Mollusc shells as metagenomic archives: The true treasure is the chest itself.

Mollusc shells, beyond the treasure of information inherently conveyed through their morphology and chemical composition also have the capacity to preserve DNA sequences over the long term in their inner structure. This has been clearly demonstrated for the first time in the study published in this issue of Molecular Ecology Resources by Der Sarkissian et al. (). With a methodology specifically dedicated to ancient DNA and solid matrices, the authors were able to successfully extract and amplify DNA from marine shells spanning the last 7,000 years. Furthermore, using metagenomic analyses, they could identify important factors affecting DNA recovery. Using reference genomes and sequences in a targeted approach to assign high-throughput sequencing reads, the authors revealed both the presence of endogenous mollusc DNA and a potent pathogen of Manilla clam. Collectively, the results presented in this study open extremely promising research avenues, from palaeogenomics and evolutionary biology to ecological genomics at population and community levels, as well as the opportunity to fine-tune diagnostic tools for conservation and aquaculture purposes. Last but not least, this study also offers exciting perspectives in epigenomics and the evolution of regulatory processes in the context of adaptation to global change. It can be easily expected that the approach developed by Der Sarkissian et al. () will be pursued and extensively investigated in the near future by the scientific community interested in these issues.