Sibyl R. Bucheli

Microbial community assembly and metabolic function during mammalian corpse decomposition

Decomposition spawns a microbial zoo The death of a large animal represents a food bonanza for microorganisms. Metcalf et al. monitored microbial activity during the decomposition of mouse and human cadavers. Regardless of soil type, season, or species, the microbial succession during decomposition was a predictable measure of time since death. An overlying corpse leaches nutrients that allow soil- and insect-associated fungi and bacteria to grow. These microorganisms are metabolic specialists that convert proteins and lipids into foul-smelling compounds such as cadaverine, putrescine, and ammonia, whose signature may persist in the soil long after a corpse has been removed. Science, this issue p. 158 As a corpse rots, the microbial succession follows a similar pattern across different types of soil. Vertebrate corpse decomposition provides an important stage in nutrient cycling in most terrestrial habitats, yet microbially mediated processes are poorly understood. Here we combine deep microbial community characterization, community-level metabolic reconstruction, and soil biogeochemical assessment to understand the principles governing microbial community assembly during decomposition of mouse and human corpses on different soil substrates. We find a suite of bacterial and fungal groups that contribute to nitrogen cycling and a reproducible network of decomposers that emerge on predictable time scales. Our results show that this decomposer community is derived primarily from bulk soil, but key decomposers are ubiquitous in low abundance. Soil type was not a dominant factor driving community development, and the process of decomposition is sufficiently reproducible to offer new opportunities for forensic investigations.

The Living Dead: Bacterial Community Structure of a Cadaver at the Onset and End of the Bloat Stage of Decomposition

Human decomposition is a mosaic system with an intimate association between biotic and abiotic factors. Despite the integral role of bacteria in the decomposition process, few studies have catalogued bacterial biodiversity for terrestrial scenarios. To explore the microbiome of decomposition, two cadavers were placed at the Southeast Texas Applied Forensic Science facility and allowed to decompose under natural conditions. The bloat stage of decomposition, a stage easily identified in taphonomy and readily attributed to microbial physiology, was targeted. Each cadaver was sampled at two time points, at the onset and end of the bloat stage, from various body sites including internal locations. Bacterial samples were analyzed by pyrosequencing of the 16S rRNA gene. Our data show a shift from aerobic bacteria to anaerobic bacteria in all body sites sampled and demonstrate variation in community structure between bodies, between sample sites within a body, and between initial and end points of the bloat stage within a sample site. These data are best not viewed as points of comparison but rather additive data sets. While some species recovered are the same as those observed in culture-based studies, many are novel. Our results are preliminary and add to a larger emerging data set; a more comprehensive study is needed to further dissect the role of bacteria in human decomposition.

Comparison of phylogenetic signal between male genitalia and non‐genital characters in insect systematics

It is generally accepted that male genitalia evolve more rapidly and divergently relative to non‐genital traits due to sexual selection, but there is little quantitative comparison of the pattern of evolution between these character sets. Moreover, despite the fact that genitalia are still among the most widely used characters in insect systematics, there is an idea that the rate of evolution is too rapid for genital characters to be useful in forming clades. Based on standard measures of fit used in cladistic analyses, we compare levels of homoplasy and synapomorphy between genital and non‐genital characters of published data sets and demonstrate that phylogenetic signal between these two character sets is statistically similar. This pattern is found consistently across different insect orders at different taxonomic hierarchical levels. We argue that the fact that male genitalia are under sexual selection and thus diverge rapidly does not necessarily equate with the lack of phylogenetic signal, because characters that evolve by descent with modification make appropriate characters for a phylogenetic analysis, regardless of the rate of evolution. We conclude that male genitalia are a composite character consisting of different components diverging separately, which make them ideal characters for phylogenetic analyses, providing information for resolving varying levels of hierarchy.

Initial insights into bacterial succession during human decomposition

Decomposition is a dynamic ecological process dependent upon many factors such as environment, climate, and bacterial, insect, and vertebrate activity in addition to intrinsic properties inherent to individual cadavers. Although largely attributed to microbial metabolism, very little is known about the bacterial basis of human decomposition. To assess the change in bacterial community structure through time, bacterial samples were collected from several sites across two cadavers placed outdoors to decompose and analyzed through 454 pyrosequencing and analysis of variable regions 3–5 of the bacterial 16S ribosomal RNA (16S rRNA) gene. Each cadaver was characterized by a change in bacterial community structure for all sites sampled as time, and decomposition, progressed. Bacteria community structure is variable at placement and before purge for all body sites. At bloat and purge and until tissues began to dehydrate or were removed, bacteria associated with flies, such as Ignatzschineria and Wohlfahrtimonas, were common. After dehydration and skeletonization, bacteria associated with soil, such as Acinetobacter, were common at most body sites sampled. However, more cadavers sampled through multiple seasons are necessary to assess major trends in bacterial succession.

Larval case architecture and implications of host-plant associations for North American Coleophora (Lepidoptera; Coleophoridae)

The case-bearing moths of North America are represented by a single genus, Coleophora, which contains approximately 144 described species. All are external seed or leaf miners that inhabit portable silk cases during most of the larval stage. Architectural and ecological characters from larval cases were used in cladistic analysis to investigate existing case groups for 32 North American species of Coleophora. Cladistic analysis confirmed monophyly of certain case groups, but not of others. Host-plant preferences were also examined. The pattern of host plant use reflects more closely preference for certain plant tissues (seeds versus leaves) and growth forms (herbaceous versus woody) with exploitation of different plant taxa, rather than preference for certain plant taxa with exploitation of different plant tissues. q 2002 The Willi Hennig

Exclusion of forensically important flies due to burying behavior by the red imported fire ant (Solenopsis invicta) in southeast Texas

On March 3, 2009, the remains of an adult male were partially buried at the Southeast Texas Applied Forensic Science (STAFS) Facility at the Center for Biological Field Studies (CBFS), Sam Houston State University, Texas. The individual was buried except for a small portion of the left abdominal region. A postmortem incised wound was created in the exposed area with the intention of attracting carrion flies. Worker ants of a colony of Solenopsis invicta Buren 1972 (red imported fire ant) filled in the wound with soil, thereby monopolizing the exposed area of the corpse and excluding expected carrion insects from the wound. During the bloating phase, approximately nine days after burial, normal decomposition processes of the gut created a sufficient disruption of the ants, such that flies oviposited and larvae were able to colonize the corpse. Estimation of the postmortem interval (PMI) based on the minimum period of fly activity would be severely skewed should the remains be discovered at this point and growth rate of Diptera larvae be used as the primary determinant for the PMI. While S. invicta is an expected member of a carrion ecosystem in southeastern Texas, and is known to distort the PMI estimation through larval and egg removal, the complete exclusion of flies from the wound by the burial behavior of S. invicta was an unexpected and until now an unpublished occurrence.

Four Forensic Entomology Case Studies: Records and Behavioral Observations on Seldom Reported Cadaver Fauna With Notes on Relevant Previous Occurrences and Ecology

ABSTRACT A yearlong survey of insect taxa associated with human decomposition was conducted at the Southeast Texas Applied Forensic Science (STAFS) facility located in the Center for Biological Field Studies of Sam Houston State University in Huntsville, TX. During this study, four insect—cadaver interactions were observed that represent previously poorly documented yet forensically significant interactions: Syrphidae maggots colonized a corpse in an aquatic situation; Psychodidae adults mated and oviposited on an algal film that was present on a corpse that had been recently removed from water; several Panorpidae were the first insects to feed upon a freshly placed corpse in the autumn; and a noctuid caterpillar was found chewing and ingesting dried human skin. Baseline knowledge of insect—cadaver interactions is the foundation of forensic entomology, and unique observations have the potential to expand our understanding of decomposition ecology.

Terrestrial laser scanning and a degenerated cylinder model to determine gross morphological change of cadavers under conditions of natural decomposition

Decomposition can be a highly variable process with stages that are difficult to quantify. Using high accuracy terrestrial laser scanning a repeated three-dimensional (3D) documentation of volumetric changes of a human body during early decomposition is recorded. To determine temporal volumetric variations as well as 3D distribution of the changed locations in the body over time, this paper introduces the use of multiple degenerated cylinder models to provide a reasonable approximation of body parts against which 3D change can be measured and visualized. An iterative closest point algorithm is used for 3D registration, and a method for determining volumetric change is presented. Comparison of the laser scanning estimates of volumetric change shows good agreement with repeated in-situ measurements of abdomen and limb circumference that were taken diurnally. The 3D visualizations of volumetric changes demonstrate that bloat is a process with a beginning, middle, and end rather than a state of presence or absence. Additionally, the 3D visualizations show conclusively that cadaver bloat is not isolated to the abdominal cavity, but also occurs in the limbs. Detailed quantification of the bloat stage of decay has the potential to alter how the beginning and end of bloat are determined by researchers and can provide further insight into the effects of the ecosystem on decomposition.

Necrophagous caterpillars provide human mtDNA evidence.

Abstract:  Decomposition of large mammalian carcasses is greatly accelerated through the action of insects. Specialized feeders capable of digesting keratin and collagen found in skin, hair, and tendons and ligaments are attracted to corpses in late stages of dry decomposition and include Tinea pellionella, the casemaking clothes moth, and Tineola bisselliella, the webbing clothes moth (Lepidoptera; Tineidae). Until now, details of the caterpillar behavior as necrophagous insects were vague. Here, we detail the behavior of each species and document the incorporation of human hair into the portable larval shelters constructed by the caterpillars of T. pellionella. Hair of the decedent used as building material for caterpillar shelters provided enough starting template to amplify and sequence the HVI and HVII sections of the control region (mtDNA) of the decedent.

A Phylogenetic Test of Ehrlich and Raven's Theory of Escape and Radiation in Insects that Feed on Toxic Plants, Based on Nearctic Depressaria Moths (Gelechioidea: Elachistidae: Depressariinae), with Discussion of the Evolution of Genitalia

Abstract A classic “escape and radiation” coevolutionary model of host shifts is examined in moths of the genus Depressaria Haworth 1811 that feed on plants of varied toxicity. A phylogeny is constructed using morphological data analyzed under the parsimony criterion, the first modern phylogeny of the subfamily that includes New World and Old World species. The results of this analysis suggest that Depressaria is monophyletic, as are historical species groups of Depressaria. Patterns of host-plant usage do not support an escape and radiation model but rather suggest that feeding on plants containing toxic furanocoumarins may be the ancestral conditions for Depressaria. Thus, a model of escape from control and colonization of more toxic hosts does not apply above the species level. Other phylogenetic results indicate Himmacia Clarke 1941 may be a basal lineage of Depressariinae and Semioscopis Hübner 1825 is not a member of this subfamily. In spite of some apparently very specialized larval features, we conclude that Hasenfussia Fetz 1994 is a member of Depressaria.