Date of this Version
Dead bodies placed on soil represent unique challenges for investigators. Although processes in soils can be used to estimate postmortem interval, we know very little about how carcasses and insects affect gravesoil microbial communities.
To address this, the current project was composed of two experiments. Experiment one was conducted to investigate the effect of surface type on carcass decomposition and evaluate soil ecology methods. Experiment two was conducted to investigate the presence of an insect population (Lucilia sericata Meigen) on gravesoil microbial communities. Both experiments were conducted in a laboratory setting using freshly killed mouse carcasses. Mouse carcasses were placed on either a plastic petri dish without soil or on a sand/soil mix (90/10 or 50/50) and calibrated to 55% water holding capacity. Carcass decomposition was measured as mass loss and total body score. Gravesoil microbial communities were analyzed as lipid-phosphorous and fatty acid methyl esters. Carcass decomposition was measured over 35 days at 20˚C (experiment 1) and 22˚C (experiment 2).
Major findings were that surface type affects the rate of carcass decomposition; carcasses decompose faster on soil. Also, the presence of a carcass on soil resulted in a significant increase in soil microbial biomass. Interestingly, the presence of insects did not affect soil microbial biomass, but it did affect the soil microbial community. Changes in microbial community structure were observed after seven days of decomposition. These gravesoils were associated with significantly different concentrations of bacteria, eukaryotes, and arbuscular mycorrhizal fungi. These findings are insightful, because they show that soil based methods in forensic science must account for the presence of insects to be accurate in estimating postmortem interval.
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