New study on Iberian Peninsula genetics

[Token]

Patterns of genetic differentiation and the footprints of historical migrations in the Iberian Peninsula


Genetic differences within or between human populations (population structure) has been studied using a variety of approaches over many years. Recently there has been an increasing focus on studying genetic differentiation at fine geographic scales, such as within countries. Identifying such structure allows the study of recent population history, and identifies the potential for confounding in association studies, particularly when testing rare, often recently arisen variants. The Iberian Peninsula is linguistically diverse, has a complex demographic history, and is unique among European regions in having a centuries-long period of Muslim rule. Previous genetic studies of Spain have examined either a small fraction of the genome or only a few Spanish regions. Thus, the overall pattern of fine-scale population structure within Spain remains uncharacterised. Here we analyse genome-wide genotyping array data for 1,413 Spanish individuals sampled from all regions of Spain. We identify extensive fine-scale structure, down to unprecedented scales, smaller than 10 Km in some places. We observe a major axis of genetic differentiation that runs from east to west of the peninsula. In contrast, we observe remarkable genetic similarity in the north-south direction, and evidence of historical north-south population movement. Finally, without making particular prior assumptions about source populations, we show that modern Spanish people have regionally varying fractions of ancestry from a group most similar to modern north Moroccans. The north African ancestry results from an admixture event, which we date to 860 - 1120 CE, corresponding to the early half of Muslim rule. Our results indicate that it is possible to discern clear genetic impacts of the Muslim conquest and population movements associated with the subsequent Reconquista.

https://www.biorxiv.org/content/early/2018/03/12/250191

[Sikeliot]

This is what I have been saying -- variation in Iberia is east to west, rather than north to south.

[Kamal900]

Hmm, so I guess the NA admixture among Iberians isn't ancient, is it? Good study nonetheless.

[Sikeliot]

From Supplementary Info. This confirms what I have said... North African input centers on Portugal and western Spain.

Iberians are basically French, with input from North-Central Italy and North Africa.

Italy cluster used here centers on North-Central Italy entirely, around Emilia and Tuscany.

"Here we discuss the ancestry profiles for the six Iberian clusters in more detail (referring to Supplementary Figure 4). Only seven of the 29 donor groups (six with >1% contribution to any group) show any meaningful contribution in ancestry profiles, and are primarily in Western and Southern Europe, and north-west Africa. For all six Iberian clusters the largest contribution comes from France, with smaller inferred contributions that relate to present-day Italian and Irish samples. Because these contributions are present and dominate overall ancestry throughout Spain, they might represent ancient ancestry components, rather than recent migration. The remaining contributions come from North Morocco and Western Sahara, and show strong (and highly significant) regional differences, varying continuously across Spain. The North Moroccan component steadily declines from 11% in the far west to near 0% in the Basque region."

"A very small (0.2%) but statistically non-zero contribution from sub-Saharan Africa is present for just one cluster (red triangles), which contains individuals largely from Portugal and regions of southern Iberia, such as Andalucia, and Murcia."

[Black Panther]

All I know is Brazilian niggas are more European than Iberians.

[GiCa]

Oh... So Muslim Al-Hispania left a genetic input.

Proofed.

This is very important.

[Sikeliot]

So basically, you go from being like a very ancient French population in the Basque country, to being a French population with minor Tuscan-like admixture in eastern Spain, to being progressively admixed with Berber admixture and a decrease in the French component (which still predominates) in western Spain and Portugal.

It is therefore entirely common sense to suggest that, as I long have, Portuguese show more phenotypical North African influence than do the Spanish overall, because it is nearly 1/8 of their ancestry. You CAN look like a great grandparent, and 1/8 of ancestry can show.

[Jana]

Hmm, so I guess the NA admixture among Iberians isn't ancient, is it? Good study nonetheless.

I think it's both:

Perhaps surprisingly, north African ancestry does not reflect proximity to north
Africa, or even regions under more extended Muslim control. The highest amounts
of north African ancestry found within Iberia are in the west (11%) including in
Galicia, despite the fact that the region of Galicia as it is defined today (north of the
Miño river), was never under Muslim rule and Berber settlements north of the
Douro river were abandoned by 741. This observation is consistent with previous
work using Y-chromosome data12.

this does not sugesst all or most north african in Iberia is moorish, quite the contrary.

[Aren]

From Supplementary Info. This confirms what I have said... North African input centers on Portugal and western Spain.

Iberians are basically French, with input from North-Central Italy and North Africa.

Italy cluster used here centers on North-Central Italy entirely, around Emilia and Tuscany.

"Here we discuss the ancestry profiles for the six Iberian clusters in more detail (referring to Supplementary Figure 4). Only seven of the 29 donor groups (six with >1% contribution to any group) show any meaningful contribution in ancestry profiles, and are primarily in Western and Southern Europe, and north-west Africa. For all six Iberian clusters the largest contribution comes from France, with smaller inferred contributions that relate to present-day Italian and Irish samples. Because these contributions are present and dominate overall ancestry throughout Spain, they might represent ancient ancestry components, rather than recent migration. The remaining contributions come from North Morocco and Western Sahara, and show strong (and highly significant) regional differences, varying continuously across Spain. The North Moroccan component steadily declines from 11% in the far west to near 0% in the Basque region."

"A very small (0.2%) but statistically non-zero contribution from sub-Saharan Africa is present for just one cluster (red triangles), which contains individuals largely from Portugal and regions of southern Iberia, such as Andalucia, and Murcia."

I litteraly just posted this to Christiano Viejo who denied any North African influence an hour ago. Seems like I get about the same numbers using nMonte.

"distance%=3.1615"

Spanish_Aragon

Barcin_N,54.2
Yamnaya_Samara,26.6
WHG,12.8
Mozabite,3.4
Yamnaya_Kalmykia,3

"distance%=2.4797"

Spanish_Castilla_La_Mancha

Barcin_N,53.4
Yamnaya_Samara,16.2
Yamnaya_Kalmykia,13.6
WHG,11.8
Mozabite,5

"distance%=2.1625"

Spanish_Galicia

Barcin_N,48.6
Yamnaya_Samara,28.8
WHG,11.6
Mozabite,11

"distance%=2.3004"

Spanish_Extremadura

Barcin_N,49.8
Yamnaya_Samara,29.2
WHG,10.8
Mozabite,10.2

[Sikeliot]

I litteraly just posted this to Christiano Viejo who denied any North African influence an hour ago. Seems like I get about the same numbers using nMonte.

"distance%=3.1615"

Spanish_Aragon

Barcin_N,54.2
Yamnaya_Samara,26.6
WHG,12.8
Mozabite,3.4
Yamnaya_Kalmykia,3

"distance%=2.4797"

Spanish_Castilla_La_Mancha

Barcin_N,53.4
Yamnaya_Samara,16.2
Yamnaya_Kalmykia,13.6
WHG,11.8
Mozabite,5

"distance%=2.1625"

Spanish_Galicia

Barcin_N,48.6
Yamnaya_Samara,28.8
WHG,11.6
Mozabite,11

"distance%=2.3004"

Spanish_Extremadura

Barcin_N,49.8
Yamnaya_Samara,29.2
WHG,10.8
Mozabite,10.2

Also, on GEDMatch, Portuguese often can be modeled as Spanish + 10-12% North African. This is no coincidence.

I also think the so called "Berid" phenotype in Iberia is a reflection of this North African influence.