Intercontinental Migration Research Articles

Pleistocene survival, regional genetic structure and interspecific gene flow among three northern peat‐mosses: Sphagnum inexspectatum, S. orientale and S. miyabeanum

AbstractAimArctic plant species are often characterized by a complex genetic structure because of changes in their population size, the fragmentation of metapopulation systems, extensive hybridization and allopolyploidization, and survival in disjunct refugia, historical features associated with Pleistocene glaciation. We assessed the biogeographical and genetic patterns in three closely related northern species of peat‐moss (Sphagnum inexspectatum, S. orientale and S. miyabeanum), especially interspecific hybridization, infraspecific geographical differentiation and Pleistocene survival in one or more refugial areas. We tested alternative hypotheses of refugial survival in three widely disjunct regions: eastern Asia, Alaska and Greenland.LocationNorth America (Canada, western USA and Greenland), China, Japan and Russia.MethodsFour hundred and forty‐three plants were genotyped at 12 microsatellite loci. Nucleotide sequences from 130 accessions for two plastid and two nuclear loci were used to reconstruct haplotype relationships. Population genetic analyses produced estimates of genetic diversity, levels of interspecific gene flow and rates of infraspecific intercontinental migration. Approximate Bayesian computation was used to test alternative biogeographical scenarios.ResultsWe found evidence of hybridization between two of the three species, but phylogenetic patterns are predominantly divergent rather than reticulate. Disjunct populations of one species, S. orientale, in Greenland, Alaska and China are genetically differentiated, but migration has occurred among all three metapopulation systems. Divergence‐time analyses strongly support the hypothesis that S. orientale survived the Last Glacial Maximum in Beringia and also in Greenland.Main conclusionsOur results indicate that Beringia served as a refugium for peat‐mosses, and therefore peatlands, which are currently extensive at high latitudes of the Northern Hemisphere. Sphagnum orientale also appears to have survived the Last Glacial Maximum in Greenland, indicating that the species persisted in multiple Pleistocene refugia. Phylogenetic patterns are relatively simple in these mosses compared with those commonly encountered in Arctic angiosperms.

Seasonal Movements and Distribution of Steller’s Eiders (<i>Polysticta stelleri</i>) Wintering at Kodiak Island, Alaska

We used satellite telemetry in 2004–06 to describe the annual movements and habitat use of a segment of the Pacific population of Steller’s Eiders ( Polysticta stelleri ) that winters at Kodiak Island, Alaska. Information about broad-scale patterns of seasonal distribution and links among annual cycle stages is critical for interpreting population trends and developing conservation strategies. We captured birds in Chiniak Bay at Kodiak Island in late February and early March and monitored the movements after departure from Kodiak Island of 24 satellite-tagged birds: 16 after-second-year (ASY) age class females, one second-year age class female, and seven ASY males. All birds used the same intercontinental migration corridor during spring, but routes and chronology of spring migration appeared to vary by year and among individuals. Sixteen of the 24 birds that were tracked migrated to breeding areas along the Arctic coast of Russia from the Chukotka Peninsula to the Taymyr Peninsula; five birds, assumed to be non-breeding, spent the summer in nearshore waters of Russia and Alaska; and the remaining three birds either died during spring migration or had failed transmitters. Thirteen birds were tracked to molt sites that were broadly distributed along the coast of Alaska. Molt sites included St. Lawrence Island, the Kuskokwim Shoals, Kamishak Bay, and three sites along the Alaska Peninsula. Twelve of these 13 birds returned to Kodiak Island to winter, and a single male wintered on the Alaska Peninsula. Steller’s Eiders marked during winter at Kodiak Island were widely distributed during the breeding season, but a large proportion of marked birds returned to molting and wintering areas in two years of the study.

Methicillin‐Resistant Staphylococcus aureus and Intercontinental Travel—“Bad Bugs on the Move!”

The pace at which newly emerging pathogens spread around the world has been greatly accelerated by intercontinental travel and migration. Every day, thousands of potentially infected human bodies interlink even the remotest parts of our world. As a consequence, the period during which new pathogens remain confined to the population from which they emerged is becoming ever shorter and their containment increasingly challenging. Against this background, there is high demand on the research community to respond to the microbiological aftermath of globalization and to provide knowledge for effective interventions. Although there is a long‐standing appreciation of the role of intercontinental travel in the pandemic spread of clinically overt infectious diseases,1 it was only recently that we learned about its contribution toward the “silent pandemic” of antimicrobial resistance.2 Extended‐spectrum β‐lactamase‐producing bacteria, for instance, use the commensal microflora of travelers to make their way around the globe.3 Obviously, our microbiome closely interacts with the environment at the destination and serves as a vehicle and reservoir for resistant bacteria. Recently, the discovery of New Delhi metallo‐β‐lactamase has drawn a lot of public attention to the link between travel and the global spread of bacterial multi‐resistance.4,5 Since then, the public fears and discussions largely circle around the threat of emerging multi‐resistance in gram‐negative bacteria. For several reasons, however, loss of effective antimicrobials against gram‐positive Staphylococcus aureus will remain high on the global health agenda. First, S. aureus spreads particularly well due to its capacity to persistently colonize the nose. From there, the organism is effectively shed onto the hands, into … Corresponding Author: PD Dr Philipp Zanger, MSc, Institute of Public Health, University of Heidelberg, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany. E‐mail: philipp.zanger{at}uni-heidelberg.de

Structure, inter-annual recurrence, and global-scale connectivity of airborne microbial communities

Dust coming from the large deserts on Earth, such as the Sahara, can travel long distances and be dispersed over thousands of square kilometers. Remote dust deposition rates are increasing as a consequence of global change and may represent a mechanism for intercontinental microbial dispersal. Remote oligotrophic alpine lakes are particularly sensitive to dust inputs and can serve as sentinels of airborne microbial transport and the ecological consequences of accelerated intercontinental microbial migration. In this study, we applied high-throughput sequencing techniques (16S rRNA amplicon pyrosequencing) to characterize the microbial communities of atmospheric deposition collected in the Central Pyrenees (NE Spain) along three years. Additionally, bacteria from soils in Mauritania and from the air-water interface of high altitude Pyrenean lakes were also examined. Communities in aerosol deposition varied in time with a strong seasonal component of interannual similarity. Communities from the same season tended to resemble more each other than those from different seasons. Samples from disparate dates, in turn, slightly tended to have more dissimilar microbial assemblages (i.e., temporal distance decay), overall suggesting that atmospheric deposition may influence sink habitats in a temporally predictable manner. The three habitats examined (soil, deposition, and air-water interface) harbored distinct microbial communities, although airborne samples collected in the Pyrenees during Saharan dust outbreaks were closer to Mauritian soil samples than those collected during no Saharan dust episodes. The three habitats shared c.a. 1.4% of the total number of microbial sequences in the dataset. Such successful immigrants were spread in different bacterial classes. Overall, this study suggests that local and regional features may generate global trends in the dynamics and distribution of airborne microbial assemblages, and that the diversity of viable cells in the high atmosphere is likely higher than previously expected.

Do migrants influence the foraging behaviour of the insectivorous Cyprus Wheatear, Oenanthe cypriaca, at a stopover site? (Aves: Passeriformes)

During their staging at stopover sites, migrants may compete with resident species over food resources (“resource competition hypothesis”), or migrants feed on surplus that is not utilised by the residents. Here, I studied foraging behaviour of the Cyprus Wheatear, Oenanthe cypriaca, a ubiquitous and common species with a broad niche range, on Cyprus, which is an important stopover site during intercontinental spring migration. During adverse weather conditions, perch height and aerial sallying were lower and perch/pounce activity was higher. Average perch height and sallying increased over the season, while perch-pounce foraging decreased. There was no influence of clock time. Bivariate correlations suggested an influence of migrants on perch height but not on other variables. Using a series of regression analyses with sex, time of day, date, weather conditions and number of migrants as independent variables revealed no influence of the number of migrants on the foraging behaviour of the Cyprus Wheatear. This suggests that the abundance of migrants does not lead to a change in the behaviour of the Cyprus Wheatear.

Replicated radiations of the alpine genus Androsace (Primulaceae) driven by range expansion and convergent key innovations.

We still have limited understanding of the contingent and deterministic factors that have fostered the evolutionary success of some species lineages over others. We investigated how the interplay of intercontinental migration and key innovations promoted diversification of the genus Androsace. Mountain ranges and cold steppes of the Northern Hemisphere. We reconstructed ancestral biogeographical ranges at regional and continental scales by means of a dispersal-extinction-cladogenesis analysis using dated Bayesian phylogenies and contrasting two migration scenarios. Based on diversification analyses under two frameworks, we tested the influence of life form on speciation rates and whether diversification has been diversity-dependent. We found that three radiations occurred in this genus, at different periods and on different continents, and that life form played a critical role in the history of Androsace. Short-lived ancestors first facilitated the expansion of the genus' range from Asia to Europe, while cushions, which appeared independently in Asia and Europe, enhanced species diversification in alpine regions. One long-distance dispersal event from Europe to North America led to the diversification of the nested genus Douglasia. We found support for a model in which speciation of the North American-European clade is diversity-dependent and close to its carrying capacity, and that the diversification dynamics of the North American subclade are uncoupled from this and follow a pure birth process. The contingency of past biogeographical connections combined with the evolutionary determinism of convergent key innovations may have led to replicated radiations of Androsace in three mountain regions of the world. The repeated emergence of the cushion life form was a convergent key innovation that fostered radiation into alpine habitats. Given the large ecological similarity of Androsace species, allopatry may have been the main mode of speciation.

Phylogeography of Neotropical trees

Special issue editorial. Freely available on the publisher's website - access full text via the Official URL link.

Complex Patterns of Genomic Admixture within Southern Africa

Within-population genetic diversity is greatest within Africa, while between-population genetic diversity is directly proportional to geographic distance. The most divergent contemporary human populations include the click-speaking forager peoples of southern Africa, broadly defined as Khoesan. Both intra- (Bantu expansion) and inter-continental migration (European-driven colonization) have resulted in complex patterns of admixture between ancient geographically isolated Khoesan and more recently diverged populations. Using gender-specific analysis and almost 1 million autosomal markers, we determine the significance of estimated ancestral contributions that have shaped five contemporary southern African populations in a cohort of 103 individuals. Limited by lack of available data for homogenous Khoesan representation, we identify the Ju/'hoan (n = 19) as a distinct early diverging human lineage with little to no significant non-Khoesan contribution. In contrast to the Ju/'hoan, we identify ancient signatures of Khoesan and Bantu unions resulting in significant Khoesan- and Bantu-derived contributions to the Southern Bantu amaXhosa (n = 15) and Khoesan !Xun (n = 14), respectively. Our data further suggests that contemporary !Xun represent distinct Khoesan prehistories. Khoesan assimilation with European settlement at the most southern tip of Africa resulted in significant ancestral Khoesan contributions to the Coloured (n = 25) and Baster (n = 30) populations. The latter populations were further impacted by 170 years of East Indian slave trade and intra-continental migrations resulting in a complex pattern of genetic variation (admixture). The populations of southern Africa provide a unique opportunity to investigate the genomic variability from some of the oldest human lineages to the implications of complex admixture patterns including ancient and recently diverged human lineages.

Molecular characterization of haemosporidian parasites from kites of the genus Milvus (Aves: Accipitridae)

Despite the ecological significance and appeal of birds of prey, many aspects of their biology remain poorly known, including the diversity of parasites infecting them in the wild. We studied the diversity and prevalence of haemosporidian parasites infecting the two species of kites of the genus Milvus, aiming to describe the phylogenetic relationships among them and with other haemosporidians, as well as their distribution in the two host species. Black kites, Milvus migrans, harboured a more diverse community of parasites, including three haplotypes of each of the three genera Plasmodium, Haemoproteus and Leucocytozoon, which also occurred at a higher prevalence than in red kites. In red kites, Milvus milvus only three haplotypes of Leucocytozoon were found. Kite parasites were not closely related to one another nor were they kite-specific: their diversity spanned various branches of the haemosporidian phylogenetic tree, and their closest relatives were found in other species (including various avian orders), although some Leucocytozoon and Haemoproteus haplotypes clustered within apparently raptor-specific parasite clades. Remarkably, Plasmodium spp. and Haemoproteus spp. infected adult black kites only, an observation which supports the hypothesis that they are transmitted at the African wintering grounds, while Leucocytozoon spp. is putatively transmitted only in Europe. Intercontinental migration of the black kite might explain the divergence of parasite diversity between these two sister species.

Migration and Rural Welfare: The Impact of Potential Policy Reforms in Europe

This paper uses an agricultural household model in an imperfect market environment and data from Burkina Faso to explore the impact of potential immigration policy reforms in Europe on the welfare of rural households. Simulation results demonstrate that, in contrast to continental migration, increased intercontinental migration has strong positive household welfare effects. Similarly, an increase in the stay abroad of intercontinental migrants impacts positively on welfare of the migrant-sending household. Results of these simulations lend support to the introduction of a TMP, which would, in addition to facilitating migration control in host economies, improve the welfare of sending households by allowing for increased engagement in intercontinental migration. The temporary nature of such a program would ensure that “Dutch disease” effects would be mitigated through eventual migrant return.

Large-scale survey for novel genotypes of Plasmodium falciparum chloroquine-resistance gene pfcrt

BackgroundIn Plasmodium falciparum, resistance to chloroquine (CQ) is conferred by a K to T mutation at amino acid position 76 (K76T) in the P. falciparum CQ transporter (PfCRT). To date, at least 15 pfcrt genotypes, which are represented by combinations of five amino acids at positions 72-76, have been described in field isolates from various endemic regions. To identify novel mutant pfcrt genotypes and to reveal the genetic relatedness of pfcrt genotypes, a large-scale survey over a wide geographic area was performed.MethodsSequences for exon 2 in pfcrt, including known polymorphic sites at amino acid positions 72, 74, 75 and 76, were obtained from 256 P. falciparum isolates collected from eight endemic countries in Asia (Bangladesh, Cambodia, Lao P.D.R., the Philippines and Thailand), Melanesia (Papua New Guinea and Vanuatu) and Africa (Ghana). A haplotype network was constructed based on six microsatellite markers located -29 kb to 24 kb from pfcrt in order to examine the genetic relatedness among mutant pfcrt genotypes.ResultsIn addition to wild type (CVMNK at positions 72-76), four mutant pfcrt were identified; CVIET, CVIDT, SVMNT and CVMNT (mutated amino acids underlined). Haplotype network revealed that there were only three mutant pfcrt lineages, originating in Indochina, Philippines and Melanesia. Importantly, the Indochina lineage contained two mutant pfcrt genotypes, CVIET (n = 95) and CVIDT (n = 14), indicating that CVIDT shares a common origin with CVIET. Similarly, one major haplotype in the Melanesian lineage contained two pfcrt genotypes; SVMNT (n = 71) and CVMNT (n = 3). In Africa, all mutant pfcrt genotypes were the CVIET of the Indochina lineage, probably resulting from the intercontinental migration of CQ resistance from Southeast Asia.ConclusionsThe number of CQ-mutant lineages observed in this study was identical to that found in previous studies. This supports the hypothesis that the emergence of novel CQ resistance is rare. However, in the mutant pfcrt genotypes, amino acid changes at positions 72, 74 and 75 appear to have recently been generated at least several times, producing distinct pfcrt mutant genotypes. The occurrence of new mutations flanking K76T may yield stronger resistance to CQ and/or a higher fitness than the original pfcrt mutant.

POPULATION STRUCTURE AND MATING TYPE DISTRIBUTION OF THE CHICKPEA BLIGHT PATHOGEN ASCOCHYTA RABIEI FROM PAKISTAN AND THE UNITED STATES

Ascochyta blight caused by the fungus Ascochyta rabiei (AR) depresses chickpea production in Pakistan and worldwide. Thirty two AR isolates representing six geographical regions of Pakistan were compared with a US-AR population for mating type frequency and genetic variation. Mating type results showed that the Pakistani AR (PAR) population had an apparent skewed (3 Mat1-2: 1 Mat1-1) distribution, although Chi-square tests showed non-significant deviation from equal distribution due to small sample sizes. The US population showed a 1:1 distribution of the two mating types. The uneven distribution of mating types indicates that sexual reproduction among the PAR is rare due to either unavailability of both mating types or lack of conducive environment, but statistical analysis showed that panmixia is there reflecting past recombinational events. Genetic variation at six microsatellite loci was assessed and each isolate was assigned to a microsatellite haplotype. Population structure of the isolates was inferred using Bayesian analyses implemented in the structure software which differentiated isolates into three distinct clusters, two clusters of PAR and one of the US isolates. However, few isolates from the US shared the same genetic background with one cluster of the PAR isolates, providing a link of inter-continental migration of the pathogen. Additionally, the two clusters of PAR-isolates are not strictly associated with geographic locations in Pakistan, suggesting frequent gene flow of AR among different locations. Future studies should extend the sampling of representative populations to overcome the limitations of the small sample size for more accurate assessment of population structure.

Low diversity and fast evolution in the population of Puccinia triticina causing durum wheat leaf rust in France from 1999 to 2009, as revealed by an adapted differential set

No internationally agreed differential set is available for characterization of virulences in populations of Puccinia triticina causing wheat leaf rust on durum wheat. In a first step, 73 potentially differential host genotypes were tested with 96 durum leaf rust isolates collected in France. A differential set, adapted to the local epidemiological context and useful for comparison with international studies was selected, including French commercial cultivars, Thatcher lines with Lr genes, and international cultivars. In the second step, a sample of 310 isolates collected in France from 1999 to 2009 was characterized on this set. Diversity was very low, as only five pathotypes were distinguished. Genotyping of a subset of 76 isolates according to 20 SSR markers confirmed this low diversity, with 73 isolates belonging to a single dominant genotype. Population was strongly shaped by cultivars, and the findings explain the successive breakdown of resistance sources deployed in French durum wheat cultivars. The gene Lr14a, suggested to be an efficient source of resistance in several European and American countries, was overcome by pathotypes frequent in France since 2000. Postulation of resistance genes in the commercial cultivars led to a proposed simplified version of the differential set. This study, providing new information about leaf rust resistance genes present in the French durum wheat germplasm, highlights the need to diversify sources of resistance to P. triticina in this germplasm. The results are also discussed in terms of relatedness and intercontinental migration of P. triticina on durum wheat.

Entangling Ancient Allotetraploidization in Asian Mitella: An Integrated Approach for Multilocus Combinations

The reconstruction of an ancient polyploidization history is often challenging, although it is a crucial step in clarifying the mechanisms underlying the contemporary success and diversity of polyploids. Phylogenetic relationships of duplicated gene pairs of polyploids, with respect to their orthologs in related diploids, have been used to address this problem, but they often result in conflicting topologies among different genes. Asimitellaria is an East Asian endemic tetraploid lineage of perennials (genus Mitella; Saxifragaceae) that has diversified in riparian habitats. Phylogenetic analyses of four nuclear-encoded, single-copy (per haploid) genes GBSSI-A, GBSSI-B, GS-II, and PepCK all supported a single allopolyploid origin of Asimitellaria, but they did not lead to a consensus about which diploid lineage gave rise to each of the Asimitellaria subgenomes. To address this issue, we used an integrated approach, whereby the four gene data sets and an additional nuclear ribosomal external transcribed spacer and internal transcribed spacer (including a 5.8S ribosomal DNA) data set were concatenated in all possible combinations, and the most probable data combination was determined together with the phylogenetic inference. This resulted in relatively robust support for the two closely related North American diploid species as the ancestral lineages of the Asimitellaria subgenomes, suggesting ancient intercontinental migration of the diploid or tetraploid lineages and subsequent tetraploid diversification in the Japanese Archipelago. The present approach enabled sorting out the duplicated genes into their original combinations in their preduplication ancestors under a maximum-likelihood framework, and its extension toward genome sequencing data may help in the reconstruction of ancestral, preduplicated, whole-genome structures.

Heterogeneous migration flows from the Central Plateau of Burkina Faso: the role of natural and social capital

This paper uses a system of labour supply equations and data from Burkina Faso collected in 2003 to test the conditions underlying two different migratory movements: continental and intercontinental migration. We provide theoretical reasoning and empirical evidence that heterogeneity in migration is related to heterogeneity in rural households. We find that comparatively asset-poor households embark on continental migration, whereas intercontinental migration takes place in comparatively wealthy households in response to opportunities for accumulation of wealth in Europe. We also find that access to religion-specific migrant networks plays a positive and negative role in explaining, respectively, intercontinental and continental migration

Intercontinental dispersal of giant thermophilic ants across the Arctic during early Eocene hyperthermals

Early Eocene land bridges allowed numerous plant and animal species to cross between Europe and North America via the Arctic. While many species suited to prevailing cool Arctic climates would have been able to cross throughout much of this period, others would have found dispersal opportunities only during limited intervals when their requirements for higher temperatures were met. Here, we present Titanomyrma lubei gen. et sp. nov. from Wyoming, USA, a new giant (greater than 5 cm long) formiciine ant from the early Eocene (approx. 49.5 Ma) Green River Formation. We show that the extinct ant subfamily Formiciinae is only known from localities with an estimated mean annual temperature of about 20°C or greater, consistent with the tropical ranges of almost all of the largest living ant species. This is, to our knowledge, the first known formiciine of gigantic size in the Western Hemisphere and the first reported cross-Arctic dispersal by a thermophilic insect group. This implies intercontinental migration during one or more brief high-temperature episodes (hyperthermals) sometime between the latest Palaeocene establishment of intercontinental land connections and the presence of giant formiciines in Europe and North America by the early middle Eocene.

Migration and technical efficiency in cereal production: evidence from Burkina Faso

AbstractThis article uses a double bootstrap procedure and survey data from Burkina Faso in a two‐stage estimation to explore ways in which continental and intercontinental migration determine efficiency in cereal production of rural households. Findings suggest that continental migration has a positive relation and intercontinental migration no relation with technical efficiency. For continental migrant households, migration has removed surplus male labor, a cause for inefficiency in production. Intercontinental migration leads to a gender imbalance in the household, which cannot be compensated for by investments in farm equipment. The failure of intercontinental migration to transform cereal production from traditional to modern is attributed to an imperfect market environment.

Remittances, Poverty, Inequality and Welfare: Evidence from the Central Plateau of Burkina Faso

This paper applies Gini and concentration coefficient decomposition as well as the Foster-Greer-Thorbecke poverty index and the Stark-Yitzhaki welfare index to new data from four villages in Burkina Faso, to compare the marginal effects of remittances from intercontinental and intra-African migration on inequality, poverty and social welfare. Evidence is found that intra-African remittances reduce inequality while intercontinental remittances have the opposite effect. Also, it is found that although remittances from intercontinental migration are associated with much lower incidence, depth and severity of poverty, the marginal impact of remittances from this form of migration on social welfare is limited because recipients do not include the rural poor.

Genetic Differentiation Within the Puccinia triticina Population in South America and Comparison with the North American Population Suggests Common Ancestry and Intercontinental Migration

Leaf rust, caused by Puccinia triticina, is the most prevalent and widespread disease of wheat in South America. The objective of this study was to determine whether genetically differentiated groups of P. triticina are currently present in South America and to compare the South American population with the previously characterized population in North America. In total, 130 isolates of P. triticina from the wheat-growing regions of Argentina, Brazil, Chile, Peru, and Uruguay, mostly from the 1990s to 2008, were tested for virulence on 20 lines of wheat with single genes for leaf rust resistance and for molecular genotypes with 23 simple-sequence repeat (SSR) markers. After removal of isolates with identical virulence and SSR genotypes, 99 isolates were included for further analysis. Principal coordinate analysis plots indicated five different groups of isolates based on SSR genotypes that also differed for virulence to leaf rust resistance genes. All pairs of groups, except for one pair, were significantly differentiated for SSR genotypes according to R(ST) statistics. All but two pairs of groups were significantly differentiated for virulence phenotype according to Phi(PT) statistics. Isolates in all five groups had high values of fixation index for SSR alleles and linkage disequilibrium was high across all isolates that indicated the clonal reproduction of urediniospores. Only one of the five P. triticina groups from South America was differentiated for SSR genotypes from all of the six P. triticina groups from North America. The high degree of similarity for SSR genotype of isolates from both South America and North America suggested a common European origin of P. triticina that was introduced to both continents. The emergence of the same P. triticina virulence phenotypes with highly related SSR genotypes in the United States in 1996 and in Uruguay in 1999 indicated the likely intercontinental migration of these genotypes from Mexico to both South America and North America.

Recent divergence, intercontinental dispersal and shared polymorphism are shaping the genetic structure of amphi‐Atlantic peatmoss populations

Several lines of evidence suggest that recent long-distance dispersal may have been important in the evolution of intercontinental distribution ranges of bryophytes. However, the absolute rate of intercontinental migration and its relative role in the development of certain distribution ranges is still poorly understood. To this end, the genetic structure of intercontinental populations of six peatmoss species showing an amphi-Atlantic distribution was investigated using microsatellite markers. Methods relying on the coalescent were applied (IM and MIGRATE) to understand the evolution of this distribution pattern in peatmosses. Intercontinental populations of the six peatmoss species were weakly albeit significantly differentiated (average F(ST) = 0.104). This suggests that the North Atlantic Ocean is acting as a barrier to gene flow even in bryophytes adapted to long-range dispersal. The im analysis suggested a relatively recent split of intercontinental populations dating back to the last two glacial periods (9000-289,000 years ago). In contrast to previous hypotheses, analyses indicated that both ongoing migration and ancestral polymorphism are important in explaining the intercontinental genetic similarity of peatmoss populations, but their relative contribution varies with species. Migration rates were significantly asymmetric towards America suggesting differential extinction of genotypes on the two continents or invasion of the American continent by European lineages. These results indicate that low genetic divergence of amphi-Atlantic populations is a general pattern across numerous flowering plants and bryophytes. However, in bryophytes, ongoing intercontinental gene flow and retained shared ancestral polymorphism must both be considered to explain the genetic similarity of intercontinental populations.