Human genetic differentiation across the Strait of Gibraltar

Laboratory of Anthropology, Genetics and Peopling history (AGP), Department of Anthropology, University of Geneva, Geneva, Switzerland.
BMC Evolutionary Biology (Impact Factor: 3.37). 08/2010; 10(1):237. DOI: 10.1186/1471-2148-10-237
Source: PubMed


The Strait of Gibraltar is a crucial area in the settlement history of modern humans because it represents a possible connection between Africa and Europe. So far, genetic data were inconclusive about the fact that this strait constitutes a barrier to gene flow, as previous results were highly variable depending on the genetic locus studied. The present study evaluates the impact of the Gibraltar region in reducing gene flow between populations from North-Western Africa and South-Western Europe, by comparing formally various genetic loci. First, we compute several statistics of population differentiation. Then, we use an original simulation approach in order to infer the most probable evolutionary scenario for the settlement of the area, taking into account the effects of both demography and natural selection at some loci.
We show that the genetic patterns observed today in the region of the Strait of Gibraltar may reflect an ancient population genetic structure which has not been completely erased by more recent events such as Neolithic migrations. Moreover, the differences observed among the loci (i.e. a strong genetic boundary revealed by the Y-chromosome polymorphism and, at the other extreme, no genetic differentiation revealed by HLA-DRB1 variation) across the strait suggest specific evolutionary histories like sex-mediated migration and natural selection. By considering a model of balancing selection for HLA-DRB1, we here estimate a coefficient of selection of 2.2% for this locus (although weaker in Europe than in Africa), which is in line with what was estimated from synonymous versus non-synonymous substitution rates. Selection at this marker thus appears strong enough to leave a signature not only at the DNA level, but also at the population level where drift and migration processes were certainly relevant.
Our multi-loci approach using both descriptive analyses and Bayesian inferences lead to better characterize the role of the Strait of Gibraltar in the evolution of modern humans. We show that gene flow across the Strait of Gibraltar occurred at relatively high rates since pre-Neolithic times and that natural selection and sex-bias migrations distorted the demographic signal at some specific loci of our genome.

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    • "In addition to our data, a number of previous studies based on different marker systems, including contemporary and ancient DNA, suggest pre-Islamic gene flow from Northwest Africa to Iberia (Arnaiz-Villena et al., 1999; Maca-Meyer et al., 2003; Goncalves et al., 2005; Alvarez et al., 2009; Currat et al., 2010; Lacan et al., 2011). Also, archeological evidence point A C C E P T E D M A N U S C R I P T "
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    ABSTRACT: At different times during recent human evolution, northern Africa has served as a conduit for migrations from the Arabian Peninsula. Although previous researchers have investigated the possibility of the Strait of Gibraltar as a conduit of migration from North Africa to Iberia, we now revisit this issue and theorize that although the Strait of Gibraltar, at the west end of this corridor, has acted as a barrier for human dispersal into Southwest Europe, it has not provided an absolute seal to gene flow. To test this hypothesis, here we use the spatial frequency distributions, STR diversity and expansion time estimates of Y chromosome haplogroups J1-P58 and E-M81 to investigate the genetic imprints left by the Arabian and Berber expansions into the Iberian Peninsula, respectively. The data generated indicate that Arabian and Berber genetic markers are detected in Iberia. We present evidence that suggest that Iberia has received gene flow from Northwest Africa during and prior to the Islamic colonization of 711 A.D. It is interesting that the highest frequencies of Arabia and Berber markers are not found in southern Spain, where Islam remained the longest and was culturally most influential, but in Northwest Iberia, specifically Galicia. We propose that Moriscos' relocations to the north during the Reconquista, the migration of cryptic Muslims seeking refuge in a more lenient society and/or more geographic extensive pre-Islamic incursions may explain the higher frequencies and older time estimates of mutations in the north of the Peninsula. These scenarios are congruent with the higher diversities of some diagnostic makers observed in Northwest Iberia. Copyright © 2015. Published by Elsevier B.V.
    Gene 02/2015; 564(2). DOI:10.1016/j.gene.2015.02.042 · 2.14 Impact Factor
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    • "Several methods have been developed in this perspective (e.g., [65, 66]), but one of the most widely used today is computer simulation of plausible scenarios for human peopling history coupled with approaches allowing the estimation of several kinds of parameters at the same time (e.g., [67]). Two studies have already applied this approach to HLA data to explore different scenarios of peopling history, that is, for the Western Mediterranean region [22] and for East Asia [68]. Both demographic parameters (population density, demographic growth, and migration) and balancing selection coefficients on several HLA loci have been estimated, leading to relative selection intensities consistent with previous studies [69, 70]. "
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    ABSTRACT: Next generation sequencing (NGS) is currently being adapted by different biotechnological platforms to the standard typing method for HLA polymorphism, the huge diversity of which makes this initiative particularly challenging. Boosting the molecular characterization of the HLA genes through efficient, rapid, and low-cost technologies is expected to amplify the success of tissue transplantation by enabling us to find donor-recipient matching for rare phenotypes. But the application of NGS technologies to the molecular mapping of the MHC region also anticipates essential changes in population genetic studies. Huge amounts of HLA sequence data will be available in the next years for different populations, with the potential to change our understanding of HLA variation in humans. In this review, we first explain how HLA sequencing allows a better assessment of the HLA diversity in human populations, taking also into account the methodological difficulties it introduces at the statistical level; secondly, we show how analyzing HLA sequence variation may improve our comprehension of population genetic relationships by facilitating the identification of demographic events that marked human evolution; finally, we discuss the interest of both HLA and genome-wide sequencing and genotyping in detecting functionally significant SNPs in the MHC region, the latter having also contributed to the makeup of the HLA molecular diversity observed today.
    Research Journal of Immunology 07/2014; 2014(1):971818. DOI:10.1155/2014/971818
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    • "This can be useful to test scenarios where not only demographic, but also environmental factors are taken into account. This approach has already provided relevant results to understand the peopling history of specific geographic regions (Currat et al. 2010) and is currently being applied to East Asia to test the " southern route " hypothesis versus the " pincer " or " overlapping " models (Di et al. (2011) In prep. Testing the peopling history of East Asia through computer simulation). "
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    ABSTRACT: Population genetic studies may provide crucial information for our knowledge on human peopling history and have been extensively applied to reconstruct East Asian prehistory in the last 10 years. However, different genetic investigations are not always consistent with each other and some results are conflicting or misinterpreted. This represents a main obstacle for scholars of other disciplines like archaeologists and linguists who try to relate the genetic information on past human migrations to their own results on the spread of domesticated crops or animals or on the dispersal of the main language families. In this paper, we review the current genetic evidence related to the peopling history of East Asia with a critical view on some interpretations. In this way, we hope to provide a useful reference for further interdisciplinary studies on our past.
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