Genetic differentiation in South Amerindians is related to environmental and cultural diversity: Evidence from the Y chromosome

The geographic structure of Y-chromosome variability has been analyzed in n ative populations of South America, through use of the high-frequency Nativ e American haplogroup defined by the DYS199-T allele and six Y-chromosome-l inked microsatellites (DYS19, DYS389A, DYS389B, DYS390, DYS391, and DYS393) , analyzed in 236 individuals. The following pattern of within- and among-p opulation variability emerges from the analysis of microsatellite data: (1) the Andean populations exhibit significantly higher levels of within- popu lation variability than do the eastern populations of South America; (2) th e spatial-autocorrelation analysis suggests a significant geographic struct ure of Y-chromosome genetic variability in South America, although a typica l evolutionary pattern could not be categorically identified; and (3) genet ic-distance analyses and the analysis of molecular variance suggest greater homogeneity between Andean populations than between non-Andean ones. On th e basis of these results, we propose a model for the evolution of the male lineages of South Amerindians that involves differential patterns of geneti c drift and gene flow. In the western part of the continent, which is assoc iated with the Andean area, populations have relatively large effective siz es and gene-flow levels among them, which has created a trend toward homoge nization of the gene pool. On the other hand, eastern populations-settled i n the Amazonian region, the central Brazilian plateau, and the Chaco region -have exhibited higher rates of genetic drift and lower levels of gene flow , with a resulting trend toward genetic differentiation. This model is cons istent with the linguistic and cultural diversity of South Amerindians, the environmental heterogeneity of the continent, and the available paleoecolo gical data.