The split of the Arara population: Comparison of genetic drift and foundereffect

The total genetic diversity of the Amerindian population is as high as that observed for other continental human populations because a large contribut ion from variation among tribes makes up for the low variation within tribe s. This is attributed mainly to genetic drift acting on small isolated popu lations. However, a small founder population with a low genetic diversity i s another factor that may contribute to the low intratribal diversity. Smal l founder populations seem to be a frequent event in the formation of new t ribes among the Amerindians, but th is event is usually not well recorded. In this paper, we analyze the genetic diversity of the Arara of Laranjal vi llage and the Arara of Iriri village, with respect to seven tandem repeat a utosomic segments (D1S80, ApoB, D4S43, vW1, vW2, F13A1 and D12S67), two Y-c hromosome-specific polymorphisms (DYS19 and DYS199), and mitochondrial DNA (mtDNA) markers (restriction fragment length polymorphisms and sequencing o f a segment of the D-loop region). The occurrence of a single Y chromosome and mtDNA haplotype, and only 1-4 alleles of the autosomic loci investigate d, corroborates historic and demographic records that the Arara of Iriri we re founded by a single couple of siblings who came from the Arara of Laranj al, the largest group. Notwithstanding this fact, the genetic distance and the molecular variance between the two Ara ra villages were greater than th ose observed between them and other Amazonian tribes, suggesting that the m icroevolutionary process among Brazilian Amerindians may be misinterpreted if historic demographic data are not considered. Copyright (C) 2000 S. Karg er AG, Basel.