Detection of environmental DNA from amphibians in Northern Europe applied in citizen science

Abstract

Many species of amphibians in Northern Europe are threatened and the local distributions are rarely described in detail. Application of modern molecular methods provides an important supplementary tool for monitoring the distribution and diversity of amphibians. For this purpose, we designed, tested, validated, and optimized 14 species-specific assays on genomic DNA extracted from tissue samples to use for quantitative polymerase chain reaction (qPCR) setups targeting mitochondrial DNA from amphibians in freshwater samples. The tests confirmed species specificity for all assays. Considering a systematic definition of the limit of detection for each of the assays, the presented qPCR assays are unlikely to return false positive detection from any co-occurring species in northern Europe. For field validation, the qPCR assays were applied in a large-scale nationwide citizen science project in which sampling and qPCR analysis was carried out by high school students. Data from the citizen science project returned the expected results when compared to the known regional distribution of the target species and confirmed the presence of nine out of 14 Danish species of amphibians in the collected freshwater samples. Four out of 2550 qPCR test sets carried out by the high school students required a professional reanalysis in multiple replicates due to initial unexpected results. This emphasizes that efforts from citizen science may generate large amounts of valuable data, as long as the results are carefully scrutinized by experts.