scholarly journals Mapping gene flow between ancient hominins through demography-aware inference of the ancestral recombination graph

2019 ◽  
Author(s):  
Melissa J. Hubisz ◽  
Amy L. Williams ◽  
Adam Siepel
Keyword(s):  
Gene Flow ◽  
Genetic Relationships ◽  
Convincing Evidence ◽  
Demographic Model ◽  
Modern Humans ◽  
Bayesian Algorithm ◽  
Branch Lengths ◽  
Mapping Gene ◽  
Ancestral Recombination Graphs ◽  
And Migration

AbstractThe sequencing of Neanderthal and Denisovan genomes has yielded many new insights about interbreeding events between extinct hominins and the ancestors of modern humans. While much attention has been paid to the relatively recent gene flow from Neanderthals and Denisovans into modern humans, other instances of introgression leave more subtle genomic evidence and have received less attention. Here, we present an extended version of the ARGweaver algorithm, ARGweaver-D, which can infer local genetic relationships under a user-defined demographic model that includes population splits and migration events. This Bayesian algorithm probabilistically samples ancestral recombination graphs (ARGs) that specify not only tree topology and branch lengths along the genome, but also indicate migrant lineages. The sampled ARGs can therefore be parsed to produce probabilities of introgression along the genome. We show that this method is well powered to detect the archaic migration into modern humans, even with only a few samples. We then show that the method can also detect introgressed regions stemming from older migration events, or from unsampled populations. We apply it to human, Neanderthal, and Denisovan genomes, looking for signatures of older proposed migration events, including ancient humans into Neanderthal, and unknown archaic hominins into Denisovans. We identify 3% of the Neanderthal genome that is putatively introgressed from ancient humans, and estimate that the gene flow occurred between 200-300kya. We find no convincing evidence that negative selection acted against these regions. We also identify 1% of the Denisovan genome which was likely introgressed from an unsequenced hominin ancestor, and note that 15% of these regions have been passed on to modern humans through subsequent gene flow.

scholarly journals DILS: Demographic Inferences with Linked Selection by using ABC

2020 ◽  
Author(s):  
Christelle Fraïsse ◽  
Iva Popovic ◽  
Clément Mazoyer ◽  
Bruno Spataro ◽  
Stéphane Delmotte ◽  
...  
Keyword(s):  
Gene Flow ◽  
Published Data ◽  
Demographic Model ◽  
Size Change ◽  
Genetic Patterns ◽  
And Migration ◽  
Approximate Bayesian ◽  
Genomic Regions ◽  
Analysis Platform ◽  
Linked Selection

ABSTRACTWe present DILS, a deployable statistical analysis platform for conducting demographic inferences with linked selection from population genomic data using an Approximate Bayesian Computation framework. DILS takes as input single-population or two-population datasets (multilocus fasta sequences) and performs three types of analyses in a hierarchical manner, identifying: 1) the best demographic model to study the importance of gene flow and population size change on the genetic patterns of polymorphism and divergence, 2) the best genomic model to determine whether the effective size Ne and migration rate N.m are heterogeneously distributed along the genome (implying linked selection) and 3) loci in genomic regions most associated with barriers to gene flow. Also available via a web interface, an objective of DILS is to facilitate collaborative research in speciation genomics. Here, we show the performance and limitations of DILS by using simulations, and finally apply the method to published data on a divergence continuum composed by 28 pairs of Mytilus mussel populations/species.

Habitat differentiation between estuarine and inland Hibiscus tiliaceus L. (Malvaceae) as revealed by retrotransposon-based SSAP marker

2011 ◽  
Vol 59 (6) ◽  
pp. 515 ◽  
Author(s):  
Tian Tang ◽  
Lian He ◽  
Feng Peng ◽  
Suhua Shi
Keyword(s):  
Genetic Variation ◽  
Gene Flow ◽  
Genetic Distance ◽  
Genetic Variance ◽  
Genetic Relationships ◽  
Principal Coordinate Analysis ◽  
Geographical Isolation ◽  
Tidal Zone ◽  
Ecological Scale ◽  
Habitat Differentiation

Hibiscus tiliaceus L. (Malvaceae) is a pantropical coastal tree that extends to the tidal zone. In this study, the retrotransposon sequence-specific amplified polymorphism (SSAP) technique was used in order to understand the genetic variation between four population pairs of H. tiliaceus from repeated estuarine and inland habitat contrasts in China. The estuarine populations were consistently more genetic variable compared with the inland ones, which may be attributed to extensive gene flow via water-drifted seeds and/or retrotransposon activation in stressful estuarine environments. An AMOVA revealed that 8.9% of the genetic variance could be explained by the habitat divergence within site, as compared with only 4.9% to geographical isolation between sites, which indicates significant habitat differentiation between the estuarine and inland populations. The estuarine populations were less differentiated (ΦST = 0.115) than the inland (ΦST = 0.152) implying frequent gene interchange in the former. Accordingly, the principal coordinate analysis of genetic distance between individuals revealed that genetic relationships are not fully consistent with the geographic association. These results suggest that despite substantial gene flow via sea-drifted seeds, habitat-related divergent selection could be one of the primary mechanisms that drive habitat differentiation in H. tiliaceus at a local ecological scale.

Gene Differentiation in Pacific Salmon (Oncorhynchus sp.): Facts and Models with Reference to Pink Salmon (O. gorbuscha)

1994 ◽  
Vol 51 (S1) ◽  
pp. 223-232 ◽  
Author(s):  
Lev A. Zhivotovsky ◽  
A. J. Gharrett ◽  
A. J. McGregor ◽  
M. K. Glubokovsky ◽  
Marcus W. Feldman
Keyword(s):  
Pacific Salmon ◽  
Gene Diversity ◽  
Genetic Relationships ◽  
Pink Salmon ◽  
Theoretical Models ◽  
Genetic Distances ◽  
Gene Drift ◽  
Gene Differentiation ◽  
Or Gene ◽  
And Migration

Analyzing population genetic data usually involves examining relationships among populations followed by analysis of the distribution of genetic variability. Genetic relationships are often depicted with multidimensional scaling or trees constructed from genetic distances; genetic variation within and among populations is partitioned using gene diversity measures such as FST or GST. Genetic distances or gene diversity are often used to estimate influences of gene drift, migration, and/or selection on observed gene differentiation. We used allozyme data for pink salmon populations to examine the theoretical models available for estimating magnitudes of these factors in Pacific salmon populations. The models included (1) mutation and gene drift; (2) mutation and migration; (3) migration and gene drift; and (4) gene drift, migration, and selection. These models suggest that gene drift and migration are probably important at the lowest levels of population hierarchy, but even very small forces such as weak heterogeneous selection and low migration levels may be important at higher levels. The accuracy of some estimates should be questioned because for many situations appropriate models are either not yet available or are not sufficiently refined. Also, the dynamic genetic structure of salmon populations makes it unlikely that the steady state assumed for many theoretical models has obtained.

scholarly journals Balancing selection and introgression of newt immune-response genes

2018 ◽  
Vol 285 (1884) ◽  
pp. 20180819 ◽  
Author(s):  
Anna Fijarczyk ◽  
Katarzyna Dudek ◽  
Marta Niedzicka ◽  
Wiesław Babik
Keyword(s):  
Gene Flow ◽  
Genetic Variants ◽  
Balancing Selection ◽  
Species Boundaries ◽  
Adaptive Introgression ◽  
Interspecific Introgression ◽  
Differential Gene ◽  
And Migration ◽  
Relevant Variation ◽  
Novel Allele

The importance of interspecific introgression as a source of adaptive variation is increasingly recognized. Theory predicts that beneficial genetic variants cross species boundaries easily even when interspecific hybridization is rare and gene flow is strongly constrained throughout the genome. However, it remains unclear whether certain classes of genes are particularly prone to adaptive introgression. Genes affected by balancing selection (BS) may constitute such a class, because forms of BS that favour novel, initially rare alleles, should facilitate introgression. We tested this hypothesis in hybridizing newts by comparing 13 genes with signatures of BS, in particular an excess of common non-synonymous polymorphisms, to the genomic background (154 genes). Parapatric hybridizing taxa were less differentiated in BS candidate genes than more closely related allopatric lineages, while the opposite was observed in the control genes. Coalescent and forward simulations that explored neutral and BS scenarios under isolation and migration showed that processes other than differential gene flow are unlikely to account for this pattern. We conclude that BS, probably involving a form of novel allele advantage, promotes introgression. This mechanism may be a source of adaptively relevant variation in hybridizing species over prolonged periods.

Genetic variation of microsatellite and mitochondrial DNA markers in broad whitefish (Coregonus nasus) in the Colville and Sagavanirktok rivers in northern Alaska

1997 ◽  
Vol 54 (7) ◽  
pp. 1548-1556 ◽  
Author(s):  
J C Patton ◽  
B J Gallaway ◽  
R G Fechhelm ◽  
M A Cronin
Keyword(s):  
Mitochondrial Dna ◽  
Genetic Variation ◽  
Gene Flow ◽  
Microsatellite Loci ◽  
Genetic Relationships ◽  
Nuclear Genome ◽  
Pcr Amplification ◽  
Colville River ◽  
Limited Gene Flow ◽  
Northern Alaska

There has been concern that a causeway leading to oil production facilities in the Alaskan Beaufort Sea could affect the extent of emigration from, and immigration into, a population of broad whitefish (Coregonus nasus) in the Sagavanirktok River. To assess this, we analyzed the genetic relationships of the broad whitefish populations in the Sagavanirktok River, and the nearest adjacent population, in the Colville River. Three microsatellite loci from the nuclear genome, and the NADH-1 gene of mitochondrial DNA (mtDNA), were analyzed. Diploid genotypes were determined with PCR amplification of the microsatellite loci, and mtDNA genotypes were identified with PCR amplification followed by sequencing of 798 nucleotides. Several alleles were identified at each locus and both populations had high levels of genetic variation. There is significant differentiation of the Sagavanirktok River and Colville River broad whitefish stocks for the three microsatellite loci (FST = 0.031) but not mtDNA (FST < 0.001). Possible explanations for the lower level of differentiation of mtDNA than microsatellites include female-mediated gene flow between populations, skewed sex ratios, natural selection, or mutation. The results indicate that there is limited gene flow between the Colville and Sagavanirktok rivers, which represent semi-isolated spawning populations.

scholarly journals Indirect measures of gene flow and migration: FST≠1/(4Nm+1)

Heredity ◽  
1999 ◽  
Vol 82 (2) ◽  
pp. 117-125 ◽  
Author(s):  
Michael C Whitlock ◽  
David E McCauley
Keyword(s):  
Gene Flow ◽  
Indirect Measures ◽  
And Migration

scholarly journals Model-based detection and analysis of introgressed Neanderthal ancestry in modern humans

2017 ◽  
Author(s):  
Matthias Steinrücken ◽  
Jeffrey P. Spence ◽  
John A. Kamm ◽  
Emilia Wieczorek ◽  
Yun S. Song
Keyword(s):  
Genetic Material ◽  
Genetic Load ◽  
Modern Human ◽  
Human Populations ◽  
Effective Population ◽  
Weak Selection ◽  
Modern Humans ◽  
High Coverage ◽  
Model Based ◽  
And Migration

AbstractGenetic evidence has revealed that the ancestors of modern human populations outside of Africa and their hominin sister groups, notably the Neanderthals, exchanged genetic material in the past. The distribution of these introgressed sequence-tracts along modern-day human genomes provides insight into the ancient structure and migration patterns of these archaic populations. Furthermore, it facilitates studying the selective processes that lead to the accumulation or depletion of introgressed genetic variation. Recent studies have developed methods to localize these introgressed regions, reporting long regions that are depleted of Neanderthal introgression and enriched in genes, suggesting negative selection against the Neanderthal variants. On the other hand, enriched Neanderthal ancestry in hair- and skin-related genes suggests that some introgressed variants facilitated adaptation to new environments. Here, we present a model-based method called diCal-admix and apply it to detect tracts of Neanderthal introgression in modern humans. We demonstrate its efficiency and accuracy through extensive simulations. We use our method to detect introgressed regions in modern human individuals from the 1000 Genomes Project, using a high coverage genome from a Neanderthal individual from the Altai mountains as reference. Our introgression detection results and findings concerning their functional implications are largely concordant with previous studies, and are consistent with weak selection against Neanderthal ancestry. We find some evidence that selection against Neanderthal ancestry was due to higher genetic load in Neanderthals, resulting from small effective population size, rather than Dobzhansky-Müller incompatibilities. Finally, we investigate the role of the X-chromosome in the divergence between Neanderthals and modern humans.

scholarly journals Cosi2 : An efficient simulator of exact and approximate coalescent with selection

2014 ◽  
Author(s):  
Ilya Shlyakhter ◽  
Pardis C. Sabeti ◽  
Stephen F. Schaffner
Keyword(s):  
Gene Conversion ◽  
Genetic Material ◽  
Small Subset ◽  
Demographic Model ◽  
Coalescent Simulation ◽  
Recombination Rates ◽  
Wide Range ◽  
Selection Gene ◽  
And Migration ◽  
Recombination Hot Spots

Motivation: Efficient simulation of population genetic samples under a given demographic model is a prerequisite for many analyses. Coalescent theory provides an efficient framework for such simulations, but simulating longer regions and higher recombination rates remains challenging. Simulators based on a Markovian approximation to the coalescent scale well, but do not support simulation of selection. Gene conversion is not supported by any published coalescent simulators that support selection. Results: We describe cosi2 , an efficient simulator that supports both exact and approximate coalescent simulation with positive selection. cosi2 improves on the speed of existing exact simulators, and permits further speedup in approximate mode while retaining support for selection. cosi2 supports a wide range of demographic scenarios including recombination hot spots, gene conversion, population size changes, population structure and migration. cosi2 implements coalescent machinery efficiently by tracking only a small subset of the Ancestral Recombination Graph, sampling only relevant recombination events, and using augmented skip lists to represent tracked genetic segments. To preserve support for selection in approximate mode, the Markov approximation is implemented not by moving along the chromosome but by performing a standard backwards-in-time coalescent simulation while restricting coalescence to node pairs with overlapping or near-overlapping genetic material. We describe the algorithms used by cosi2 and present comparisons with existing selection simulators.

scholarly journals The evolutionary history of human spindle genes includes back-and-forth gene flow with Neandertals

2021 ◽  
Author(s):  
Stéphane Peyrégne ◽  
Janet Kelso ◽  
Benjamin Marco Peter ◽  
Svante Pääbo
Keyword(s):  
Gene Flow ◽  
Evolutionary History ◽  
Common Ancestor ◽  
Modern Human ◽  
Modern Humans ◽  
Ancestral Gene ◽  
Cytoskeletal Structure ◽  
Spindle Apparatus ◽  
History Of ◽  
Segregation Of Chromosomes

Proteins associated with the spindle apparatus, a cytoskeletal structure that ensures the proper segregation of chromosomes during cell division, experienced an unusual number of amino acid substitutions in modern humans after the split from the ancestors of Neandertals and Denisovans. Here, we analyze the history of these substitutions and show that some of the genes in which they occur may have been targets of positive selection. We also find that the two changes in the kinetochore scaffold 1 (KNL1) protein, previously believed to be specific to modern humans, were present in some Neandertals. We show that the KNL1 gene of these Neandertals shared a common ancestor with present-day Africans about 200,000 years ago due to gene flow from the ancestors (or relatives) of modern humans into Neandertals. Subsequently, some non-Africans inherited this modern human-like gene variant from Neandertals, but none inherited the ancestral gene variants. These results add to the growing evidence of early contacts between modern humans and archaic groups in Eurasia and illustrate the intricate relationships among these groups.

scholarly journals Development of an agent-based demographic model of Russia and its supercomputer implementation

2018 ◽  
pp. 368-378
Author(s):  
В.Л. Макаров ◽  
А.Р. Бахтизин ◽  
Е.Д. Сушко ◽  
Г.Б. Сушко
Keyword(s):  
Numerical Experiments ◽  
Agent Based Modeling ◽  
Human Migration ◽  
Demographic Model ◽  
Model Decomposition ◽  
Agent Based ◽  
Agent Model ◽  
Artificial Society ◽  
Administrative Division ◽  
And Migration

Рассмотрено применение агент-ориентированного подхода при моделировании естественного движения населения. Представлена демографическая модель России с учетом ее административного деления, в которой на основе моделирования поведения отдельных членов искусственного общества имитируются процессы смертности, рождаемости и миграции. Для моделирования поведения искусственного общества в целом требуется проведение модельных расчетов с числом агентов до $10^9$ и использование суперкомпьютерных технологий. Важной задачей в таких расчетах становится оптимальное распределение агентов по процессорам кластера. Показано применение декомпозиции модели с использованием алгоритма METIS с учетом основных особенностей агентной модели. Обсуждаются результаты апробации модели. The application of the agent-based modeling approach to the problem of natural human migration is considered. A demographic model of Russia is presented. This model takes into account the administrative division of Russia and simulates the processes of fertility, mortality and migration on the basis of modeling the behavior of individual members of the artificial society. In order to simulate the behavior of the artificial society as a whole, it is necessary to perform numerical experiments with the number of agents up to $10^9$ and to use supercomputer technologies. In such experiments, an important problem is the implementation of an optimal automatic distribution of agents across the cluster processors. The application of model decomposition using the METIS algorithm with consideration of the main features of the agent model is shown. The obtained numerical results are discussed.

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