Human decomposition: A mosaic model for community succession and implications for future forensic research

Decomposition is a mosaic ecosystem where an intimate association between biotic factors (such as the corpse, intrinsic and extrinsic bacteria, and insects) and abiotic factors (such as weather and climate) exists. Despite the integral role of bacteria in the decomposition process, very little is understood regarding the bacterial basis of decomposition or its function in insect recruitment (or repulsion) to a corpse. Based on a recent call from the National Research Councils Committee on Identifying the Needs of the Forensic Sciences (2009), we argue that viewing the ecosystem of decomposition as a static snapshot in time will yield an inaccurate representation of the dynamic process of decomposition. To accomplish our goal of understanding decomposition as a mosaic ecosystem, we propose to conduct the first holistic investigation uniting the disparate fields of microbiology, entomology, and chemistry to better investigate the sum of the parts of the ecosystem. We will attempt to characterize the bacterial species community (microbiome) through the entire decomposition process by 1) attempting to identify bacteria significant to the decomposition process of the body, introduced by the soil, and introduced by flies, 2) attempting to collect and characterize gasses emanating from the cadaver at different times during decomposition, 3) attempting to correlate species of insects present with bacteria present by linking them through their bacterial gaseous by-products, and 4) designing specific and novel comparative and forecasting models to characterize the change in bacterial and insect succession through time, which will ultimately aid in estimation of the postmortem interval through providing a more precise method of analysis. For our experiment, we will identify bacteria, gasses produced, and insects present during the stages of decomposition by testing a set of two cadavers per season for three years. Bacterial samples will be taken from four locations on each body throughout the decomposition process and also be sampled from soil and colonizing flies. We anticipate that bacterial species guild (i.e., complexes of species in an ecosystem that exploit the same resources) change over time will modulate the rate of decomposition. Our research will link together disparate areas of biology, chemistry, and forensics allowing us to test our ultimate hypothesis: that bacterial species guild changes over time drive decomposition and fundamentally modulate the tempo and mode of decomposition. ca/ncf