A new study takes a look at Sicilian haploid genetics in its wider geographical context.
Stephania Samo et al., An Ancient Mediterranean Melting Pot: Investigating the Uniparental Genetic Structure and Population History of Sicily and Southern Italy. PLoS ONE 2014. Open access → LINK [doi:10.1371/journal.pone.0096074]
Due to their strategic geographic location between three different continents, Sicily and Southern Italy have long represented a major Mediterranean crossroad where different peoples and cultures came together over time. However, its multi-layered history of migration pathways and cultural exchanges, has made the reconstruction of its genetic history and population structure extremely controversial and widely debated. To address this debate, we surveyed the genetic variability of 326 accurately selected individuals from 8 different provinces of Sicily and Southern Italy, through a comprehensive evaluation of both Y-chromosome and mtDNA genomes. The main goal was to investigate the structuring of maternal and paternal genetic pools within Sicily and Southern Italy, and to examine their degrees of interaction with other Mediterranean populations. Our findings show high levels of within-population variability, coupled with the lack of significant genetic sub-structures both within Sicily, as well as between Sicily and Southern Italy. When Sicilian and Southern Italian populations were contextualized within the Euro-Mediterranean genetic space, we observed different historical dynamics for maternal and paternal inheritances. Y-chromosome results highlight a significant genetic differentiation between the North-Western and South-Eastern part of the Mediterranean, the Italian Peninsula occupying an intermediate position therein. In particular, Sicily and Southern Italy reveal a shared paternal genetic background with the Balkan Peninsula and the time estimates of main Y-chromosome lineages signal paternal genetic traces of Neolithic and post-Neolithic migration events. On the contrary, despite showing some correspondence with its paternal counterpart, mtDNA reveals a substantially homogeneous genetic landscape, which may reflect older population events or different demographic dynamics between males and females. Overall, both uniparental genetic structures and TMRCA estimates confirm the role of Sicily and Southern Italy as an ancient Mediterranean melting pot for genes and cultures.
No particular haplogroup is dominant in the island in the Y-DNA side and, although H has some clear prevalence among mtDNA haplogroups, it is actually well under the normal European levels for this common haplogroup.
|Table 1. Age estimates (in YBP) of STR and HVS variation for the most frequent haplogroups in Sicily and Southern Italy.|
We can see how the following patrilineages are more common: J2a (16%), G2a (12%) and E1b1b1a1b1a (10%) and R1b1a2a1a2 (9%). R1a1a (5%), J1 (5%) R1b1a2a1a1 (4%) and J2b (4%) are less common instead.
|Fig, S2(a) - Principal Component Analysis (PCA) based on haplogroup frequencies for Y-chromosome (a) (...). Population codes as in Table S1. Colour codes for geographic affiliations as in the legends at the bottom-left of each plot. Legend abbreviations: NAFR: North-Africa, LEV: Levant, BALK: Balkans, SSI: Sicily and South-Italy, NCI: North-Central Italy, IBE: Iberian Peninsula, GER: Germany.|
There is an interesting tendency in Agrigento (AG) towards Lebanon (which in this graph includes all the LEV category), while other areas of Sicily and Southern Italy (Lecce, Cosenza, Enna) tend instead towards the Aegean (Pho, Smy). These tendencies could be interpreted (at least partly) in terms of historical colonization events by Phoenicians and Greeks. Catania instead tends towards Central-North Italy, maybe reflecting its important role under Roman rule and a historical colonization in the times of Augustus.
The Southern Italian towns of Matera (Basilicata) and Campobasso (Molise) also show a tendency towards the Northern Balcans (represented by Serbia here).
The authors confirm previous impressions of a West-East Y-DNA duality in the Mediterranean that divides Italy:
When comparing SSI with Mediterranean reference populations, Y-chromosome results (Figure 1 and Figure S2) revealed a clear-cut genetic differentiation between the North-Western vs. the Central- and South-Eastern Mediterranean genetic pools (as confirmed by both sPCA G-test and AMOVA FCT statistically significant tests). These results are consistent with our previous study about Italy , in which we detected a discontinuous paternal genetic structure, clearly separating the South-Eastern and the North-Western parts of the Italian Peninsula. Here this pattern appears extended to the whole Mediterranean Basin, particularly suggesting a shared genetic background between South-Eastern Italy and the South-Eastern Mediterranean cluster from one side, and between North-Western Italy and the Western Europe from the other side (Figure 2).
The main matrilinages of Sicily are H (28%) T (13%), J (10%) and HV(xH) (5%). U5 is also well under the usual European frequencies with just 3% of prevalence.
While the AMOVA statistical significance tests say that PC2 in the following graph is not really significant. However PC1 is still relevant, I understand.
|Fig S1(b) - Principal Component Analysis (PCA) based on haplogroup frequencies for (...) mtDNA (b). Population codes as in Table S1. Colour codes for geographic affiliations as in the legends at the bottom-left of each plot. Legend abbreviations: NAFR: North-Africa, LEV: Levant, BALK: Balkans, SSI: Sicily and South-Italy, NCI: North-Central Italy, IBE: Iberian Peninsula, GER: Germany.|
If anything there is some discrepancy between Y-DNA tendencies and those of mtDNA. For example the "Phoenician" Agrigento in the Y-DNA graph, looks "Iberian" or "Tuscan" in the mtDNA one.
The authors believe that mtDNA lineages could be older than Y-DNA ones in many cases:
Y-chromosome results however contrast with the lack of statistical support to the sPCA global structure observed for mtDNA diversity, excepted for a similar NW-SE genetic pattern identified by sPC1 (Figure 3). The common South-East to North-West pattern in the distribution of genetic variation across the European and Mediterranean domain, could be interpreted as reflecting the same SE to NW genetic cline extensively reported in literature for the whole of Europe –. However, the general lack of statistical support to the global structure observed for mtDNA markers suggests a higher homogeneity for maternal than paternal genetic pools in the Mediterranean genetic landscape. These results could be ascribed to older population events and/or different demographic and historical dynamics for females than males. (...) In fact, whereas the different continental and within continental contributions to the current SSI genetic pool appeared to be more equally distributed on the maternal side (despite a noteworthy contribution of Levantine females), the paternal counterpart appeared to be clearly affected by South-Eastern Mediterranean, mainly Balkan [Aegean], males.