Patterns of nuclear DNA degeneration over time--a case study in historic teeth samples

Museum Genomics Provide Evidence for Persistent Genetic Differentiation in a Threatened Seabird Species in the Western Atlantic

Connectivity among wildlife populations facilitates exchange of genetic material between groups. Changes to historical connectivity patterns resulting from anthropogenic activities can therefore have negative consequences for genetic diversity, particularly for small or isolated populations. DNA obtained from museum specimens can enable direct comparison of temporal changes in connectivity among populations, which can aid in conservation planning and contribute to the understanding of population declines. However, museum DNA can be degraded and only available in low quantities, rendering it challenging for use in population genomic analyses. Applications of genomic methodologies such as targeted sequencing address this issue by enabling capture of shared variable sites, increasing quantity and quality of recovered genomic information. We used targeted sequencing of ultra-conserved Elements (UCEs) to evaluate potential changes in connectivity and genetic diversity of roseate terns (Sterna dougallii) with a breeding distribution in the northwestern Atlantic and the Caribbean. Both populations experienced range contractions and population declines due to anthropogenic activity in the 20th century, which has the potential to alter historical connectivity regimes. Instead, we found that the two populations were differentiated historically as well as contemporaneously, with little evidence of migration between them for either time period. We also found no evidence for temporal changes in genetic diversity, although these interpretations may have been limited due to sequencing artifacts caused by the degraded nature of the museum samples. Population structuring in migratory seabirds is typically reflective of low rates of divergence and high connectivity among geographically segregated subpopulations. Our contrasting results suggest the potential presence of ecological mechanisms driving population differentiation, and highlight the value of targeted sequencing on DNA derived from museum specimens to uncover long-term patterns of genetic differentiation in wildlife populations.

Variability in ITS1 and ITS2 sequences of historic herbaria and extant (fresh) Phalaris species (Poaceae)

BACKGROUND

Phalaris species (Poaceae) occupy diverse environments throughout all continents except Antarctica. Phalaris arundinacea is an important forage, ornamental, wetland restoration and biofuel crop grown globally as well as being a wetland invasive. The nuclear ribosomal internal transcribed spacer (ITS) region has been used for Phalaris barcoding as a DNA region with high nucleotide diversity for Phalaris species identification. Recent findings that P. arundinacea populations in Minnesota USA are most likely native and not European prompted this analysis to determine whether Eurasian vs. native North American P. arundinacea differed in ITS regions. Our objectives were to amplify and compare ITS regions (ITS1 and ITS2) of historic herbaria (1882-2001) and extant (fresh) Phalaris specimens; analyze ITS regions for species-specific polymorphisms (diagnostic SNPs) and compare ITS regions of historic Phalaris specimens with known, extant Phalaris species.

RESULTS

We obtained complete ITS1 and ITS2 sequences from 31 Phalaris historic (herbaria samples, 1908 to 2001) and five extant (fresh) specimens. Herbaria Phalaris specimens did not produce new SNPs (single nucleotide polymorphisms) not present in extant specimens. Diagnostic SNPs were identified in 8/12 (66.6%) Phalaris species. This study demonstrates the use of herbaria tissue for barcoding as a means for improved species identification of Phalaris herbaria specimens. No significant correlation between specimen age and genomic DNA concentration was found. Phalaris arundinacea showed high SNP variation within its clade, with the North American being distinctly different than other USA and most Eurasian types, potentially allowing for future identification of specific SNPs to geographic origin.

CONCLUSIONS

While not as efficient as extant specimens to obtain DNA, Phalaris herbaria specimens can produce high quality ITS sequences to evaluate historic genetic resources and facilitate identification of new species-specific barcodes. No correlation between DNA concentration and age of historic samples (119 year range) occurred. Considerable polymorphism was exhibited in the P. arundinacea clade with several N. American accessions being distinct from Eurasian types. Further development of within species- and genus-specific barcodes could contribute to designing PCR primers for efficient and accurate identification of N. American P. arundinacea. Our finding of misidentified Phalaris species indicates the need to exercise stringent quality control measures on newly generated sequence data and to approach public sequence databases in a critical way.

Mining museums for historical DNA: advances and challenges in museomics

Historical DNA (hDNA), obtained from museum and herbarium specimens, has yielded spectacular new insights into the history of organisms. This includes documenting historical genetic erosion and extinction, discovering species new to science, resolving evolutionary relationships, investigating epigenetic effects, and determining origins of infectious diseases. However, the development of best-practices in isolating, processing, and analyzing hDNA remain under-explored, due to the substantial diversity of specimen preparation types, tissue sources, archival ages, and collecting histories. Thus, for hDNA to reach its full potential, and justify the destructive sampling of the rarest specimens, more experimental work using time-series collections, and the development of improved methods to correct for data asymmetries and biases due to DNA degradation are required.

Viral Sequences Recovered From Puma Tooth DNA Reconstruct Statewide Viral Phylogenies

Monitoring pathogens in wildlife populations is imperative for effective management, and for identifying locations for pathogen spillover among wildlife, domestic species and humans. Wildlife pathogen surveillance is challenging, however, as sampling often requires the capture of a significant proportion of the population to understand host pathogen dynamics. To address this challenge, we assessed the ability to use hunter-collected teeth from puma across Colorado to recover genetic data of two feline retroviruses, feline foamy virus (FFV) and feline immunodeficiency virus (FIVpco) and show they can be utilized for this purpose. Comparative phylogenetic analyses of FIVpco and FFV from tooth and blood samples to previous analyses conducted with blood samples collected over a nine-year period from two distinct areas was undertaken highlighting the value of tooth derived samples. We found less FIVpco phylogeographic structuring than observed from sampling only two regions and that FFV data confirmed previous findings of endemic infection, minimal geographic structuring, and supported frequent cross-species transmission from domestic cats to pumas. Viral analysis conducted using intentionally collected blood samples required extensive financial, capture and sampling efforts. This analysis illustrates that viral genomic data can be cost effectively obtained using tooth samples incidentally-collected from hunter harvested pumas, taking advantage of samples collected for morphological age identification. This technique should be considered as an opportunistic method to provide broad geographic sampling to define viral dynamics more accurately in wildlife.

Assessing genotyping errors in mammalian museum study skins using high-throughput genotyping-by-sequencing

The use of museum specimens held in natural history repositories for population and conservation genetic research is increasing in tandem with the use of massively parallel sequencing technologies. Short Tandem Repeats (STRs), or microsatellite loci, are commonly used genetic markers in wildlife and population genetic studies. However, they traditionally suffered from a host of issues including length homoplasy, high costs, low throughput, and difficulties in reproducibility across laboratories. Massively parallel sequencing technologies can address these problems, but the incorporation of museum specimen derived DNA suffers from significant fragmentation and exogenous DNA contamination. Combatting these issues requires extra measures of stringency in the lab and during data analysis, yet there have not been any high-throughput sequencing studies evaluating microsatellite allelic dropout from museum specimen extracted DNA. In this study, we evaluate genotyping errors derived from mammalian museum skin DNA extracts for previously characterized microsatellites across PCR replicates utilizing high-throughput sequencing. We found it useful to classify samples based on DNA concentration, which determined the rate by which genotypes were accurately recovered. Longer microsatellites performed worse in all museum specimens. Allelic dropout rates across loci were dependent on sample quantity, with high concentration museum specimens performing as well and recovering quality metrics nearly as high as the frozen tissue sample. Based on our results, we provide a set of best practices for quality assurance and incorporation of reliable genotypes from museum specimens.

Characterizing the elusive Vancouver Island wolverine, Gulo gulo vancouverensis, using historical DNA

The wolverine (Gulo gulo) is a Holarctic species found in North America primarily across the boreal forest, the subarctic, and along the Pacific coast, including Vancouver Island (VI), British Columbia. While wolverines on VI are rare and possibly extirpated, they have been previously described as a unique subspecies, G. g. vancouverensis, distinct from G. g. luscus from the mainland of North America. However, the validity of the VI subspecies is contentious, with conflicting results from studies of skull morphology. Here, we used molecular analyses to characterize the genetic diversity of the VI population and resolve this taxonomic debate to assist with conservation priorities. Historical DNA of VI wolverines was obtained from museum specimens, amplified at 16 nuclear microsatellite loci, and sequenced at the mitochondrial D-loop control region to compare with wolverines from mainland British Columbia. The VI population had lower allelic richness and was fixed for a single common mtDNA haplotype. Bayesian and non-Bayesian assignments using microsatellites generally revealed admixture across populations, implying allele frequencies between the VI and mainland populations were not significantly different. Hence, both types of genetic markers showed little evolutionary divergence between VI and the mainland population. Combined, these results do not provide evidence of significant genetic distinction for VI wolverines, nor support the subspecific classification. Immediate conservation efforts should focus on estimating population size, while future conservation planning can assume VI wolverines likely are not a unique genetic population and there remains the potential for natural recolonization of wolverines to VI.

Accurate Sex Identification of Ancient Elephant and Other Animal Remains Using Low-Coverage DNA Shotgun Sequencing Data

Sex identification of ancient animal biological remains can benefit our understanding of historical population structure, demography and social behavior. Traditional methods for sex identification (e.g., osteological and morphometric comparisons) may be ineffective when animal remains are not well preserved, when sex distinguishing characteristics have not yet developed, or where organisms do not exhibit sex-associated phenotypic dimorphisms. Here we adapt a method developed for human sex determination so that it can be used to identify the sex of ancient and modern animal taxa. The method identifies sex by calculating the ratio of DNA reads aligning to the X chromosome to DNA reads aligning to autosomes (termed the Rx ratio). We tested the accuracy of this method using low coverage genomes from 15 modern elephants (Loxodonta africana) for which sex was known. We then applied this method to ancient elephant ivory samples for which sex was unknown, and describe how this method can be further adapted to the genomes of other taxa. This method may be especially useful when only low-coverage genomic data are obtainable. Furthermore, because this method relies on only the X and not the Y chromosome, it can be used to determine the sex of organisms for which a reference genome was obtained from a female or for which only the X chromosome is reported. Such taxa include the domestic cat, sheep, goat, and horse; and non-domesticated animals such as the Sumatran orangutan, western lowland gorilla and meerkat.

Evaluation of DNA degradation and establishment of a degradation analysis model for Lepidoptera specimens

Millions of museum specimens are integral to biodiversity studies; however, DNA degradation may limit the ability to obtain DNA sequences. In this study, a degradation analysis model for Lepidoptera specimens was established. Based on this model, we revealed the characteristics of DNA fragment distribution caused by external DNA damage factors during specimen preservation. We found that the degree of DNA degradation increased over time; DNA degradation of spread and dried adult specimens was significantly higher than that in the folded and formalin-fixed larval specimens. However, the effects of folding wings on DNA degradation and the effects of the preservation method/stage (formalin-fixed larval vs air-dried adult specimens) were different for different species.

Consideration of sample source for establishing reliable genetic microsatellite data from mammalian carnivore specimens held in natural history collections

Specimens from natural history collections (NHCs) are increasingly being used for genetic studies and can provide information on extinct populations, facilitate comparisons of historical and contemporary populations, produce baseline data before environmental changes, and elucidate patterns of change. Destructive sampling for DNA may be in disagreement with NHC goals of long-term care and maintenance. Differentiating quality among sample sources can direct destructive sampling to the source predicted to yield the highest quality DNA and most reliable data, potentially reducing damage to specimens, laboratory costs, and genotyping errors. We used the kit fox (Vulpes macrotis) as a model species and evaluated the quality and reliability of genetic data obtained from carnivoran specimens via three different sample sources: cranial bones, nasal bones, and toepads. We quantified variation in microsatellite amplification success and genotyping error rates and assessed the reliability of source-specific genic data. Toepads had the highest amplification success rates and lowest genotyping error rates. Shorter loci had higher amplification success and lower allelic dropout rates than longer loci. There were substantial differences in the reliability of resulting multilocus genotypes. Toepads produced the most reliable data, required the fewest replicates, and therefore, had the lowest costs to achieve reliable data. Our results demonstrate that the quality of DNA obtained from specimens varies by sample source and can inform NHCs when evaluating requests for destructive sampling. Our results suggest that prior to large-scale specimen sampling, researchers should conduct pilot studies to differentiate among source-specific data reliability, identify high performing loci, reduce costs of analyses, and minimize destructive sampling.

The Two Brothers: an enlightening study of ancient Egyptian teeth

The 'Two Brothers', two 4,000-year-old Egyptian mummies, were discovered buried alongside each other in an ancient Egyptian tomb in 1907, and were later relocated to the Manchester Museum. The hieroglyphic inscriptions on the coffins indicate that the mummies, Nakht-Ankh and Khnum-Nakht, were brothers but when the mummies were unwrapped and investigated in 1908, the skeletal morphologies were found to be quite different, suggesting an absence of family relationship. In 2017, their teeth were re-examined and, similar to most ancient Egyptian teeth, they display evidence of excessive tooth wear but there is little indication of carious lesions. Khnum-Nakht presents the rare developmental disorder of fusion of the left maxillary incisor and gemination of the right incisor, probably the earliest recorded instance of this irregularity. Analysis of the DNA from their molar teeth has been able to shed some light on the longstanding question of the kinship of the Two Brothers.

A novel proof of concept for capturing the diversity of endophytic fungi preserved in herbarium specimens

Herbarium specimens represent important records of morphological and genetic diversity of plants that inform questions relevant to global change, including species distributions, phenology and functional traits. It is increasingly appreciated that plant microbiomes can influence these aspects of plant biology, but little is known regarding the historic distribution of microbes associated with plants collected in the pre-molecular age. If microbiomes can be observed reliably in herbarium specimens, researchers will gain a new lens with which to examine microbial ecology, evolution, species interactions. Here, we describe a method for accessing historical plant microbiomes from preserved herbarium specimens, providing a proof of concept using two plant taxa from the imperiled boreal biome (Andromeda polifolia and Ledum palustre subsp. groenlandicum, Ericaceae). We focus on fungal endophytes, which occur within symptomless plant tissues such as leaves. Through a three-part approach (i.e. culturing, cloning and next-generation amplicon sequencing via the Illumina MiSeq platform, with extensive controls), we examined endophyte communities in dried, pressed leaves that had been processed as regular herbarium specimens and stored at room temperature in a herbarium for four years. We retrieved only one endophyte in culture, but cloning and especially the MiSeq analysis revealed a rich community of foliar endophytes. The phylogenetic distribution and diversity of endophyte assemblages, especially among the Ascomycota, resemble endophyte communities from fresh plants collected in the boreal biome. We could distinguish communities of endophytes in each plant species and differentiate likely endophytes from fungi that could be surface contaminants. Taxa found by cloning were observed in the larger MiSeq dataset, but species richness was greater when subsets of the same tissues were evaluated with the MiSeq approach. Our findings provide a proof of concept for capturing endophyte DNA from herbarium specimens, supporting the importance of herbarium records as roadmaps for understanding the dynamics of plant-associated microbial biodiversity in the Anthropocene.This article is part of the theme issue 'Biological collections for understanding biodiversity in the Anthropocene'.

Salmo macrostigma (Teleostei, Salmonidae): Nothing more than a brown trout (S. trutta) lineage?

We examined specimens of the macrostigma trout Salmo macrostigma, which refers to big black spots on the flanks, to assess whether it is an example of taxonomic inflation within the brown trout Salmo trutta complex. Using new specimens, publicly available data and a mitogenomic protocol to amplify the control and cytochrome b regions of the mitochondrial genome from degraded museum samples, including one syntype specimen, the present study shows that the macrostigma trout is not a valid species. Our results suggest the occurrence of a distinct evolutionary lineage of S. trutta in North Africa and Sicily. The name of the North African lineage is proposed for this lineage, which was found to be sister to the Atlantic lineage of brown trout, S. trutta.

Extraction of DNA from Human Skeletal Material

In recent years the recovery and analysis of DNA from skeletal remains has been applied to several contexts ranging from disaster victim identification to the identification of the victims of conflict. Here are described procedures for processing the bone and tooth samples including mechanical and chemical cleaning, cutting and powdering in the presence of liquid nitrogen, complete demineralization of bone and tooth powder, DNA extraction, DNA purification using magnetic beads, and the precautions and strategies implemented to avoid and detect contamination. It has proven highly successful in the analysis of bones and teeth from Second World War victims' skeletal remains that have been excavated from mass graves in Slovenia and is also suitable for genetic identification of relatively fresh human remains.

Re-inventing ancient human DNA

For a long time, the analysis of ancient human DNA represented one of the most controversial disciplines in an already controversial field of research. Scepticism in this field was only matched by the long-lasting controversy over the authenticity of ancient pathogen DNA. This ambiguous view on ancient human DNA had a dichotomous root. On the one hand, the interest in ancient human DNA is great because such studies touch on the history and evolution of our own species. On the other hand, because these studies are dealing with samples from our own species, results are easily compromised by contamination of the experiments with modern human DNA, which is ubiquitous in the environment. Consequently, some of the most disputed studies published - apart maybe from early reports on million year old dinosaur or amber DNA - reported DNA analyses from human subfossil remains. However, the development of so-called next- or second-generation sequencing (SGS) in 2005 and the technological advances associated with it have generated new confidence in the genetic study of ancient human remains. The ability to sequence shorter DNA fragments than with PCR amplification coupled to traditional Sanger sequencing, along with very high sequencing throughput have both reduced the risk of sequencing modern contamination and provided tools to evaluate the authenticity of DNA sequence data. The field is now rapidly developing, providing unprecedented insights into the evolution of our own species and past human population dynamics as well as the evolution and history of human pathogens and epidemics. Here, we review how recent technological improvements have rapidly transformed ancient human DNA research from a highly controversial subject to a central component of modern anthropological research. We also discuss potential future directions of ancient human DNA research.

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.

Curriculum and course materials for a forensic DNA biology course

The Forensic Science Education Programs Accreditation Commission (FEPAC) requires accredited programs offer a "coherent curriculum" to ensure each student gains a "thorough grounding of the natural…sciences." Part of this curriculum includes completion of a minimum of 15 semester-hours forensic science coursework, nine of which can involve a class in forensic DNA biology. Departments that have obtained or are pursuing FEPAC accreditation can meet this requirement by offering a stand-alone forensic DNA biology course; however, materials necessary to instruct students are often homegrown and not standardized; in addition, until recently, the community lacked commercially available books, lab manuals, and teaching materials, and many of the best pedagogical resources were scattered across various peer-reviewed journals. The curriculum discussed below is an attempt to synthesize this disparate information, and although certainly not the only acceptable methodology, the below discussion represents "a way" for synthesizing and aggregating this information into a cohesive, comprehensive whole.

Preservation of bacterial DNA by human dentin

INTRODUCTION

The capacity of dentin and collagen to bind DNA and protect against spontaneous and nuclease-induced degradation was evaluated individually and by the incubation of DNA with nuclease-producing bacteria in a mixed culture.

METHODS

Extracted Fusobacterium nucleatum DNA was incubated with dentin shavings or collagen for 90 minutes. The DNA-bound substrates were incubated in different media (water, sera, and DNase I) for up to 3 months. Amplifiable DNA was released from dentin using EDTA,or from collagen using proteinase K, and evaluated by polymerase chain reaction (PCR). The stability of dentin-bound DNA was also assessed in a mixed culture (Parvimonas micra and Pseudoramibacter alactolyticus) containing a DNase-producing species, Prevotella intermedia. Samples were analyzed for amplifiable DNA.

RESULTS

In water, dentin-bound DNA was recoverable by PCR at 3 months compared with no detectable DNA after 4 weeks in controls (no dentin). DNA bound to collagen was detectable by PCR after 3 months of incubation in water. In 10% human sera, amplifiable DNA was detectable at 3 months when dentin bound and in controls (no dentin). In mixed bacterial culture, dentin-bound DNA was recoverable throughout the experimental period (3 months), compared with no recoverable F. nucleatum DNA within 24 hours in controls (no dentin).

CONCLUSIONS

There is a strong binding affinity between DNA and dentin, and between DNA and serum proteins or collagen. These substrates preserve DNA against natural decomposition and protect DNA from nuclease activity, factors that may confound molecular analysis of the endodontic microbiota yet favor paleomicrobiological studies of ancient DNA.

Extracting DNA from museum bird eggs, and whole genome amplification of archive DNA

We present a comprehensive protocol for extracting DNA from egg membranes and other internal debris recovered from the interior of blown museum bird eggs. A variety of commercially available DNA extraction methods were found to be applicable. DNA sequencing of polymerase chain reaction (PCR) products for a 176-bp fragment of mitochondrial DNA was successful for most egg samples (> 78%) even though the amount of DNA extracted (mean = 14.71 ± 4.55 ng/µL) was significantly less than that obtained for bird skin samples (mean = 67.88 ± 4.77 ng/µL). For PCR and sequencing of snipe (Gallinago) DNA, we provide eight new primers for the 'DNA barcode' region of COI mtDNA. In various combinations, the primers target a range of PCR products sized from 72 bp to the full 'barcode' of 751 bp. Not all possible combinations were tested with archive snipe DNA, but we found a significantly better success rate of PCR amplification for a shorter 176-bp target compared with a larger 288-bp fragment (67% vs. 39%). Finally, we explored the feasibility of whole genome amplification (WGA) for extending the use of archive DNA in PCR and sequencing applications. Of two WGA approaches, a PCR-based method was found to be able to amplify whole genomic DNA from archive skins and eggs from museum bird collections. After WGA, significantly more archive egg samples produced visible PCR products on agarose (56.9% before WGA vs. 79.0% after WGA). However, overall sequencing success did not improve significantly (78.8% compared with 83.0%).

Optimizing the use of shed feathers for genetic analysis

Shed feathers obtained by noninvasive genetic sampling (NGS) are a valuable source of DNA for genetic studies of birds. They can be collected across a large geographical range and facilitate research on species that would otherwise be extremely difficult to study. A limitation of this approach is uncertainty concerning the quality of the extracted DNA. Here we investigate the relationship between feather type, feather condition and DNA quality (amplification success) in order to provide a simple, cost-effective method for screening samples prior to genetic analysis. We obtained 637 shed feathers of the powerful owl (Ninox strenua) from across its range in southeastern Australia. The extracted DNA was amplified using polymerase chain reaction for a range of markers including mitochondrial DNA, ND3 and nuclear DNA, a simple sequence repeat (Nst02) and a portion of the CHD-1 gene (P2/P8). We found that feather condition significantly influenced the amplification success of all three loci, with feathers characterized as 'good' having greater success. Feather type was found to be of lower importance, with good quality feathers of all types consistently producing high success for all three loci. We also found that the successful amplification of multilocus genotypes was dependant on the condition of the starting material and was highly correlated with successful amplification of the sex-linked CHD-1 locus. Samples with low DNA quality have a higher probability of amplification failure and are more likely to produce incorrect genotypes; therefore, identifying samples with high DNA quality can save substantial time and cost associated with the genetic analysis of NGS. As a result, we propose a method for screening shed feathers in order to provide a subset of samples which will have a greater probability of containing high quality DNA suitable for the amplification of multilocus genotypes.

High efficiency protocol of DNA extraction from Micromys minutus mandibles from owl pellets: a tool for molecular research of cryptic mammal species

Owl pellets have high potential as a source of DNA. However, this noninvasive method of collecting DNA is rarely used, and its methodological aspects are poorly understood. We investigated the methodology for DNA extraction and amplification from owl pellets containing the smallest European rodent—the Harvest mouse Micromys minutus—as an example. We used mandibles identified in owl pellets for mitochondrial and nuclear DNA amplification. For DNA extraction, we tested two commercial protocols and utilized a protocol being a combination of two commercial kits which ensured high efficiency of DNA extraction. Additionally, we recorded that the amount of DNA was five times higher in extracts from teeth as compared to DNA extracts from jawbones derived from the same mandible. The quantity of DNA was significantly positively correlated with biological sample weight; however, the age of the pellet remains had an impact on the level of inhibition. We recorded inhibition in 40 % of mtDNA extracts derived from pellets older than 150 months, whereas in DNA extracts from pellets younger than 80 months, we did not observe a negative impact of inhibition on PCR efficiency. The amplification success rate was 89.9 % for the mitochondrial fragment and 39.4 % in the case of the nuclear fragment. We observed partial degradation of DNA evidenced by the fact that the longest fragments that we were able to amplify in the case of mtDNA were 450 and 200 bp for nuDNA. The study shows that pellets can be considered as a source of DNA and have high potential for molecular research in the case of threatened species and species that are difficult to study using standard field techniques.

Monitoring DNA contamination in handled vs. directly excavated ancient human skeletal remains

Bones, teeth and hair are often the only physical evidence of human or animal presence at an archaeological site; they are also the most widely used sources of samples for ancient DNA (aDNA) analysis. Unfortunately, the DNA extracted from ancient samples, already scarce and highly degraded, is widely susceptible to exogenous contaminations that can affect the reliability of aDNA studies. We evaluated the molecular effects of sample handling on five human skeletons freshly excavated from a cemetery dated between the 11 to the 14(th) century. We collected specimens from several skeletal areas (teeth, ribs, femurs and ulnas) from each individual burial. We then divided the samples into two different sets: one labeled as "virgin samples" (i.e. samples that were taken by archaeologists under contamination-controlled conditions and then immediately sent to the laboratory for genetic analyses), and the second called "lab samples"(i.e. samples that were handled without any particular precautions and subject to normal washing, handling and measuring procedures in the osteological lab). Our results show that genetic profiles from "lab samples" are incomplete or ambiguous in the different skeletal areas while a different outcome is observed in the "virgin samples" set. Generally, all specimens from different skeletal areas in the exception of teeth present incongruent results between "lab" and "virgin" samples. Therefore teeth are less prone to contamination than the other skeletal areas we analyzed and may be considered a material of choice for classical aDNA studies. In addition, we showed that bones can also be a good candidate for human aDNA analysis if they come directly from the excavation site and are accompanied by a clear taphonomic history.

A sensitive and specific multiplex PCR approach for sex identification of ursine and tremarctine bears suitable for non-invasive samples

We report a new approach for molecular sex identification of extant Ursinae and Tremarctinae bears. Two Y-specific fragments (SMCY and 318.2) and one X-specific fragment (ZFX) are amplified in a multiplex PCR, yielding a double test for male-specific amplification and an internal positive control. The primers were designed and tested to be bear-specific, thereby minimizing the risk of cross-amplification in other species including humans. The high sensitivity and small amplicon sizes (100, 124, 160 base pairs) facilitate analysis of non-invasively obtained DNA material. DNA from tissue and blood as well as from 30 non-invasively collected hair and faeces yielded clear and easily interpretable results. The fragments were detected both by standard gel electrophoresis and automated capillary electrophoresis.

Ancient DNA studies: new perspectives on old samples

In spite of past controversies, the field of ancient DNA is now a reliable research area due to recent methodological improvements. A series of recent large-scale studies have revealed the true potential of ancient DNA samples to study the processes of evolution and to test models and assumptions commonly used to reconstruct patterns of evolution and to analyze population genetics and palaeoecological changes. Recent advances in DNA technologies, such as next-generation sequencing make it possible to recover DNA information from archaeological and paleontological remains allowing us to go back in time and study the genetic relationships between extinct organisms and their contemporary relatives. With the next-generation sequencing methodologies, DNA sequences can be retrieved even from samples (for example human remains) for which the technical pitfalls of classical methodologies required stringent criteria to guaranty the reliability of the results. In this paper, we review the methodologies applied to ancient DNA analysis and the perspectives that next-generation sequencing applications provide in this field.

Microsatellite genotyping reveals end-Pleistocene decline in mammoth autosomal genetic variation

The last glaciation was a dynamic period with strong impact on the demography of many species and populations. In recent years, mitochondrial DNA sequences retrieved from radiocarbon-dated remains have provided novel insights into the history of Late Pleistocene populations. However, genotyping of loci from the nuclear genome may provide enhanced resolution of population-level changes. Here, we use four autosomal microsatellite DNA markers to investigate the demographic history of woolly mammoths (Mammuthus primigenius) in north-eastern Siberia from before 60 000 years ago up until the species' final disappearance c.4000 years ago. We identified two genetic groups, implying a marked temporal genetic differentiation between samples with radiocarbon ages older than 12 thousand radiocarbon years before present (ka) and those younger than 9ka. Simulation-based analysis indicates that this dramatic change in genetic composition, which included a decrease in individual heterozygosity of approximately 30%, was due to a multifold reduction in effective population size. A corresponding reduction in genetic variation was also detected in the mitochondrial DNA, where about 65% of the diversity was lost. We observed no further loss in genetic variation during the Holocene, which suggests a rapid final extinction event.

A simple and accurate method to sex savannah, forest and Asian elephants using noninvasive sampling techniques

We report the development of a reliable and efficient method for molecular sexing of all extant elephant taxa. We developed primers that amplify two short Y-specific fragments (SRY1 and AMELY2) and one longer X-specific fragment (PLP1), developed from elephant sequences in one multiplex PCR. All fragments were designed to be short (< 200 basepairs) for use with degraded DNA and to be 50 basepairs apart to optimize visualization on agarose gels or as electropherograms. The multiplex PCR method matched sexes for at least 97.9% of the noninvasive savannah elephant samples and produced the expected female/male banding patterns for 14 African forest and 11 Asian elephant samples. We found this method to be more robust, efficient and less prone to contamination than previously developed sexing methods for elephants.

Factors affecting the STR amplification success in poorly preserved bone samples

Background

Factors affecting the success of short tandem repeat (STR) amplification of poorly preserved samples are generally known, but as of yet, they have seldom been systematically assessed. Using two different maximum likelihood-based methods, the relative importance of DNA quantity, degradation and inhibition in STR genotyping was studied with DNA extracts from a set of old bone samples. First, the effects of different factors related to PCR amplification were estimated with a generalized linear mixed model. Second, error rates of allelic drop-out and drop-in were estimated on the basis of the frequency and nature of mismatches between replicates.

Results

In autosomal STR analyses, the most important factor was the DNA quantity, followed by the degradation, whereas in Y-chromosomal STR analysis, the most important factor was the degradation. Inhibition was a minor concern in STR analyses of poorly preserved bones.

Conclusions

The success of PCR amplification depends largely on the template DNA quality (amount and degradation), but these problems can be partly compensated for by different primer design and amplification chemistry. Consequently, the relative roles of the compromising factors differ according to the kit used.

Allele-specific extension allows base-pair neutral homozygotes to be discriminated by high-resolution melting of small amplicons

Not all single-nucleotide polymorphisms (SNPs) can be determined using high-resolution melting (HRM) of small amplicons, especially class 3 and 4 SNPs. This is due mainly to the small shift in the melting temperature (Tm) between two types of homozygote. Choosing rs1869458 (a class 4 SNP) as a sample, we developed a modified small amplicon HRM assay. An allele-specific extension (ASE) primer, which ended at an SNP site and matched only one of the alleles, was added to the reaction as well as additional thermal steps for ASE. Following asymmetric polymerase chain reaction and melting curve analysis, heterozygotes were easily identified. Two types of homozygote were also distinguishable, indicating that extension primers 11 to 13 bases in length worked efficiently in an allele-specific way. Modification of the limiting amplification primer with locked nucleic acid increased the Tm difference between extension and amplification peaks and facilitated subsequent genotyping. In addition, 194 human genomic DNA samples were genotyped with the developed assay and by direct sequencing, with the different methods providing identical genotyping results. In conclusion, ASE-HRM is a simple, inexpensive, closed-tube genotyping method that can be used to examine all types of SNP.

Searching for DNA in museum specimens: a comparison of sources in a mammal species

The number of genetic studies that use preserved specimens as sources of DNA has been steadily increasing during the last few years. Therefore, selecting the sources that are more likely to provide a suitable amount of DNA of enough quality to be amplified and at the minimum cost to the original specimen is an important step for future research. We have compared different types of tissue (hides vs. bones) from museum specimens of Iberian lynx and multiple alternative sources within each type (skin, footpad, footpad powder, claw, diaphysis, maxilloturbinal bone, mastoid process and canine) for DNA yield and probability of amplification of both mitochondrial and nuclear targets. Our results show that bone samples yield more and better DNA than hides, particularly from sources from skull, such as mastoid process and canines. However, claws offer an amplification success as high as bone sources, which makes them the preferred DNA source when no skeletal pieces have been preserved. Most importantly, these recommended sources can be sampled incurring minimal damage to the specimens while amplifying at a high success rate for both mitochondrial and microsatellite markers.

"Orthograde entrance technique" to recover DNA from ancient teeth preserving the physical structure

Milling methods utilized by molecular researchers destruct the morphological structure of ancient teeth, crucial in anthropological evaluation. This causes researchers to be reluctant to try DNA analyses. Retrograde, reverse root canal technique, which is from root apex to the tooth crown, provides both a dentine rich sample and a procedure that overcomes this problem. However, this technique has some disadvantages due to the relatively fragile, permeable and weak nature of the tooth root. On the other hand, "orthograde entrance technique", straight from tooth crown to the root apex, both preserves the morphological structure and deals with the problems related to the root structure by providing an entrance from the enamel surface. Moreover comparable amplification results to prior studies in the literature were also achieved.

Single nucleotide polymorphism genotyping by mini-primer allele-specific amplification with universal reporter primers for identification of degraded DNA

Single nucleotide polymorphism (SNP) is informative for human identification, and much shorter regions are targeted in analysis of biallelic SNP compared with highly polymorphic short tandem repeat (STR). Therefore, SNP genotyping is expected to be more sensitive than STR genotyping of degraded human DNA. To achieve simple, economical, and sensitive SNP genotyping for identification of degraded human DNA, we developed 18 loci for a SNP genotyping technique based on the mini-primer allele-specific amplification (ASA) combined with universal reporter primers (URP). The URP/ASA-based genotyping consisted of two amplifications followed by detection using capillary electrophoresis. The sizes of the target genome fragments ranged from 40 to 67bp in length. In the Japanese population, the frequencies of minor alleles of 18 SNPs ranged from 0.36 to 0.50, and these SNPs are informative for identification. The success rate of SNP genotyping was much higher than that of STR genotyping of artificially degraded DNA. Moreover, we applied this genotyping method to case samples and showed successful SNP genotyping of severely degraded DNA from a 4-year buffered formalin-fixed tissue sample for human identification.

DNA damage in preserved specimens and tissue samples: a molecular assessment

The extraction of genetic information from preserved tissue samples or museum specimens is a fundamental component of many fields of research, including the Barcode of Life initiative, forensic investigations, biological studies using scat sample analysis, and cancer research utilizing formaldehyde-fixed, paraffin-embedded tissue. Efforts to obtain genetic information from these sources are often hampered by an inability to amplify the desired DNA as a consequence of DNA damage.

Previous studies have described techniques for improved DNA extraction from such samples or focused on the effect of damaging agents – such as light, oxygen or formaldehyde – on free nucleotides.

We present ongoing work to characterize lesions in DNA samples extracted from preserved specimens. The extracted DNA is digested to single nucleosides with a combination of DNase I, Snake Venom Phosphodiesterase, and Antarctic Phosphatase and then analyzed by HPLC-ESI-TOF-MS.

We present data for moth specimens that were preserved dried and pinned with no additional preservative and for frog tissue samples that were preserved in either ethanol, or formaldehyde, or fixed in formaldehyde and then preserved in ethanol. These preservation methods represent the most common methods of preserving animal specimens in museum collections. We observe changes in the nucleoside content of these samples over time, especially a loss of deoxyguanosine. We characterize the fragmentation state of the DNA and aim to identify abundant nucleoside lesions. Finally, simple models are introduced to describe the DNA fragmentation based on nicks and double-strand breaks.

New developments in ancient genomics

Ancient DNA research is on the crest of a 'third wave' of progress due to the introduction of a new generation of DNA sequencing technologies. Here we review the advantages and disadvantages of the four new DNA sequencers that are becoming available to researchers. These machines now allow the recovery of orders of magnitude more DNA sequence data, albeit as short sequence reads. Hence, the potential reassembly of complete ancient genomes seems imminent, and when used to screen libraries of ancient sequences, these methods are cost effective. This new wealth of data is also likely to herald investigations into the functional properties of extinct genes and gene complexes and will improve our understanding of the biological basis of extinct phenotypes.