January 16, 2009

Ancient mtDNA from Iceland

From the paper:
Using the sequence data described in Table 1, we obtained an estimate of 58% ancestry from Scotland and Ireland for contemporary Icelanders (95% C.I.: 44.6–71.2%). In comparison, the IEMS [DP: Iceland Early Medieval Sample] yielded an estimate of 64.7% (95% C.I.: 36.8–90.3%), indicating a similar excess of matrilineal ancestry from Scotland and Ireland.
PLoS Genetics doi: 10.1371/journal.pgen.1000343

Sequences From First Settlers Reveal Rapid Evolution in Icelandic mtDNA Pool

Agnar Helgason et al.

Abstract

A major task in human genetics is to understand the nature of the evolutionary processes that have shaped the gene pools of contemporary populations. Ancient DNA studies have great potential to shed light on the evolution of populations because they provide the opportunity to sample from the same population at different points in time. Here, we show that a sample of mitochondrial DNA (mtDNA) control region sequences from 68 early medieval Icelandic skeletal remains is more closely related to sequences from contemporary inhabitants of Scotland, Ireland, and Scandinavia than to those from the modern Icelandic population. Due to a faster rate of genetic drift in the Icelandic mtDNA pool during the last 1,100 years, the sequences carried by the first settlers were better preserved in their ancestral gene pools than among their descendants in Iceland. These results demonstrate the inferential power gained in ancient DNA studies through the application of population genetics analyses to relatively large samples.

Link

9 comments:

Maju said...

It's well known that Vikings enslaved many Irish and that Irish women captured in this fashion (some men too) made up the majority of early Icelandic female population.

So far so good.

What I don't really understand is this:

Due to a faster rate of genetic drift in the Icelandic mtDNA pool during the last 1,100 years, the sequences carried by the first settlers were better preserved in their ancestral gene pools than among their descendants in Iceland.

Wouldn't be the slight change 65% to 58% (not really significative, I'd say) due to mere sampling bias and/or later migration from Scandinavia?

pconroy said...

Maju,

A few points:
1. Many of the settlers of Iceland were Hiberno-Norse or Gallgaels - that is people of mixed Viking (Y DNA) and Irish or Scottish (mtDNA) - so there needn't be as many slaves (aka thralls) involved in the settlement. Of course there was prior Irish settlement in Iceland, which many have contributed to the founding population too.

2. I agree that the differences in percentages seem slight, between old and modern, and many be due to sampling bias, or to the fact that low class descendants of slaves were less likely to survive, or alternatively that some mtDNA groups from Scandinavia have more fitness in a frigid environment like Iceland, which is much closer in climate to Norway than Ireland.

alobrix said...

Haplotype matches with southwestern Europe= 31, Scots and Irish=31. Why? Hipotheses?

alobrix said...

I'm sorry, Hypotheses? I think there is a relationship with the atlantic façade ancient population.

Dragon Horse said...

Ice has experience two times in it's history a 50% decline in their population...once due to disease (plague in the 14th century), the other, I believe, due to climate (18th century).

There could have been some "fitness" issue in certain MtDNA lines during one of these episodes that caused the imbalance.

Antigonos said...

So physical anthropology once more proved to be correct!
Coon in his "Races of Europe" indicated that anatomy showed a mixed Icelander population of Celtic elements with Scandinavian ones.

Paul_Johnsen said...

"Using the sequence data described in Table 1, we obtained an estimate of 58% ancestry from Scotland and Ireland for contemporary Icelanders (95% C.I.: 44.6–71.2%). In comparison, the IEMS [DP: Iceland Early Medieval Sample] yielded an estimate of 64.7% (95% C.I.: 36.8–90.3%), indicating a similar excess of matrilineal ancestry from Scotland and Ireland."

In my opinion these estimates are highly dubious. The Norse element is represented with a sample collection pooled from all Scandinavian countries. It should be sampled only from Western Norway + Trøndelag where the Icelandic came from. So far there has been no evidence to support the assumption that the mtdna distribution within Scandinavia is homogeneous or even that the it is homogeneous within the various regions in Norway. I think the Celtic vs Norse input estimate is very much premature.

Maju said...

Good caveat, Paul. Though I suspect it wouldn't alter things too much. While Sweden does normally appear as more "easterner" than Norway, Denmark instead appears more "westerner", so one should compensate the other, more or less.

Paul_Johnsen said...

"Good caveat, Paul. Though I suspect it wouldn't alter things too much. While Sweden does normally appear as more "easterner" than Norway, Denmark instead appears more "westerner", so one should compensate the other, more or less."

Possible, but judging from various entries in mitosearch and in the Scandinavian mtdna-project and the Norway project, there does appear to be likely substructures even within Norway regionally.