Rate of DNA Degradation in Pygmy Killer Whales for the Estimation of Post-Mortem Interval

Abstract

Marine mammals are vital to the health of ocean ecosystems. To better protect these animals, it is important to understand the threats they face. The University of Hawai‘i Health and Stranding Lab (HSL) maintains an archive of tissues from stranded cetaceans (whales, dolphins, and porpoises) in the North Pacific and conducts research examining health related metrics of these animals. For much of this research, having an estimation of the post-mortem interval (PMI), or the time between death of an animal and the recovery of its carcass, can be useful for identifying the cause of death. However, there is currently no quantative method to determine the PMI in marine mammals. Current methods require observational and qualitative measures to estimate the PMI. Forensic research has utilized the degradation of DNA post-mortem to establish a quantitative tool for estimating PMI. Measuring DNA concentration over time, thereby evaluating DNA degration rate, could be used to develop a model for estimation of the PMI. Archived tissues from pygmy killer whales that were euthanized in a mass stranding event were selected to represent freshly dead animals for this study. From each cetacean, seven tissue types were left to degrade in both a replicated land and water stranding. Tissues were sampled over a period of 28-days and DNA concentrations were measured. The DNA concentrations were evaluated against two intervals of degradation time. The most significant relationships were seen in liver and lung tissues (R2 =0.877 and 0.81) in the shorter time interval indicating they would be most useful in future estimations of PMI in animals.