The taphonomy of submerged remains: comparing the macroscopic and microscopic asset of bone tissue to DNA yield

After death, a body is continuously subjected to transformations and alterations caused by its context. Considering submerged bodies, few studies have investigated the influence of seawater on skeletal remains and the taphonomical transformations which affect bones and the genetic material it contains. In order to understand the decomposition process in a marine environment, 80 bodies of the migrant victims of the greatest shipwreck which occurred in Libya on April, 18th 2015, recovered in a period between three months and one year, were analysed focusing especially on bone preservation and DNA recovery. In order to verify a relation between morphological asset, DNA yield and environmental variables (the position in the boat, clothing, state of decomposition, time), femurs or tibiae that had been collected from each body during autopsy were submitted to anthropological and molecular analyses. Macroscopic and microscopic (Oxford Histological Index, OHI) bone appearance, as well as the amount of DNA extracted from the same bones, were evaluated and compared with time of recovery, the state of preservation of cadavers and position in the boat (outside, cargo, deck). Macroscopic and microscopic analyses showed a good preservation of bone tissue and its osteological components in the majority of the samples, as highlighted also by the high OHI score recorded, which is favourable to anthropological diagnoses such as age and pathology. In contrast, quantitation results of the extracted DNA revealed a low recovery rate of the molecule, without any relation with the position in the boat and time. Other variables investigated such as body decomposition, presence of clothes and the type of bone element selected also had no influence on molecular results and bone preservation. In conclusion, preliminary analyses performed on a sample of submerged bodies for a period between three months and one year revealed a good microscopic preservation of bone micromorphology, but a low recovery rate of the genetic material. In order to better investigate these results, further investigations will be carried out using microscopic and radiological analyses.