Geographic Patterns of mtDNA Diversity in Europe

Abstract

Genetic diversity in Europe has been interpreted as a reflection of phenomena occurring during the Paleolithic ( approximately 45,000 years before the present [BP]), Mesolithic ( approximately 18,000 years BP), and Neolithic ( approximately 10,000 years BP) periods. A crucial role of the Neolithic demographic transition is supported by the analysis of most nuclear loci, but the interpretation of mtDNA evidence is controversial. More than 2,600 sequences of the first hypervariable mitochondrial control region were analyzed for geographic patterns in samples from Europe, the Near East, and the Caucasus. Two autocorrelation statistics were used, one based on allele-frequency differences between samples and the other based on both sequence and frequency differences between alleles. In the global analysis, limited geographic patterning was observed, which could largely be attributed to a marked difference between the Saami and all other populations. The distribution of the zones of highest mitochondrial variation (genetic boundaries) confirmed that the Saami are sharply differentiated from an otherwise rather homogeneous set of European samples. However, an area of significant clinal variation was identified around the Mediterranean Sea (and not in the north), even though the differences between northern and southern populations were insignificant. Both a Paleolithic expansion and the Neolithic demic diffusion of farmers could have determined a longitudinal cline of mtDNA diversity. However, additional phenomena must be considered in both models, to account both for the north-south differences and for the greater geographic scope of clinical patterns at nuclear loci. Conversely, two predicted consequences of models of Mesolithic reexpansion from glacial refugia were not observed in the present study.

Using mitochondrial DNA to test the hypothesis of a European post-glacial human recolonization from the Franco-Cantabrian refuge

“…In general, our results are congruent with the apparent lack of mtDNA structure found for continental Europe compared with the more differentiated Mediterranean peninsulas (Simoni et al, 2000). These results are also in accordance with the different patterns found for the Y-chromosome haplogroup distribution in continental Europe compared with the Mediterranean peninsulas, with smooth clines and gradients apparent in continental areas (Rosser et al, 2000;Semino et al, 2000) contrasting to the focal expansions detected in Iberia (Flores et al, 2004), Italy and Greece (Di Giacomo et al, 2003).…”

“…For instance, diversity values for haplogroup V are significantly higher in Southern Iberia than in the Cornice and, confirming previous results (Simoni et al, 2000), we have not found significant latitudinal clines for this haplogroup. Furthermore, focussing on haplotype sharing, the Cornice is the most divergent area, despite North-east Iberia being the closest region to the rest of Europe.…”

“…It was first questioned on the basis of a lack of V representatives in ancient Basque samples (Izagirre and de la Rua, 1999) and its later presence in a historical sample from Alava (Alzualde et al, 2005), and second, for a lack of any directional gene-flow process of V along the proposed north-west European transects (Simoni et al, 2000). It was suggested that perhaps the Cantabrian area was a more probable expansion centre than the Basque Country (Maca-Meyer et al, 2003).…”

Human X-chromosomal lineages in Europe reveal Middle Eastern and Asiatic contacts

“…The lack of observed geographic structure in X-chromosome diversity in Europe resembles that of European mtDNA diversity 18 (though see Richards et al 20 ). However, many other previously studied genetic markers, including protein, Y-chromosome and autosomal DNA markers, have all described east -west gradients suggestive of immigration from the Near East.…”

“…Indeed, most studies of mtDNA in Europe have revealed a lack of clinal variation. 14,15,17,18 It is therefore likely that the higher rate of female gene flow in Europe is a major cause of the different patterns of X-chromosome markers when compared to autosomal and Y-chromosome DNA. Thirdly, and as suggested by Sokal et al, 41 the absence of clines at certain loci can be fully consistent with the demic-diffusion model, as only loci at which haplotype frequencies were markedly different for pre-Neolithic European hunter gatherers and Neolithic farmers are expected to show clinal variation across Europe.…”