Multiple and differentiated contributions to the male gene pool of pastoral and farmer populations of the African Sahel

Abstract

The African Sahel is conducive to studies of divergence/admixture genetic events as a result of its population history being so closely related with past climatic changes. Today, it is a place of the co-existence of two differing food-producing subsistence systems, i.e., that of sedentary farmers and nomadic pastoralists, whose populations have likely been formed from several dispersed indigenous hunter-gatherer groups. Using new methodology, we show here that the male gene pool of the extant populations of the African Sahel harbors signatures of multiple and differentiated contributions from different genetic sources. We also show that even if the Fulani pastoralists and their neighboring farmers share high frequencies of four Y chromosome subhaplogroups of E, they have drawn on molecularly differentiated subgroups at different times. These findings, based on combinations of SNP and STR polymorphisms, add to our previous knowledge and highlight the role of differences in the demographic history and displacements of the Sahelian populations as a major factor in the segregation of the Y chromosome lineages in Africa. Interestingly, within the Fulani pastoralist population as a whole, a differentiation of the groups from Niger is characterized by their high presence of R1b-M343 and E1b1b1-M35. Moreover, the R1b-M343 is represented in our dataset exclusively in the Fulani group and our analyses infer a north-to-south African migration route during a recent past.

Genetic history of the African Sahelian populations

“…Interestingly, phylogeography of both these lineages suggests that contemporary Sahelian pastoralists share genetic characteristics with populations of western rather than eastern Mediterranean ancestry, contrarily to what could be expected with a cattle domestication centre in the Near East. It can be added that a north African contribution of NRY markers to the Fulani pastoralists’ gene pool was also documented previously through a study of NRY haplogroups’ frequency distributions in wide African data sets . Last but not least, similar age estimates to those inferred for west Eurasian mtDNA haplogroups, that is, around 8000 years ago, were obtained by analysing the NRY lineage R1b‐V88, which is again more frequent in the nomadic pastoralists across the Sahel, although not only in the Fulani population …”

“…It can be added that a north African contribution of NRY markers to the Fulani pastoralists' gene pool was also documented previously through a study of NRY haplogroups' frequency distributions in wide African data sets. 68 Last but not least, similar age estimates to those inferred for west Eurasian mtDNA haplogroups, that is, around 8000 years ago, were obtained by analysing the NRY lineage R1b-V88, which is again more frequent in the nomadic pastoralists across the Sahel, although not only in the Fulani population. 69 The African Sahel also likely received recent genetic inputs from the Arabian Peninsula.…”

“…Populations of the Sahel/Savannah belt bear mtDNA haplogroups not only of sub‐Saharan origin but also of west Eurasian, and these occur more frequently among pastoralists (Figure ) . One study on mtDNA lineages H1cb1 and U5b1b1b, that are found almost exclusively among the Fulani, revealed that their internal diversification may correspond to periods when, according to archaeological data, cattle keepers first settled the Sahel/Savannah belt .…”

“…66 Populations of the Sahel/Savannah belt bear mtDNA haplogroups not only of sub-Saharan origin but also of west Eurasian, and these occur more frequently among pastoralists ( Figure 1). 67,68 One study 69 on mtDNA lineages H1cb1 and U5b1b1b, that are found almost exclusively among the Fulani, revealed that their internal diversification may correspond to periods when, according to archaeological data, cattle keepers first settled the Sahel/Savannah belt. 69 Interestingly, phylogeography of both these lineages suggests that contemporary Sahelian pastoralists share genetic characteristics with populations of western rather than eastern Mediterranean ancestry, contrarily to what could be expected with a cattle domestication centre in the Near East.…”

The Genetic Impact of the Lake Chad Basin Population in North Africa as Documented by Mitochondrial Diversity and Internal Variation of the L3e5 Haplogroup

“…Uniparental genetic markers provide rather contradictory evidence for these linguistic proposals; while the mtDNA L3f3 clade supports Blench's vision (Černý et al, 2009), the Y chromosome R1b1a-V88 clade favors Ehret's concept (Cruciani et al, 2010a). However, recently analyzed male genetic contributions of the LCB populations showed a significant North African R1b contribution only in the Fulani pastoralists belonging to the Niger-Congo linguistic family and not to the Chadic groups (Bučková et al, 2013). It seems thus that LCB Y chromosomal variation is still difficult to interpret, likely because of its higher susceptibility to genetic drift than that of mtDNA (Pereira et al, 2001a) or due to insufficient sampling in as large a region as is the LCB.…”