Jujuy Province (NW Argentina): STR Markers Unveil Microgeographic Differentiation Over a Steep Mountainous Landscape

This study explores potential signals of microdifferentiation on the gene pool of three high-altitude populations from Jujuy province (NW Argentina) using highly polymorphic markers. These human communities are characterized by extreme living conditions and very low population densities owing to considerable height above sea level and steep orography. A set of autosomal STRs located at chromosome 6 (6p21.3) was typed in samples from Quebrada estimated through the observed (Ho) and expected (He) heterozygosities, and the haplotype diversity. Analyses of the molecular variance (AMOVA) and population differentiation tests based on allele and haplotype frequencies were performed to assess genetic heterogeneity among subgroups. No deviation from HWE expectations was detected for each separate subpopulation; yet, significant departures were detected in the analysis considering the whole area (D6S2792 and D6S105 loci). Overall, genetic diversity showed a decreasing trend as the altitude increases. Thus, allele and haplotype frequencies showed the most significant differences between Puna and Quebrada Baja, which are the populations sited at the edges of the altitude range. The trend to the reduction of the heterozygosity with altitude proves to be compatible with historical patterns of colonization, interregional migration trends, population density, and genetic admixture. The main consequence of the complex mountainous landscape of Jujuy would be an imbalance in the interplay gene flow-genetic drift favoring the latter. The combined effect of restricted gene flow with intense genetic drift would have promoted local genetic differentiation between Jujuy highlands' subpopulations, leading to spatial patterning of the allele frequencies not entirely attributable to geographic distance. Our findings corroborate the effectiveness of STRs to identify microevolutionary changes. Genomic markers of quite different nature have been used to identify microevolutionary changes in human populations. Among them, polymorphisms from noncoding DNA regions are assumed to be selectively neutral, so their evolution in populations can be mostly explained by the interplay between gene flow and genetic drift. Because of their hypervariable nature, microsatellite or short tandem repeat (STR) polymorphisms have been extensively analyzed in various fields of population genetics. Microsatellites feature comparatively high mutation rates that range between 3.3 x 10-4 per locus per generation (Forster et al., 2000) and 15.2 x 10-4 per locus per generation (Zhivotovsky et al., 2004), considering generations of 25 years. The high mutation rate of human STRs may thus provide valuable genetic information for the elucidation of human population history and for studying genetic The timing of early human dispersal in South …