Demographic history and genetic structure in pre-Hispanic Central Mexico.

Aridoamerica and Mesoamerica are two distinct cultural areas in northern and central Mexico, respectively, that hosted numerous pre-Hispanic civilizations between 2500 BCE and 1521 CE. The division between these regions shifted southward because of severe droughts ~1100 years ago, which allegedly drove a population replacement in central Mexico by Aridoamerican peoples. In this study, we present shotgun genome-wide data from 12 individuals and 27 mitochondrial genomes from eight pre-Hispanic archaeological sites across Mexico, including two at the shifting border of Aridoamerica and Mesoamerica. We find population continuity that spans the climate change episode and a broad preservation of the genetic structure across present-day Mexico for the past 2300 years. Lastly, we identify a contribution to pre-Hispanic populations of northern and central Mexico from two ancient unsampled "ghost" populations.

Ancient viral genomes reveal introduction of human pathogenic viruses into Mexico during the transatlantic slave trade.

After the European colonization of the Americas, there was a dramatic population collapse of the Indigenous inhabitants caused in part by the introduction of new pathogens. Although there is much speculation on the etiology of the Colonial epidemics, direct evidence for the presence of specific viruses during the Colonial era is lacking. To uncover the diversity of viral pathogens during this period, we designed an enrichment assay targeting ancient DNA (aDNA) from viruses of clinical importance and applied it to DNA extracts from individuals found in a Colonial hospital and a Colonial chapel (16th-18th century) where records suggest that victims of epidemics were buried during important outbreaks in Mexico City. This allowed us to reconstruct three ancient human parvovirus B19 genomes and one ancient human hepatitis B virus genome from distinct individuals. The viral genomes are similar to African strains, consistent with the inferred morphological and genetic African ancestry of the hosts as well as with the isotopic analysis of the human remains, suggesting an origin on the African continent. This study provides direct molecular evidence of ancient viruses being transported to the Americas during the transatlantic slave trade and their subsequent introduction to New Spain. Altogether, our observations enrich the discussion about the etiology of infectious diseases during the Colonial period in Mexico.

The arrival of European colonists to the Americas, beginning in the 15^th century, contributed to the spread of new viruses amongst Indigenous people. This led to massive outbreaks of disease, and millions of deaths that caused an important Native population to collapse. The exact viruses that caused these outbreaks are unknown, but smallpox, measles, and mumps are all suspected. During these times, traders and colonists forcibly enslaved and displaced millions of people mainly from the West Coast of Africa to the Americas. The cruel, unsanitary, and overcrowded conditions on ships transporting these people across the Atlantic contributed to the spread of infectious diseases onboard. Once on land, infectious diseases spread quickly, partly due to the poor conditions that enslaved and ndigenous people were made to endure. Native people were also immunologically naïve to the newly introduced pathogens, making them susceptible to severe or fatal outcomes. The new field of paleovirology may help scientists identify the viruses that were circulating in the first years of colonization and trace how viruses arrived in the Americas. Using next-generation DNA sequencing and other cutting-edge techniques, Guzmán-Solís et al. extracted and enriched viral DNA from skeletal remains dating back to the 16^th century. These remains were found in mass graves that were used to bury epidemic victims at a colonial hospital and chapel in what is now Mexico City. The experiments identified two viruses, human parvovirus B19 and a human hepatitis B virus. These viral genomes were recovered from human remains of first-generation African people in Mexico, as well as an individual who was an Indigenous person. Although the genetic material of these ancient viruses resembled pathogens that originated in Africa, the study did not determine if the victims died from these viruses or another cause. On the other hand, the results indicate that viruses frequently found in modern Africa were circulating in the Americas during the slave trade period of Mexico. Finally, the results provide evidence that colonists who forcibly brought African people to the Americas participated in the introduction of viruses to Mexico. This constant influx of viruses from the old world, led to dramatic declines in the populations of Indigenous people in the Americas.

Community-curated and standardised metadata of published ancient metagenomic samples with AncientMetagenomeDir.

Ancient DNA and RNA are valuable data sources for a wide range of disciplines. Within the field of ancient metagenomics, the number of published genetic datasets has risen dramatically in recent years, and tracking this data for reuse is particularly important for large-scale ecological and evolutionary studies of individual taxa and communities of both microbes and eukaryotes. AncientMetagenomeDir (archived at https://doi.org/10.5281/zenodo.3980833 ) is a collection of annotated metagenomic sample lists derived from published studies that provide basic, standardised metadata and accession numbers to allow rapid data retrieval from online repositories. These tables are community-curated and span multiple sub-disciplines to ensure adequate breadth and consensus in metadata definitions, as well as longevity of the database. Internal guidelines and automated checks facilitate compatibility with established sequence-read archives and term-ontologies, and ensure consistency and interoperability for future meta-analyses. This collection will also assist in standardising metadata reporting for future ancient metagenomic studies.

Paleogenomic insights into the red complex bacteria Tannerella forsythia in Pre-Hispanic and Colonial individuals from Mexico.

The 'red complex' is an aggregate of three oral bacteria (Tannerella forsythia, Porphyromonas gingivalis and Treponema denticola) responsible for severe clinical manifestation of periodontal disease. Here, we report the first direct evidence of ancient T.forsythia DNA in dentin and dental calculus samples from archaeological skeletal remains that span from the Pre-Hispanic to the Colonial period in Mexico. We recovered twelve partial ancient T. forsythia genomes and observed a distinct phylogenetic placement of samples, suggesting that the strains present in Pre-Hispanic individuals likely arrived with the first human migrations to the Americas and that new strains were introduced with the arrival of European and African populations in the sixteenth century. We also identified instances of the differential presence of genes between periods in the T. forsythia ancient genomes, with certain genes present in Pre-Hispanic individuals and absent in Colonial individuals, and vice versa. This study highlights the potential for studying ancient T. forsythia genomes to unveil past social interactions through analysis of disease transmission. Our results illustrate the long-standing relationship between this oral pathogen and its human host, while also unveiling key evidence to understand its evolutionary history in Pre-Hispanic and Colonial Mexico. This article is part of the theme issue 'Insights into health and disease from ancient biomolecules'.