Mitochondrial and nuclear DNA diversity in the Chocó and Chibcha Amerinds of Panamá.

Mitochondrial and nuclear DNA diversities were determined for two Chocó-speaking Amerind populations, the Emberá and Wounan, sampled widely across their geographic range in eastern Panamá. These data were compared with mitochondrial and nuclear diversities determined here and previously for neighboring Chibcha-speaking Ngöbé and Kuna populations. Chocoan groups exhibited mitochondrial diversity levels typical for Amerind populations while Chibchan groups revealed reduced mitochondrial diversity. A slight reduction in autosomal levels of heterozygosity was determined for the Chibcha while X and Y variation appeared equivalent in all populations. Genetic distinctiveness of the two linguistic groups contradicts the anthropological theory that Paleoindians migrated repeatedly through the isthmian region and, instead, supports the idea of cultural adaptation by endogenous populations. Reduced genetic diversity in Chibchan populations has been proposed to represent a population bottleneck dating to Chibchan ethnogenesis. The relative sensitivities of haplotype pairwise difference distributions and Tajima's D to detect demographic events such as population bottlenecks are examined. Also, the potential impact of substitution rate heterogeneity, population subdivision, and genetic selection on pairwise difference distributions are discussed. Evidence is presented suggesting that a larger effective population size may obscure the historical signal obtained from nuclear genes while the single mitochondrial locus may provide a moderately strong signal.