Sedimentary ancient DNA from caves: Challenges and opportunities

Caves are unique depositional environments that hold great potential for long-term preservation of DNA due to their typically cool and stable internal climates, buffered from external climate extremes. Bones from caves have long been recognised as an excellent source of ancient DNA, yet the potential for DNA preservation in cave sediments themselves has only recently begun to be explored. Here, we discuss features of caves that make them well-suited to the long-term preservation of sedimentary ancient DNA (sedaDNA), focussing specifically on sources, taphonomy and preservation of cave sedaDNA. We also highlight opportunities for future work to improve our understanding of the processes influencing long-term DNA preservation within cave sediments. These recommendations seek to improve our understanding of sedimentary ancient DNA taphonomy within caves and enhance the level of insights about the past that can be gained from it and include: (1) designation of reference sections and sample repositories; (2) routine collection of sediment, mineralogy and geochemistry data; (3) routine collection of cave climate data; (4) increased application of microstratigraphic and spatial analyses; (5) advocating use of multiple proxies when interpreting results and (6) ensuring ethical best practices are followed.