Inference and visualization of DNA damage patterns using a grade of membership model

Ancient environmental microbiomes and the cryosphere

In this review, we delineate the unique set of characteristics associated with cryosphere environments (namely, ice and permafrost) which present both challenges and opportunities for studying ancient environmental microbiomes (AEMs). In a field currently reliant on several assumptions, we discuss the theoretical and empirical feasibility of recovering microbial nucleic acids (NAs) from ice and permafrost with varying degrees of antiquity. We also summarize contamination control best practices and highlight considerations for the latest approaches, including shotgun metagenomics, and downstream bioinformatic authentication approaches. We review the adoption of existing software and provide an overview of more recently published programs, with reference to their suitability for AEM studies. Finally, we summarize outstanding challenges and likely future directions for AEM research.

Long genetic and social isolation in Neanderthals before their extinction

Neanderthal genomes have been recovered from sites across Eurasia, painting an increasingly complex picture of their populations' structure that mostly indicates that late European Neanderthals belonged to a single metapopulation with no significant evidence of population structure. Here, we report the discovery of a late Neanderthal individual, nicknamed "Thorin," from Grotte Mandrin in Mediterranean France, and his genome. These dentognathic fossils, including a rare example of distomolars, are associated with a rich archeological record of Neanderthal final technological traditions in this region ∼50-42 thousand years ago. Thorin's genome reveals a relatively early divergence of ∼105 ka with other late Neanderthals. Thorin belonged to a population with a small group size that showed no genetic introgression with other known late European Neanderthals, revealing some 50 ka of genetic isolation of his lineage despite them living in neighboring regions. These results have important implications for resolving competing hypotheses about causes of the disappearance of the Neanderthals.

Multiscale analysis of count data through topic alignment

Topic modeling is a popular method used to describe biological count data. With topic models, the user must specify the number of topics $K$. Since there is no definitive way to choose $K$ and since a true value might not exist, we develop a method, which we call topic alignment, to study the relationships across models with different $K$. In addition, we present three diagnostics based on the alignment. These techniques can show how many topics are consistently present across different models, if a topic is only transiently present, or if a topic splits into more topics when $K$ increases. This strategy gives more insight into the process of generating the data than choosing a single value of $K$ would. We design a visual representation of these cross-model relationships, show the effectiveness of these tools for interpreting the topics on simulated and real data, and release an accompanying R package, alto.

AuthentiCT: a model of ancient DNA damage to estimate the proportion of present-day DNA contamination

Contamination from present-day DNA is a fundamental issue when studying ancient DNA from historical or archaeological material, and quantifying the amount of contamination is essential for downstream analyses. We present AuthentiCT, a command-line tool to estimate the proportion of present-day DNA contamination in ancient DNA datasets generated from single-stranded DNA libraries. The prediction is based solely on the patterns of post-mortem damage observed on ancient DNA sequences. The method has the power to quantify contamination from as few as 10,000 mapped sequences, making it particularly useful for analysing specimens that are poorly preserved or for which little data is available.

Present-Day DNA Contamination in Ancient DNA Datasets

Present-day contamination can lead to false conclusions in ancient DNA studies. A number of methods are available to estimate contamination, which use a variety of signals and are appropriate for different types of data. Here an overview of currently available methods highlighting their strengths and weaknesses is provided, and a classification based on the signals used to estimate contamination is proposed. This overview aims at enabling researchers to choose the most appropriate methods for their dataset. Based on this classification, potential avenues for the further development of methods are discussed.

Genetic history from the Middle Neolithic to present on the Mediterranean island of Sardinia

The island of Sardinia has been of particular interest to geneticists for decades. The current model for Sardinia's genetic history describes the island as harboring a founder population that was established largely from the Neolithic peoples of southern Europe and remained isolated from later Bronze Age expansions on the mainland. To evaluate this model, we generate genome-wide ancient DNA data for 70 individuals from 21 Sardinian archaeological sites spanning the Middle Neolithic through the Medieval period. The earliest individuals show a strong affinity to western Mediterranean Neolithic populations, followed by an extended period of genetic continuity on the island through the Nuragic period (second millennium BCE). Beginning with individuals from Phoenician/Punic sites (first millennium BCE), we observe spatially-varying signals of admixture with sources principally from the eastern and northern Mediterranean. Overall, our analysis sheds light on the genetic history of Sardinia, revealing how relationships to mainland populations shifted over time.