presence of a clown featherback (Chitala ornata) in a confined environment

BACKGROUND

The importance of the inland fisheries sector in food security as a provider of much-needed protein and income supplier has been highlighted. This is especially the case in poor rural communities in developing countries. Inland capture fisheries in Thailand are in place nationwide in rivers, lakes, swamps and reservoirs. The clown featherback (Chitala ornata) is popularly consumed and is an economically important fish in Thailand which is often used in food products such as fish balls and fish cakes. Along with other fish species, the clown featherback is one of fish of inland fisheries at Phayao Lake. Recent fish surveys from 2016-2018 at Phayao Lake using netting and electrofishing found that the number of clown featherback have been reducing since 2016 and could not be detected at all by 2018. This is despite the fact that there are still reports of their presence in the lake from locals.

METHODS

We developed an eDNA-based method for detection of the clown featherback in Phayao Lake as an alternative tool. Water samples were collected in three different sampling months (February, June and September) at six sites located in the lake. Species-specific primers and the probe were designed to amplify a 183 bp fragment of the cytB region of the clown featherback.

RESULTS

eDNA of the clown featherback can be detected in all different sampling months and sites. Concentration of the clown featherback found in Prayao Lake showed no difference over sampling month but between collecting sites. This proves that eDNA based survey is a sensitive and useful tool for monitoring and surveying the clown featherback at any time of the year.