December 22, 2010

mtDNA haplogroup U6 late Pleistocene expansion

BMC Evolutionary Biology 2010, 10:390doi:10.1186/1471-2148-10-390

Population expansion in the North African Late Pleistocene signalled by mitochondrial DNA haplogroup U6

Luisa Pereira et al.

Abstract (provisional)

The archaeology of North Africa remains enigmatic, with questions of population continuity versus discontinuity taking centre-stage. Debates have focused on population transitions between the bearers of the Middle Palaeolithic Aterian industry and the later Upper Palaeolithic populations of the Maghreb, as well as between the late Pleistocene and Holocene.

Improved resolution of the mitochondrial DNA (mtDNA) haplogroup U6 phylogeny, by the screening of 39 new complete sequences, has enabled us to infer a signal of moderate population expansion using Bayesian coalescent methods. To ascertain the time for this expansion, we applied both a mutation rate accounting for purifying selection and one with an internal calibration based on four approximate archaeological dates: the settlement of the Canary Islands, the settlement of Sardinia and its internal population re-expansion, and the split between haplogroups U5 and U6 around the time of the first modern human settlement of the Near East.

A Bayesian skyline plot placed the main expansion in the time frame of the Late Pleistocene, around 20 ka, and spatial smoothing techniques suggested that the most probable geographic region for this demographic event was to the west of North Africa. A comparison with U6's European sister clade, U5, revealed a stronger population expansion at around this time in Europe. Also in contrast with U5, a weak signal of a recent population expansion in the last 5,000 years was observed in North Africa, pointing to a moderate impact of the late Neolithic on the local population size of the southern Mediterranean coast.



Anonymous said...

I am not a fan of the dating of haplogroups and tying to archaeological events which are themselves iffy as far as dating goes, but this report has made some interesting claims.

Basically the report confirms the continuation of present day Northwest Africans with ancient ones but only as far as the Ibero-Mauresians. The report does provide dates for many U mtDNA subclades including ones found only in Sardinia.

German Dziebel said...

Notably, Sub-Saharan L lineages don't appear in North Africa until the Holocene. This is consistent with the lack of L lineages in Taforalt remains (12,000 YBP). This means that we don't have evidence for sub-Saharan L3 lineages differentiating in North or East Africa to spawn macrohaplogroup M and N. All we know is that L lineages are late arrival in the North.

Anonymous said...

@ German Dziebel : If my memory doesn't betray me, one mtDNA haplogroup of the Taforalt was considered either L3, M or N by the authors.
M1 would make sense but so would L3.

German Dziebel said...

@waggg. Good call. I checked the paper and yes, indeed, one sequence didn't fall into any of the R haplogroups but instead showed the 16223T substitution compatible with M, N or L3. It could be M1, N1, X1/X2 or L3.