Early Holocenic and Historic mtDNA African Signatures in the Iberian Peninsula: The Andalusian Region as a Paradigm

Mitochondrial DNA in Human Diversity and Health: From the Golden Age to the Omics Era

Mitochondrial DNA (mtDNA) is a small fraction of our hereditary material. However, this molecule has had an overwhelming presence in scientific research for decades until the arrival of high-throughput studies. Several appealing properties justify the application of mtDNA to understand how human populations are-from a genetic perspective-and how individuals exhibit phenotypes of biomedical importance. Here, I review the basics of mitochondrial studies with a focus on the dawn of the field, analysis methods and the connection between two sides of mitochondrial genetics: anthropological and biomedical. The particularities of mtDNA, with respect to inheritance pattern, evolutionary rate and dependence on the nuclear genome, explain the challenges of associating mtDNA composition and diseases. Finally, I consider the relevance of this single locus in the context of omics research. The present work may serve as a tribute to a tool that has provided important insights into the past and present of humankind.

Phylogeography of Sub-Saharan Mitochondrial Lineages Outside Africa Highlights the Roles of the Holocene Climate Changes and the Atlantic Slave Trade

Despite the importance of ancient DNA for understanding human prehistoric dispersals, poor survival means that data remain sparse for many areas in the tropics, including in Africa. In such instances, analysis of contemporary genomes remains invaluable. One promising approach is founder analysis, which identifies and dates migration events in non-recombining systems. However, it has yet to be fully exploited as its application remains controversial. Here, we test the approach by evaluating the age of sub-Saharan mitogenome lineages sampled outside Africa. The analysis confirms that such lineages in the Americas date to recent centuries—the time of the Atlantic slave trade—thereby validating the approach. By contrast, in North Africa, Southwestern Asia and Europe, roughly half of the dispersal signal dates to the early Holocene, during the “greening” of the Sahara. We elaborate these results by showing that the main source regions for the two main dispersal episodes are distinct. For the recent dispersal, the major source was West Africa, but with two exceptions: South America, where the fraction from Southern Africa was greater, and Southwest Asia, where Eastern Africa was the primary source. These observations show the potential of founder analysis as both a supplement and complement to ancient DNA studies.

The relevance of late MSA mandibles on the emergence of modern morphology in Northern Africa

North Africa is a key area for understanding hominin population movements and the expansion of our species. It is home to the earliest currently known Homo sapiens (Jebel Irhoud) and several late Middle Stone Age (MSA) fossils, notably Kébibat, Contrebandiers 1, Dar-es-Soltane II H5 and El Harhoura. Mostly referred to as “Aterian” they fill a gap in the North African fossil record between Jebel Irhoud and Iberomaurusians. We explore morphological continuity in this region by quantifying mandibular shape using 3D (semi)landmark geometric morphometric methods in a comparative framework of late Early and Middle Pleistocene hominins (n = 15), Neanderthals (n = 27) and H. sapiens (n = 145). We discovered a set of mixed features among late MSA fossils that is in line with an accretion of modern traits through time and an ongoing masticatory gracilization process. In Northern Africa, Aterians display similarities to Iberomaurusians and recent humans in the area as well as to the Tighenif and Thomas Quarry hominins, suggesting a greater time depth for regional continuity than previously assumed. The evidence we lay out for a long-term succession of hominins and humans emphasizes North Africa’s role as source area of the earliest H. sapiens.

Genetic variation patterns of β-thalassemia in Western Andalusia (Spain) reveal a structure of specific mutations within the Iberian Peninsula

BACKGROUND

Analyses of the genomic variation in the western Mediterranean population are being used to reveal its evolutionary history and to understand the molecular basis of particular diseases.

AIM

To observe the β-thalassemia mutational spectrum in western Andalusia, Spain, in the context of the Mediterranean. In addition, associations between disease and neutral gene variants within the β-globin gene (HBB) were also evaluated.

SUBJECTS AND METHODS

This study included 63 unrelated individuals diagnosed with β-thalassemia. In addition, 97 unrelated, healthy subjects of the same territory were also analysed as proxies of the normal genetic background. Allele associations and population genetic structure analyses were performed using different methodologies.

RESULTS

Data have revealed a rather restricted spectrum of β-thalassemia mutations in the analysed sample. Although the detected variants fit well with the Mediterranean pattern, certain singularities support a structure of some specific β-thalassemia alleles. The IVSI-1 (G > A) shows a strong regionalisation. The spatial correlogram revealed a typically narrow wave structure, presumably linked to genetic isolation and genetic drift.

CONCLUSIONS

The long history of endemic malaria in the study territory, the rather high consanguinity rates among its autochthonous population, and other demographic features have been used here to understand the western Andalusian β-thalassemia molecular portrait.

Biomolecular insights into North African-related ancestry, mobility and diet in eleventh-century Al-Andalus

Historical records document medieval immigration from North Africa to Iberia to create Islamic al-Andalus. Here, we present a low-coverage genome of an eleventh century CE man buried in an Islamic necropolis in Segorbe, near Valencia, Spain. Uniparental lineages indicate North African ancestry, but at the autosomal level he displays a mosaic of North African and European-like ancestries, distinct from any present-day population. Altogether, the genome-wide evidence, stable isotope results and the age of the burial indicate that his ancestry was ultimately a result of admixture between recently arrived Amazigh people (Berbers) and the population inhabiting the Peninsula prior to the Islamic conquest. We detect differences between our sample and a previously published group of contemporary individuals from Valencia, exemplifying how detailed, small-scale aDNA studies can illuminate fine-grained regional and temporal differences. His genome demonstrates how ancient DNA studies can capture portraits of past genetic variation that have been erased by later demographic shifts-in this case, most likely the seventeenth century CE expulsion of formerly Islamic communities as tolerance dissipated following the Reconquista by the Catholic kingdoms of the north.

Human Genomic Diversity Where the Mediterranean Joins the Atlantic

Throughout the past few years, a lively debate emerged about the timing and magnitude of the human migrations between the Iberian Peninsula and the Maghreb. Several pieces of evidence, including archaeological, anthropological, historical, and genetic data, have pointed to a complex and intermingled evolutionary history in the western Mediterranean area. To study to what extent connections across the Strait of Gibraltar and surrounding areas have shaped the present-day genomic diversity of its populations, we have performed a screening of 2.5 million single-nucleotide polymorphisms in 142 samples from southern Spain, southern Portugal, and Morocco. We built comprehensive data sets of the studied area and we implemented multistep bioinformatic approaches to assess population structure, demographic histories, and admixture dynamics. Both local and global ancestry inference showed an internal substructure in the Iberian Peninsula, mainly linked to a differential African ancestry. Western Iberia, from southern Portugal to Galicia, constituted an independent cluster within Iberia characterized by an enriched African genomic input. Migration time modeling showed recent historic dates for the admixture events occurring both in Iberia and in the North of Africa. However, an integrative vision of both paleogenomic and modern DNA data allowed us to detect chronological transitions and population turnovers that could be the result of transcontinental migrations dating back from Neolithic times. The present contribution aimed to fill the gaps in the modern human genomic record of a key geographic area, where the Mediterranean and the Atlantic come together.

Complete mitogenome data for the Serbian population: the contribution to high-quality forensic databases

Mitochondrial genome (mtDNA) is a valuable resource in resolving various human forensic casework. The usage of variability of complete mtDNA genomes increases their discriminatory power to the maximum and enables ultimate resolution of distinct maternal lineages. However, their wider employment in forensic casework is nowadays limited by the lack of appropriate reference database. In order to fill in the gap in the reference data, which, considering Slavic-speaking populations, currently comprises only mitogenomes of East and West Slavs, we present mitogenome data for 226 Serbians, representatives of South Slavs from the Balkan Peninsula. We found 143 (sub)haplogroups among which West Eurasian ones were dominant. The percentage of unique haplotypes was 85%, and the random match probability was as low as 0.53%. We support previous findings on both high levels of genetic diversity in the Serbian population and patterns of genetic differentiation among this and ten studied European populations. However, our high-resolution data supported more pronounced genetic differentiation among Serbians and two Slavic populations (Russians and Poles) as well as expansion of the Serbian population after the Last Glacial Maximum and during the Migration period (fourth to ninth century A.D.), as inferred from the Bayesian skyline analysis. Phylogenetic analysis of haplotypes found in Serbians contributed towards the improvement of the worldwide mtDNA phylogeny, which is essential for the interpretation of the mtDNA casework.

Evolutionary analysis of Mycobacterium bovis genotypes across Africa suggests co-evolution with livestock and humans

Mycobacterium bovis is the pathogenic agent responsible for bovine tuberculosis (bTB), a zoonotic disease affecting mostly cattle, but also transmittable to humans and wildlife. Genetic studies on M. bovis allow to detect possible routes of bTB transmission and the identification of genetic reservoirs that may provide an essential framework for public health action.

We used a database with 1235 M. bovis genotypes collected from different regions in Africa with 45 new Mozambican samples. Our analyses, based on phylogeographic and population genetics’ approaches, allowed to identify two clear trends. First, the genetic diversity of M. bovis is geographically clustered across the continent, with the only incidences of long-distance sharing of genotypes, between South Africa and Algeria, likely due to recent European introductions. Second, there is a broad gradient of diversity from Northern to Southern Africa with a diversity focus on the proximity to the Near East, where M. bovis likely emerged with animal domestication in the last 10,000 years.

Diversity indices are higher in Eastern Africa, followed successively by Northern, Central, Southern and Western Africa, roughly correlating with the regional archaeological records of introduction of animal domesticates. Given this scenario M. bovis in Africa was probably established millennia ago following a concomitant spread with cattle, sheep and goat. Such scenario could translate into long-term locally adapted lineages across Africa.

This work describes a novel scenario for the spread of M. bovis in Africa using the available genetic data, opening the field to further studies using higher resolution genomic data.

We describe the genetic diversity distribution in Africa of the pathogen Mycobacterium bovis, the responsible for bovine tuberculosis, mostly present in cattle but also transmittable to other animals including humans. This diversity is geographically clustered within the African continent meaning that the genetic diversity was established through independent evolution within different areas. Higher diversity values of M. bovis are found in Eastern and Northern Africa, followed by Central Africa, with Western and Southern Africa displaying the lowest diversity. These levels of diversity correlate well with the introduction of domesticated livestock in the different regions of Africa, following their domestication in the Near East 10,000 ago. We hypothesize that M. bovis emerged in the Near East and it was carried across Africa together with domesticated animals and people that developed herding practices and biological tolerance for digesting milk in adulthood. Such scenario implies a strong evolution and co-evolution of M. bovis across Africa leading to locally adapted strains that could prove a challenge for public health actions.

Paternal lineages in southern Iberia provide time frames for gene flow from mainland Europe and the Mediterranean world

BACKGROUND

The geography of southern Iberia and an abundant archaeological record of human occupation are ideal conditions for a full understanding of scenarios of genetic history in the area. Recent advances in the phylogeography of Y-chromosome lineages offer the opportunity to set upper bounds for the appearance of different genetic components.

AIM

To provide a global knowledge on the Y haplogroups observed in Andalusia with their Y microsatellite variation. Preferential attention is given to the vehement debate about the age, origin and expansion of R1b-M269 clade and sub-lineages.

SUBJECT AND METHODS

Four hundred and fourteen male DNA samples from western and eastern autochthonous Andalusians were genotyped for a set of Y-SNPs and Y-STRs. Gene diversity, potential population genetic structures and coalescent times were assessed.

RESULTS

Most of the analysed samples belong to the European haplogroup R1b1a1a2-M269, whereas haplogroups E, J, I, G and T show lower frequencies. A phylogenetic dissection of the R1b-M269 was performed and younger time frames than those previously reported in the literature were obtained for its sub-lineages.

CONCLUSION

The particular Andalusian R1b-M269 assemblage confirms the shallow topology of the clade. Moreover, the sharing of lineages with the rest of Europe indicates the impact in Iberia of an amount of pre-existing diversity, with the possible exception of R1b-DF27. Lineages such as J2-M172 and G-M201 highlight the importance of maritime travels of early farmers who reached the Iberian Peninsula.

Mitogenomes illuminate the origin and migration patterns of the indigenous people of the Canary Islands

The Canary Islands’ indigenous people have been the subject of substantial archaeological, anthropological, linguistic and genetic research pointing to a most probable North African Berber source. However, neither agreement about the exact point of origin nor a model for the indigenous colonization of the islands has been established. To shed light on these questions, we analyzed 48 ancient mitogenomes from 25 archaeological sites from the seven main islands. Most lineages observed in the ancient samples have a Mediterranean distribution, and belong to lineages associated with the Neolithic expansion in the Near East and Europe (T2c, J2a, X3a…). This phylogeographic analysis of Canarian ancient mitogenomes, the first of its kind, shows that some lineages are restricted to Central North Africa (H1cf, J2a2d and T2c1d3), while others have a wider distribution, including both West and Central North Africa, and, in some cases, Europe and the Near East (U6a1a1, U6a7a1, U6b, X3a, U6c1). In addition, we identify four new Canarian-specific lineages (H1e1a9, H4a1e, J2a2d1a and L3b1a12) whose coalescence dates correlate with the estimated time for the colonization of the islands (1^st millennia CE). Additionally, we observe an asymmetrical distribution of mtDNA haplogroups in the ancient population, with certain haplogroups appearing more frequently in the islands closer to the continent. This reinforces results based on modern mtDNA and Y-chromosome data, and archaeological evidence suggesting the existence of two distinct migrations. Comparisons between insular populations show that some populations had high genetic diversity, while others were probably affected by genetic drift and/or bottlenecks. In spite of observing interinsular differences in the survival of indigenous lineages, modern populations, with the sole exception of La Gomera, are homogenous across the islands, supporting the theory of extensive human mobility after the European conquest.

Mitochondrial variability in the Mediterranean area: a complex stage for human migrations

CONTEXT

The Mediterranean area has always played a significant role in human dispersal due to the large number of migratory events contributing to shape the cultural features and the genetic pool of its populations.

OBJECTIVE

This paper aims to review and diachronically describe the mitogenome variability in the Mediterranean population and the main demic diffusions that occurred in this area over time.

METHODS

Frequency distributions of the leading mitochondrial haplogroups have been geographically and chronologically evaluated. The variability of U5b and K lineages has been focussed to broaden the knowledge of their genetic histories.

RESULTS

The mitochondrial genetic makeup of Palaeolithic hunter-gatherers is poorly defined within the extant Mediterranean populations, since only a few traces of their genetic contribution are still detectable. The Neolithic lineages are more represented, suggesting that the Neolithic revolution had a marked effect on the peopling of the Mediterranean area. The largest effect, however, was provided by historical migrations.

CONCLUSION

Although the mitogenome variability has been widely used to try and clarify the evolution of the Mediterranean genetic makeup throughout almost 50 000 years, it is necessary to collect whole genome data on both extinct and extant populations from this area to fully reconstruct and interpret the impact of multiple migratory waves and their cultural and genetic consequences on the structure of the Mediterranean populations.

Pleistocene North African genomes link Near Eastern and sub-Saharan African human populations

North Africa is a key region for understanding human history, but the genetic history of its people is largely unknown. We present genomic data from seven 15,000-year-old modern humans, attributed to the Iberomaurusian culture, from Morocco. We find a genetic affinity with early Holocene Near Easterners, best represented by Levantine Natufians, suggesting a pre-agricultural connection between Africa and the Near East. We do not find evidence for gene flow from Paleolithic Europeans to Late Pleistocene North Africans. The Taforalt individuals derive one-third of their ancestry from sub-Saharan Africans, best approximated by a mixture of genetic components preserved in present-day West and East Africans. Thus, we provide direct evidence for genetic interactions between modern humans across Africa and Eurasia in the Pleistocene.

Reconciling evidence from ancient and contemporary genomes: a major source for the European Neolithic within Mediterranean Europe

Important gaps remain in our understanding of the spread of farming into Europe, due partly to apparent contradictions between studies of contemporary genetic variation and ancient DNA. It seems clear that farming was introduced into central, northern, and eastern Europe from the south by pioneer colonization. It is often argued that these dispersals originated in the Near East, where the potential source genetic pool resembles that of the early European farmers, but clear ancient DNA evidence from Mediterranean Europe is lacking, and there are suggestions that Mediterranean Europe may have resembled the Near East more than the rest of Europe in the Mesolithic. Here, we test this proposal by dating mitogenome founder lineages from the Near East in different regions of Europe. We find that whereas the lineages date mainly to the Neolithic in central Europe and Iberia, they largely date to the Late Glacial period in central/eastern Mediterranean Europe. This supports a scenario in which the genetic pool of Mediterranean Europe was partly a result of Late Glacial expansions from a Near Eastern refuge, and that this formed an important source pool for subsequent Neolithic expansions into the rest of Europe.

Ancient and recent Middle Eastern maternal genetic contribution to North Africa as viewed by mtDNA diversity in Tunisian Arab populations

OBJECTIVES

Through previous mitochondrial DNA studies, the Middle Eastern maternal genetic contribution to Tunisian populations appears limited. In fact, most of the studied communities were cosmopolitan, or of Berber or Andalusian origin. To provide genetic evidence for the actual contribution of Middle Eastern mtDNA lineages to Tunisia, we focused on two Arab speaking populations from Kairouan and Wesletia known to belong to an Arab genealogical lineage.

MATERIALS AND METHODS

A total of 114 samples were sequenced for the mtDNA HVS-I and HVS-II regions. Using these data, we evaluated the distribution of Middle Eastern haplogroups in the study populations, constructed interpolation maps, and established phylogenetic networks allowing estimation of the coalescence time for three specific Middle Eastern subclades (R0a, J1b, and T1).

RESULTS

Both studied populations displayed North African genetic structure and Middle Eastern lineages with a frequency of 12% and 28.12% in Kairouan and Wesletia, respectively. TMRCA estimates for haplogroups T1a, R0a, and J1b in Tunisian Arabian samples were around 15 000 YBP, 9000 to 5000 YBP, and 960 to 600 YBP, respectively.

CONCLUSIONS

The Middle Eastern maternal genetic contribution to Tunisian populations, as to other North African populations, occurred mostly in deep prehistory. They were brought in different migration waves during the Upper Paleolithic, probably with the expansion of Iberomaurusian culture, and during Epipaleolithic and Early Neolithic periods, which are concomitant with the Capsian civilization. Middle Eastern lineages also came to Tunisia during the recent Islamic expansion of the 7th CE and the subsequent massive Bedouin migration during the 11th CE.

Contacts in the last 90,000 years over the Strait of Gibraltar evidenced by genetic analysis of wild boar (Sus scrofa)

Contacts across the Strait of Gibraltar in the Pleistocene have been studied in different research papers, which have demonstrated that this apparent barrier has been permeable to human and fauna movements in both directions. Our study, based on the genetic analysis of wild boar (Sus scrofa), suggests that there has been contact between Africa and Europe through the Strait of Gibraltar in the Late Pleistocene (at least in the last 90,000 years), as shown by the partial analysis of mitochondrial DNA. Cytochrome b and the control region from North African wild boar indicate a close relationship with European wild boar, and even some specimens belong to a common haplotype in Europe. The analyses suggest the transformation of the wild boar phylogeography in North Africa by the emergence of a natural communication route in times when sea levels fell due to climatic changes, and possibly through human action, since contacts coincide with both the Last Glacial period and the increasing human dispersion via the strait.

The distribution of mitochondrial DNA haplogroup H in southern Iberia indicates ancient human genetic exchanges along the western edge of the Mediterranean

BACKGROUND

The structure of haplogroup H reveals significant differences between the western and eastern edges of the Mediterranean, as well as between the northern and southern regions. Human populations along the westernmost Mediterranean coasts, which were settled by individuals from two continents separated by a relatively narrow body of water, show the highest frequencies of mitochondrial haplogroup H. These characteristics permit the analysis of ancient migrations between both shores, which may have occurred via primitive sea crafts and early seafaring. We collected a sample of 750 autochthonous people from the southern Iberian Peninsula (Andalusians from Huelva and Granada provinces). We performed a high-resolution analysis of haplogroup H by control region sequencing and coding SNP screening of the 337 individuals harboring this maternal marker. Our results were compared with those of a wide panel of populations, including individuals from Iberia, the Maghreb, and other regions around the Mediterranean, collected from the literature.

RESULTS

Both Andalusian subpopulations showed a typical western European profile for the internal composition of clade H, but eastern Andalusians from Granada also revealed interesting traces from the eastern Mediterranean. The basal nodes of the most frequent H sub-haplogroups, H1 and H3, harbored many individuals of Iberian and Maghrebian origins. Derived haplotypes were found in both regions; haplotypes were shared far more frequently between Andalusia and Morocco than between Andalusia and the rest of the Maghreb. These and previous results indicate intense, ancient and sustained contact among populations on both sides of the Mediterranean.

CONCLUSIONS

Our genetic data on mtDNA diversity, combined with corresponding archaeological similarities, provide support for arguments favoring prehistoric bonds with a genetic legacy traceable in extant populations. Furthermore, the results presented here indicate that the Strait of Gibraltar and the adjacent Alboran Sea, which have often been assumed to be an insurmountable geographic barrier in prehistory, served as a frequently traveled route between continents.

The mitogenome of a 35,000-year-old Homo sapiens from Europe supports a Palaeolithic back-migration to Africa

After the dispersal of modern humans (Homo sapiens) Out of Africa, hominins with a similar morphology to that of present-day humans initiated the gradual demographic expansion into Eurasia. The mitogenome (33-fold coverage) of the Peştera Muierii 1 individual (PM1) from Romania (35 ky cal BP) we present in this article corresponds fully to Homo sapiens, whilst exhibiting a mosaic of morphological features related to both modern humans and Neandertals. We have identified the PM1 mitogenome as a basal haplogroup U6*, not previously found in any ancient or present-day humans. The derived U6 haplotypes are predominantly found in present-day North-Western African populations. Concomitantly, those found in Europe have been attributed to recent gene-flow from North Africa. The presence of the basal haplogroup U6* in South East Europe (Romania) at 35 ky BP confirms a Eurasian origin of the U6 mitochondrial lineage. Consequently, we propose that the PM1 lineage is an offshoot to South East Europe that can be traced to the Early Upper Paleolithic back migration from Western Asia to North Africa, during which the U6 lineage diversified, until the emergence of the present-day U6 African lineages.