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Thursday, February 9, 2017

Irish Travellers


Open access at Scientific Reports:

Abstract: The Irish Travellers are a population with a history of nomadism; consanguineous unions are common and they are socially isolated from the surrounding, ‘settled’ Irish people. Low-resolution genetic analysis suggests a common Irish origin between the settled and the Traveller populations. What is not known, however, is the extent of population structure within the Irish Travellers, the time of divergence from the general Irish population, or the extent of autozygosity. Using a sample of 50 Irish Travellers, 143 European Roma, 2232 settled Irish, 2039 British and 6255 European or world-wide individuals, we demonstrate evidence for population substructure within the Irish Traveller population, and estimate a time of divergence before the Great Famine of 1845–1852. We quantify the high levels of autozygosity, which are comparable to levels previously described in Orcadian 1st/2nd cousin offspring, and finally show the Irish Traveller population has no particular genetic links to the European Roma. The levels of autozygosity and distinct Irish origins have implications for disease mapping within Ireland, while the population structure and divergence inform on social history.

Gilbert, E. et al. Genomic insights into the population structure and history of the Irish Travellers. Sci. Rep. 7, 42187; doi: 10.1038/srep42187 (2017).

11 comments:

mickeydodds1 said...

Has been known for years.

Grey said...

"Has been known for years."

yes - and people didn't think "how come they're culturally so like roma when roma are from the other end of the IE expansion?"

Matt said...

15 generation split - 300 / 450 years. 1550 - 1700.

I found it interesting that the Welsh Roma in the clustering were unlike other Roma in having the same cluster membership as Irish Travellers and Scotland Ireland. At the same time, supplement membership shows Welsh Roma ROH to be among the highest of Roma.

Another interesting facet: Our fineStructure tree qualitatively agrees with the topology presented by Leslie et al although there are some differences. For example, in the tree presented here, the Irish and individuals from south-west Scotland are grouped on one branch, with the rest of Scotland and England placed on a separate branch. fineStructure tree building is sensitive to the sample size, and due to the larger proportion of Irish genomes in our analysis, compared to Leslie et al.’s analysis (300 versus 44), it is not surprising that the Irish branch is placed differently. So that's new (N Scotland is on the same branch as English, SW Scotland in the Irish subtree. Migration? "Scots Irish"?).

Matt said...

In the general Euro and world wide context, I thought it was also cool that they included a matrix of outgroup f3s as well as an Fst matrix, as it makes them as general methods easy to compare and contrast.

MDS Plots based on using fst and outgroup f3s: http://i.imgur.com/T32NDTh.png

Neighbour Joining Clustering based on using fst and outgroup f3s: http://i.imgur.com/XRPiJxO.png

Fst is a distance measure weighted down by genetic diversity and up by lineage specific genetic drift.

Outgroup f3 is a similarity measure which discards much of lineage specific genetic drift that contributes to population differentiation, and is weighted down in more diverse groups (more diversity meaning less likely to share the same variant, less apparently similar via this method). So for instance the highest Spanish sharing is with Wales in this table of outgroup f3s, not Italy (Italy higher in diversity).

Matrices: FST - http://i.imgur.com/PJNrlmN.png, Outgroup f3 - http://i.imgur.com/t9aeEdh.png (They're in the supplement).

(Slight shame they didn't include outgroup f3 sharing within group computed over random subsets though.)

Paul Ó Duḃṫaiġ said...

The trimeframe isn't that surprising given that Ireland suffered 5 major "wars" during period 1534 to 1691. In case of Cromwellian conquest anywhere between 25-40% of population perished.

Given the high level of Gaelic Irish surnames among travellers it make sense that their origin lies in the destruction of Gaelic Irish society brought about by the Tudor conquest of Ireland.

Matt said...

One point: "We assumed a demographic model for the two populations (Fig. 5A), in which an ancestral Irish population has entered a period of exponential expansion before the ancestors of the present day settled Irish and Irish Travellers split. After this split, the settled Irish continued the exponential expansion, whilst the Irish Travellers experienced an exponential population contraction.

So is this a good model - equal population size for Settled / Traveller at time of divergence, then constant contraction in Traveller and constant expansion in Settled? I've skim read a lot of this, seems like explicitly comparing effective population size graphs over time would preferable.

Contrasting model applied to Ashkenazi Jews by same authors (Carmi, etc.)- http://www.nature.com/articles/ncomms5835. Initial bottleneck + population explosion. Seems like there is an explicit inference of model - "We used the lengths of shared segments (Fig. 3c) to infer the parameters of a recent AJ bottleneck (effective size 250–420; 25–32 generations ago) followed by rapid exponential expansion (rate per generation 16–53%; Fig. 4, bottom)". Why assume a model and not infer? Has the non-genetic data led to their preferred population model? (Surnames, birth rates, survival rates).

Only justification I can think of is the 50 Irish Traveller sample does not have enough statistical power for models vs 128 whole genomes in Ashkenazi study.

Grey said...

"Gaelic Irish society"

if travellers were a surviving relic of that society how far back in time does that society go - bronze age?

Grey said...

i had various dealings with gypsies and irish travellers a very long time ago and my memory may be totally wrong on this but my memory is both travellers and gypsies had the belief that the body above the waist was clean and below the waist was unclean

(and that non-gypsies were unclean because they didn't respect that division)

which is a bit of a coincidence if travellers have no connection to roma

(this side of the bronze age)

but my memory could easily be wrong on that so i'm not 100% sure

Garvan said...

This paper confirms what we were thought in school 45 years ago about the origin of travelers.

There were very few Roma groups in Ireland when I was growing up. I never saw any, so I tried to find out when the first groups arrived and I found this reference.

Roma Educational Needs in Ireland - Louise Lesovitch
"Roma have been travelling in Ireland since the beginning of the nineteenth century, but the poverty of Ireland in the early 1900s presented limited employment opportunities. In 1911, Roma coppersmith families travelled from Britain and, in the 1940s, English Romany families came to live in Ireland. Pre–1990 Roma migration to Ireland largely comprised temporary, seasonal farm labour with Roma travelling from England and/or Europe"

There were traveler kids in my school in Ireland, who stayed for a few months at a time before moving on to other areas. The possibility of any relationship between travelers and Roma, other than through marriage, is non-existent.

If Mr. Grey sees commonality in hygiene beliefs between the two groups then I would suggest it is because they both live beside the road with limited water supply and no hot water, in climates where washing in cold water is not pleasant.











Matt said...

May be possible to have some relationship between Irish Travellers and Romani via a group like Welsh Romani, who appear to be an autosomally Europe (British?) group with Indian mtdna - http://www.cell.com/current-biology/fulltext/S0960-9822(12)01260-2.

("Thus, our data suggest that either the Welsh Romani admixed in situ with non-Romani Europeans and afterward underwent strong isolation, or that they received genetic admixture with an already isolated local population, such as the so-called “native travelers”").

So could be possible to have

Continental Europe Romani->Migrate to England as a small population, autosomal and y-dna washes to replace with British, keep some Indian mtdna and Romani cultural identification->Migrate to Ireland, absorbed into an Irish group and lose last of Indian mtdna and language->Irish Travellers who keep some culture from Romani and the basic practices of nomadism but lose language and all genetic connection.

(Romani populations have almost a serial bottleneck across Europe from Romania and it looks like Welsh Romani, as proxy for general British Romani, were reduced to a particularly small population with a lot of influx from local husbands / brides and isolation as long ROH are particularly high.)

But it seems very indirect and I don't know if *any* cultural or historical evidence for anything like that (besides GW's anecdote).

Grey said...

Garvan

"The possibility of any relationship between travelers and Roma, other than through marriage, is non-existent."

yes - not a recent relationship anyway

#

"If Mr. Grey sees commonality in hygiene beliefs between the two groups then I would suggest it is because they both live beside the road with limited water supply and no hot water, in climates where washing in cold water is not pleasant."

It's more of a religious belief than a hygiene one but yeah, maybe so

#

Matt

welsh romani - could be that

(plus my memory may be wrong)