Pig decomposition in lotic aquatic systems: the potential use of algal growth in establishing a postmortem submersion interval (PMSI)

While algal community composition has been examined as a qualitative indicator of postmortem submersion interval (PMSI), there have been no quantitative studies on using algal growth rates as PMSI estimators. The present study was undertaken to examine pig decomposition in streams and to develop a more quantitative approach to estimate a PMSI. Pigs and ceramic tiles were completely submerged and regularly sampled for periphyton growth. Five stages of decomposition were identified for the submerged pig carcasses according to physical characteristics. Algal growth rates, measured quantitatively as a function of chlorophyll-a concentration, were greater on pigs compared with tiles; however, microhabitat (pools versus riffles) did not significantly influence algal growth. Additionally, there was a strong correlation between algal growth rate and time on pigs and tile substrates. This strong correlation was observed after significant rain events. Our study documents for the first time a quantitative technique to determine the length of time a corpse has been submerged in water. We suggest that algal growth rates may be a useful quantitative indicator in criminal investigations involving corpses that are completely submerged in stream or riverine habitats.     

Diel Activity and Effect of Carcass Decomposition on the Attractiveness to the Forensically Important Species Oxelytrum Discicolle (Coleoptera: Silphidae)†

Oxelytrum discicolle is a carrion beetle commonly found in the Neotropical region, mainly associated with cadavers and carcasses. Information on behavior related to the likelihood of cadaver colonization is scarce. We performed two field experiments in peri‐urban forest in Brazil in order to strengthen our knowledge on O. discicolle behavior. In the first experiment, we assessed the preference for piglet carcasses at different stages of decomposition offered simultaneously in two seasons, dry and rainy, while in the second experiment we investigated the diel activity of adults. A total of 493 adults were collected in the experiments. A significantly higher abundance was detected in the rainy season. There was a marked preference for carcasses at advanced stages. Adults exhibited a typical nocturnal behavior, the number trapped at night was 17 times greater than those collected during the day. Oxelytrum discicolle is nocturnal species that prefers carcasses in advanced stage of decomposition.     

Marine bacterial succession as a potential indicator of postmortem submersion interval

The process of decomposition of bodies in the marine environment is poorly understood and almost nothing is currently known about the microorganisms involved. This study aimed to investigate the microbes involved in decomposition in the sea and to evaluate the potential use of marine bacterial succession for postmortem submersion interval (PMSI) estimation, for which there is currently no reliable method. Partial pig remains were completely submerged during autumn and winter and were regularly sampled to document marine bacterial colonisation and the changes in community composition over time. Five stages of decomposition were recognised, some of which exhibited characters specific for partial carrion. Marine bacteria rapidly colonised the submerged remains in a successional manner. Seasonal differences were observed for the rate of decomposition and also for several groups of colonising bacteria. Marine bacteria specific for particular PMSIs were identified. This study provides an insight into the involvement of saprophytic marine bacteria in the decomposition of mammalian remains in the sea and is the first to explore the use of marine bacterial colonisation and succession as a novel tool for PMSI estimation. We propose that with further study, marine bacterial succession will prove useful for determination of the length of time a body may have been immersed in a marine environment.     

Initial study of arthropods succession and pig carrion decomposition in two freshwater ecosystems in the Colombian Andes

Entomological succession and trophic roles of arthropods associated with different stages of carcass decomposition were studied to estimate the post-mortem submersion interval in two freshwater ecosystems in the Colombian Andes, at an altitude of 2614 m. Pig carcasses were employed as models placed 68 m apart, one in a stream (lotic) and another in an artificial lake (lentic). Decomposition time to skeletal remains was 74 days in the lake and 80 days in the stream. Six phases of decomposition were established: submerged fresh, early floating, floating decay, bloated deterioration, floating remains and sunken remains. A total of 18,832 organisms associated with the carcasses were collected: 11,487 in the lake (four orders, 19 families and 33 species) and 7345 in the stream (eight orders, 15 families and 25 species). Organisms were classified in the following ecological categories: shredders, collectors, predators, necrophagous, sarcosaprophagous and opportunists. Physical and chemical properties of the habitats, such as water temperature, CO(2) and conductivity, varied according to rainfall. In the lake, shredders (Coleoptera: Tropisternus sp. and Berosus sp.) and collectors (Diptera: Chironomus sp.) were found to be associated with submerged phases. Predators (Odonata) were only present during the first phases. Coleoptera (Dytiscidae) were found during floating decay and bloated deterioration stages. In the stream, shredders (Hyalella sp.) and collectors (Simulium sp.) were found during all stages, whereas the predator Oxelytrum discicolle was found exclusively during the floating stages, during which body temperature increased in a fashion similar to active decay in terrestrial environments.     

Effect of carcass size on rate of decomposition and arthropod succession patterns.

Decomposition studies were conducted using two carcasses of domestic pigs, Sus scrofa L., 8.4 kg and 15.1 kg in weight, to determine the effects of carcass size on the rate of decomposition, composition of the arthropod fauna, and succession patterns. A total of 46 arthropod taxa were recovered during this study. No size-related differences were observed between carcasses with respect to composition of the arthropod fauna or patterns of succession. A greater number of arthropods were observed attracted to the 15.1-kg carcass, and the rate of decomposition observed was more rapid for the 15.1-kg carcass than for the 8.4-kg carcass. Internal temperatures of the 8.4-kg carcass were more directly related to external ambient temperatures during the fresh and bloated stages of decomposition. During the decay stage, both carcasses generated internal temperatures significantly above ambient temperatures. Following this stage, internal temperatures fell to approximate ambient temperatures during the postdecay and remains stages.     

Caddisflies assist with homicide case: determining a postmortem submersion interval using aquatic insects

Although few indicators of time since death for corpses found in aquatic ecosystems are comparable in precision to the insect indicators used in terrestrial cases, there are observations that can be useful in suggesting or ruling out an approximate PMSI (postmortem submersion interval). For example, the time intervals required for certain growth phases of aquatic insects, such as caddisflies, that may attach themselves to the submerged remains can be used to estimate a minimum PMSI. Approximately 8 of the 13 orders of insects containing species with aquatic or semi-aquatic stages are likely to be associated with carrion or corpses in aquatic habitats. We present a case study in which portions of a body from an adult male were discovered in a south central Michigan stream. The body was dismembered and portions were recovered from two bags floating and submerged in the stream. Insect specimens collected from mesh and plastic bags consisted of one fly larva belonging to the family Muscidae, and caddisfly larvae belonging to two families: the Limnephilidae. (case-makers) and the Hydropsychidae, (net spinners). We used unique case-building behaviors of the limnephilid caddisflies found on the remains to elucidate a PMSI range consistent with the disappearance of the victim. It is important for forensic investigators to understand that although some precision is lost in estimating a PMSI with aquatic insects, these organisms should not be ignored in gathering evidence from aquatic crime scenes, and in fact, they can provide valuable details in estimating a PMSI.     

Potential Use of Bacterial Community Succession in Decaying Human Bone for Estimating Postmortem Interval,,

Bacteria are taphonomic agents of human decomposition, potentially useful for estimating postmortem interval (PMI) in late‐stage decomposition. Bone samples from 12 individuals and three soil samples were analyzed to assess the effects of decomposition and advancing time on bacterial communities. Results indicated that partially skeletonized remains maintained a presence of bacteria associated with the human gut, whereas bacterial composition of dry skeletal remains maintained a community profile similar to soil communities. Variation in the UniFrac distances was significantly greater between groups than within groups (p < 0.001) for the unweighted metric and not the weighted metric. The members of the bacterial communities were more similar within than between decomposition stages. The oligotrophic environment of bone relative to soft tissue and the physical protection of organic substrates may preclude bacterial blooms during the first years of skeletonization. Therefore, community membership (unweighted) may be better for estimating PMI from skeletonized remains than community structure (weighted).     

Comparison of Protocols for Measuring and Calculating Postmortem Submersion Intervals for Human Analogs in Fresh Water

Protocols for determining postmortem submersion interval (PMSI) have long been problematic for forensic investigators due to the wide variety of factors affecting the rate of decomposition of submerged carrion. Likewise, it has been equally problematic for researchers to develop standardized experimental protocols to monitor underwater decomposition without artificially affecting the decomposition rate. This study compares two experimental protocols: (i) underwater in situ evaluation with photographic documentation utilizing the Heaton et al. total aquatic decomposition (TAD) score and (ii) weighing the carrion before and after submersion. Complete forensic necropsies were performed as a control. Perinatal piglets were used as human analogs. The results of this study indicate that in order to objectively measure decomposition over time, the human analog should be examined at depth using the TAD scoring system rather than utilizing a carrion weight evaluation. The acquired TAD score can be used to calculate an approximate PMSI.     

Comparison of patterns of decomposition in a hanging carcass and a carcass in contact with soil in a xerophytic habitat on the Island of Oahu, Hawaii

Decomposition studies were conducted to determine differences in rates and patterns of decomposition of carcasses hanging and exposed on the surface of the soil. These studies were conducted between 17 October and 17 December 1997 inside of Diamond Head Crater on the island of Oahu, Hawaii. The animal model was the domestic pig. Sus scrofa. The rate of biomass removal from the hanging carcass was significantly slower than that observed for the control carcass during the bloat and decay stages of decomposition. Internal temperatures for the control carcass were elevated above the ambient air temperatures during the earlier stages of decomposition (bloated and decay), while those recorded for the hanging carcass approximated the ambient air temperatures. There was a greater diversity of arthropod species recorded and numbers of individuals observed were higher for the control carcass. A significant site of arthropod activity was observed on the surface of the soil immediately under the hanging carcass and this became the primary site of arthropod activity as decomposition progressed.     

An analytical evaluation of eight on-site oral fluid drug screening devices using laboratory confirmation results from oral fluid

A decaying cadaver emits volatile organic compounds that are used by necrophilous and necrophagous insects in order to find their brood substrate. Although volatile organic compounds (VOCs) that are released by carcasses have been identified, little is known about the specific compounds that are used by these insects while searching for a brood substrate. Therefore, we have investigated the chemical ecology involved in the attraction of the necrophagous hide beetle Dermestes maculatus, which feeds as an adult and larva upon decomposing carcasses. Our aims have been to identify the responsible compounds in the odours of the carcass that are important for the attraction of the beetles. Furthermore, we have studied sex- and age-related differences in beetle attraction and tested whether the hide beetle can distinguish between various stages of decomposition by means of the emitted odours. Headspace collection of volatiles released from piglet carcasses (bloated stage, post-bloating stage, advanced decay and dry remains), coupled gas chromatography-mass spectrometry (GC-MS), gas chromatography with electroantennographic detection (GC-EAD) and bioassays were conducted to identify the volatiles responsible for the attraction of the beetles. Freshly emerged male beetles were attracted by the odour of piglets in the post-bloating stage (9 days after death; T(mean) = 27 °C) and the EAD-active compound benzyl butyrate. Statistical analysis revealed a higher relative proportion of benzyl butyrate in the odour bouquet of the post-bloating stage in comparison with the other stages. We therefore conclude that this compound plays an important role in the attraction of hide beetles to carcass odour. This underlines the potential use of D. maculatus for the estimation of the post mortem interval. The decomposition stage at which the female beetles are attracted to the odour of a cadaver remains unknown, as does the nature of this attraction. Pheromones (sexual or aggregation pheromones) might play an essential role correlated with their attraction to carrion and consequently with their attraction to the substrate for mating and ovipositioning.     

The analysis of dyes in ball point pen inks on single paper fibres using laser desorption ionisation time of flight mass spectrometry (LDI-TOFMS)

A preliminary field study in the summer in a rural village in El-Qalyubiya Governorate (Egypt) compared the necrophagous insects colonizing the cadavers of two male rabbits (Oryctolagus cunicullus domesticus L.) killed by asphyxia (control), with two poisoned by the organophosphate (OP) pesticide pirimiphos-methyl (test). Decay of control carcasses was rapid since they reached the skeletal stage in only 19 days. Test carcasses did not decay completely, even 40 days post-killing. Insect species colonizing both carcasses types were not different, indicating that despite its odor, the OP were not masking the decomposition odors which were drawing the species to the bodies. The blowfly Chrysomya albiceps (Weidemann) constituted 76.6% of all samples collected. They were the first colonizers and played a major role in the decomposition process of control carcasses and in the partial decay of the test ones. They were significantly fewer numbers of immature stages developing on the test carcasses which probably contributed to their distinct lag and poor decomposition. Samples indicate that 17.3% of the insects were members of the Formicidae. This family was present in all carcasses, mostly in the early stages of decomposition. Formicidae may be considered omnivorous, and one of the fauna which use the cadaver as a refuge, to obtain humidity and food. This study provides additional knowledge in the context of Egyptian forensic entomology and the influence of OP which is of relevance to forensic science.     

Variation in decomposition stages and carrion insect succession in a dry tropical climate and its effect on estimating postmortem interval

Insects have an important role in minimum postmortem interval (PMI_min) estimation. An accurate PMI_min estimation relies on a comprehensive study of the development and succession of local carrion insects. No published research on carrion insect succession exists for tropical north Queensland. To address this, we aimed to obtain preliminary observational data concerning the rate of decomposition and insect succession on pig carcasses in Townsville and compare these with other regions of Australia and overseas. Adult insects were collected daily from three pig carcasses for 30 d during summer and identified to family level. Observations of decomposition rate were made each day and progression through the stages of decomposition were recorded. Adult insects were identified to family and their presence/absence used as a proxy for arrival at/departure from the remains, respectively. These preliminary data highlight several interesting trends that may be informative for forensic PMI_min estimation. Decomposition was rapid: all carcasses were at the dry/remains stage by Day 5, which was substantially quicker than all other regions in the comparison. Differences were also observed in the presence/absence of insect families and their arrival and departure times. Given the rapid progression through early decomposition, we argue that later-arriving coleopteran taxa may be more forensically informative in tropical Australia, in contrast with temperate regions where Diptera appear most useful. This research contributes preliminary observational data to understanding insect succession patterns in tropical Australia and demonstrates the critical need for comprehensive local succession data for each climatic region of Australia to enable accurate PMI_min estimation. These data will inform future research targeted at gaining a more comprehensive understanding of insect succession in the Australian tropics.

Key points:

• We obtained preliminary observational data concerning the rate of decomposition and insect succession on pig carcasses in tropical Australia.
• Decomposition was rapid: all carcasses were at the dry/remains stage by Day 5.
• Coleopteran taxa may be more forensically informative in tropical Australia than dipterans.

     

Impact of plastic wrapping on carcass decomposition and arthropod colonisation in northern Africa during spring

The effect of plastic wrapping on decomposition rate and carrion fauna of rabbits (Oryctolagus cuniculus L.) was examined in spring in a semi-urban area in North Algeria. All decomposition stages were observed in all carcasses, with the same durations in the control but different durations in the wrapped carcasses. Decomposition of the carcasses in the plastic wrapping was significantly slower than that of the exposed ones. A total of 12,516 specimens, belonging to 36 families and 69 species, were morphologically identified. Thirteen species of forensic relevance were also identified at the molecular level using the cytochrome c oxidase I (COI) barcode region, and the sequences were submitted to online databases. Wrapping had a significant effect on species composition (χ² = 569.269, df = 55, p < 0.001). Higher species richness, abundance, and diversity were found in the control group. No significant difference in species abundance was observed between the treatments. The plastic wrap did not influence the accessibility of carcasses to insects, nor did it delay the arrival of necrophagous flies. This study provides basic information on the decomposition and arthropod colonisation of wrapped remains and contributes to the literature on North African carrion fauna.     

Decomposition and Arthropod Succession in Whitehorse,Yukon Territory,Canada

Forensic arthropod succession patterns are known to vary between regions. However, the northern habitats of the globe have been largely left unstudied. Three pig carcasses were studied outdoors in Whitehorse, Yukon Territory. Adult and immature insects were collected for identification and comparison. The dominant Diptera and Coleoptera species at all carcasses were Protophormia terraneovae (R‐D) (Fam: Calliphoridae) and Thanatophilus lapponicus (Herbst) (Fam: Silphidae), respectively. Rate of decomposition, patterns of Diptera and Coleoptera succession, and species dominance were shown to differ from previous studies in temperate regions, particularly as P. terraenovae showed complete dominance among blowfly species. Rate of decomposition through the first four stages was generally slow, and the last stage of decomposition was not observed at any carcass due to time constraints. It is concluded that biogeoclimatic range has a significant effect on insect presence and rate of decomposition, making it an important factor to consider when calculating a postmortem interval.     

Algal colonization of submerged carcasses in a mid-order woodland stream

One of the primary goals of forensic pathology is the determination of time of death. In aquatic systems, one method to do this is to analyze the colonization of a corpse by algae. Algal communities typically follow a serial colonization pattern, therefore the taxa present at any given time may provide clues about postmortem submersion time. This study was undertaken to examine the algal colonization on rat carcasses in a medium-order woodland stream. Two habitats were studied: a low flow pool and a high flow riffle, with rats being removed from each site every 3 to 6 days over 31 days. The diversity of colonizing taxa increased at both sites as the study progressed, and after 17 days similar taxa were present (Sorensen's similarity index >60%) in each site. Some taxa, such as desmids (Chlorophyta), tended to increase in diversity throughout the study, making them possible indicators of submersion time. Diatoms were the most abundant taxa found in each site and accounted for 63 of the 92 total taxa identified. Due to their ubiquitous presence in nearly all streams, we suggest that diatoms may be the key organisms for the study of postmortem submersion in lotic systems.     

嗜尸性甲虫在尸体上的演替及其法医学应用前景

作为法医昆虫学的主要研究对象之一,嗜尸性甲虫在腐败晚期干化和白骨化尸体的死亡时间推断中具有双翅目昆虫所无法取代的重要意义,并对尸体的腐败、破坏、分解和姿势改变发挥着不容忽视的作用。本文阐述了嗜尸性甲虫在尸体上的演替,分析了嗜尸性甲虫演替的影响因素,介绍了嗜尸性甲虫在法医学中的应用和前景。虽然目前对嗜尸性甲虫的研究还很少,但嗜尸性甲虫在法医鉴定中的作用将在今后受到越来越多法医工作者的重视。