Archaeoentomological SedaDNA from two French gallo-roman wells reveals the presence of arthropods not identified by sclerotized remains

Archaeoentomology reconstructs past environments and human activities through the analysis of insect remains preserved in archaeological deposits. Although different arthropod groups can be identified when preservation conditions allow, taxonomic resolution often depends on the preservation of diagnostic sclerotized structures, which limits the detection of poorly preserved or very small taxa. Here, we evaluate whether ancient sedimentary DNA (sedaDNA) can complement conventional morphological identifications and provide comparable and reproducible information from the same archaeological samples. We analyzed sediments from two water-saturated Gallo-Roman wells in France using a metabarcoding approach and directly compared the molecular results with morphological identifications made on the corresponding layers. Several groups detected by sedaDNA were absent from the morphological assemblages, despite being ecologically plausible in the studied contexts. Conversely, some beetle taxa, despite being well represented morphologically, were not detected in the DNA data. SedaDNA and morphological data revealed different communities for the two wells. One well exhibited low taxonomic and phylogenetic diversity and was largely dominated by bird mites, generalist decomposers, and other weakly sclerotized arthropods, while the other well had greater overall diversity and was dominated by insects associated with an open environment, likely consisting of arable land. Despite these differences in taxonomic composition, these results highlight the role of local environmental conditions and human practices in shaping distinct arthropod communities at the two archaeological sites. By integrating molecular and morphological data, this comparison demonstrates that sedaDNA does not replace the fossil record but expands the detectable fraction of the arthropod community.