Publications by authors named "Chantal Radimilahy"

11 Publications

  • Page 1 of 1

African Gene Flow Reduces Beta-Ionone Anosmia/Hyposmia Prevalence in Admixed Malagasy Populations.

Brain Sci 2021 Oct 25;11(11). Epub 2021 Oct 25.

Equipe de Médecine Evolutive, URU EVOLSAN, Faculté de Chirurgie Dentaire, Université de Toulouse III, 31073 Toulouse, France.

While recent advances in genetics make it possible to follow the genetic exchanges between populations and their phenotypic consequences, the impact of the genetic exchanges on the sensory perception of populations has yet to be explored. From this perspective, the present study investigated the consequences of African gene flow on odor perception in a Malagasy population with a predominantly East Asian genetic background. To this end, we combined psychophysical tests with genotype data of 235 individuals who were asked to smell the odorant molecule beta-ionone (βI). Results showed that in this population the ancestry of the OR5A1 gene significantly influences the ability to detect βI. At the individual level, African ancestry significantly protects against specific anosmia/hyposmia due to the higher frequency of the functional gene (OR ratios = 14, CI: 1.8-110, -value = 0.012). At the population level, African introgression decreased the prevalence of specific anosmia/hyposmia to this odorous compound. Taken together, these findings validate the conjecture that in addition to cultural exchanges, genetic transfer may also influence the sensory perception of the population in contact.
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http://dx.doi.org/10.3390/brainsci11111405DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8615941PMC
October 2021

Genetic evidence and historical theories of the Asian and African origins of the present Malagasy population.

Hum Mol Genet 2021 Apr;30(R1):R72-R78

Équipe de Médecine Evolutive, Faculté de Chirurgie Dentaire URU EVOLSAN Université Toulouse III, France.

The origin of the Malagasy population has been a subject of speculation since the 16th century. Contributions of African, Asian, Indian, Melanesian, Arabic and Persian populations have been suggested based on physical and cultural anthropology, oral tradition, linguistics and later also by archaeology. In the mid-20th century, increased knowledge of heredity rules and technical progress enabled the identification of African and Asian populations as main contributors. Recent access to the genomic landscape of Madagascar demonstrated pronounced regional variability in the relative contributions of these two ancestries, yet with significant presence of both African and Asian components throughout Madagascar. This article reviews the extent to which genetic results have settled historical questions concerning the origin of the Malagasy population. After an overview of the early literature, the genetic results of the 20th and 21th centuries are discussed and then complemented by the latest results in genome-wide analyses. While there is still much uncertainty regarding when, how and the circumstances under which the ancestors of the modern Malagasy population arrived on the island, we propose a scenario based on historical texts and genomic results.
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http://dx.doi.org/10.1093/hmg/ddab018DOI Listing
April 2021

New evidence of megafaunal bone damage indicates late colonization of Madagascar.

PLoS One 2018 10;13(10):e0204368. Epub 2018 Oct 10.

Ecology and Evolution Group, College of Science and Engineering, Flinders University, Adelaide SA, Australia.

The estimated period in which human colonization of Madagascar began has expanded recently to 5000-1000 y B.P., six times its range in 1990, prompting revised thinking about early migration sources, routes, maritime capability and environmental changes. Cited evidence of colonization age includes anthropogenic palaeoecological data 2500-2000 y B.P., megafaunal butchery marks 4200-1900 y B.P. and OSL dating to 4400 y B.P. of the Lakaton'i Anja occupation site. Using large samples of newly-excavated bone from sites in which megafaunal butchery was earlier dated >2000 y B.P. we find no butchery marks until ~1200 y B.P., with associated sedimentary and palynological data of initial human impact about the same time. Close analysis of the Lakaton'i Anja chronology suggests the site dates <1500 y B.P. Diverse evidence from bone damage, palaeoecology, genomic and linguistic history, archaeology, introduced biota and seafaring capability indicate initial human colonization of Madagascar 1350-1100 y B.P.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0204368PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6179221PMC
March 2019

Strong selection during the last millennium for African ancestry in the admixed population of Madagascar.

Nat Commun 2018 03 2;9(1):932. Epub 2018 Mar 2.

Laboratoire d'Anthropologie Moléculaire et Imagerie de Synthèse, UMR 5288 CNRS, Université de Toulouse, 31073, Toulouse, France.

While admixed populations offer a unique opportunity to detect selection, the admixture in most of the studied populations occurred too recently to produce conclusive signals. By contrast, Malagasy populations originate from admixture between Asian and African populations that occurred ~27 generations ago, providing power to detect selection. We analyze local ancestry across the genomes of 700 Malagasy and identify a strong signal of recent positive selection, with an estimated selection coefficient >0.2. The selection is for African ancestry and affects 25% of chromosome 1, including the Duffy blood group gene. The null allele at this gene provides resistance to Plasmodium vivax malaria, and previous studies have suggested positive selection for this allele in the Malagasy population. This selection event also influences numerous other genes implicated in immunity, cardiovascular diseases, and asthma and decreases the Asian ancestry genome-wide by 10%, illustrating the role played by selection in recent human history.
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http://dx.doi.org/10.1038/s41467-018-03342-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5834599PMC
March 2018

Reconstructing Asian faunal introductions to eastern Africa from multi-proxy biomolecular and archaeological datasets.

PLoS One 2017 17;12(8):e0182565. Epub 2017 Aug 17.

Max Planck Institute for the Science of Human History, Jena, Germany.

Human-mediated biological exchange has had global social and ecological impacts. In sub-Saharan Africa, several domestic and commensal animals were introduced from Asia in the pre-modern period; however, the timing and nature of these introductions remain contentious. One model supports introduction to the eastern African coast after the mid-first millennium CE, while another posits introduction dating back to 3000 BCE. These distinct scenarios have implications for understanding the emergence of long-distance maritime connectivity, and the ecological and economic impacts of introduced species. Resolution of this longstanding debate requires new efforts, given the lack of well-dated fauna from high-precision excavations, and ambiguous osteomorphological identifications. We analysed faunal remains from 22 eastern African sites spanning a wide geographic and chronological range, and applied biomolecular techniques to confirm identifications of two Asian taxa: domestic chicken (Gallus gallus) and black rat (Rattus rattus). Our approach included ancient DNA (aDNA) analysis aided by BLAST-based bioinformatics, Zooarchaeology by Mass Spectrometry (ZooMS) collagen fingerprinting, and direct AMS (accelerator mass spectrometry) radiocarbon dating. Our results support a late, mid-first millennium CE introduction of these species. We discuss the implications of our findings for models of biological exchange, and emphasize the applicability of our approach to tropical areas with poor bone preservation.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0182565PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5560628PMC
October 2017

Genomic landscape of human diversity across Madagascar.

Proc Natl Acad Sci U S A 2017 08 17;114(32):E6498-E6506. Epub 2017 Jul 17.

L'Institut des Mondes Africains (IMAF)-CNRS, 94200 Ivry-sur-Seine, France.

Although situated ∼400 km from the east coast of Africa, Madagascar exhibits cultural, linguistic, and genetic traits from both Southeast Asia and Eastern Africa. The settlement history remains contentious; we therefore used a grid-based approach to sample at high resolution the genomic diversity (including maternal lineages, paternal lineages, and genome-wide data) across 257 villages and 2,704 Malagasy individuals. We find a common Bantu and Austronesian descent for all Malagasy individuals with a limited paternal contribution from Europe and the Middle East. Admixture and demographic growth happened recently, suggesting a rapid settlement of Madagascar during the last millennium. However, the distribution of African and Asian ancestry across the island reveals that the admixture was sex biased and happened heterogeneously across Madagascar, suggesting independent colonization of Madagascar from Africa and Asia rather than settlement by an already admixed population. In addition, there are geographic influences on the present genomic diversity, independent of the admixture, showing that a few centuries is sufficient to produce detectable genetic structure in human populations.
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http://dx.doi.org/10.1073/pnas.1704906114DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5559028PMC
August 2017

Ancient crops provide first archaeological signature of the westward Austronesian expansion.

Proc Natl Acad Sci U S A 2016 06 31;113(24):6635-40. Epub 2016 May 31.

School of Archaeology, University of Oxford, Oxford OX1 2PG, United Kingdom; Department of Archaeology, Max Planck Institute for the Science of Human History, D-07743 Jena, Germany.

The Austronesian settlement of the remote island of Madagascar remains one of the great puzzles of Indo-Pacific prehistory. Although linguistic, ethnographic, and genetic evidence points clearly to a colonization of Madagascar by Austronesian language-speaking people from Island Southeast Asia, decades of archaeological research have failed to locate evidence for a Southeast Asian signature in the island's early material record. Here, we present new archaeobotanical data that show that Southeast Asian settlers brought Asian crops with them when they settled in Africa. These crops provide the first, to our knowledge, reliable archaeological window into the Southeast Asian colonization of Madagascar. They additionally suggest that initial Southeast Asian settlement in Africa was not limited to Madagascar, but also extended to the Comoros. Archaeobotanical data may support a model of indirect Austronesian colonization of Madagascar from the Comoros and/or elsewhere in eastern Africa.
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http://dx.doi.org/10.1073/pnas.1522714113DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4914162PMC
June 2016

Genetic Admixture and Flavor Preferences: Androstenone Sensitivity in Malagasy Populations.

Hum Biol 2015 Jan;87(1):59-70

1 Université de Toulouse, Centre National de la Recherche Scientifique, Laboratoire d'Anthropologie Moléculaire et Imagerie de Synthèse, Unité Mixte de Recherche 5288, 31073 Toulouse, France.

The genetic basis of androstenone anosmia has been well studied due to androstenone's putative role as a human sex pheromone and its presence in pork meat. Polymorphisms have been identified on the olfactory receptor gene OR7D4, which significantly affect perception of androstenone pleasantness and intensity in several Western populations. This study aims to investigate androstenone sensitivity and the influence of OR7D4 polymorphisms in non-Western populations. Androstenone perception was tested in 132 individuals from Madagascar using a double three-alternative choice test with two concentrations of androstenone (0.17 and 1.7 µg/ml). We found that Malagasy populations described this molecule in a similar way to European populations, and 21% of the sample was not able to smell androstenone. In contrast to previous studies, there was no significant evidence of the influence of rs61729907: C>T (R88W) and rs5020278: C>T polymorphisms (T133M) on androstenone sensitivity in Malagasy populations. We found, however, a significant effect of the polymorphism rs61732668 (P79L) and a significant difference in androstenone perception between populations in different locations across Madagascar. This study indicates the existence of population-specific factors in androstenone sensitivity, suggesting that population history has a role in shaping an individual's smell and flavor preferences and food preferences in general.
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http://dx.doi.org/10.13110/humanbiology.87.1.0059DOI Listing
January 2015

Genome-wide evidence of Austronesian-Bantu admixture and cultural reversion in a hunter-gatherer group of Madagascar.

Proc Natl Acad Sci U S A 2014 Jan 6;111(3):936-41. Epub 2014 Jan 6.

Laboratoire d'Anthropologie Moléculaire et Imagerie de Synthèse, Unité Mixte de Recherche 5288, Centre National de la Recherche Scientifique, Université de Toulouse, 31073 Toulouse, France.

Linguistic and cultural evidence suggest that Madagascar was the final point of two major dispersals of Austronesian- and Bantu-speaking populations. Today, the Mikea are described as the last-known Malagasy population reported to be still practicing a hunter-gatherer lifestyle. It is unclear, however, whether the Mikea descend from a remnant population that existed before the arrival of Austronesian and Bantu agriculturalists or whether it is only their lifestyle that separates them from the other contemporary populations of South Madagascar. To address these questions we have performed a genome-wide analysis of >700,000 SNP markers on 21 Mikea, 24 Vezo, and 24 Temoro individuals, together with 50 individuals from Bajo and Lebbo populations from Indonesia. Our analyses of these data in the context of data available from other Southeast Asian and African populations reveal that all three Malagasy populations are derived from the same admixture event involving Austronesian and Bantu sources. In contrast to the fact that most of the vocabulary of the Malagasy speakers is derived from the Barito group of the Austronesian language family, we observe that only one-third of their genetic ancestry is related to the populations of the Java-Kalimantan-Sulawesi area. Because no additional ancestry components distinctive for the Mikea were found, it is likely that they have adopted their hunter-gatherer way of life through cultural reversion, and selection signals suggest a genetic adaptation to their new lifestyle.
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http://dx.doi.org/10.1073/pnas.1321860111DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3903192PMC
January 2014

Stone tools and foraging in northern Madagascar challenge Holocene extinction models.

Proc Natl Acad Sci U S A 2013 Jul 15;110(31):12583-8. Epub 2013 Jul 15.

Department of Anthropology, Yale University, New Haven, CT 06520-8277, USA.

Past research on Madagascar indicates that village communities were established about AD 500 by people of both Indonesian and East African heritage. Evidence of earlier visits is scattered and contentious. Recent archaeological excavations in northern Madagascar provide evidence of occupational sites with microlithic stone technologies related to foraging for forest and coastal resources. A forager occupation of one site dates to earlier than 2000 B.C., doubling the length of Madagascar's known occupational history, and thus the time during which people exploited Madagascar's environments. We detail stratigraphy, chronology, and artifacts from two rock shelters. Ambohiposa near Iharana (Vohémar) on the northeast coast, yielded a stratified assemblage with small flakes, microblades, and retouched crescentic and trapezoidal tools, probably projectile elements, made on cherts and obsidian, some brought more that 200 km. (14)C dates are contemporary with the earliest villages. No food remains are preserved. Lakaton'i Anja near Antsiranana in the north yielded several stratified assemblages. The latest assemblage is well dated to A.D. 1050-1350, by (14)C and optically stimulated luminescence dating and pottery imported from the Near East and China. Below is a series of stratified assemblages similar to Ambohiposa. (14)C and optically stimulated luminescence dates indicate occupation from at least 2000 B.C. Faunal remains indicate a foraging pattern. Our evidence shows that foragers with a microlithic technology were active in Madagascar long before the arrival of farmers and herders and before many Late Holocene faunal extinctions. The differing effects of historically distinct economies must be identified and understood to reconstruct Holocene histories of human environmental impact.
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http://dx.doi.org/10.1073/pnas.1306100110DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3732966PMC
July 2013

Patterns of loss and regeneration of tropical dry forest in Madagascar: the social institutional context.

PLoS One 2007 May 2;2(5):e402. Epub 2007 May 2.

Department of Systems Ecology, Stockholm University, Stockholm, Sweden.

Loss of tropical forests and changes in land-use/land-cover are of growing concern worldwide. Although knowledge exists about the institutional context in which tropical forest loss is embedded, little is known about the role of social institutions in influencing regeneration of tropical forests. In the present study we used Landsat images from southern Madagascar from three different years (1984, 1993 and 2000) and covering 5500 km(2), and made a time-series analysis of three distinct large-scale patterns: 1) loss of forest cover, 2) increased forest cover, and 3) stable forest cover. Institutional characteristics underlying these three patterns were analyzed, testing the hypothesis that forest cover change is a function of strength and enforcement of local social institutions. The results showed a minor decrease of 7% total forest cover in the study area during the whole period 1984-2000, but an overall net increase of 4% during the period 1993-2000. The highest loss of forest cover occurred in a low human population density area with long distances to markets, while a stable forest cover occurred in the area with highest population density and good market access. Analyses of institutions revealed that loss of forest cover occurred mainly in areas characterized by insecure property rights, while areas with well-defined property rights showed either regenerating or stable forest cover. The results thus corroborate our hypothesis. The large-scale spontaneous regeneration dominated by native endemic species appears to be a result of a combination of changes in precipitation, migration and decreased human population and livestock grazing pressure, but under conditions of maintained and well-defined property rights. Our study emphasizes the large capacity of a semi-arid system to spontaneously regenerate, triggered by decreased pressures, but where existing social institutions mitigate other drivers of deforestation and alternative land-use.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0000402PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1853233PMC
May 2007
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