Evaluation of large-scale genetic structure in complex demographic and historical scenarios: the mitochondrial DNA and Y-chromosome pools of the Iberian Atlantic façade.

Genetic structural patterns of human populations are usually a combination of long-term evolutionary forces and short-term social, cultural, and demographic processes. Recently, using mitochondrial DNA and Y-chromosome loci, various studies in northern Spain have found evidence that the geographical distribution of Iron Age tribal peoples might have influenced current patterns of genetic structuring in several autochthonous populations. Using the wealth of data that are currently available from the whole territory of the Iberian Peninsula, we have evaluated its genetic structuring in the spatial scale of the Atlantic façade. Hierarchical tree modeling procedures, combined with a classic analysis of molecular variance (AMOVA), were used to model known sociocultural divisions from the third century BCE to the eighth century CE, contrasting them with uniparental marker data. Our results show that, while mountainous and abrupt areas of the Iberian North bear the signals of long-term isolation in their maternal and paternal gene pools, the makeup of the Atlantic façade as a whole can be related to tribal population groups that predate the Roman conquest of the Peninsula. The maintenance through time of such a structure can be related to the numerous geographic barriers of the Iberian mainland, which have historically conditioned its settlement patterns and the occurrence of genetic drift processes.