Bayesian Coalescent Analysis Research Articles

Mitochondrial Phylogeography and Population History of the Large Japanese Wood Mouse (Apodemus speciosus) on Sado Island, Japan

Abstract. A phylogeographic study of the large Japanese wood mouse, Apodemus speciosus, on Sado Island, Japan, was performed based on sequences of the mitochondrial cytochrome b gene (1,140 bp). Our previous study covered the entire species range and suggested that the mice on Sado Island are monophyletic, exhibiting two well diverged lineages throughout the island. The present data also supported two lineages (the average number of nucleotide difference was 11.4), showing a weak phylogeographic structure. Given the high sequence divergence observed, we assumed historically subdivided populations within the island. Bayesian coalescent analysis supported a dual-population model rather than that of one large population. The times to most recent common ancestor of all sequences were 293,000 years ago [ka; 95% highest probability density (HPD) 85–634 ka] and 292 ka (HPD 102–605 ka) for the one- and dual-population models, respectively. These results suggest that the populations have undergone repeated separat...

Phylodynamic Reconstruction Reveals Norovirus GII.4 Epidemic Expansions and their Molecular Determinants

Noroviruses are the most common cause of viral gastroenteritis. An increase in the number of globally reported norovirus outbreaks was seen the past decade, especially for outbreaks caused by successive genogroup II genotype 4 (GII.4) variants. Whether this observed increase was due to an upswing in the number of infections, or to a surveillance artifact caused by heightened awareness and concomitant improved reporting, remained unclear. Therefore, we set out to study the population structure and changes thereof of GII.4 strains detected through systematic outbreak surveillance since the early 1990s. We collected 1383 partial polymerase and 194 full capsid GII.4 sequences. A Bayesian MCMC coalescent analysis revealed an increase in the number of GII.4 infections during the last decade. The GII.4 strains included in our analyses evolved at a rate of 4.3–9.0×10−3 mutations per site per year, and share a most recent common ancestor in the early 1980s. Determinants of adaptation in the capsid protein were studied using different maximum likelihood approaches to identify sites subject to diversifying or directional selection and sites that co-evolved. While a number of the computationally determined adaptively evolving sites were on the surface of the capsid and possible subject to immune selection, we also detected sites that were subject to constrained or compensatory evolution due to secondary RNA structures, relevant in virus-replication. We highlight codons that may prove useful in identifying emerging novel variants, and, using these, indicate that the novel 2008 variant is more likely to cause a future epidemic than the 2007 variant. While norovirus infections are generally mild and self-limiting, more severe outcomes of infection frequently occur in elderly and immunocompromized people, and no treatment is available. The observed pattern of continually emerging novel variants of GII.4, causing elevated numbers of infections, is therefore a cause for concern.

Genetic variation and spatial autocorrelation among young-of-the-year red snapper (Lutjanus campechanus) in the northern Gulf of Mexico

AbstractSaillant, E., Bradfield, S. C., and Gold, J. R. 2010. Genetic variation and spatial autocorrelation among young-of-the-year red snapper (Lutjanus campechanus) in the northern Gulf of Mexico. – ICES Journal of Marine Science, 67: 1240–1250. Temporal and spatial genetic variations at 18 nuclear-encoded microsatellites were assayed among age-0 Gulf red snapper (Lutjanus campechanus), sampled from the 2004 and 2005 cohorts in each of five regions in the northern Gulf of Mexico (Gulf) and from a mixed-age group sampled off northwest Florida. Hierarchical analysis of molecular variance revealed genetic heterogeneity among habitat patches within regions, but not among regions. A significant, positive spatial autocorrelation of microsatellite genotypes among fish sampled within the geographic range 50–100 km was detected. Bayesian coalescent analysis of historical demography indicated a decline of nearly an order of magnitude in the effective population size for red snapper across the area surveyed. The highest posterior probability for the current effective population size was 2163, approximately four orders of magnitude smaller than the estimates of red snapper census size. The results of the study demonstrate that spatial genetic structuring among young-of-the-year red snapper in the Gulf occurs at small geographic scales and is consistent with a metapopulation stock-structure model of partially connected populations. This accentuates the importance of maintaining healthy local spawning populations of red snapper in all regions across the northern Gulf.

High prevalence of hepatitis C virus genotype 1b infection in a small town of Argentina. Phylogenetic and Bayesian coalescent analysis.

Previous studies in Argentina have documented a general prevalence of Hepatitis C Virus (HCV) infection close to 2%. In addition, a high prevalence of HCV has been recently reported in different Argentinean small rural communities. In this work, we performed a study aimed at analyzing the origins and diversification patterns of an HCV outbreak in Wheelwright, a small rural town located in Santa Fe province (Argentina).A total of 89 out of 1814 blood samples collected from people living in Wheelwright, were positive for HCV infection. The highest prevalence (4.9%) was observed in people older than 50 years, with the highest level for the group aged between 70–79 years (22%). The RFLP analyses showed that 91% of the positive samples belonged to the HCV-1b genotype. The E1/E2 and NS5B genes were sequenced, and their phylogenetic analysis showed that the HCV-1b sequences from Wheelwright were monophyletic. Bayesian coalescent-based methods were used to estimate substitution rates and time of the most recent common ancestor (tMRCA). The mean estimated substitution rates and the tMRCA for E1/E2 with and without HVR1 and NS5B were 7.41E-03 s/s/y and 61 years, 5.05E-03 s/s/y and 58 years and 3.24E-03 s/s/y and 53 years, respectively. In summary, the tMRCA values, the demographic model with constant population size, and the fact that the highest prevalence of infection was observed in elder people support the hypothesis that the HCV-1b introduction in Wheelwright initially occurred at least five decades ago and that the early epidemic was characterized by a fast rate of virus transmission. The epidemic seems to have been controlled later on down to the standard transmission rates observed elsewhere.

Ancient common ancestry of Crimean-Congo hemorrhagic fever virus

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne RNA virus responsible for outbreaks of severe hemorrhagic fever in humans. Although CCHF was first detected in the 1940s, high levels of genomic diversity argue against a recent origin. Here, Bayesian coalescent analyses were used to estimate the rate of evolution and relative age of the virus. A total of 43 S, 34 M, and 23 L segment sequences from samples collected between 1956 and 2005 were analyzed from across the broad geographic range of the virus. Using a relaxed molecular clock model, nucleotide substitutions were estimated to have occurred at a rate of 1.09 × 10 −4, 1.52 × 10 −4, and 0.58 × 10 −4 substitutions/site/year for the S, M, and L segments, respectively. The most recent common ancestor of the viruses existed approximately 3100–3500 years before present, or around 1500–1100 BC. Changes in agricultural practices and climate occurring near the time of the most recent common ancestor of CCHFV may have contributed to its emergence and spread.

A history estimate and evolutionary analysis of rabies virus variants in China

To investigate the evolutionary dynamics of rabies virus (RABV) in China, we collected and sequenced 55 isolates sampled from 14 Chinese provinces over the last 40 years and performed a coalescent-based analysis of the G gene. This revealed that the RABV currently circulating in China is composed of three main groups. Bayesian coalescent analysis estimated the date of the most recent common ancestor for the current RABV Chinese strains to be 1412 (with a 95 % confidence interval of 1006-1736). The estimated mean substitution rate for the G gene sequences (3.961x10(-4) substitutions per site per year) was in accordance with previous reports for RABV.

Analysis of HIV-1 pol sequences from Panama: Identification of phylogenetic clusters within subtype B and detection of antiretroviral drug resistance mutations

We report the first study to examine phylogenetic relationships and drug resistance mutations in HIV-1 pol sequences from Panama. For this study, we used plasma RNA samples from 135 HIV-1-infected subjects from Panama, of which 82 (61%) had AIDS and 53 (39%) were asymptomatic drug-naïve individuals. Phylogenetic analyses revealed that 133 (98%) subjects were infected with subtype B viruses and 2 AIDS patients harboured recombinant viruses, CRF02_AG/A3 and CRF12_BF/B, respectively. Using a Bayesian phylogeny inference method, 5 strongly supported clusters of ≥5 sequences, designated B-PA1 to B-PA5, were identified within subtype B, together comprising 87 (65.4%) subtype B viruses. Cluster B-PA1 ( n = 42) was significantly associated with East Panama and clusters B-PA2 ( n = 15) and B-PA4 ( n = 10) were associated with West Panama. A Bayesian coalescent analysis indicated that the most recent common ancestors of the four largest clusters were dated in the 1980s and that of the fifth in the early 1990s. The analysis of antiretroviral drug resistance-associated mutations revealed that 8 (9.7%) AIDS patients, all of them antiretroviral drug-experienced, harboured mutations conferring high or intermediate resistance levels to antiretroviral drugs. No drug resistance mutations were detected among the asymptomatic drug-naïve individuals. In conclusion, the phylogenetic analysis of HIV-1 pol sequences from Panama reveals that a majority of subtype B viruses, which are predominant in Panama, branch within well supported intrasubtype phylogenetic clusters, most of them originating in the 1980s, and some with geographical associations, which may reflect either multiple HIV-1 subtype B introductions or the existence of local transmission networks originating in the early epidemic in Panama.

Ecological Niche Models and Coalescent Analysis of Gene Flow Support Recent Allopatric Isolation of Parasitoid Wasp Populations in the Mediterranean

BackgroundThe integration of multiple complementary approaches is a powerful way to understand the processes of diversification and speciation. The parasitoid wasp Aphidius transcaspicus Telenga (Hymenoptera: Braconidae) is a parasitoid of Hyalopterus aphids across a wide geographic range. This species shows a remarkable degree of genetic structure among western, central, and eastern Mediterranean population clusters. In this paper we attempt to better characterize this genetic structure.Methodology/Principal FindingsWe use a Bayesian coalescent analysis of gene flow under the Isolation with Migration model using mitochondrial and microsatellite markers together with climate-based ecological niche models to better understand the genetic structure of A. transcaspicus in the Mediterranean. The coalescent analysis revealed low levels of migration among western and eastern Mediterranean populations (Nm<1) that were not statistically distinguishable from zero. Niche models showed that localities within population clusters each occupy areas of continuously high environmental suitability, but are separated from each other by large regions of completely unsuitable habitat that could limit dispersal. Overall, environmental characteristics were similar among the population clusters, though significant differences did emerge.Conclusions/SignificanceThese results support contemporary allopatric isolation of Mediterranean populations of A. transcaspicus, which together with previous analyses indicating partial behaviorally mediated reproductive isolation, suggest that the early stages of cryptic speciation may be in progress.

Ocean currents drive secondary contact between Anguilla marmorata populations in the Indian Ocean

Understanding the evolutionary processes underlying population structuring of fresh- water eels is an essential step toward comprehending their exceptional life cycle. However, in order to infer evolutionary scenarios that account for the genetic structure of current populations, it is nec- essary to unravel the history of gene flow from the onset of population divergence to the present. We used a combination of population-genetics methods and Bayesian coalescent analyses, to search specifically for the gene flow history that could explain contemporary genetic patterns of 2 Anguilla marmorata populations previously identified in the Indian Ocean. The population structure of A. mar- morata was analyzed by genotyping 444 eels sampled from both sides of the Indian Ocean. Using 2 mitochondrial 16S rRNA single-nucleotide polymorphisms (SNPs) and 10 nuclear microsatellite loci, we first provided corroborative evidence of the existence of 2 genetic stocks: the Sumatran and the southwestern Indian Ocean (SWIO) populations (nuclear FST = 0.025 to 0.039). High frequencies of Sumatran haplotypes were found in SWIO localities (27 to 43%). Fitting the isolation-with-migration model to 16S rRNA sequence data led us to reject the hypotheses of inherited ancestral polymor- phism and divergence with gene flow, but supported a recent secondary contact with unidirectional migration following a period of isolation. This scenario was confirmed by a cytonuclear disequilib- rium found in SWIO, which also indicated that unidirectional migration was in progress. Finally, fit- ting simulated models of population composition to Bayesian assignments estimated from nuclear data suggested that Sumatran migrants are integrated in the SWIO breeding pool after their disper- sal induced by the South Equatorial Current.

Evolutionary history and dynamics of dog rabies virus in western and central Africa

The burden of rabies in Africa is estimated at 24,000 human deaths year(-1), almost all of which result from infection with dog rabies viruses (RABV). To investigate the evolutionary dynamics of RABV in western and central Africa, 92 isolates sampled from 27 African countries over 29 years were collected and sequenced. This revealed that RABV currently circulating in dogs in this region fell into a single lineage designated 'Africa 2'. A detailed analysis of the phylogeographical structure of this Africa 2 lineage revealed strong population subdivision at the country level, with only limited movement of virus among localities, including a possible east-to-west spread across Africa. In addition, Bayesian coalescent analysis suggested that the Africa 2 lineage was introduced into this region of Africa only recently (probably <200 years ago), in accordance with the timescale of expanding European colonial influence and urbanization, and then spread relatively slowly, perhaps occupying the entire region in a 100 year period.

Diversification of rice yellow mottle virus and related viruses spans the history of agriculture from the neolithic to the present.

The mechanisms of evolution of plant viruses are being unraveled, yet the timescale of their evolution remains an enigma. To address this critical issue, the divergence time of plant viruses at the intra- and inter-specific levels was assessed. The time of the most recent common ancestor (TMRCA) of Rice yellow mottle virus (RYMV; genus Sobemovirus) was calculated by a Bayesian coalescent analysis of the coat protein sequences of 253 isolates collected between 1966 and 2006 from all over Africa. It is inferred that RYMV diversified approximately 200 years ago in Africa, i.e., centuries after rice was domesticated or introduced, and decades before epidemics were reported. The divergence time of sobemoviruses and viruses of related genera was subsequently assessed using the age of RYMV under a relaxed molecular clock for calibration. The divergence time between sobemoviruses and related viruses was estimated to be approximately 9,000 years, that between sobemoviruses and poleroviruses approximately 5,000 years, and that among sobemoviruses approximately 3,000 years. The TMRCA of closely related pairs of sobemoviruses, poleroviruses, and luteoviruses was approximately 500 years, which is a measure of the time associated with plant virus speciation. It is concluded that the diversification of RYMV and related viruses has spanned the history of agriculture, from the Neolithic age to the present.

Bayesian Coalescent Analysis Reveals a High Rate of Molecular Evolution in GB Virus C

GB virus C/hepatitis G (GBV-C) is an RNA virus of the family Flaviviridae. Despite replicating with an RNA-dependent RNA polymerase, some previous estimates of rates of evolutionary change in GBV-C suggest that it fixes mutations at the anomalously low rate of approximately 10(-7) nucleotide substitution per site, per year. However, these estimates were largely based on the assumption that GBV-C and its close relative GBV-A (New World monkey GB viruses) codiverged with their primate hosts over millions of years. Herein, we estimated the substitution rate of GBV-C using the largest set of dated GBV-C isolates compiled to date and a Bayesian coalescent approach that utilizes the year of sampling and so is independent of the assumption of codivergence. This revealed a rate of evolutionary change approximately four orders of magnitude higher than that estimated previously, in the range of 10(-2) to 10(-3) sub/site/year, and hence in line with those previously determined for RNA viruses in general and the Flaviviridae in particular. In addition, we tested the assumption of host-virus codivergence in GBV-A by performing a reconciliation analysis of host and virus phylogenies. Strikingly, we found no statistical evidence for host-virus codivergence in GBV-A, indicating that substitution rates in the GB viruses should not be estimated from host divergence times.

Divergence with gene flow between Ponto‐Caspian refugia in an anadromous cyprinid Rutilus frisii revealed by multiple gene phylogeography

The Black and Caspian Seas have experienced alternating periods of isolation and interconnection over many Milankovitch climate oscillations and most recently became separated when the meltwater overflow from the Caspian Sea ceased at the end of the last glaciation. Climate-induced habitat changes have indisputably had profound impacts on distribution and demography of aquatic species, yet uncertainties remain about the relative roles of isolation and dispersal in the response of species shared between the Black and Caspian Sea basins. We examined these issues using phylogeographical analysis of an anadromous cyprinid fish Rutilus frisii. Bayesian coalescence analyses of sequence variation at two nuclear and one mitochondrial genes suggest that the Black and Caspian Seas supported separate populations of R. frisii during the last glaciation. Parameter estimates from the fitted isolation-with-migration model showed that their separation was not complete, however, and that the two populations continued to exchange genes in both directions. These analyses also suggested that majority of migrations occurred during the Pleistocene, showing that the variation shared between the Black and Caspian Seas is the result of ancient dispersal along the temporary natural connections between the basins, rather than of incomplete lineage sorting or recent human-mediated dispersal. Gene flow between the refugial populations was therefore an important source of genetic variation, and we suggest that it facilitated the evolutionary response of the populations to changing climate.