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López S, van Dorp L, Hellenthal G. Human Dispersal Out of Africa: A Lasting Debate. Evol Bioinform Online 2016; 11:57-68. [PMID: 27127403 PMCID: PMC4844272 DOI: 10.4137/ebo.s33489] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 02/21/2016] [Accepted: 02/21/2016] [Indexed: 01/01/2023] Open
Abstract
Unraveling the first migrations of anatomically modern humans out of Africa has invoked great interest among researchers from a wide range of disciplines. Available fossil, archeological, and climatic data offer many hypotheses, and as such genetics, with the advent of genome-wide genotyping and sequencing techniques and an increase in the availability of ancient samples, offers another important tool for testing theories relating to our own history. In this review, we report the ongoing debates regarding how and when our ancestors left Africa, how many waves of dispersal there were and what geographical routes were taken. We explore the validity of each, using current genetic literature coupled with some of the key archeological findings.
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Affiliation(s)
- Saioa López
- Department of Genetics, Evolution and Environment, University College London, London, UK
| | - Lucy van Dorp
- Department of Genetics, Evolution and Environment, University College London, London, UK
- Centre for Mathematics and Physics in the Life Sciences and Experimental Biology (CoMPLEX), University College London, London, UK
| | - Garrett Hellenthal
- Department of Genetics, Evolution and Environment, University College London, London, UK
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Paixão-Côrtes VR, Meyer D, Pereira TV, Mazières S, Elion J, Krishnamoorthy R, Zago MA, Silva WA, Salzano FM, Bortolini MC. Genetic variation among major human geographic groups supports a peculiar evolutionary trend in PAX9. PLoS One 2011; 6:e15656. [PMID: 21298044 PMCID: PMC3029280 DOI: 10.1371/journal.pone.0015656] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2010] [Accepted: 11/19/2010] [Indexed: 11/18/2022] Open
Abstract
A total of 172 persons from nine South Amerindian, three African and one Eskimo populations were studied in relation to the Paired box gene 9 (PAX9) exon 3 (138 base pairs) as well as its 5'and 3'flanking intronic segments (232 bp and 220 bp, respectively) and integrated with the information available for the same genetic region from individuals of different geographical origins. Nine mutations were scored in exon 3 and six in its flanking regions; four of them are new South American tribe-specific singletons. Exon3 nucleotide diversity is several orders of magnitude higher than its intronic regions. Additionally, a set of variants in the PAX9 and 101 other genes related with dentition can define at least some dental morphological differences between Sub-Saharan Africans and non-Africans, probably associated with adaptations after the modern human exodus from Africa. Exon 3 of PAX9 could be a good molecular example of how evolvability works.
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Affiliation(s)
- Vanessa R. Paixão-Côrtes
- Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Diogo Meyer
- Departamento de Genética e Biologia Evolutiva, Instituto de Biociências, Universidade de São Paulo, São Paulo, São Paulo, Brazil
| | - Tiago V. Pereira
- Departamento de Bioquímica, Universidade Federal de São Paulo, São Paulo, São Paulo, Brazil
| | - Stéphane Mazières
- Laboratoire d'Anthropobiologie, FRE2960, CNRS, Toulouse, France
- Anthropologie Bioculturelle, Faculté de Médecine, CS80011, Marseille, France
| | - Jacques Elion
- Insern, UMR 763, Université Paris Diderot, Hôpital Robert Debré, Paris, France
| | | | - Marco A. Zago
- Departamento de Clínica Médica, Faculdade de Medicina, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Wilson A. Silva
- Departamento de Genética, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
| | - Francisco M. Salzano
- Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
| | - Maria Cátira Bortolini
- Departamento de Genética, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
- * E-mail:
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Hamilton MJ, Burger O, DeLong JP, Walker RS, Moses ME, Brown JH. Population stability, cooperation, and the invasibility of the human species. Proc Natl Acad Sci U S A 2009; 106:12255-60. [PMID: 19592508 PMCID: PMC2718330 DOI: 10.1073/pnas.0905708106] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2009] [Indexed: 11/18/2022] Open
Abstract
The biogeographic expansion of modern humans out of Africa began approximately 50,000 years ago. This expansion resulted in the colonization of most of the land area and habitats throughout the globe and in the replacement of preexisting hominid species. However, such rapid population growth and geographic spread is somewhat unexpected for a large primate with a slow, density-dependent life history. Here, we suggest a mechanism for these outcomes by modifying a simple density-dependent population model to allow varying levels of intraspecific competition for finite resources. Reducing intraspecific competition increases carrying capacities, growth rates, and stability, including persistence times and speed of recovery from perturbations. Our model suggests that the energetic benefits of cooperation in modern humans may have outweighed the slow rate of human population growth, effectively ensuring that once modern humans colonized a region long-term population persistence was near inevitable. Our model also provides insight into the interplay of structural complexity and stability in social species.
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Affiliation(s)
| | - Oskar Burger
- Departments of Anthropology
- SWCA Environmental Consultants, 295 Interlocken Boulevard, Suite 300, Bloomfield, CO 80021
| | | | - Robert S. Walker
- Department of Anthropology, University of Missouri, Columbia, MO 65211; and
| | - Melanie E. Moses
- Computer Science University of New Mexico, Albuquerque, NM 87131
| | - James H. Brown
- Biology, and
- Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501
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Städler T, Haubold B, Merino C, Stephan W, Pfaffelhuber P. The impact of sampling schemes on the site frequency spectrum in nonequilibrium subdivided populations. Genetics 2009; 182:205-16. [PMID: 19237689 PMCID: PMC2674817 DOI: 10.1534/genetics.108.094904] [Citation(s) in RCA: 158] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2008] [Accepted: 02/17/2009] [Indexed: 11/18/2022] Open
Abstract
Using coalescent simulations, we study the impact of three different sampling schemes on patterns of neutral diversity in structured populations. Specifically, we are interested in two summary statistics based on the site frequency spectrum as a function of migration rate, demographic history of the entire substructured population (including timing and magnitude of specieswide expansions), and the sampling scheme. Using simulations implementing both finite-island and two-dimensional stepping-stone spatial structure, we demonstrate strong effects of the sampling scheme on Tajima's D (D(T)) and Fu and Li's D (D(FL)) statistics, particularly under specieswide (range) expansions. Pooled samples yield average D(T) and D(FL) values that are generally intermediate between those of local and scattered samples. Local samples (and to a lesser extent, pooled samples) are influenced by local, rapid coalescence events in the underlying coalescent process. These processes result in lower proportions of external branch lengths and hence lower proportions of singletons, explaining our finding that the sampling scheme affects D(FL) more than it does D(T). Under specieswide expansion scenarios, these effects of spatial sampling may persist up to very high levels of gene flow (Nm > 25), implying that local samples cannot be regarded as being drawn from a panmictic population. Importantly, many data sets on humans, Drosophila, and plants contain signatures of specieswide expansions and effects of sampling scheme that are predicted by our simulation results. This suggests that validating the assumption of panmixia is crucial if robust demographic inferences are to be made from local or pooled samples. However, future studies should consider adopting a framework that explicitly accounts for the genealogical effects of population subdivision and empirical sampling schemes.
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Affiliation(s)
- Thomas Städler
- Faculty of Mathematics and Physics, University of Freiburg, D-79104 Freiburg, Germany.
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Atkinson QD, Gray RD, Drummond AJ. Bayesian coalescent inference of major human mitochondrial DNA haplogroup expansions in Africa. Proc Biol Sci 2009; 276:367-73. [PMID: 18826938 DOI: 10.1098/rspb.2008.0785] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Past population size can be estimated from modern genetic diversity using coalescent theory. Estimates of ancestral human population dynamics in sub-Saharan Africa can tell us about the timing and nature of our first steps towards colonizing the globe. Here, we combine Bayesian coalescent inference with a dataset of 224 complete human mitochondrial DNA (mtDNA) sequences to estimate effective population size through time for each of the four major African mtDNA haplogroups (L0-L3). We find evidence of three distinct demographic histories underlying the four haplogroups. Haplogroups L0 and L1 both show slow, steady exponential growth from 156 to 213kyr ago. By contrast, haplogroups L2 and L3 show evidence of substantial growth beginning 12-20 and 61-86kyr ago, respectively. These later expansions may be associated with contemporaneous environmental and/or cultural changes. The timing of the L3 expansion--8-12kyr prior to the emergence of the first non-African mtDNA lineages--together with high L3 diversity in eastern Africa, strongly supports the proposal that the human exodus from Africa and subsequent colonization of the globe was prefaced by a major expansion within Africa, perhaps driven by some form of cultural innovation.
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Affiliation(s)
- Quentin D Atkinson
- Institute of Cognitive and Evolutionary Anthropology, University of Oxford, 64 Banbury Road, Oxford OX2 6PN, UK.
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High levels of genetic differentiation between Ugandan Glossina fuscipes fuscipes populations separated by Lake Kyoga. PLoS Negl Trop Dis 2008; 2:e242. [PMID: 18509474 PMCID: PMC2386243 DOI: 10.1371/journal.pntd.0000242] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2008] [Accepted: 04/24/2008] [Indexed: 12/03/2022] Open
Abstract
Background Glossina fuscipes fuscipes is the major vector of human African trypanosomiasis, commonly referred to as sleeping sickness, in Uganda. In western and eastern Africa, the disease has distinct clinical manifestations and is caused by two different parasites: Trypanosoma brucei rhodesiense and T. b. gambiense. Uganda is exceptional in that it harbors both parasites, which are separated by a narrow 160-km belt. This separation is puzzling considering there are no restrictions on the movement of people and animals across this region. Methodology and Results We investigated whether genetic heterogeneity of G. f. fuscipes vector populations can provide an explanation for this disjunct distribution of the Trypanosoma parasites. Therefore, we examined genetic structuring of G. f. fuscipes populations across Uganda using newly developed microsatellite markers, as well as mtDNA. Our data show that G. f. fuscipes populations are highly structured, with two clearly defined clusters that are separated by Lake Kyoga, located in central Uganda. Interestingly, we did not find a correlation between genetic heterogeneity and the type of Trypanosoma parasite transmitted. Conclusions The lack of a correlation between genetic structuring of G. f. fuscipes populations and the distribution of T. b. gambiense and T. b. rhodesiense indicates that it is unlikely that genetic heterogeneity of G. f. fuscipes populations explains the disjunct distribution of the parasites. These results have important epidemiological implications, suggesting that a fusion of the two disease distributions is unlikely to be prevented by an incompatibility between vector populations and parasite. The two types of sleeping sickness in West and East Africa are markedly distinct, require different treatments, and are caused by different parasites. The only country where both parasites are present is Uganda, where they are separated by a narrow 160 km disease-free belt. Because there is no restriction on the movement of humans and animals between the two disease zones, this separation is puzzling. We asked whether this disjunct distribution can be explained by variation within the tsetse fly that is largely responsible for transmitting both diseases in Uganda, Glossina fuscipes fuscipes. We therefore examined whether this tsetse subspecies is genetically uniform across Uganda. Our results indicate that G. f. fusicipes is not genetically different between the two disease zones, but there are clear genetic differences between northern and southern populations, which are separated by Lake Kyoga. Therefore, it is unlikely that variation in the tsetse fly determines the distribution of the two parasites. This implies that the two diseases may fuse in the near future, which would greatly complicate diagnosis and treatment of sleeping sickness in any potential area of overlap.
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Garrigan D, Mobasher Z, Kingan SB, Wilder JA, Hammer MF. Deep haplotype divergence and long-range linkage disequilibrium at xp21.1 provide evidence that humans descend from a structured ancestral population. Genetics 2005; 170:1849-56. [PMID: 15937130 PMCID: PMC1449746 DOI: 10.1534/genetics.105.041095] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fossil evidence links human ancestry with populations that evolved from modern gracile morphology in Africa 130,000-160,000 years ago. Yet fossils alone do not provide clear answers to the question of whether the ancestors of all modern Homo sapiens comprised a single African population or an amalgamation of distinct archaic populations. DNA sequence data have consistently supported a single-origin model in which anatomically modern Africans expanded and completely replaced all other archaic hominin populations. Aided by a novel experimental design, we present the first genetic evidence that statistically rejects the null hypothesis that our species descends from a single, historically panmictic population. In a global sample of 42 X chromosomes, two African individuals carry a lineage of noncoding 17.5-kb sequence that has survived for >1 million years without any clear traces of ongoing recombination with other lineages at this locus. These patterns of deep haplotype divergence and long-range linkage disequilibrium are best explained by a prolonged period of ancestral population subdivision followed by relatively recent interbreeding. This inference supports human evolution models that incorporate admixture between divergent African branches of the genus Homo.
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Affiliation(s)
- Daniel Garrigan
- Genomic Analysis and Technology Core, University of Arizona, Tucson, Arizona 85721, USA
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Nachman MW, D'Agostino SL, Tillquist CR, Mobasher Z, Hammer MF. Nucleotide variation at Msn and Alas2, two genes flanking the centromere of the X chromosome in humans. Genetics 2005; 167:423-37. [PMID: 15166166 PMCID: PMC1470878 DOI: 10.1534/genetics.167.1.423] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The centromeric region of the X chromosome in humans experiences low rates of recombination over a considerable physical distance. In such a region, the effects of selection may extend to linked sites that are far away. To investigate the effects of this recombinational environment on patterns of nucleotide variability, we sequenced 4581 bp at Msn and 4697 bp at Alas2, two genes situated on either side of the X chromosome centromere, in a worldwide sample of 41 men, as well as in one common chimpanzee and one orangutan. To investigate patterns of linkage disequilibrium (LD) across the centromere, we also genotyped several informative sites from each gene in 120 men from sub-Saharan Africa. By studying X-linked loci in males, we were able to recover haplotypes and study long-range patterns of LD directly. Overall patterns of variability were remarkably similar at these two loci. Both loci exhibited (i) very low levels of nucleotide diversity (among the lowest seen in the human genome); (ii) a strong skew in the distribution of allele frequencies, with an excess of both very-low and very-high-frequency derived alleles in non-African populations; (iii) much less variation in the non-African than in the African samples; (iv) very high levels of population differentiation; and (v) complete LD among all sites within loci. We also observed significant LD between Msn and Alas2 in Africa, despite the fact that they are separated by approximately 10 Mb. These observations are difficult to reconcile with a simple demographic model but may be consistent with positive and/or purifying selection acting on loci within this large region of low recombination.
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Affiliation(s)
- Michael W Nachman
- Department of Ecology and Evolutionary Biology, Division of Biotechnology, University of Arizona, Tucson, Arizona 85721, USA.
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Stead JDH, Jeffreys AJ. Structural analysis of insulin minisatellite alleles reveals unusually large differences in diversity between Africans and non-Africans. Am J Hum Genet 2002; 71:1273-84. [PMID: 12404181 PMCID: PMC378563 DOI: 10.1086/344513] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2002] [Accepted: 08/28/2002] [Indexed: 11/03/2022] Open
Abstract
The insulin minisatellite (INS VNTR) associates with susceptibility to a variety of diseases. We have developed a high-resolution system for analyzing variant repeat distributions applicable to all known minisatellite alleles, irrespective of size, which allows lineages of related alleles to be identified. This system has previously revealed extremely low structural diversity in the minisatellite among northern Europeans from the United Kingdom, with all alleles belonging to one of only three highly diverged lineages called "I," "IIIA," and "IIIB." To explore the origins of this remarkably limited lineage diversity, we have characterized an additional 780 alleles from three non-African and three African populations. In total, 22 highly diverged lineages were identified, with structural intermediates absent from extant populations, suggesting a bottleneck within the ancestry of all humans. The difference between levels of diversity in Africans and non-Africans is unusually large, with all 22 lineages identified in Africa compared with only three lineages seen not only in the United Kingdom but also in the other non-African populations. We also find evidence for overrepresentation of lineage I chromosomes in non-Africans. These data are consistent with a common out-of-Africa origin and an unusually tight bottleneck within the ancestry of all non-African populations, possibly combined with differential and positive selection for lineage I alleles in non-Africans. The important implications of these data for future disease-association studies are discussed.
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Affiliation(s)
- John D H Stead
- Department of Genetics, University of Leicester, United Kingdom
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Wooding SP, Watkins WS, Bamshad MJ, Dunn DM, Weiss RB, Jorde LB. DNA sequence variation in a 3.7-kb noncoding sequence 5' of the CYP1A2 gene: implications for human population history and natural selection. Am J Hum Genet 2002; 71:528-42. [PMID: 12181774 PMCID: PMC379190 DOI: 10.1086/342260] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2002] [Accepted: 06/10/2002] [Indexed: 11/04/2022] Open
Abstract
CYP1A2 is a cytochrome P450 gene that is involved in human physiological responses to a variety of drugs and toxins. To investigate the role of population history and natural selection in shaping genetic diversity in CYP1A2, we sequenced a 3.7-kb region 5' from CYP1A2 in a diverse collection of 113 individuals from three major continental regions of the Old World (Africa, Asia, and Europe). We also examined sequences in the 90-member National Institutes of Health DNA Polymorphism Discovery Resource (PDR). Eighteen single-nucleotide polymorphisms (SNPs) were found. Most of the high-frequency SNPs found in the Old World sample were also found in the PDR sample. However, six SNPs were detected in the Old World sample but not in the PDR sample, and two SNPs found in the PDR sample were not found in the Old World sample. Most pairs of SNPs were in complete linkage disequilibrium with one another, and there was no indication of a decline of disequilibrium with physical distance in this region. The average +/- SD nucleotide diversity in the Old World sample was 0.00043+/-0.00026. The African population had the highest level of nucleotide diversity and the lowest level of linkage disequilibrium. Two distinct haplotype clusters with broadly overlapping geographical distributions were present. Of the 17 haplotypes found in the Old World sample, 12 were found in the African sample, 8 were found in Indians, 5 were found in non-Indian Asians, and 5 were found in Europeans. Haplotypes found outside Africa were mostly a subset of those found within Africa. These patterns are all consistent with an African origin of modern humans. Seven SNPs were singletons, and the site-frequency spectrum showed a significant departure from neutral expectations, suggesting population expansion and/or natural selection. Comparison with outgroup species showed that four derived SNPs have achieved high (>0.90) frequencies in human populations, a trend consistent with the action of positive natural selection. These patterns have a number of implications for disease-association studies in CYP1A2 and other genes.
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Affiliation(s)
- S. P. Wooding
- Departments of Human Genetics and Pediatrics, University of Utah, Salt Lake City
| | - W. S. Watkins
- Departments of Human Genetics and Pediatrics, University of Utah, Salt Lake City
| | - M. J. Bamshad
- Departments of Human Genetics and Pediatrics, University of Utah, Salt Lake City
| | - D. M. Dunn
- Departments of Human Genetics and Pediatrics, University of Utah, Salt Lake City
| | - R. B. Weiss
- Departments of Human Genetics and Pediatrics, University of Utah, Salt Lake City
| | - L. B. Jorde
- Departments of Human Genetics and Pediatrics, University of Utah, Salt Lake City
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Lessios HA, Garrido MJ, Kessing BD. Demographic history of Diadema antillarum, a keystone herbivore on Caribbean reefs. Proc Biol Sci 2001; 268:2347-53. [PMID: 11703875 PMCID: PMC1088886 DOI: 10.1098/rspb.2001.1806] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The sea urchin Diadema antillarum was the most important herbivore on Caribbean reefs until 1983, when mass mortality reduced its populations by more than 97%. Knowledge of its past demography is essential to reconstruct reef ecology as it was before human impact, which has been implicated as having caused high pre-mortality Diadema abundance. To determine the history of its population size, we sequenced the ATPase 6 and 8 region of mitochondrial DNA from populations in the Caribbean and in the eastern Atlantic (which was not affected by the mass mortality), as well as from the eastern Pacific D. mexicanum. The Caribbean population harbours an order of magnitude more molecular diversity than those of the eastern Pacific or the eastern Atlantic and, despite the recent mass mortality, its DNA sequences bear the genetic signature of a previous population expansion. By estimating mutation rates from divergence between D. antillarum and D. mexicanum, that were separated at a known time by the Isthmus of Panama, and by using estimates of effective population size derived from mismatch distributions and a maximum likelihood coalescence algorithm, we date the expansion as having occurred no more recently than 100 000 years before the present. Thus, Diadema was abundant in the Caribbean long before humans could have affected ecological processes; the genetic data contain no evidence of a recent, anthropogenically caused, population increase.
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Affiliation(s)
- H A Lessios
- Smithsonian Tropical Research Institute, Box 2072, Balboa, Panama.
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Affiliation(s)
- A R Rogers
- Anthropology Department, William Stewart Building, 270 S. 1400 East, Room 102, University of Utah, Salt Lake City, UT 84112, USA.
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