Mitochondrial Haplogroup U5b3: A Distant Echo of the Epipaleolithic in Italy and the Legacy of the Early Sardinians

Abstract

There are extensive data indicating that some glacial refuge zones of southern Europe (Franco-Cantabria, Balkans, and Ukraine) were major genetic sources for the human recolonization of the continent at the beginning of the Holocene. Intriguingly, there is no genetic evidence that the refuge area located in the Italian Peninsula contributed to this process. Here we show, through phylogeographic analyses of mitochondrial DNA (mtDNA) variation performed at the highest level of molecular resolution (52 entire mitochondrial genomes), that the most likely homeland for U5b3-a haplogroup present at a very low frequency across Europe-was the Italian Peninsula. In contrast to mtDNA haplogroups that expanded from other refugia, the Holocene expansion of haplogroup U5b3 toward the North was restricted by the Alps and occurred only along the Mediterranean coasts, mainly toward nearby Provence (southern France). From there, approximately 7,000-9,000 years ago, a subclade of this haplogroup moved to Sardinia, possibly as a result of the obsidian trade that linked the two regions, leaving a distinctive signature in the modern people of the island. This scenario strikingly matches the age, distribution, and postulated geographic source of a Sardinian Y chromosome haplogroup (I2a2-M26), a paradigmatic case in the European context of a founder event marking both female and male lineages.

Human paleogenetics of Europe – The known knowns and the known unknowns

“…Malyarchuk et al (2010) studied the modern-day distribution of subhaplogroup U5 in particular and proposed different places of origin during the Upper Paleolithic for each of the sub-clades, with U5b in the West and U5a in the East. This is in accordance with studies that linked sub-haplogroups of U5b, such as U5b1b1 and U5b3, with an expansion after the Last Glacial Maximum from southwestern refugia in Franco-Cantabria and Italy, respectively (Achilli et al, 2005;Pala et al, 2009). So far, final conclusions cannot be drawn from the small number of ancient individuals from each separate aDNA study.…”

Dissecting the genetic make-up of North-East Sardinia using a large set of haploid and autosomal markers

“…U5b3a appears to be specific to Sardinians, although the low frequency suggests that its origin is more recent than the Ia2a2 haplogroup of the Y chromosome. 33 Mitochondrial haplogroup frequencies from the Sardinian sample were compared with the estimates from other populations. 34,35 Table 2b shows that, similar to the Y chromosome haplogroup system, there was population differentiation between the Sardinians and neighboring populations, but not with other samples from Sardinia.…”

Complex interplay between neutral and adaptive evolution shaped differential genomic background and disease susceptibility along the Italian peninsula

“…Also during Last Glacial Maximum (LGM, 25–19 kya), when ice sheets or permafrost covered most of Northern/Central Europe, Central and Southern Italy plausibly represented one of the few refuge areas where human groups contracted and from which re-peopled the whole continent23456. The peninsula then appeared to be involved in migratory events that enabled diffusion of agricultural techniques from the Aegean Sea to Western Europe7.…”