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Wednesday, December 22, 2010

Mid-Holocene arrival of mtDNA haplogroups C and D in Europe


The middle Holocene was a time when the climate warmed up across North Eurasia, triggering human migrations across great distances, like from Siberia to Europe. Signals of these movements have now been picked up by a new study looking at mtDNA haplogroups C and D.

It appears that European branch C5c1 is more differentiated, as far as two of three sequenced Polish mtDNAs formed a separate branch (C5c1a), defined by a coding region mutation at np 7694. The relatively large amount of internal variation accumulated in the Polish branch of C5c would mean that C5c1 arose in situ in Europe after the arrival of a C5c1 founder mtDNA from southern Siberia, and that C5c1 affiliation is a marker of maternal Siberian ancestry. The phylogeny depicted in Figure S1 provides additional information concerning the entry time of the founder mtDNA – the age of C5c node is estimated as 9.7 (3.17; 16.49) kya when using the sequence variation of the entire genome, and 9.2±4.74 when only synonymous mutations are considered (Table S3). The early presence of mtDNA lineages of eastern Asian ancestry in Europe is further confirmed by the discovery of a N9a haplotype in a Neolithic skeleton from the Szarvas site, located in southeastern Hungary that belonged to the Körös Culture, which appeared in eastern Hungary in the early 8th millennium B.P. [29].

What the above suggests is that East Eurasian mtDNA lineages don't have a single, recent origin in Europe. They came in dribs and drabs over several millennia, often via Siberia and the Volga-Ural region, with a large proportion arriving during the Neolithic.

Table S1.

Population distribution and frequencies of haplogroup C and its subhaplogroups C1, C5 and C*.

Table S2.

Population distribution and frequencies of haplogroup D and its subhaplogroups D2, D4 and D5.

Derenko M, Malyarchuk B, Grzybowski T, Denisova G, Rogalla U, et al. (2010)
Origin and Post-Glacial Dispersal of Mitochondrial DNA Haplogroups C and D in Northern Asia. PLoS ONE 5(12): e15214. doi:10.1371/journal.pone.0015214

Thursday, April 22, 2010

Tracing early intra-European migrations via mtDNA U5


The upshot of this Malyarchuk et al. article, published in PLoS One today, is that mitochondrial haplogroup U5 originated somewhere around the Mediterranean 25,000 to 30,000 years ago. It was then taken east via Central Europe, most likely as things warmed up following the Ice Age (LGM). Also, the authors suggest that pre-LGM Eastern Europeans carried U2, citing the recent discovery of this marker in Upper Paleolithic remains from Kostenki, Russia.

Genetic data obtained in this study allows the suggestion that during the LGM period, central European territories probably represented the area of intermingling between human flow from refugial zones in the Balkans, the Mediterranean coastline and the Pyrenees, as U5a and U5b gene flows occurred from there. Based on dating analysis of the U5 subclusters, it seems very likely that, despite the archaeological evidence testifying to the presence of humans in eastern Europe during the Ice Age, this part of Eurasia might have only been re-populated by modern humans at the end of the LGM, i.e. later than central Europe. In addition, U5b gene flow from central to eastern Europe become much more intense after the LGM.

It's impressive how far east this putatively Central European gene flow pushed, with traces of it popping up in modern Tatar and Siberian groups. This illustrates how Europe was not only a destination for migrants, but also potentially a major migrant source, particularly to the steppe and forest-steppe zones of Asia.

Subcluster U5a1d has been detected in eastern Europe (in Russians, Belorussians and Tatars) and southern Siberia (in Buryats) (Figure 1, Figure S1). The presence of such old U5a1 lineages in eastern part of Europe may be indicative of eastern European origin of the whole U5a1 subcluster, however ancestral haplotype for U5a1 has been found in central Europe in Czechs (Figure 1).

...

A recent ancient DNA study of Stone Age hunter-gatherers from central and eastern Europe has shown that most of the samples studied (.80%) shared mtDNA haplotypes belonging to haplogroups U5 and U4, haplogroups that notably are relatively rare in central Europe today [7]. Among them, sample 5830a from Hohlenstein-Stadel (Germany), defined as U5a2a, based on the HVS I sequence 16114A 16192-16256-16294-16311, was detected. Its closest HVS I relatives in modern populations can be found among eastern Europeans (in Latvians, Russians, Tatars and Mordvins).

But despite the fact that U5 seems to have originated around the Mediterranean, it's now most often found in Northeastern Europe. What appears to have happened is that when frequencies of mtDNA U dropped like a stone across much of Europe, probably during the Neolithic transition, the northeast was less affected by these changes. This possibly indicates that today the populations with the most sizeable amount of indigenous European hunter-gatherer ancestry live on the eastern shores of the Baltic. This view is seemingly backed up by genome-wide studies, which show Baltic and Balto-Finnic groups as the most distant genetically from modern-day Southern Europeans, who likely are of overwhelmingly Near Eastern Neolithic farmer origin (for example, see here).

Malyarchuk B, Derenko M, Grzybowski T, Perkova M, Rogalla U, et al. (2010) The Peopling of Europe from the Mitochondrial Haplogroup U5 Perspective. PLoS ONE 5(4): e10285. doi:10.1371/journal.pone.0010285