Historical Collections of Tropical Marine Mammals Are an Excellent Resource for Ancient DNA.

The ability to predict ancient DNA sequencing success in natural history collections is critical to reducing the amount of destructive sampling of a finite resource. So far, studies investigating such success have predominantly focused on taxa with ranges restricted to temperate or cold environments at northern latitudes, which likely aids DNA preservation. Here, we report remarkably high aDNA sequencing success in Sirenia, herbivorous marine mammals of which the distribution is currently constrained to the global tropics. We investigate 91 samples from 85 specimens comprising all four contemporary species and one extinct species, comparing different sample types (cranial/post-cranial bone, skin and cartilage), species, collections, and material age. We obtained remarkably high (e.g., > 20%) endogenous DNA preservation for the majority (e.g., ~57% percent) of samples. Sequencing success was linked to sample type, with cranial bones (including petrous and tympanic bones) yielding significantly higher endogenous DNA. Additionally, we obtained variable, but potentially superior DNA results for preserved cartilage and hide samples that can be associated with historical bone. Although such tissue is not always present, this type of material is easy to sample, with very limited destructive impacts on the associated bones, and we therefore highlight its untapped potential as a source of DNA. Overall, our results show the high success of ancient DNA retrieval from historical collections of species with a tropical distribution, expanding on the types of specimens that are available for temporal genomic analyses.