Berbers and Arabs: Tracing the genetic diversity and history of Southern Tunisia through genome wide analysis

Understanding the genomic heterogeneity of North African Imazighen: from broad to microgeographical perspectives

The strategic location of North Africa has led to cultural and demographic shifts, shaping its genetic structure. Historical migrations brought different genetic components that are evident in present-day North African genomes, along with autochthonous components. The Imazighen (plural of Amazigh) are believed to be the descendants of autochthonous North Africans and speak various Amazigh languages, which belong to the Afro-Asiatic language family. However, the arrival of different human groups, especially during the Arab conquest, caused cultural and linguistic changes in local populations, increasing their heterogeneity. We aim to characterize the genetic structure of the region, using the largest Amazigh dataset to date and other reference samples. Our findings indicate microgeographical genetic heterogeneity among Amazigh populations, modeled by various admixture waves and different effective population sizes. A first admixture wave is detected group-wide around the twelfth century, whereas a second wave appears in some Amazigh groups around the nineteenth century. These events involved populations with higher genetic ancestry from south of the Sahara compared to the current North Africans. A plausible explanation would be the historical trans-Saharan slave trade, which lasted from the Roman times to the nineteenth century. Furthermore, our investigation shows that assortative mating in North Africa has been rare.

The Impact of Recent Demography on Functional Genetic Variation in North African Human Groups

The strategic location of North Africa has made the region the core of a wide range of human demographic events, including migrations, bottlenecks, and admixture processes. This has led to a complex and heterogeneous genetic and cultural landscape, which remains poorly studied compared to other world regions. Whole-exome sequencing is particularly relevant to determine the effects of these demographic events on current-day North Africans' genomes, since it allows to focus on those parts of the genome that are more likely to have direct biomedical consequences. Whole-exome sequencing can also be used to assess the effect of recent demography in functional genetic variation and the efficacy of natural selection, a long-lasting debate. In the present work, we use newly generated whole-exome sequencing and genome-wide array genotypes to investigate the effect of demography in functional variation in 7 North African populations, considering both cultural and demographic differences and with a special focus on Amazigh (plur. Imazighen) groups. We detect genetic differences among populations related to their degree of isolation and the presence of bottlenecks in their recent history. We find differences in the functional part of the genome that suggest a relaxation of purifying selection in the more isolated groups, allowing for an increase of putatively damaging variation. Our results also show a shift in mutational load coinciding with major demographic events in the region and reveal differences within and between cultural and geographic groups.

Isotopic evidence for human mobility in late antique Bulla Regia (Tunisia)

This paper represents the first isotopic study on late antique human mobility in North Africa, using the urban site of Bulla Regia in Tunisia as a case study. We also present the first values for bioavailable ⁸⁷Sr/⁸⁶Sr in northern Tunisia, analysing 63 plant and snail samples, as well as a simple method for the pre-processing of plants in the field to facilitate their export. Bulla Regia was a prominent Roman and late antique town situated on an important axis of transport and communication in North Africa and is therefore an ideal site to explore mobility in the region during this time period. Strontium (⁸⁷Sr/⁸⁶Sr) and oxygen (δ¹⁸O_Carb) isotopic analysis of 22 late antique individuals from a Christian church and cemetery identified at least seven or eight non-locals, while comparative analysis of five Roman individuals from a funerary enclosure on the same site classified all but one of them as potential locals. Most non-local individuals exhibit ⁸⁷Sr/⁸⁶Sr values that match various areas of northern Tunisia, which supports regional mobility rather than long-distance migration, although when combined with the oxygen results, inter-regional mobility from an area with a warmer climate may be hypothesised for some individuals. Examination of the spatial distribution of non-local individuals in their cemetery setting reveals that they were privileged individuals, thus they may reflect the mobility of wealthier town-dwellers in late antiquity, particularly perhaps along the Carthage-Hippo route.

Genetic relationships of Southwest Asian and Mediterranean populations

The Southwest Asian, circum-Mediterranean, and Southern European populations (collectively, SWAMSE) together with Northern European populations form one of five "continental" groups of global populations in many analyses of population relationships. This region is of great anthropologic and forensic interest but relationships of large numbers of populations within the region have not been able to be cleanly resolved with autosomal genetic markers. To examine the genetic boundaries to the SWAMSE region and whether internal structure can be detected we have assembled data for a total of 151 separate autosomal genetic markers on populations in this region and other parts of the world for a global set of 95 populations. The markers include 83 ancestry informative SNPs as singletons and 68 microhaplotype loci defined by 204 SNPs. The 151 loci are ancestry informative on a global scale, identifying at least five biogeographic clusters. One of those clusters is a clear grouping of 37 populations containing the SWAMSE plus northern European populations to the exclusion of populations in South Central Asia and populations from farther East. A refined analysis of the 37 populations shows the northern European populations clustering separately from the SWAMSE populations. Within Southwest Asia the Samaritans and Shabaks are distinct outliers. The Yemenite Jews, Saudi, Kuwaiti, Palestinian Arabs, and Southern Tunisians cluster together loosely while the remaining populations from Northern Iraq, Mediterranean Europe, the Caucasus region, and Iran cluster in a more complex graded fashion. The majority of the SWAMSE populations from the mainland of Southwest Asia form a cluster with little internal structure reflecting a very complex history of endogamy and migrations. The set of 151 DNA polymorphisms not only distinguishes major geographical regions globally but can distinguish ancestry to a small degree within geographical regions such as SWAMSE. We discuss forensic characteristics of the polymorphisms and also identify those that rank highest by Rosenberg's I_n measure for the SWAMSE region populations and for the global set of populations analyzed. DATA AVAILABILITY: Genotypes on all 151 markers for all 3790 individuals typed in the Kidd Lab on the 72 Kidd lab populations have been deposited in the Zenodo archive and can be freely accessed at https://doi.org/10.5281/zenodo.4658892. Some of the data has been made public previously as supplemental files appended to publications. Data for the additional individuals included in the analyses was taken from already public datasets as indicated in the text.