Depicting environmental gradients from Malaise trap samples: Is ethanol-based DNA metabarcoding enough?

DNA metabarcoding is revolutionising biodiversity research, as it offers researchers a holistic taxonomic approach across lineages. Many studies are dedicated to testing its application and optimising workflows. One topic of discussion is the nature of samples used for sequencing and comparing taxonomic results. However, in ecological and environmental studies, where scientists always work with subsets of species, it may be less important whether different methods provide different subsets but more important if ecological and environmental information is conserved equally. Numerous studies have successfully applied destructive and non-destructive metabarcoding approaches to evaluate patterns in biodiversity and in this respect, we aim to determine for the very first time whether environmental information is also conserved in the preservative ethanol of terrestrial arthropod bulk samples. To test this, we applied DNA metabarcoding on tissue DNA and on ethanol-based DNA of the same Malaise trap samples. The arthropod material was collected with eight traps located in three different habitats: forest, meadow, and riparian. We identified more than 3000 operational taxonomic units and demonstrate that ethanol-based DNA sequencing did not provide information on ecological gradients, except for the case of seasonal patterns, which was well conserved for some taxa. The conserved seasonality is an interesting starting point for further investigations. Until future research has provided more successful results, we recommend researchers dealing with terrestrial ecosystems to be careful when using ethanol DNA.