A Rare Deep-Rooting D0 African Y-Chromosomal Haplogroup and Its Implications for the Expansion of Modern Humans Out of Africa

Abstract

Present-day humans outside Africa descend mainly from a single expansion out ∼50,000-70,000 years ago, but many details of this expansion remain unclear, including the history of the male-specific Y chromosome at this time. Here, we reinvestigate a rare deep-rooting African Y-chromosomal lineage by sequencing the whole genomes of three Nigerian men described in 2003 as carrying haplogroup DE* Y chromosomes, and analyzing them in the context of a calibrated worldwide Y-chromosomal phylogeny. We confirm that these three chromosomes do represent a deep-rooting DE lineage, branching close to the DE bifurcation, but place them on the D branch as an outgroup to all other known D chromosomes, and designate the new lineage D0. We consider three models for the expansion of Y lineages out of Africa ∼50,000-100,000 years ago, incorporating migration back to Africa where necessary to explain present-day Y-lineage distributions. Considering both the Y-chromosomal phylogenetic structure incorporating the D0 lineage, and published evidence for modern humans outside Africa, the most favored model involves an origin of the DE lineage within Africa with D0 and E remaining there, and migration out of the three lineages (C, D, and FT) that now form the vast majority of non-African Y chromosomes. The exit took place 50,300-81,000 years ago (latest date for FT lineage expansion outside Africa - earliest date for the D/D0 lineage split inside Africa), and most likely 50,300-59,400 years ago (considering Neanderthal admixture). This work resolves a long-running debate about Y-chromosomal out-of-Africa/back-to-Africa migrations, and provides insights into the out-of-Africa expansion more generally.

Keywords: Human Y chromosome; YAP+ Y chromosomes; out-of-Africa migration; phylogeography.

Figure 1

Y Chromosome phylogenetic tree from worldwide samples. (A) A maximum-likelihood tree of 180 Y-chromosome sequences from worldwide populations. Different branch colors and symbols represent different haplogroups assigned based on ISOGG v11.01. The Nigerian chromosomes sequenced in this study are highlighted in blue and assigned to the novel D0 haplogroup. Bootstrap values from 1000 replications are shown on the branches. (B) Map showing location of the studied individuals with colored symbols reflecting the haplogroups assigned in A. The clade consisting of the D0 and D haplogroups is represented by blue squares and is observed in Africa and East Asia. (C) Ages of the nodes leading to haplogroup D0 in the phylogenetic tree (point estimates; branch lengths are not to scale). Haplogroups D0 and D are estimated to have split 71,400 (63,100–81,000) years ago while the D0 individuals in this study coalesced 2500 (2200–2800) years ago.

Figure 2

Models for the early movements of Y-chromosomal haplogroups out of Africa and back. (A) Simplified Y-chromosomal phylogeny showing the key lineages, including D0. Lineages currently located in Africa are colored yellow; those currently outside Africa are blue. Triangle widths are not meaningful, except that they show that E and FT are the predominant lineages inside and outside Africa, respectively. The small orange triangle in FT represents the R1b-V88 back-to-Africa migration that took place after the time period considered here. (B–D) Models for lineage movements that could lead to the present-day African or non-African distributions of lineages, using point estimates of dates derived from the phylogeny (see Table S2). The three models represent migrations out of Africa at different time intervals, indicated by the purple, brown, and green shading in A. Arrows in B–D indicate intercontinental movements and their direction, but do not represent particular locations or routes. The first colored arrow(s) represent the lineage(s) that migrated out, during the time period shown at the top of the maps. Additional uncolored arrows represent subsequent migrations and their time intervals needed to produce the present-day distributions.

Figure 3

Estimation of the time of the out-of-Africa migration incorporating information from Y-chromosomal lineages (green, this work), archaeological dates (brown, Fu et al. 2014), and ancient DNA (red, Fu et al. 2014).