Unraveling Signatures of Local Adaptation among Indigenous Groups from Mexico.

Few studies have addressed how selective pressures have shaped the genetic structure of the current Native American populations, and they have mostly limited their inferences to admixed Latin American populations. Here, we searched for local adaptation signals, based on integrated haplotype scores and population branch statistics, in 325 Mexican Indigenous individuals with at least 99% Native American ancestry from five previously defined geographical regions. Although each region exhibited its own local adaptation profile, only PPARG and AJAP1, both negative regulators of the Wnt/ß catenin signaling pathway, showed significant adaptation signals in all the tested regions. Several signals were found, mainly in the genes related to the metabolic processes and immune response. A pathway enrichment analysis revealed the overrepresentation of selected genes related to several biological phenotypes/conditions, such as the immune response and metabolic pathways, in agreement with previous studies, suggesting that immunological and metabolic pressures are major drivers of human adaptation. Genes related to the gut microbiome measurements were overrepresented in all the regions, highlighting the importance of studying how humans have coevolved with the microbial communities that colonize them. Our results provide a further explanation of the human evolutionary history in response to environmental pressures in this region.

The genomic landscape of Mexican Indigenous populations brings insights into the peopling of the Americas.

The genetic makeup of Indigenous populations inhabiting Mexico has been strongly influenced by geography and demographic history. Here, we perform a genome-wide analysis of 716 newly genotyped individuals from 60 of the 68 recognized ethnic groups in Mexico. We show that the genetic structure of these populations is strongly influenced by geography, and our demographic reconstructions suggest a decline in the population size of all tested populations in the last 15-30 generations. We find evidence that Aridoamerican and Mesoamerican populations diverged roughly 4-9.9 ka, around the time when sedentary farming started in Mesoamerica. Comparisons with ancient genomes indicate that the Upward Sun River 1 (USR1) individual is an outgroup to Mexican/South American Indigenous populations, whereas Anzick-1 was more closely related to Mesoamerican/South American populations than to those from Aridoamerica, showing an even more complex history of divergence than recognized so far.

Reconstruction of ancient microbial genomes from the human gut.

Loss of gut microbial diversity1-6 in industrial populations is associated with chronic diseases7, underscoring the importance of studying our ancestral gut microbiome. However, relatively little is known about the composition of pre-industrial gut microbiomes. Here we performed a large-scale de novo assembly of microbial genomes from palaeofaeces. From eight authenticated human palaeofaeces samples (1,000-2,000 years old) with well-preserved DNA from southwestern USA and Mexico, we reconstructed 498 medium- and high-quality microbial genomes. Among the 181 genomes with the strongest evidence of being ancient and of human gut origin, 39% represent previously undescribed species-level genome bins. Tip dating suggests an approximate diversification timeline for the key human symbiont Methanobrevibacter smithii. In comparison to 789 present-day human gut microbiome samples from eight countries, the palaeofaeces samples are more similar to non-industrialized than industrialized human gut microbiomes. Functional profiling of the palaeofaeces samples reveals a markedly lower abundance of antibiotic-resistance and mucin-degrading genes, as well as enrichment of mobile genetic elements relative to industrial gut microbiomes. This study facilitates the discovery and characterization of previously undescribed gut microorganisms from ancient microbiomes and the investigation of the evolutionary history of the human gut microbiota through genome reconstruction from palaeofaeces.

Ancient mitochondrial DNA and ancestry of Paquimé inhabitants, Casas Grandes (A.D. 1200-1450).

OBJECTIVES: The Casas Grandes (Paquimé) culture, located in the Northwest of Chihuahua, Mexico reached its apogee during the Medio Period (A.D. 1200-1450). Paquimé was abandoned by the end of the Medio Period (A.D. 1450), and the ancestry of its inhabitants remains unsolved. Some authors suggest that waves of Mesoamerican immigrants, possibly merchants, stimulated Paquimé's development during the Medio Period. Archaeological evidence suggests possible ties to groups that inhabited the Southwestern US cultures. This study uses ancient DNA analysis from fourteen samples to estimate genetic affinities of ancient Paquimé inhabitants. MATERIALS AND METHODS: DNA was extracted from 14 dental ancient samples from Paquimé. PCR and Sanger sequencing were used to obtain mitochondrial control region sequences. Networks, PCoA, and Nei genetic distances were estimated to compare Paquimé haplotypes against available past haplotypes data from Southwestern and Mesoamerican groups. RESULTS: Haplogroups were characterized for 11 of the samples, and the results revealed the presence of four distinct Amerindian mitochondrial lineages: B (n = 5; 45%), A (n = 3; 27%), C (n = 2; 18%) and D (n = 1; 10%). Statistical analysis of the haplotypes, haplogroup frequencies, and Nei genetic distances showed close affinity of Paquimé with Mimbres. DISCUSSION: Although our results provide strong evidence of genetic affinities between Paquimé and Mimbres, with the majority of haplotypes shared or derived from ancient Southwest populations, the causes of cultural development at Paquimé still remain a question. These preliminary results provide evidence in support of other bioarchaeological studies, which have shown close biological affinities between Paquimé and Mimbres, a Puebloan culture, in the Southwestern US.