Ana Magdalena Hurtado

Geographic patterns of genome admixture in Latin American Mestizos.

The large and diverse population of Latin America is potentially a powerful resource for elucidating the genetic basis of complex traits through admixture mapping. However, no genome-wide characterization of admixture across Latin America has yet been attempted. Here, we report an analysis of admixture in thirteen Mestizo populations (i.e. in regions of mainly European and Native settlement) from seven countries in Latin America based on data for 678 autosomal and 29 X-chromosome microsatellites. We found extensive variation in Native American and European ancestry (and generally low levels of African ancestry) among populations and individuals, and evidence that admixture across Latin America has often involved predominantly European men and both Native and African women. An admixture analysis allowing for Native American population subdivision revealed a differentiation of the Native American ancestry amongst Mestizos. This observation is consistent with the genetic structure of pre-Columbian populations and with admixture having involved Natives from the area where the Mestizo examined are located. Our findings agree with available information on the demographic history of Latin America and have a number of implications for the design of association studies in population from the region.

Y-Chromosome Evidence for Differing Ancient Demographic Histories in the Americas

To scrutinize the male ancestry of extant Native American populations, we examined eight biallelic and six microsatellite polymorphisms from the nonrecombining portion of the Y chromosome, in 438 individuals from 24 Native American populations (1 Na Dené and 23 South Amerinds) and in 404 Mongolians. One of the biallelic markers typed is a recently identified mutation (M242) characterizing a novel founder Native American haplogroup. The distribution, relatedness, and diversity of Y lineages in Native Americans indicate a differentiated male ancestry for populations from North and South America, strongly supporting a diverse demographic history for populations from these areas. These data are consistent with the occurrence of two major male migrations from southern/central Siberia to the Americas (with the second migration being restricted to North America) and a shared ancestry in central Asia for some of the initial migrants to Europe and the Americas. The microsatellite diversity and distribution of a Y lineage specific to South America (Q-M19) indicates that certain Amerind populations have been isolated since the initial colonization of the region, suggesting an early onset for tribalization of Native Americans. Age estimates based on Y-chromosome microsatellite diversity place the initial settlement of the American continent at approximately 14,000 years ago, in relative agreement with the age of well-established archaeological evidence.

Female Subsistence Strategies Among Ache Hunter- Gatherers of Eastern Paraguay

Anthropologists have frequently proposed that sexual division of labor is produced by childcare constraints on womens subsistence work. We present data on the forest activities of Ache women that show that differences in parental investment partially account for variation in food acquisition among individual women. Data also suggest that childcare constraints are important in understanding the sexual division of labor.

Food transfers among Hiwi foragers of Venezuela: tests of reciprocity.

Although food sharing has been observed in many traditional societies, we still do not have a deep understanding of how various ecological conditions produce variation in who gives and who receives specific resources. To understand better the behavioral ecology of food sharing, we present data collected with the Hiwi of Venezuela and focus on two questions: (a) How do characteristics of food resources and acquirers determine how much is transfered to others? (b) How do characteristics of nuclear families A and B influence how much is transferred between A and B? We use path modeling in an attempt to tease apart the relative contribution of biological kinship, geographical proximity between households, family size, and quantities family B gave to family A on the expected quantities that family A gives to family B. Reciprocal altruism is shown to be an important link in the chain of factors, but not in the tit-for-tat form common in theoretical treatments of reciprocity.

Y-chromosome biallelic polymorphisms and Native American population structure

It has been proposed that women had a higher migration rate than men throughout human evolutionary history. However, in a recent study of South American natives using mtDNA restriction fragment polymorphisms and Y-chromosome microsatellites we failed to detect a significant difference in estimates of migration rates between the sexes. As the high mutation rate of microsatellites might affect estimates of population structure, we now examine biallelic polymorphisms in both mtDNA and the Y-chromosome. Analyses of these markers in Amerinds from North, Central and South America agree with our previous findings in not supporting a higher migration rate for women in these populations. Furthermore, they underline the importance of genetic drift in the evolution of Amerinds and suggest the existence of a North to South gradient of increasing drift in the Americas.

Contrasting Patterns of Nuclear and mtDNA Diversity in Native American Populations

We report an integrated analysis of nuclear (autosomal, X‐ and Y‐chromosome) short tandem repeat (STR) data and mtDNA D‐loop sequences obtained in the same set of 22 Native populations from across the Americas. A north to south gradient of decreasing population diversity was observed, in agreement with a settlement of the Americas from the extreme northwest of the continent. This correlation is stronger with “least cost distances,” which consider the coasts as facilitators of migration. Continent‐wide estimates of population structure are highest for the Y‐chromosome and lowest for the autosomes, consistent with the effective size of the different marker systems examined. Population differentiation is highest in East South America and lowest in Meso America and the Andean region. Regional analyses suggest a deviation from mutation–drift equilibrium consistent with population expansion in Meso America and the Andes and population contraction in Northwest and East South America. These data hint at an early divergence of Andean and non‐Andean South Americans and at a contrasting demographic history for populations from these regions.

Extremely limited mitochondrial DNA variability among the Aché Natives of Paraguay.

Background: The Aché Natives are an especially interesting group of people, due to their distinctive morphological aspect and the fact that only in the last three decades have they established more permanent contact with outside populations. The objectives of the present study were: (a) to verify their distinctiveness in relation to mitochondrial DNA (mtDNA) variability; (b) to ascertain whether the pattern observed was congruent with other genetic studies performed among them; and (c) to establish historical inferences that would explain the eventual similarities or differences. Subjects and methods: Sample collection was made at two localities in eastern Paraguay. DNA from 64 maternally unrelated subjects were tested in relation to the mtDNA hypervariable segment 1 (HVS-1) by automatic sequencing. Results: Fifty-six individuals presented exactly the same haplogroup B founder haplotype; another differed from it by a single transition polymorphism at site 16362, while six other subjects showed an identical haplogroup A founding haplotype. An A/G heteroplasmy at the 16269 site was seen in one haplogroup B individual, probably due to a somatic mutation. Conclusions: The Aché present distinctive differences and reduced mtDNA HVS-1 variability compared to other South American Natives. Similar differences were observed for other genetic systems. At present it is not clear whether their peculiarities already existed in their founding populations or whether they were secondarily acquired due to a long period of isolation in the humid, subtropical forest.

Ache at the settlement: Contrasts between farming and foraging

The Northern Ache comprise a small continuously interacting population with a shared community history. Full-time hunter-gatherers until recently, they now divide their time between mobile foraging and settled farming. Here we describe adult time allocation at the settlement and contrast it with our previous descriptions of time allocation during foraging periods. We report that at the settlement men and women work fewer hours each day than they do in the forest, people eat less, women do more work apart from their children, and men invest more in direct parental care. Explanations for differences in time allocation between foragers and farmers should apply to the variation in work effort, production goals, division of labor, and parenting strategies reported here, and conversely.

APOE polymorphism distribution among Native Americans and related populations

Background: Apolipoprotein E (apoE, protein; APOE, gene) plays a central role in lipid metabolism. Three common alleles, E*2, E*3 and E*4 have quantitative effects on lipid and lipoproteins levels, which are major risk determinants of cardiovascular diseases in several populations. Given their clinical significance, it is of interest to know the distribution of APOE variants in populations from diverse ethnic groups, as well as to determine if this polymorphism presents variations that might be associated with given evolutionary factors. Aim: We report the distribution of APOE polymorphisms in Native American populations from South America, comparing it with other native populations of the Americas and Siberia. Subjects and methods: The sample consisted of 315 individuals from nine Native American populations living at subtropical latitudes of Argentina, Brazil and Paraguay. The extended analysis included 50 populations across South and North America, Greenland and Siberia. The geographic patterns of the variation were investigated through correlation analysis, spatial autocorrelation and analysis molecular of variance (AMOVA). Results: The incidence of the most common allele (APOE*3) in the sample analysed ranged from 0.78 to 0.98. The second allele in prevalence, APOE*4, varied from 0.00 to 0.17. The rare allele APOE*2 was found in five of the nine populations investigated. This variant was found in a male with both maternal and paternal Native American lineages, suggesting that this allele is present in Native Americans and hence should not be used as an indicator of admixture. APOE*3 and APOE*4 present, respectively, positive and negative associations with latitude, although the pattern is much more pronounced in the Northern Hemisphere than in South America. APOE*2 increases its frequency with latitude but this pattern is statistically significant only in South America. Conclusion: The overall APOE spatial pattern seems, in general, compatible with a directional demographic expansion which occurred in north-eastern Asia and much of the New World. The APOE*2 allele shows this pattern in South America but a random distribution in the Northern Hemisphere, suggesting that the possibility of selection should not be discarded.

Cytokine gene polymorphisms are associated with susceptibility to tuberculosis in an Amerindian population.

SETTING Cytokines play an important role in anti-tuberculosis immune response, combined with antigen-presenting cells and lymphocytes. Immune response gene polymorphisms have been reported to be associated with tuberculosis (TB) susceptibility in some but not all studies. OBJECTIVE To evaluate the association of immune response genes with susceptibility to tuberculin skin test (TST) reactivity and/or TB. DESIGN Fourteen single nucleotide polymorphisms were genotyped in 96 individuals of the Aché, a native Paraguayan population, by allelic discrimination using real-time polymerase chain reaction. Univariate and multivariate Poisson regression were employed to assess risk genotypes. RESULTS A higher prevalence of purified protein derivative reactivity was associated with the TNF-α CCA/TCG haplotype (PR 1.298, 95%CI 1.059-1.589) and with the IL-10 AT/CC diplotype (PR 1.181, 95% CI 1.024-1.362), and the presence of the IL-8 rs4073 T allele was associated with protection against TB (PR 0.482, 95%CI 0.273-0.851). CONCLUSIONS These results suggest that polymorphisms in genes associated with immune response are involved in TST reactivity and susceptibility to TB in the Aché population.