Cold Case Experiment Demonstrates the Potential Utility of Aquatic Microbial Community Assembly in Estimating a Postmortem Submersion Interval.

Microbial community assembly (MCA) of both human and nonhuman animal carcasses provides indicators useful for estimating the postmortem interval (PMI) in terrestrial settings. However, there are fewer studies estimating postmortem submersion intervals (PMSIs) in aquatic habitats. No aquatic studies to date assessed MCA in the context of a death investigation, with all previous studies focusing on important basic ecological questions. Within the context of a cold case investigation, we performed an experiment using replicate adult swine carcasses to describe postmortem MCA variability within a nonflowing aquatic habitat. Using high-throughput sequencing of carcass postmortem microbiomes, we described MCA variability and identified key taxa associated with decomposition in an aquatic habitat similar to the cold case body recovery site. We also modeled key taxa for estimating PMSIs, modeling within ±3 days (mean square error) postmortem using random forest regression. Our findings show significant changes in microbial communities as decomposition progressed, and several taxa were identified as important indicator taxa which may be useful for future estimates of PMSI. While descriptive, this study provides initial findings quantifying MCA variability within a nonflowing aquatic habitat. Within the context of the cold case investigation, we discuss how postmortem microbial samples collected at the time of body recovery could have been an important piece of evidence for understanding the PMSI of recovered remains. Additional experimental studies are needed to explicitly test and identify mechanisms associated with postmortem MCA variability in other habitats and under different temperature (e.g., seasons) conditions.

Adult Blow Fly (Diptera: Calliphoridae) Community Structure Across Urban-Rural Landscapes in Michigan, United States.

Necrophagous insects play an important role in the decomposition of vertebrate carrion. The documented colonization, development, and succession of blow flies (Diptera: Calliphoridae) and other arthropods on decomposing carcasses make their communities relevant for use in decomposition ecology and forensic investigations. This relevance relies on the local pool of species available to colonize a carcass, but such community level survey data are not always available. The objective of this research was to conduct a baseline survey of adult Calliphoridae communities from urban-rural land use types in the Great Lakes region. To test how adult blow fly distribution varies with changing landscape in Mid-Michigan, sampling with baited jars and hanging traps was implemented over the summer months of June, July, and August 2017. To determine how blow fly communities differed in urban to rural land cover, seven cities were selected with site locations ranging from high intensity developed areas to cultivated crop fields. Over 97,000 individual flies were captured represented by 11 Calliphoridae species. The adult Calliphoridae communities were primarily structured by land use type and month of collection, with these two factors interacting, suggesting that the effect of location varied by time of year. The two most abundant species, Phormia regina (Meigen) and Lucilia sericata (Meigen), cumulatively comprised 88.5% adult flies from Mid-Michigan. These findings provide a baseline database of Great Lakes Calliphoridae, with potential use in forensic research and casework.