Y chromosomes and mtDNA from Soqotra

UPDATE (18/11): see a related post on the age of the new mtDNA lineages [end update]

Soqotra is an island in the Indian Ocean which belongs to Yemen. What is most interesting -to me- about this paper, is that 71.4% of the Y-chromosomes belong to haplogroup J*(xJ1, J2) which is found at trace frequencies elsewhere. Interestingly, haplogroup J2 is not found in this isolated region, while haplogroup J1 is found at a frequency of 14.3%.

The authors write:

For the perspective of the Y-chromosome data, a high
frequency of haplogroup J1 in Soqotra is consistent with
a gradient of this haplogroup in the Arabian Peninsula
(Cadenas et al., 2008). These authors estimated ages for
J1 in Arabia (9.7 +/ 2.4 in Yemen, 7.4 +/- 2.3 in Qatar and
6.4 +/- 1.4 KYBP in UAE), consistent with a Neolithic
expansion from the north (where Y-chromosome STR diversity
is higher). However, we report a much higher frequency
of J* (lack of M267 and M172) in Soqotra. Since
this lineage was not found by Cadenas et al. (2008) in
the Arabian Peninsula, this raises the possibility of an
earlier input for these lineages or more probably very
strong genetic drift of a low frequency Arabian lineage
in the Y-chromosome gene pool of Soqotra.

The early dates from Cadenas et al. are due to the use of an evolutionary mutation rate, and thus need to be downgraded to about ~1,000BC onwards, coinciding (within wide confidence intervals) with the formation of the earliest Arabian kingdoms. It seems probable that J*(xJ1, J2) was commoner in the past, and contributed to the population of Soqotra, but this population was later overwhelmed by the expansion of J1-carriers who dominate the Arabian peninsula to this day.

It is unfortunate that apparently many J2 downstream markers were typed even though there is no J2 on the island, whereas haplogroup E, occurring at a frequency of 9.5% was not further resolved. This underscores the need for a more flexible typing stratgy; at this level it is not clear whether this E came to the island from Africa or from Arabia.

American Journal of Physical Anthropology doi: 10.1002/ajpa.20960

Out of Arabia - The settlement of Island Soqotra as revealed by mitochondrial and Y chromosome genetic diversity

Viktor Cerny et al.

Abstract

The Soqotra archipelago is one of the most isolated landmasses in the world, situated at the mouth of the Gulf of Aden between the Horn of Africa and southern Arabia. The main island of Soqotra lies not far from the proposed southern migration route of anatomically modern humans out of Africa 60,000 years ago (kya), suggesting the island may harbor traces of that first dispersal. Nothing is known about the timing and origin of the first Soqotri settlers. The oldest historical visitors to the island in the 15th century reported only the presence of an ancient population. We collected samples throughout the island and analyzed mitochondrial DNA and Y-chromosomal variation. We found little African influence among the indigenous people of the island. Although the island population likely experienced founder effects, links to the Arabian Peninsula or southwestern Asia can still be found. In comparison with datasets from neighboring regions, the Soqotri population shows evidence of long-term isolation and autochthonous evolution of several mitochondrial haplogroups. Specifically, we identified two high-frequency founder lineages that have not been detected in any other populations and classified them as a new R0a1a1 subclade. Recent expansion of the novel lineages is consistent with a Holocene settlement of the island ~6 kya.

Link