Objectives: The Sahel belt is occupied by populations who use two types of subsistence strategy, nomadic pastoralism and sedentary farming, and who belong to three linguistic families, Niger-Congo, Nilo-Saharan, and Afro-Asiatic. Little is known, however, about the origins of these two populations and their mutual genetic relationships. Materials and Methods:We have built a large dataset of mitochondrial DNA sequences and Y chromosomal STR haplotypes of pastoralists and farmers belonging to all three linguistic phyla in the western, central, and eastern parts of the Sahel. We calculated pairwise genetic, geographic, and linguistic distances between populations and analyzed the effects of geography, language, and subsistence on population genetic structure.Results: We found that subsistence mode significantly contributed to the generally low population structure in the Sahel and that language affiliation plays a more important role for pastoralists than for farmers. We also demonstrated that geographic isolation significantly influenced the population structure of sedentary farmers but not of nomadic pastoralists. Finally, we found haplotypes shared between the Fulani and Arabic-speaking Baggara, supporting the theory of Baggarization, which explains the recent adaptation of Arabic-speaking nomads in the Sahel region through contact with autochthonous sub-Saharan populations.

Even if the age of the most recent common ancestor of -13,915*G is ∼4 ka as shown in a previous study, our results suggest that its spread to Africa was more recent, which is consistent with the migrations of Arabic tribes. Because the incidence of sub-Saharan mtDNA haplotypes is negatively correlated with the occurrence of -13,915*G, we suggest that the decrease of its frequency in Africa has been caused by progressive admixture of the Arabian nomads with sub-Saharan populations.

1 Male and female Wistar rats were given 100 mg L-1 of nickel (as nickel sulfate) in drinking water for 6 months. Lactate dehydrogenase, total proteins, N-acetyl-β-D-glucosaminidase (NAG), albumin and β2-microglobulin were measured in 24 h urine after 3 and 6 months of exposure. Body and kidney weights were also recorded. 2 After 6 months, urinary excretion of albumin in control and exposed rats was 354 and 1319 μg 24 h-1 for female rats (P<0.05) and 989 and 2065 μg 24 h-1 for male rats (P = non significant). Kidney weights were significantly increased in the exposed groups. No significant changes were observed in other parameters. 3 The results suggest that low-level oral exposure to soluble nickel either induces changes of glomerular permeability in female and possibly in male rats, or enhances the normal age-related glomerular nephritis lesions of ageing rats. The intake was probably not high enough to induce significant tubular changes. The female rat seems to be more sensitive to the nephrotoxic effect of nickel than the male rat.

Objectives: Archeological evidence shows that first nomadic pastoralists came to the African Sahel from northeastern Sahara, where milking is reported by 7.5 ka. A second wave of pastoralists arrived with the expansion of Arabic tribes in 7th-14th century CE. All Sahelian pastoralists depend on milk production but genetic diversity underlying their lactase persistence (LP) is poorly understood. Materials and methods: We investigated SNP variants associated with LP in 1,241 individuals from 29 mostly pastoralist populations in the Sahel. Then, we analyzed six SNPs in the neighboring fragment (419 kb) in the Fulani and Tuareg with the −13910*T mutation, reconstructed haplotypes, and calculated expansion age and growth rate of this variant. Results: Our results reveal a geographic localization of two different LP variants in the Sahel: −13910*T west of Lake Chad (Fulani and Tuareg pastoralists) and −13915*G east of there (mostly Arabic-speaking pastoralists). We show that −13910*T has a more diversified haplotype background among the Fulani than among the Tuareg and that the age estimate for expansion of this variant among the Fulani (8.5 ka) corresponds to introduction of cattle to the area.

The Sahel/Savannah belt harbors diverse populations with different demographic histories and different subsistence patterns. However, populations from this large African region are notably under-represented in genomic research. To investigate the population structure and adaptation history of populations from the Sahel/Savannah space, we generated dense genome-wide genotype data of 327 individuals—comprising 14 ethnolinguistic groups, including ten previously unsampled populations. Our results highlight fine-scale population structure and complex patterns of admixture, particularly in Fulani groups and Arabic-speaking populations. Among all studied Sahelian populations, only the Rashaayda Arabic-speaking population from eastern Sudan shows a lack of gene flow from African groups, which is consistent with the short history of this population in the African continent. They are recent migrants from Saudi Arabia with evidence of strong genetic isolation during the last few generations and a strong demographic bottleneck. This population also presents a strong selection signal in a genomic region around the CNR1 gene associated with substance dependence and chronic stress. In Western Sahelian populations, signatures of selection were detected in several other genetic regions, including pathways associated with lactase persistence, immune response, and malaria resistance. Taken together, these findings refine our current knowledge of genetic diversity, population structure, migration, admixture and adaptation of human populations in the Sahel/Savannah belt and contribute to our understanding of human history and health.