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Estavoyer M, François O. Theoretical analysis of principal components in an umbrella model of intraspecific evolution. Theor Popul Biol 2022; 148:11-21. [PMID: 36122755 DOI: 10.1016/j.tpb.2022.08.002] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 08/23/2022] [Accepted: 08/23/2022] [Indexed: 10/14/2022]
Abstract
Principal component analysis (PCA) is one of the most frequently-used approach to describe population structure from multilocus genotype data. Regarding geographic range expansions of modern humans, interpretations of PCA have, however, been questioned, as there is uncertainty about the wave-like patterns that have been observed in principal components. It has indeed been argued that wave-like patterns are mathematical artifacts that arise generally when PCA is applied to data in which genetic differentiation increases with geographic distance. Here, we present an alternative theory for the observation of wave-like patterns in PCA. We study a coalescent model - the umbrella model - for the diffusion of genetic variants. The model is based on genetic drift without any particular geographical structure. In the umbrella model, splits from an ancestral population occur almost continuously in time, giving birth to small daughter populations at a regular pace. Our results provide detailed mathematical descriptions of eigenvalues and eigenvectors for the PCA of sampled genomic sequences under the model. When variants uniquely represented in the sample are removed, the PCA eigenvectors are defined as cosine functions of increasing periodicity, reproducing wave-like patterns observed in equilibrium isolation-by-distance models. Including singleton variants in the analysis, the eigenvectors corresponding to the largest eigenvalues exhibit complex wave shapes. The accuracy of our predictions is further investigated with coalescent simulations. Our analysis supports the hypothesis that highly structured wave-like patterns could arise from genetic drift only, and may not always be artificial outcomes of spatially structured data. Genomic data related to the peopling of the Americas are reanalyzed in the light of our new theory.
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Affiliation(s)
- Maxime Estavoyer
- Université Grenoble-Alpes, Centre National de la Recherche Scientifique, Grenoble INP, TIMC UMR 5525, 38000 Grenoble, France
| | - Olivier François
- Université Grenoble-Alpes, Centre National de la Recherche Scientifique, Grenoble INP, TIMC UMR 5525, 38000 Grenoble, France; Inria Grenoble - Rhône-Alpes Inovallée, 655 Avenue de l'Europe - CS 90051 38334 Montbonnot, France.
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2
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Ferreiro D, Núñez-Estévez B, Canedo M, Branco C, Arenas M. Evaluating Causes of Current Genetic Gradients of Modern Humans of the Iberian Peninsula. Genome Biol Evol 2021; 13:6219947. [PMID: 33837782 PMCID: PMC8086631 DOI: 10.1093/gbe/evab071] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/06/2021] [Indexed: 12/18/2022] Open
Abstract
The history of modern humans in the Iberian Peninsula includes a variety of population arrivals sometimes presenting admixture with resident populations. Genetic data from current Iberian populations revealed an overall east–west genetic gradient that some authors interpreted as a direct consequence of the Reconquista, where Catholic Kingdoms expanded their territories toward the south while displacing Muslims. However, this interpretation has not been formally evaluated. Here, we present a qualitative analysis of the causes of the current genetic gradient observed in the Iberian Peninsula using extensive spatially explicit computer simulations based on a variety of evolutionary scenarios. Our results indicate that the Neolithic range expansion clearly produces the orientation of the observed genetic gradient. Concerning the Reconquista (including political borders among Catholic Kingdoms and regions with different languages), if modeled upon a previous Neolithic expansion, it effectively favored the orientation of the observed genetic gradient and shows local isolation of certain regions (i.e., Basques and Galicia). Despite additional evolutionary scenarios could be evaluated to more accurately decipher the causes of the Iberian genetic gradient, here we show that this gradient has a more complex explanation than that previously hypothesized.
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Affiliation(s)
- David Ferreiro
- CINBIO, Universidade de Vigo, Spain.,Universidade de Vigo, Departamento de Bioquímica, Xenética e Immunoloxía, Spain
| | - Bernabé Núñez-Estévez
- CINBIO, Universidade de Vigo, Spain.,Universidade de Vigo, Departamento de Bioquímica, Xenética e Immunoloxía, Spain
| | - Mateo Canedo
- CINBIO, Universidade de Vigo, Spain.,Universidade de Vigo, Departamento de Bioquímica, Xenética e Immunoloxía, Spain
| | - Catarina Branco
- CINBIO, Universidade de Vigo, Spain.,Universidade de Vigo, Departamento de Bioquímica, Xenética e Immunoloxía, Spain
| | - Miguel Arenas
- CINBIO, Universidade de Vigo, Spain.,Universidade de Vigo, Departamento de Bioquímica, Xenética e Immunoloxía, Spain
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3
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Currat M, Arenas M, Quilodràn CS, Excoffier L, Ray N. SPLATCHE3: simulation of serial genetic data under spatially explicit evolutionary scenarios including long-distance dispersal. Bioinformatics 2020; 35:4480-4483. [PMID: 31077292 PMCID: PMC6821363 DOI: 10.1093/bioinformatics/btz311] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2019] [Revised: 04/18/2019] [Accepted: 04/29/2019] [Indexed: 01/25/2023] Open
Abstract
SUMMARY SPLATCHE3 simulates genetic data under a variety of spatially explicit evolutionary scenarios, extending previous versions of the framework. The new capabilities include long-distance migration, spatially and temporally heterogeneous short-scale migrations, alternative hybridization models, simulation of serial samples of genetic data and a large variety of DNA mutation models. These implementations have been applied independently to various studies, but grouped together in the current version. AVAILABILITY AND IMPLEMENTATION SPLATCHE3 is written in C++ and is freely available for non-commercial use from the website http://www.splatche.com/splatche3. It includes console versions for Linux, MacOs and Windows and a user-friendly GUI for Windows, as well as detailed documentation and ready-to-use examples.
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Affiliation(s)
- Mathias Currat
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva 1205, Switzerland.,Institute of Genetics and Genomics in Geneva (IGE3), University of Geneva, Geneva 1211, Switzerland
| | - Miguel Arenas
- Department of Biochemistry, Genetics and Immunology, Vigo 36310, Spain.,Biomedical Research Center (CINBIO), University of Vigo, Vigo 36310, Spain
| | - Claudio S Quilodràn
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva 1205, Switzerland
| | - Laurent Excoffier
- Computational and Molecular Population Genetics Laboratory, Institute of Ecology and Evolution, University of Bern, Bern 3012, Switzerland.,Swiss Institute of Bioinformatics, Lausanne 1015, Switzerland
| | - Nicolas Ray
- Institute of Global Health, GeoHealth Group, University of Geneva, Geneva 1205, Switzerland.,Institute for Environmental Sciences, University of Geneva, Geneva 1205, Switzerland
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4
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Branco C, Ray N, Currat M, Arenas M. Influence of Paleolithic range contraction, admixture and long-distance dispersal on genetic gradients of modern humans in Asia. Mol Ecol 2020; 29:2150-2159. [PMID: 32436243 DOI: 10.1111/mec.15479] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 05/08/2020] [Accepted: 05/11/2020] [Indexed: 12/29/2022]
Abstract
Cavalli-Sforza and coauthors originally explored the genetic variation of modern humans throughout the world and observed an overall east-west genetic gradient in Asia. However, the specific environmental and population genetics processes causing this gradient were not formally investigated and promoted discussion in recent studies. Here we studied the influence of diverse environmental and population genetics processes on Asian genetic gradients and identified which could have produced the observed gradient. To do so, we performed extensive spatially-explicit computer simulations of genetic data under the following scenarios: (a) variable levels of admixture between Paleolithic and Neolithic populations, (b) migration through long-distance dispersal (LDD), (c) Paleolithic range contraction induced by the last glacial maximum (LGM), and (d) Neolithic range expansions from one or two geographic origins (the Fertile Crescent and the Yangzi and Yellow River Basins). Next, we estimated genetic gradients from the simulated data and we found that they were sensible to the analysed processes, especially to the range contraction induced by LGM and to the number of Neolithic expansions. Some scenarios were compatible with the observed east-west genetic gradient, such as the Paleolithic expansion with a range contraction induced by the LGM or two Neolithic range expansions from both the east and the west. In general, LDD increased the variance of genetic gradients among simulations. We interpreted the obtained gradients as a consequence of both allele surfing caused by range expansions and isolation by distance along the vast east-west geographic axis of this continent.
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Affiliation(s)
- Catarina Branco
- Department of Biochemistry, Genetics and Immunology, University of Vigo, Vigo, Spain.,Biomedical Research Center (CINBIO), University of Vigo, Vigo, Spain
| | - Nicolas Ray
- GeoHealth Group, Institute of Global Health, University of Geneva, Geneva, Switzerland.,Institute for Environmental Sciences, University of Geneva, Geneva, Switzerland
| | - Mathias Currat
- Laboratory of Anthropology, Genetics and Peopling History, Department of Genetics and Evolution - Anthropology Unit, University of Geneva, Geneva, Switzerland.,Institute of Genetics and Genomics in Geneva (IGE3), University of Geneva, Geneva, Switzerland
| | - Miguel Arenas
- Department of Biochemistry, Genetics and Immunology, University of Vigo, Vigo, Spain.,Biomedical Research Center (CINBIO), University of Vigo, Vigo, Spain
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Quilodrán CS, Ruegg K, Sendell‐Price AT, Anderson EC, Coulson T, Clegg SM. The multiple population genetic and demographic routes to islands of genomic divergence. Methods Ecol Evol 2019. [DOI: 10.1111/2041-210x.13324] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
| | - Kristen Ruegg
- Department of Zoology University of Oxford Oxford UK
- Center for Tropical Research Institute of the Environment and Sustainability University of California, Los Angeles Los Angeles CA USA
- Department of Biology Colorado State University Fort Collins CO USA
| | | | - Eric C. Anderson
- Fisheries Ecology Division Southwest Fisheries Science Center National Marine Fisheries ServiceNOAA Santa Cruz CA USA
| | - Tim Coulson
- Department of Zoology University of Oxford Oxford UK
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Illera JC, Arenas M, López-Sánchez CA, Obeso JR, Laiolo P. Gradual Distance Dispersal Shapes the Genetic Structure in an Alpine Grasshopper. Genes (Basel) 2019; 10:E590. [PMID: 31387238 PMCID: PMC6724060 DOI: 10.3390/genes10080590] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2019] [Revised: 08/01/2019] [Accepted: 08/02/2019] [Indexed: 11/16/2022] Open
Abstract
The location of the high mountains of southern Europe has been crucial in the phylogeography of most European species, but how extrinsic (topography of sky islands) and intrinsic features (dispersal dynamics) have interacted to shape the genetic structure in alpine restricted species is still poorly known. Here we investigated the mechanisms explaining the colonisation of Cantabrian sky islands in an endemic flightless grasshopper. We scrutinised the maternal genetic variability and haplotype structure, and we evaluated the fitting of two migration models to understand the extant genetic structure in these populations: Long-distance dispersal (LDD) and gradual distance dispersal (GDD). We found that GDD fits the real data better than the LDD model, with an onset of the expansion matching postglacial expansions after the retreat of the ice sheets. Our findings suggest a scenario with small carrying capacity, migration rates, and population growth rates, being compatible with a slow dispersal process. The gradual expansion process along the Cantabrian sky islands found here seems to be conditioned by the suitability of habitats and the presence of alpine corridors. Our findings shed light on our understanding about how organisms which have adapted to live in alpine habitats with limited dispersal abilities have faced new and suitable environmental conditions.
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Affiliation(s)
- Juan Carlos Illera
- Research Unit of Biodiversity (UMIB, UO-CSIC-PA), Oviedo University, 33600 Mieres, Spain.
| | - Miguel Arenas
- Department of Biochemistry, Genetics and Immunology, University of Vigo, 36310 Vigo, Spain
- Biomedical Research Center (CINBIO), University of Vigo, 36310 Vigo, Spain
| | - Carlos A López-Sánchez
- Department of Biology, Organisms and Systems, GIS-Forest Group, Oviedo University, 33600 Mieres, Spain
| | - José Ramón Obeso
- Research Unit of Biodiversity (UMIB, UO-CSIC-PA), Oviedo University, 33600 Mieres, Spain
| | - Paola Laiolo
- Research Unit of Biodiversity (UMIB, UO-CSIC-PA), Oviedo University, 33600 Mieres, Spain
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Selecting among Alternative Scenarios of Human Evolution by Simulated Genetic Gradients. Genes (Basel) 2018; 9:genes9100506. [PMID: 30340387 PMCID: PMC6210830 DOI: 10.3390/genes9100506] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Revised: 10/11/2018] [Accepted: 10/16/2018] [Indexed: 11/16/2022] Open
Abstract
Selecting among alternative scenarios of human evolution is nowadays a common methodology to investigate the history of our species. This strategy is usually based on computer simulations of genetic data under different evolutionary scenarios, followed by a fitting of the simulated data with the real data. A recent trend in the investigation of ancestral evolutionary processes of modern humans is the application of genetic gradients as a measure of fitting, since evolutionary processes such as range expansions, range contractions, and population admixture (among others) can lead to different genetic gradients. In addition, this strategy allows the analysis of the genetic causes of the observed genetic gradients. Here, we review recent findings on the selection among alternative scenarios of human evolution based on simulated genetic gradients, including pros and cons. First, we describe common methodologies to simulate genetic gradients and apply them to select among alternative scenarios of human evolution. Next, we review previous studies on the influence of range expansions, population admixture, last glacial period, and migration with long-distance dispersal on genetic gradients for some regions of the world. Finally, we discuss this analytical approach, including technical limitations, required improvements, and advice. Although here we focus on human evolution, this approach could be extended to study other species.
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