Abstract
Human mitochondrial DNA haplogroup U is among the initial maternal founders in Southwest Asia and Europe and one that best indicates matrilineal genetic continuity between late Pleistocene hunter-gatherer groups and present-day populations of Europe. While most haplogroup U subclades are older than 30 thousand years, the comparatively recent coalescence time of the extant variation of haplogroup U7 (~16–19 thousand years ago) suggests that its current distribution is the consequence of more recent dispersal events, despite its wide geographical range across Europe, the Near East and South Asia. Here we report 267 new U7 mitogenomes that – analysed alongside 100 published ones – enable us to discern at least two distinct temporal phases of dispersal, both of which most likely emanated from the Near East. The earlier one began prior to the Holocene (~11.5 thousand years ago) towards South Asia, while the later dispersal took place more recently towards Mediterranean Europe during the Neolithic (~8 thousand years ago). These findings imply that the carriers of haplogroup U7 spread to South Asia and Europe before the suggested Bronze Age expansion of Indo-European languages from the Pontic-Caspian Steppe region.
Highlights
Compared to other subclades of hg U, both the phylogenetic structure and the ancestral origin of hg U7 are rather obscure
It has been previously shown that low-frequency mitochondrial haplogroups with relict distributions, similar to hg U7, can be disproportionately informative about ancient human dispersal events[36,37,38]
The maximum-parsimony reconstruction of 367 sequences of hg U7 yielded a tree with a basal hard polytomy that cannot be resolved at the level of whole-mtDNA sequence data: we identified eight independent branches that coalesce at the root of U7 (Fig. 1A and Supplementary Figure S1)
Summary
The maximum-parsimony reconstruction of 367 sequences of hg U7 yielded a tree with a basal hard polytomy that cannot be resolved (to a dichotomous one) at the level of whole-mtDNA sequence data: we identified eight independent branches that coalesce at the root of U7 (Fig. 1A and Supplementary Figure S1). Consistent with previous studies, we found that three major branches, U7a–c, capture most (96%) of the U7 mitogenomes Besides these three previously known branches, we identified three additional clades, hereby designated as U7d, U7e, and U7f (Table 1). U7a is the dominant branch of U7 throughout the Near East and South Asia with subclades specific to Central Asia (U7a12–15), Mediterranean and Southeast Europe (U7a17 and U7a19; Figs 1B and 2B, Supplementary Figure S1). U7b exhibits a higher frequency than U7a in Europe with elevated levels of diversity in the Mediterranean and southeastern regions (Figs 1C and 2C and Supplementary Figure S1) It is distributed in the Near East, South and Central Asia. U7 is distributed unevenly in Central Asia; it is most frequent in its southern
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