November 06, 2011

Y-chromosomes of the Bahamas

I like the line about there being substantially more Y-STR variation in E1b1a7a-U174 and E1b1ba8-U175 in the Bahamas than any African collection. I have argued for years that the central assumption of phylogeography, that the location of highest Y-STR diversity is not necessarily the point of origin of a haplogroup, since Y-STR diversity can be affected both by antiquity and by admixture. Nonetheless, I keep reading papers where tiny differences in Y-STR variation, even if we forget about the noisiness of Y-STRs themselves, are taken as evidence of ancient migrations. Thankfully, the time when Y-STRs were used to infer ancient migrations is over, and the huge collection of Y-STR haplotypes amassed by population geneticists, forensic specialists, and genealogists alike can be put to uses for which it is more amenable.

I can't say I know much about the history of the Bahamas, but this was something I had not heard of before:
Over the last 150 years, the Bahamas has been witness to a varied array of settlers, including Chinese immigrant workers, Greek spongers, Jewish business-men and individuals of Lebanese descent fleeing religious persecution. The extent to which each group has contributed genetically to the Bahamian paternal gene pool, however, is unknown. Our findings suggest that the Greeks, which exhibit relatively high frequencies of haplogroups E1b1b1a*-M78, J2a*-M410, and R1b1b1*-L23 (Semino et al., 2004; Myres et al., 2011), are a likely source of these lineages in the Bahamas, although the presence of M78 derived chromosomes may also signal gene flow from Lebanon (Zalloua et al., 2008). J1e-P58 lineages, on the other hand, which are characteristic of Jewish populations (Hammer et al., 2009) and Arab speaking groups (Chiaroni et al., 2010), may represent genetic signatures of Eastern European Jews and/or Lebanese migrants entering the Bahamas in the early twentieth century.
Another interesting tidbit:
Western European colonialism, although short-lived, appears to have left marked genetic imprints throughout the Bahamian archipelago, with Long Island receiving the strongest European genetic signals and Exuma, the weakest; a distribution pattern consistent with our earlier reports utilizing autosomal STR markers (Simms et al., 2008, 2011). The higher frequency of M269 derived individuals in the Long Island population (55.8%), when compared with the other five Bahamian islands surveyed (ranging from 8.5% to 18.3%), suggests higher gene flow from European males (Saunders, 2003b). According to the 1851 census, Long Island possessed one of the smallest European components (13.1%) yet, by 1953, almost 50% of this population was of ‘‘mixed’’ ancestry (Craton, 1998).
R-M269 seems quintessentially European today, and most living R-M269 men probably have West European ancestry. But, the finding of a high frequency in a Bahamian spot ought to remind us that Y-chromosomes can achieve high frequencies in little time, given the right conditions. Indeed, we can very well draw a parallel between the prehistoric spread of R-M269 into Europe, an event that is still shrouded in mystery, with the late historical movement of the same haplogroup into the Americas. Taking the broad view, these two unrelated events represent two pulses of the same westward spread of a successful Y-chromosome lineage.

It is also nice that scientists are beginning to take notice of very basal Y-chromosomes, going back to Y-chromosome Adam.

Two samples that fell outside of haplogroups B-T (defined by M42) were observed in Abaco (1.5%) and New Providence (0.7%), two Bahamian islands separated by a total of 139.4 km, as well as in a single sample from Haiti (unpublished data). When tested for V171, which, according to Cruciani et al. (2011a) defines the A2-T lineage, all three samples exhibited the ancestral allele. Instead, each individual was derived for the paralogous V152 mutation that determines the A1b lineage. It should be noted that each of the three samples possessed an eight base pair long Poly-T stretch at the M91 locus, indicative of the monophyletic haplogroup A defined by Karafet et al. (2008). However, as a result of the rearrangement of the tree by Cruciani et al. (2011a), haplogroup A no longer represents a monophyletic group, as the A2 and A3 lineages are now united with all haplogroup A lineages other than A1 by their shared possession of V171.
Haplogroup A chromosomes have been collected as isolated examples in many genealogical projects and scientific studies. It's a great idea for someone to take the initiative and collect the most divergent ones, invest in genotyping them fully, and push the boundaries of what we know about the most ancient history of modern human patrilineages.

AJPA DOI: 10.1002/ajpa.21616

Paternal lineages signal distinct genetic contributions from British Loyalists and continental Africans among different Bahamian islands

Tanya M. Simms et al.

Over the past 500 years, the Bahamas has been influenced by a wide array of settlers, some of whom have left marked genetic imprints throughout the archipelago. To assess the extent of each group's genetic contributions, high-resolution Y-chromosome analyses were performed, for the first time, to delineate the patriarchal ancestry of six islands in the Northwest (Abaco and Grand Bahama) and Central (Eleuthera, Exuma, Long Island, and New Providence) Bahamas and their genetic relationships with previously published reference populations. Our results reveal genetic signals emanating primarily from African and European sources, with the predominantly sub-Saharan African and Western European haplogroups E1b1a-M2 and R1b1b1-M269, respectively, accounting for greater than 75% of all Bahamian patrilineages. Surprisingly, we observe notable discrepancies among the six Bahamian populations in their distribution of these lineages, with E1b1a-M2 predominating Y-chromosomes in the collections from Abaco, Exuma, Eleuthera, Grand Bahama, and New Providence, whereas R1b1b1-M269 is found at elevated levels in the Long Island population. Substantial Y-STR haplotype variation within sub-haplogroups E1b1a7a-U174 and E1b1ba8-U175 (greater than any continental African collection) is also noted, possibly indicating genetic influences from a variety of West and Central African groups. Furthermore, differential European genetic contributions in each island (with the exception of Exuma) reflect settlement patterns of the British Loyalists subsequent to the American Revolution.



terryt said...

"I have argued for years that the central assumption of phylogeography, that the location of highest Y-STR diversity is not necessarily the point of origin of a haplogroup, since Y-STR diversity can be affected both by antiquity and by admixture".

And I still regularly argue with Maju over that problem. Interesting about A.

AdygheChabadi said...

I have this paper...I poosted about it on my Facebook page some weeks ago.

An island called, "Long Island" has about 7% Y-haplogroup T...they don't further delineate the subgroups like with E1b1a and R1b...

It would have been interesting to know what sublineages of Y-Haplogroup T those belonged to.

E1b1a and it's sublineages dominate the Bahamas. The majority of the population is of West African ancestry, at least, by the Y-Chromosome haplogoups anyway.

Anonymous said...

From observation and its history, the Bahamas must be a top candidate for the most admixed nation on earth.

Anonymous said...

Hi there, I used to post on a few anthropology forum a while back. I lost interest because it was too time consuming and found some members too annoying. The Bahamas is my homeland and I have try to explain the history of settlers to the Bahamas, I decided to create a blog to update every now and then. I recently did an entry on The Bahamas and Bermuda ;