Postmortem Processes Research Articles

Benthic foraminifers as a proxy of the range of the tidal wave in the Oyambre Estuary (Cantabria, Spain)

Recent benthic foraminifers from the Oyambre estuary (north of Spain) have been studied in order to learn their biological response to drastic anthropic environmental changes that this estuary has undergone within the last centuries. Up to 41 species have been identified and 24 of them showed live specimens during the sampling period. The most abundant species are Ammonia tepida, Balticammina pseudomacrescens, Cribroelphidium williamsoni, Entzia macrescens, Haynesina germanica, Cibicidoides lobatulus, Miliammina fusca and Trochammina inflata. The statistical analysis (cluster and correspondence analysis) has allowed the differentiation of four groups of samples that are characterized by three assemblages that define the following environments: sandy outer estuary with marine influence (C. lobatulus), mid and inner estuary that comprises an euryhaline subtidal environment with silty sediment (A. tepida and H. germanica), intertidal channels with the lowest salinity levels (C. williamsoni), and marshes (B. pseudomacrescens, E. macrescens, M. fusca and T. inflata).The great number of species with agglutinated shells reveals the ongoing draining in mud-flat areas, as well as the establishment of the vegetated high marsh, where the invasive exotic plant Baccharis halimifolia is removing the reed bed ecosystem and filling, blocking and reducing main and secondary channels. As a result, there is hardly any sandy low marsh left, which in other nearby estuaries of Cantabria is delimited by the species M. fusca. Thus, areas with tidal levels between MHWNT (Mean High Water Neap Tide) and MHW (Mean High Waters) are scarce. However, foraminifer species that live in the high marsh above MHW are dominant. Entzia macrescens and T. inflata mark the interval between MHW and MHWST (Mean High Water Spring Tide), while B. pseudomacrescens the one from MHSWST to the barren zone (vegetated high marshes, closest to land).A comparison between the biocoenosis and thanatocoenosis assemblages generally shows a good similarity (Sanders’ index > 60%). The few samples with a low similarity reveal the effect of post-mortem processes, specially decantation, and, to a lesser extent, suspended transport, which once again points to the lack of hydrodynamism in the estuary. The percentage of exotic or allochthonous species that are deposited in this estuary is very low (the average ranges from 13.4% in the mouth to 0.7% in the inner area), which reveals that the Oyambre estuary has a mesotidal character in its mouth, while in the mid and inner area it can be considered a microtidal estuary. All these data expose that the works conducted in order to recover the Oyambre estuary between years 2009 and 2010 seem not to have been successful in restoring the marshes to their original hydrodynamic conditions.

Toughness in Santa Inês lamb meat has negative impact on consumer evaluation

SUMMARY Meat tenderness is a major attribute for consumers worldwide. However, few studies investigate the importance of lamb meat tenderness for Brazilian consumers. This study assessed consumers’ evaluation of lamb meat with high shear forces. Eight lambs were slaughtered at 32.5±2.5kg of live weight and 5 to 6 months of age. The Longissimus dorsi muscle from both half carcasses was randomly assigned to four different postmortem processes: Tough Meat (TM), obtained by cold shortening, Fresh Meat (FM), Aging for 3 (A3) and 7 (A7) days postmortem . The variables measured were the sarcomere length, shear force (WBSF) and myofibrillar fragmentation index. We also applied the sensory analysis using affective acceptance tests with hedonic scale of nine points to measure texture, juiciness and overall quality of the meat. The postmortem processing for TM resulted in shorter sarcomere and greater shear values (p <0.05) compared to all other samples, while FM, A3 and A7, did not differ between the samples. Myofibrillar fragmentation was greater for A7 compared to TM (p <0.05), while FM and A3 showed intermediate values that did not differ between the treatments. In the sensory analysis, TM samples received significantly lower scores (p <0.01) for all attributes compared to other treatments and the attributes were not different between the post rigor processes. Consumers identified and evaluated negatively the meat samples with high WBSF. However, further studies are needed to elucidate the impact of smaller differences in WBSF, at intermediate values, on consumers’ evaluation.

Contextualising the dead – Combining geoarchaeology and osteo-anthropology in a new multi-focus approach in bone histotaphonomy

Histotaphonomy has become an important area of research in funerary archaeology. It focuses on diagenetic alterations in bone microstructure and the reconstruction of post-mortem processes. Microbial bioerosion is the most common diagenetic change observed in archaeological bone, and its probable causes have been the subject of ongoing discussions.This paper presents a new integrative approach that combines methods from physical anthropology and geoarchaeology. The aim is to contextualise samples in regard to their sedimentary milieu (sediment type), the sedimentation processes they underwent, and the specific archaeological features they originate from. The analysis is based on 208 human and animal skeletal fragments from the Late La Tène site of Basel-Gasfabrik recovered from various feature types and embedded in different sediments. Both 80 μm and 30 μm thin sections were graded semi-quantitatively on a scale of 0 or 1 to 5 in regard to bacterial attack (BAI), Wedl tunnels (WTI), cyanobacterial attack (CAI), the formation of cracks (CRI), the collagen content (COI), and thermal alterations (HEI).Our results evinced no correlations between the intensity of bacterial attack and sediment types or sedimentation processes respectively. We therefore deduce that bacterial degradation of bone is mainly caused by endogenous gut bacteria. Wedl tunnels, on the other hand, are chiefly found in bones from exposed surfaces. Bone collagen content, as measured by birefringence, is dependent on a variety of factors, with thermal alteration being among the most important. Unlike the 80 μm sections used in anthropological investigations, the 30 μm thin sections typically utilized in geoarchaeological analyses permitted a reliable distinction of microbial bioerosion types. Our context-oriented histotaphonomic approach allows detailed conclusions on the causes of microbial bioerosion in bone. Moreover, it provides an important tool for reconstructing the post-mortem biographies of human and animal remains, especially in regard to (multi-stage) mortuary practices and the analysis of sedimentation processes. Thus, this novel approach generates a wealth of information from individual skeletal elements as well as from bone fragments embedded in soil samples.

Rapid and reliable detection of previous freezing of cerebral tissue by computed tomography and magnetic resonance imaging.

Due to slowing or even inhibition of postmortem processes, freezing may make an estimation of the time-since-death very difficult. This is also true in previously frozen and subsequently thawed bodies. Knowledge of prior freezing is important, as it may lead to a different assessment of the time since death. Twelve pig heads were frozen at -20°C, and 6 heads were either kept at room temperature (approximately 20°C) or in a cooling cell (approximately 5°C). The frozen brains and cadavers were thawed at either room temperature or in a cooling cell. All specimens underwent repeated CT and MRI scanning until the brains were sampled for histological examination. Two radiologists assessed the images and two pathologists reviewed the histological slides with regard to thawing artifacts and putrefaction. All raters were blinded regarding whether the samples had been frozen, for how long and how they had been thawed. Imaging revealed distinct, tiny bubble-like artifacts only in previously frozen specimens. Histology also revealed artifacts only seen in such cases, namely very distinct, columnar bubbles in the cerebral cortex. All raters successfully identified previously unfrozen brains (100% specificity) and nearly all previously frozen brains. Our results suggest that initial post-mortem imaging can be of enormous importance in everyday forensic practice by identifying possible cases of previous freezing - cases that would therefore warrant closer scrutiny and thus raise caution regarding the time of death.

Evaluation of the usefulness of the immunoradiometric method for post-mortem measurement of insulin concentration in the intraocular fluid: preliminary results.

In medicolegal practice, rare cases associated with suicidal, criminal or accidental overdose of insulin are both analytically and forensically challenging. The determination of insulin in post-mortem blood has limited diagnostic value, mainly on account of post-mortem chemical degradation processes (particularly hemolysis), and hence is not useful in medicolegal practice. The aims of the study were: 1) to assess the usefulness of the immunoradiometric method, used in clinical practice, for post-mortem measurement of insulin concentration in the intraocular fluid, 2) to preliminarily evaluate the usefulness of the obtained results for toxicological and medicolegal assessment, and 3) to verify on the basis of our own material the validity of the cited literature data on the effect of hemolysis on the result of insulin level determination in post-mortem blood. The study material consisted of 93 samples of intraocular fluid collected during consecutive medicolegal autopsies performed in the Department of Forensic Medicine and Forensic Toxicology, Medical University of Silesia in Katowice. In addition, 10 samples of peripheral blood taken from living people (5 women and 5 men) for clinical and diagnostic purposes were analyzed. Insulin(e) IRMA KIT from IMMUNOTECH was used for the analyses. In 86 (92.5%) samples, the insulin concentration was below the analytical sensitivity of the method (less than 0.5 μIU/ml), while in 7 cases it was in the range of 1.42-24.42 μIU/ml. Determination of the insulin level in the intraocular fluid by the immunoradiometric method provides an opportunity for objective verification of poisoning, however this claim requires further research.

Use of high resolution computed tomography to diagnose ante-mortem dental root fractures in archaeological samples

Dental root fractures are rarely documented in past human populations, but when they are observed, diagnosing ante-mortem events as causal factors can be difficult due to postmortem alteration. Can high resolution X-ray computed tomography (CT) improve our ability to diagnose if a dental fracture was caused ante- or post-mortem? To test this, a case study of two individuals with previously diagnosed dental root fractures were re-examined with high resolution CT to confirm or refute the original diagnoses. For individual 4170, use of high resolution CT supported the original diagnosis of an ante-mortem root fracture on the right mandibular central incisor that was made based on planar X-ray. With the new analyses, the root fracture was found to be associated with evidence of calcification, and with radicular and alveolar bone resorption, which are positive correlates of an ante-mortem origin. Resolving this level of detail of bone modification was not possible without using high resolution CT. For individual 4172, the use of high resolution CT enabled visualisation of fracturing and cracking throughout several molars and crowns of other teeth that were not evident in planar X-ray, suggesting that these fractures were likely produced by post-mortem taphonomic processes rather than ante-mortem events as originally diagnosed. In this case study, high resolution CT offered critical advantages compared to a planar X-ray approach, such as using 3D multiple slice views without superimposing alveolar bone and teeth as in planar X-ray imaging. This study demonstrates the potential of high resolution CT in confirming and refuting ante-mortem processes, and that visualisation of 3D structures is crucial for arriving at definitive diagnoses.

Pediatric Postmortem CT: Initial Experience at a Tertiary Care Children’s Hospital

Pediatric postmortem imaging is a new and rapidly growing discipline. A review of recent literature is discussed along with a brief overview of common imaging findings on postmortem CT that may simulate antemortem pathology. The authors describe their own experience in establishing a postmortem imaging program as well as a discussion of the unique challenges in developing a program and performing and interpreting postmortem CT. Postmortem CT may provide valuable information in understanding the cause of death and disease processes in children; however, collaboration and research are needed to confirm the reliability of postmortem imaging diagnoses and to differentiate postmortem processes and antemortem pathology.

Gene expression in the twilight of death: The increase of thousands of transcripts has implications to transplantation, cancer, and forensic research.

After a vertebrate dies, many of its organ systems, tissues, and cells remain functional while its body no longer works as a whole. We define this state as the "twilight of death" - the transition from a living body to a decomposed corpse. We claim that the study of the twilight of death is important to ethical, legal and medical science. We examined gene expression at the twilight of death in the zebrafish and mouse reaching the conclusion that apparently thousands of transcripts significantly increase in abundance from life to several hours/days postmortem relative to live controls. Transcript dynamics of different genes provided "proof-of-principle" that models accurately predict an individual's elapsed-time-of-death (i.e. postmortem interval). While many transcripts were associated with survival and stress compensation, others were associated with epigenetic factors, developmental control, and cancer. Future studies are needed to determine whether the high incidence of cancer in transplant recipients is due to the postmortem processes in donor organs.

Fluorescent Immunohistochemistry: An Important Tool to Reveal Proteins From Tissues in Ancient Mummified Remains.

During the restoration of the Saint Antonio Abate Cathedral in Castelsardo, Sardinia, Italy, numerous human remains were found in a crypt. The burial site contained upwards of 120 individuals organized in successive layers from the bottom of the crypt; of these, 18 partially mummified individuals have been identified, including the last 2 individuals buried in the crypt. In the present study, we focused on these 2 individuals by initially adopting a morphologic and anthropological approach. The anthropological analysis of the remains showed that the 2 bodies were partially mummified and that most of the organs were not available; for this reason, the sex was determined by secondary sexual characteristics of the skulls and the long bones. The aim of this research was to describe the general state of the mummified bodies and tissues by morphologic and ultrastructural analysis using light and electron microscopy techniques. To ensure the preservation of specific tissue proteins, immunohistochemical fluorescence analysis was used. Limited information is available regarding the preservation of mummified tissues. Thus, this study demonstrated the presence of muscle and skin tissue markers in a good state of preservation, even though the tissues had undergone a slow mummification process. Our results demonstrate that several types of tissues and cell proteins may survive over a prolonged period and that these materials survive the postmortem processes.

Osteopathology and insect traces in the Australopithecus africanus skeleton StW 431


 
 
 We present the first application of high-resolution micro computed tomography in an analysis of both the internal and external morphology of the lumbar region of StW 431 – a hominin skeleton recovered from Member 4 infill of the Sterkfontein Caves (South Africa) in 1987. The lumbar vertebrae of the individual present a number of proliferative and erosive bony processes, which were investigated in this study. Investigations suggest a complex history of taphonomic alteration to pre-existing spinal degenerative joint disease (SDJD) as well as post-mortem modification by an unknown insect. This study is in agreement with previous pathological diagnoses of SDJD which affected StW 431 and is the first time insect traces on this hominin are described. The results of this analysis attest to the complex series of post-mortem processes affecting the Sterkfontein site and its fossil assemblages.
 
 
 
 
 Significance: 
 
 
 
 First application of high-resolution micro computed tomography of the lumbar region of StW 431, a partial skeleton of Australopithecus africanus, attests to pre-existing degenerative joint disease and identifies post-mortem modification by an unknown insect.
 The co-occurrence of degenerative pathology and insect modification may not be unique to StW 431. A combination of traditional morphoscopic analysis and non-invasive high-resolution tomography is recommended.
 
 
 

First application of a protein-based approach for time since death estimation

Awareness of postmortem degradation processes in a human body is fundamental to develop methods for forensic time since death estimation (TDE). Currently, applied approaches are all more or less limited to certain postmortem phases, or have restrictions on behalf of circumstances of death. Novel techniques, however, rarely exceed basic research phases due to various reasons. We report the first application of a novel method, based on decay of muscle proteins, in a recent case of murder-suicide, where other TDE methods failed to obtain data. We detected considerably different protein degradation profiles in both individuals involved and compared the data to our presently available database. We obtained statistical evidence for un-simultaneous death and therefore received valuable information to trace the progression of events based on protein degradation. Although we could not sensibly convert the data to respective times of death, this case highlights the potential for future application and elucidates the necessary further steps to develop a viable TDE method.

Rare earth elements in conodont apatite: Seawater or pore-water signatures?

Rare earth element (REE) compositions of Lower Palaeozoic conodont microfossils from different sites in Laurentia are presented and compared to modern pore-water REE compositions reported in the literature. These data are modelled to account for matrix-induced fractionation of REEs during uptake by apatite. The apatite-water partition co-efficients (Kd) for adsorption of REEs are applied to a range of modern pore-water compositions (i.e. Pore-waterN×Kd), the resultant data being similar to Palaeozoic conodont apatite compositions. Similar resemblances to modern pore-water REE compositions are shown by palaeofluids derived from conodonts using the inverse relationship in REE adsorption kinetics (i.e. Bioapatite/Kd), with rare low concentration samples yielding HREE-enriched patterns. These results clearly show the importance of matrix effects and hence the post-mortem physico-chemical processes by which elemental uptake occurs in fossil biogenic minerals, which are crucial to consider when interpreting geochemical signatures. Furthermore, the similarities between apatite REE compositions of conodonts and those derived from modern pore-waters challenge prior hypotheses of seawater REE evolution inferred directly from conodont apatite, and question the reliability of conodont apatite as archives of seawater REE chemistry. These outcomes likely have broader implications for fossil bioapatites in general given the physico-chemical processes occurring within marine sediments and the inherent behaviour of apatite-REE systematics.

Postmortem Changes in Animal Carcasses and Estimation of the Postmortem Interval.

A thorough understanding of the physical and chemical changes that occur in the body after death is critical for accurate interpretation of gross and microscopic pathology at autopsy. Furthermore, knowledge of the postmortem processes and the factors that affect them will aid in the estimation of the postmortem interval (PMI). The estimation of the PMI is important in many human and animal death investigations. Despite many decades of research, accuracy in estimation of the time of death has not significantly improved, and no single method can be reliably used to accurately estimate the time of death. Great care should be taken when formulating such an estimate, for it is dependent on multiple circumstantial and environmental factors, and the accuracy and precision of the estimate decrease as the PMI increases. The majority of the research in the field has been conducted on human bodies, but many relevant conclusions may be drawn regarding the expected postmortem changes in animals and the estimation of the PMI. The veterinary pathologist must use great caution when attempting to extrapolate data and apply formulas designed for use in humans. Methods reviewed include gross changes, microscopic changes, temperature-based methods, postmortem chemistry, molecular methods, microbial assay, ocular changes, radiography, entomology, and others. Although only several of these methods are currently practical for use in the workup of cases, it is expected that future research will result in improved techniques with enhanced accuracy in the estimation of the PMI, which will benefit both human and veterinary forensic investigations.

Time-dependent postmortem redistribution of butyrfentanyl and its metabolites in blood and alternative matrices in a case of butyrfentanyl intoxication

A fatal case of butyrfentanyl poisoning was investigated at the Zurich Institute of Forensic Medicine. At admission at the institute approx. 9h after death (first time point, t1), femoral and heart blood (right ventricle) was collected, as well as samples from the lung, liver, kidney, spleen, muscle and adipose tissue using computed tomography (CT)-guided biopsy sampling. At autopsy (t2), samples from the same body regions were collected manually. Additionally, urine, heart blood (left ventricle), gastric content, brain samples and hair were collected. Butyrfentanyl concentrations and relative concentrations of the metabolites carboxy-, hydroxy-, nor-, and desbutyrfentanyl were determined by LC⿿MS/MS and LC-QTOF. At t1, butyrfentanyl concentrations were 66ng/mL in femoral blood, 39ng/mL in heart blood, 110ng/g in muscle, 57ng/g in liver, 160ng/g in kidney, 3100ng/g in lung, 590ng/g in spleen and 550ng/g in adipose tissue. At t2, butyrfentanyl concentration in urine was 1100ng/mL, in gastric content 2000ng/mL, in hair 11,000pg/mg and brain concentrations ranged between 200⿿340ng/g. Carboxy- and hydroxybutyrfentanyl were identified as most abundant metabolites. Comparison of t1 and t2 showed a concentration increase of butyrfentanyl in femoral blood of 120%, in heart blood of 55% and a decrease in lung of 30% within 19h. No clear concentration changes could be observed in the other matrices. Postmortem concentration changes were also observed for the metabolites. In conclusion, butyrfentanyl seems to be prone to postmortem redistribution processes and concentrations in forensic death cases should be interpreted with caution.

Categorization of shell fragments provides a proxy for environmental energy and predation intensity

Shell fragments are extremely abundant in many marine environments; the origins of these fragments can largely be attributed to either crushing by predators or post-mortem processes such as transport. We present and test a new approach to identifying the origin of shell fragments in marine environments by examining modern mollusc assemblages from three wave-exposed, low-predation and three wave-sheltered, high-predation intertidal localities in Bamfield, British Columbia. We hypothesized that fragments with all-rounded edges (AR) or a combination of rounded and sharp edges (R&S) are indicative of taphonomic processes such as transport and so should occur more often in wave-exposed, low-predation localities whereas fragments with all sharp edges (AS) or a combination of intact and sharp edges (I&S), indicative of predation, should be more common in wave-sheltered, high-predation settings. In keeping with the prediction, All-Rounded (AR) and Rounded and Sharp (R&S) fragments are more abundant at the wave-exposed localities than at wave-sheltered localities whereas Intact and Sharp (I&S) and All-Sharp (AS) fragments are more abundant at high-predation localities than at low-predation localities. The two types of localities were statistically distinguishable for either gastropod or bivalve fragments. This supports the hypothesis that I&S and AS result from predation, whereas AR and R&S have a taphonomic genesis.

Calcareous assemblages of the southeastern Mediterranean low-tide estuaries — Seasonal dynamics and paleo-environmental implications

The study of estuarine ecosystems is essential for protecting and reestablishing their threatened biota. In this research the spatio-temporal variations in the distribution patterns of foraminifera, ostracods and molluscs are analyzed in surficial sediments sampled in 2012/13 at six low-tide estuaries of the southeastern Mediterranean coast. Live assemblages are studied using multivariate statistical analyses to determine their ecological preferences and seasonal dynamics whereas the dead assemblages are used to establish a reference baseline for future paleoenvironmental reconstruction.The statistical analysis indicates that salinity, TOC and % carbonate are the main environmental factors explaining 60% of the cumulative variance and controlling the distribution pattern of the different brackish taxa encountered in these estuaries. The foraminifera Ammonia tepida and some miliolids (Quinqueloculina and Varidentella) inhabit most estuaries during summer when salinities of 13–18psu and temperatures of 26–34°C occur. At the Naaman stream the agglutinated species Birsteiniolla macrostoma and Trichohyalus aguayoi dominate the assemblage during autumn and winter, respectively when salinities of 3–7psu and temperature of 18–24°C prevail. High abundance of the monospecific assemblage of the ostracod Cyprideis torosa was encountered at the Tanninim year round in oligohaline water. The gastropod Heleobia phaeniciaca prefers living at the Naaman and Tanninim streams while Pyrgophorus sp., an invasive and low salinity species, continue colonizing more stream reaches along the Israeli coast.The dead assemblages are composed of high numbers of local and transported species. It includes post storm-surge sediments containing high numbers of inland fresh and brackish water species transported by the floods. Those are mixed with inner to mid-shelf benthic and planktonic foraminifera, ostracods and molluscs. Transportation of the marine organisms a few hundred of meters inland via the estuaries indicates that the coastal areas are prone to storm surge events that are preserved clearly on the coast.The present study demonstrates that the combined use of different multi-proxy faunal records enhances significantly the understanding of the dynamics of low-tide estuaries. This can be applied also to other low-tide estuaries worldwide and facilitate better management of these threatened environments. Additionally, it enables understanding of the post-mortem processes that control the transition from the living to the death assemblages and by that improve paleoenvironmental reconstruction of the lower reaches of low-tide estuaries.

The common pattern of postmortem changes on whole body CT scans

The postmortem changes on postmortem computed tomography (PMCT) seem to have a regular pattern over time. Studying these changes could lead to a better understanding of postmortem physiology and to differentiate between normal and pathological aspects. We studied the patterns and aspects of the postmortem changes and made correlations to the postmortem interval (PMI). Five deceased bodies (4M, 1F; mean age 79 years; 2 cancer, 3 unknown cause of death) that were donated to science underwent total body PMCT scanning every hour, starting 6–10 h and up to 36 h after death. The bodies stayed on the scanner table during the whole scanning period, in supine position without moving. We measured Hounsfield units (HU) of the cerebrospinal fluid (CSF), vitreous humor (VH) and lungs. Volumes of lung, liver and bowel were calculated with semi-automated software. We made correlations to the PMI. We made timelapse movies to visualize the postmortem changes. We found increasing radiodensities of VH and CSF in correlation to the PMI. Pulmonary radiodensity and volume could show both increase or decrease over time. Liver volume decreased and bowel volume increased over time. The timelapse movies visualized these normal postmortem processes in the body. We conclude that postmortem changes on PMCT show partly a regular and partly diverging pattern between patients. The increasing radiodensity of CSF is correlated to PMI and might be helpful in estimating the time of death, however further study is needed.

Assessment of the Role Played by N-propanol Found in Postmortem Blood in the Discrimination Between Antemortem Consumption and Postmortem Formation of Ethanol Using Rats.

This study disproves the reliability of n-propanol as a biomarker to establish whether the ethanol found in postmortem blood is derived from antemortem ingestion or postmortem putrefactive processes. Two groups of rats were given ethanol or normal saline solution, respectively, and sacrificed 1.5 h later. After putrefaction, blood and, in a few cases, urine samples from the rats were analyzed for ethanol and n-propanol by head-space gas chromatography equipped with flame ionization detection. Although the concentration ratios of ethanol/n-propanol in the postmortem blood collected from the bodies without prior alcohol consumption were expected to be <20 (as per limited case reports and previous in vitro studies), in samples from several rats that were on saline solution, this ratio was found to exceed 20. In conclusion, the concentration ratio of ethanol/n-propanol in postmortem blood does not allow for the discernment between antemortem ingestion and the postmortem synthesis of ethanol.

On the benefits of being redundant: low compositional fidelity of diatom death assemblages does not hamper the preservation of environmental gradients in shallow lakes

AbstractComparisons between death assemblages and their source living communities are among the most common actualistic methods of evaluating the preservation of compositional and environmental information in fossil assemblages. Although live-dead studies have commonly focused on marine mollusks, the potential of diatoms to preserve ecological information in continental settings has been overlooked. Thus, little is known about the nature and magnitude of the taphonomic biases affecting live-dead agreement of diatom assemblages, despite their extensive application as modern and fossil bioindicators in paleoecological and paleoenvironmental reconstructions. In this study, I analyzed three live-dead data sets in order to evaluate the compositional and environmental fidelity exhibited by diatom death assemblages in shallow lakes. I find that diatom death assemblages (DAs) do differ significantly in their taxonomic composition from living assemblages (LAs), mainly as a consequence of (1) differences in the temporal resolution between time-averaged DAs and non-averaged LAs, and (2) differential preservation of diatom taxa related to the intrinsic properties of their valves. Despite compositional dissimilarities, DAs were able to capture the same environmental gradients as LAs, with high significance. This decoupling between live-dead agreement in community composition and community response to gradients can be related to the existence of at least two mutually exclusive subsets of species that significantly captured compositional dissimilarities based on the full set of the species in the three lakes. This functional redundancy implies that the between-sample relationships of living assemblages can be significantly preserved by DAs even if some taxa are removed by taphonomic processes. The preservation of environmental gradients thus does not require good preservation of all living taxa. Structural redundancy compensates for the loss of compositional fidelity caused by postmortem processes in the diatom data set.

The use of museum specimens with high-throughput DNA sequencers

Natural history collections have long been used by morphologists, anatomists, and taxonomists to probe the evolutionary process and describe biological diversity. These biological archives also offer great opportunities for genetic research in taxonomy, conservation, systematics, and population biology. They allow assays of past populations, including those of extinct species, giving context to present patterns of genetic variation and direct measures of evolutionary processes. Despite this potential, museum specimens are difficult to work with because natural postmortem processes and preservation methods fragment and damage DNA. These problems have restricted geneticists' ability to use natural history collections primarily by limiting how much of the genome can be surveyed. Recent advances in DNA sequencing technology, however, have radically changed this, making truly genomic studies from museum specimens possible. We review the opportunities and drawbacks of the use of museum specimens, and suggest how to best execute projects when incorporating such samples. Several high-throughput (HT) sequencing methodologies, including whole genome shotgun sequencing, sequence capture, and restriction digests (demonstrated here), can be used with archived biomaterials.