Absence Of Genetic Structure Research Articles

Effect of fire and thinning on fine-scale genetic structure and gene flow in fire-suppressed populations of sugar pine (Pinus lambertiana Dougl.)

Historically, frequent, low-severity fires in dry western North American forests were a major driver of ecological patterns and processes, creating resilient ecosystems dominated by widely-spaced pine species. However, a century of fire-suppression has caused overcrowding, altering forest composition to shade-tolerant species, while increasing competition and leaving trees stressed and susceptible to pathogens, insects, and high-severity fire. Exacerbating the issue, fire incidence is expected to increase with changing climate, while fire season has been observed to begin earlier and last longer than historic trends. Forest thinning and prescribed fire have been identified as important management tools to mitigate these risks. Yet little is known of how thinning, fire, or their interaction affect contemporary evolutionary processes of constituent pine species that influence fitness and play an important role in the opportunity for selection and population persistence. We assessed the impact of widely used fuel reduction treatments on fine-scale gene flow on an ecologically important and historically dominant shade-intolerant pine species of the Sierra Nevada, Pinus lambertiana Dougl. Treatment prescription (no-thin-no-fire, thin-no-fire, and fire-and-thin) was found to differentially affect both fine-scale spatial and genetic structure as well as effective gene flow in this species. Specifically, the thin-no-fire prescription increases genetic structure (spatial autocorrelation of relatives) between adults and seedlings, while seed and pollen dispersal increase and decrease, respectively, as a function of increasing disturbance intensity. While these results may be specific to the stands at our study site, they indicate how assumptions relating to genetic effects based on spatial structure can be misleading (for instance, in many stands the presence or absence of spatial structure was not indicative the presence or absence of genetic structure). It is likely that these disequilibrated systems will continue to evolve on unknown evolutionary trajectories. The long-term impacts of management practices on reduced fitness from inbreeding depression should be continually monitored to ensure resilience to increasingly frequent and severe fire, drought, and pest stresses.

Genetic diversity and population structure of the blue jack mackerel Trachurus picturatus across its western distribution.

Blue jack mackerel Trachurus picturatus collected at six sampling locations of the north-east Atlantic Ocean (Azores, Madeira, Canaries, and Matosinhos, Peniche and Portimão, mainland Portugal) and one location in the Mediterranean (Sicily), were used to examine the genetic structure of this species. Three mitochondrial gene regions (cytochrome c oxidase subunit I, cytochrome b and control region) were used to study the genetic structure of the species in Macaronesia, as well as to compare the genetic diversity of this region with published results from its eastern distribution. All markers indicated the absence of genetic structure among populations, with high indices of genetic diversity. These results suggest that the species went through a bottleneck event, followed by a recent population expansion. Moreover, the comparison with previously published results from the T. picturatus Mediterranean distribution suggests the existence of a single panmictic population throughout the species' full range. This was, however, an unexpected result since other methodologies have shown the presence of, at least, three different population-units in the NE Atlantic Ocean.

Phenological and genetic characterization of Mediterranean plants at the peripheral range: the case of Cistus albidus near Lake Garda

The potential effects of climate change on the distribution of Mediterranean plants at their peripheral range make them extremely vulnerable to environmental fluctuations. The northern-most Italian population of Cistus albidus provides an outstanding case for study, as it grows at the extreme northern edge of its range and because phenological data have been available since the early XIX century.In the period 2012–2017, we analysed the population demography and spatial structure, growth and flowering phenology, and genetic variability to understand the history, current state and possible evolution of this population. Lastly, the population data were tested for association with environmental factors.The population studied consists of plants on average 10 years old, showing the highest growth rates in spring and autumn. Anthesis starts in April and ends in early June and is significantly dependent on temperature. High levels of genetic variability are present (average He = 0.471), with heterozygote excess detected at four loci out of five. Bayesian analysis does not support any genetic structuring of the population.The aggregated pattern in the distribution of individuals and their phenological traits, together with the absence of genetic structuring, seem to suggest that this extreme geographical population is not currently endangered.

Performance, genetic and ecological insights for the conservation of the endangered large pink, Dianthus superbus L. (Caryophyllaceae) in semi-natural grassland

ABSTRACTThe traditional management of hay meadows has allowed them to maintain a notable part of biodiversity currently threatened by recent changes in agricultural uses. In the North Eastern region of France, the large pink, Dianthus superbus L. (Caryophyllaceae), mainly grows in hay meadows, and its protected status implies a conservation strategy merging information about its demography, its genetic diversity and its ecology. This study has revealed that the population size of D. superbus is correlated with the trophic status of meadows, with a decrease from mesotrophic to eutrophic meadows. No relation has been established between population size and habitat size, spatial isolation or habitat connectivity. Moreover, AFLPs genetic fingerprints indicated equivalent genetic diversities among meadows, without impact of population size or habitat characteristics. The absence of genetic structure and the lack of population differentiation suggest a large genetic admixture at the regional scale. The most crucial issue for the conservation of D. superbus in the North Eastern region of France seems to be the modification of its habitat due to the eutrophication of hay meadows.

Dual pathways in social evolution: Population genetic structure of group-living and solitary species of kleptoparasitic spiders (Argyrodinae: Theridiidae).

Group-living behavior is taxonomically widespread but rare in spiders. The conventional view is that the main pathways to group-living in spiders are either sub-social, where extended maternal care leads to prolonged sibling association; or communal living, where individuals aggregate to exploit a common resource. Female egg-sac guarding behavior occurs throughout kleptoparasitic spiders in the subfamily Argyrodinae (Theridiidae), while individuals in group-living species cohabit in the resource rich webs of their host spiders. These attributes fit both sub-social and communal routes to group-living, which offers new insights to study the early stages of social evolution. We investigated whether members of kleptoparasitic groups in natural populations comprise related individuals by comparing the population structure of two group-living species, Argyrodes miniaceus and A. cf. fissifrons, and two solitary species, A. fasciatus and Neospintharus trigonum. We found that: (1) genetic-spatial autocorrelation in group-living species was highest among spiders sharing the same host web and declined steeply with increasing distance, but no significant autocorrelation at any scale for solitary species; (2) there was high relatedness among group members in two cases of group-living species, which indicated relatedness was not an adhesive agent in most of the groups, but no high relatedness in solitary species; and (3) the host web boundary was not the sole predictor of genetic structures in group-living species. These results suggest that population genetic structure in the group-living species is caused by limited dispersal of group members that is favored by ecological conditions, including the nature and size of resources. In contrast, the absence of genetic structuring in populations of solitary species indicates a high level of dispersal with individual interactions unlikely to have fitness benefits.

Genetic comparison of the red shrimp Pleoticus muelleri (Decapoda: Solenoceridae) using the barcode gene reveals the absence of cryptic speciation along its distribution

Differences in biological traits (abundance, longevity, size at the onset of sexual maturity, and maximum size) appearing in populations of Pleoticus muelleri from the Western Atlantic are currently considered as phenotypic plasticity. However, they may also be related to intraspecific genetic differentiation and to the occurrence of cryptic speciation. Thus, to assess the genetic diversity and population structure of P. muelleri along its distribution range, we compared cytochrome c oxidase subunit I (COI; the barcode gene) and 16S sequences of individuals from seven localities from the southeastern coast of Brazil and Argentina. Ten polymorphic sites were observed in eleven COI haplotypes, but only one polymorphic site was observed in two 16S haplotypes. The haplotype network, maximum likelihood phylogram, and analyses of molecular variance (AMOVA) indicated the absence of genetic structure between populations, which in turn, points to the absence of cryptic speciation. Therefore, the known phenotypic variations may be indeed a consequence of different environmental conditions.

Worming its way into Patagonia: an integrative approach reveals the cryptic invasion by Eulalia clavigera (Annelida: Phyllodocidae)

A phyllodocid polychaete belonging to the genus Eulalia is reported from Nuevo Gulf, Patagonia (South-western Atlantic Ocean) with abundant populations thriving in the intertidal zone. Morphological and molecular data allowed assigning this population to Eulalia clavigera (Audouin & Milne-Edwards, 1834), a species typically occurring along the north-eastern Atlantic coast. The absence of genetic structuring between north-eastern and south-western Atlantic E. clavigera strongly supports a non-native origin of the Patagonian population. Conversely, the majority of the Mediterranean Eulalia cf. clavigera analysed in this study turned out to belong to a different, probably undescribed species, suggesting that the diversity and taxonomy of green Eulalia is more complex than previously supposed. The high adaptation capabilities to stressed environments showed by E. clavigera, along with its possible high impact on native assemblages through predation, compel to carefully monitor its spread along the Patagonian coasts.

Strong genetic structure and signs of population bottlenecks in the land snailHumboldtiana durangoensisin the Sierra Madre Occidental of Western Mexico

Phylogeographic studies of different montane biological groups in Mexico have revealed complex patterns in a broad scale but an absence of genetic structure within local mountain systems such as the Sierra Madre Occidental. In this study, we estimate the genetic structure and demographic history of the endemic land snail Humboldtiana durangoensis within this mountain range. Nine polymorphic microsatellite loci in 178 individuals from 16 localities throughout the complete geographic distribution were analyzed. Strong deviations from Hardy–Weinberg equilibrium and low levels of heterozygosity were detected in the seven genetic clusters. The gene flow between two of the main geographic regions (North and South) was symmetric (≈4 individuals). In addition, the analysis detected changes in the effective population size indicating that both geographic regions experienced a drastic reduction in their effective population size probably associated with the Pleistocene climatic changes.

Lack of population genetic structure in the marine nematodes Ptycholaimellus pandispiculatus and Terschellingia longicaudata in beaches of the Persian Gulf, Iran

AbstractWe investigated genetic diversity and population genetic structure of two common benthic nematode species, Ptycholaimellus pandispiculatus and Terschellingia longicaudata, from sandy beaches in the area of Bandar Abbas (Iran), Persian Gulf. Based upon partial mitochondrial cytochrome oxidase c subunit 1 (COI) gene data, 17 and two haplotypes were found for P. pandispiculatus and Te. longicaudata, respectively. Analysis of molecular variance did not reveal a significant population genetic structure for either species. The absence of genetic structuring indicates substantial dispersal and gene flow in our study area. To assess the species structure of Te. longicaudata at a larger geographic scale, we compared 18S rDNA and COI sequences from Iran and the Scheldt Estuary in The Netherlands to ascertain whether they truly belong to the same species. Our data confirmed previous studies that Te. longicaudata likely constitutes a complex of multiple cryptic species, with one of these species having a (near) cosmopolitan distribution.

Genetic diversity of Diaphorina citri and its endosymbionts across east and south-east Asia.

Diaphorina citri is the vector of 'Candidatus Liberibacter asiaticus', the most widespread pathogen associated huanglongbing, the most serious disease of citrus. To enhance our understanding of the distribution and origin of the psyllid, we investigated the genetic diversity and population structures of 24 populations in Asia and one from Florida based on the mtCOI gene. Simultaneously, genetic diversity and population structures of the primary endosymbiont (P-endosymbiont) 'Candidatus Carsonella ruddii' and secondary endosymbiont (S-endosymbiont) 'Candidatus Profftella armatura' of D. citri were determined with the housekeeping genes. AMOVA analysis indicated that populations of D. citri and its endosymbionts in east and south-east Asia were genetically distinct from populations in Pakistan and Florida. Furthermore, P-endosymbiont populations displayed a strong geographical structure across east and south-east Asia, while low genetic diversity indicated the absence of genetic structure among the populations of D. citri and its S-endosymbiont across these regions. The 'Ca. C. ruddii' is more diverse and structured than the D. citri and the 'Ca. P. armatura' across east and south-east Asia. Multiple introductions of the psyllid have occurred in China. Management application for controlling the pest is proposed based on the genetic information of D. citri and its endosymbionts. © 2017 Society of Chemical Industry.

High gene flow in the American badger overrides habitat preferences and limits broadscale genetic structure.

Habitat associations are a function of habitat preferences and dispersal capabilities, both of which can influence how species responded to Quaternary climatic changes and contemporary habitat heterogeneity. Predicting resultant genetic structure is not always straightforward, especially in species where high dispersal potential and habitat preferences yield opposing predictions. The American badger has high dispersal capabilities that predict widespread panmixia, but avoids closed-canopy forests and clay soils, which could restrict gene flow and create ecologically based population genetic structure. We used mitochondrial sequence and microsatellite data sets to characterize how these opposing forces contribute to genetic structure in badgers at a continent-wide scale. Our data revealed an overall lack of ecologically based population genetic structure, suggesting that high dispersal capabilities were sufficiently realized to overcome most habitat-based genetic structure. At a broadscale, badger gene flow is limited only by geographic distance (isolation by distance) and large water barriers (Lake Michigan and the Mississippi River). The absence of genetic structure in a species with strong avoidance of unsuitable habitats advances our understanding of when and how genetic structure emerges in widespread, highly mobile species.

Ecology and population structure of a tree wound-infecting fungus in a native South African forest environment

Ceratocystis tsitsikammensis was first isolated from bark harvesting wounds on two indigenous tree species in the Afromontane forests of the Western Cape Province of South Africa. Inoculation studies indicated that it is a potential pathogen of native Rapanea melanophloeos trees. In this study, we investigated the distribution, ecology and biology of C. tsitsikammensis in the Garden Route National Park of South Africa. Isolates were obtained from wounds on R. melanophloeos, three non-native hosts as well as from nitidulid and staphylinid beetles visiting wounds on these trees. The genetic diversity and population biology of the fungus was examined using microsatellite markers. Its mating strategy was also determined by amplifying its mating type genes and the fungus was shown to be homothallic. Despite the homothallic nature of the fungus, high levels of random mating and absence of genetic structure was found in the investigated population, suggesting a strong effect of gene flow, probably linked to insect dispersal. The gene diversity of C. tsitsikammensis was similar to that of a related fungus, Ceratocystis albifundus, that is known to be native in Africa. This, together with the fact that C. tsitiskamensis is not known elsewhere, within or outside South Africa, suggests that it is native and endemic to the Cape Afromontane region.

Evolutionary history of birds across southern Australia: structure, history and taxonomic implications of mitochondrial DNA diversity in an ecologically diverse suite of species

Recent phylogeographic studies have examined the location and timing of putative Plio-Pleistocene bio-geographical barriers in moulding present-day patterns of diversity in southern Australian vertebrates. We previously investigated the divergence history of an assemblage of southern Australian birds. Here we more explicitly incorporate idiosyncratic effects of dietary ecology and habitat on the long-term demographic stability and the presence or absence of genetic structure on each of 12 species of bird. Our data suggest that the Eyrean Barrier (Flinders Ranges—Lake Eyre Basin) has been critical in shaping present-day diversity, especially that of mesic and mallee environments, and that other barriers (e.g. Murchison Barrier, Nullarbor Barrier) have played a lesser role. In contrast, nectarivory and occurrence in patchily distributed habitats are correlated with weak or no phylogeographic structure. Population expansions were most prevalent in western parts of species’ ranges. Substantial genetic divergences accompanied by moderate or no phenotypic divergence challenge traditional approaches to taxonomy in the Blue Bonnet (Northiella haematogaster), Chestnut Quail-thrush (Cinclosoma castanotum), White-eared Honeyeater (Nesoptilotis leucotis) and Scarlet Robin (Petroica boodang) and we suggest taxonomic treatments for each of these species that accommodate existing data. We elevate some taxa to species rank and note where further analyses of gene flow will be useful in clarifying remaining issues. Further phylogeographic study in the region of the Mount Lofty Ranges, Flinders Ranges, Spencer Gulf and Gulf St Vincent) of South Australia is warranted.

Absence of genetic structure in Baylisascaris schroederi populations, a giant panda parasite, determined by mitochondrial sequencing.

BackgroundInfection with the parasitic nematode, Baylisascaris schroederi (Ascaridida: Nematoda), is one of the most important causes of death in giant pandas, and was responsible for half of deaths between 2001 and 2005. Mitochondrial (mt) DNA sequences of parasites can unveil their genetic diversity and depict their likely dynamic evolution and therefore may provide insights into parasite survival and responses to host changes, as well as parasite control.MethodsBased on previous studies, the present study further annotated the genetic variability and structure of B. schroederi populations by combining two different mtDNA markers, ATPase subunit 6 (atp6) and cytochrome c oxidase subunit I (cox1). Both sequences were completely amplified and genetically analyzed among 57 B. schroederi isolates, which were individually collected from ten geographical regions located in three important giant panda habitats in China (Minshan, Qionglai and Qinling mountain ranges).ResultsFor the DNA dataset, we identified 20 haplotypes of atp6, 24 haplotypes of cox1, and 39 haplotypes of atp6 + cox1. Further haplotype network and phylogenetic analyses demonstrated that B. schroederi populations were predominantly driven by three common haplotypes, atp6 A1, cox1 C10, and atp6 + cox1 H11. However, due to low rates of gene differentiation between the three populations, both the atp6 and cox1 genes appeared not to be significantly associated with geographical divisions. In addition, high gene flow was detected among the B. schroederi populations, consistent with previous studies, suggesting that this parasite may be essentially homogenous across endemic areas. Finally, neutrality tests and mismatch analysis indicated that B. schroederi had undergone earlier demographic expansion.ConclusionsThese results confirmed that B. schroederi populations do not follow a pattern of isolation by distance, further revealing the possible existence of physical connections before geographic separation. This study should also contribute to an improved understanding of the population genetics and evolutionary biology of B. schroederi and assist in the control of baylisascariasis in giant pandas.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-014-0606-3) contains supplementary material, which is available to authorized users.

Should I stay or should I go? Dispersal and population structure in small, isolated desert populations of West African crocodiles.

The maintenance of both spatial and genetic connectivity is paramount to the long-term persistence of small, isolated populations living in environments with extreme climates. We aim to identify the distribution of genetic diversity and assess population sub-structuring and dispersal across dwarfed desert populations of Crocodylus suchus, which occur in isolated groups, usually less than five individuals, along the mountains of Mauritania (West Africa). We used both invasive and non-invasive sampling methods and a combination of mitochondrial DNA (12 S and ND4) and microsatellite markers (32 loci and a subset of 12 loci). Our results showed high genetic differentiation and geographic structure in Mauritanian populations of C. suchus. We identified a metapopulation system acting within four river sub-basins (high gene flow and absence of genetic structure) and considerable genetic differentiation between sub-basins (F ST range: 0.12–0.24) with rare dispersal events. Effective population sizes tend to be low within sub-basins while genetic diversity is maintained. Our study suggests that hydrographic networks (temporal connections along seasonal rivers during rainy periods) allow C. suchus to disperse and maintain metapopulation dynamics within sub-basins, which attenuate the loss of genetic diversity and the risk of extinction. We highlight the need of hydrographic conservation to protect vulnerable crocodiles isolated in small water bodies. We propose C. suchus as an umbrella species in Mauritania based on ecological affinities shared with other water-dependent species in desert environments.

Next‐generation sequencing for molecular ecology: a caveat regarding pooled samples

We develop a model based on the Dirichlet-compound multinomial distribution (CMD) and Ewens sampling formula to predict the fraction of SNP loci that will appear fixed for alternate alleles between two pooled samples drawn from the same underlying population. We apply this model to next-generation sequencing (NGS) data from Baltic Sea herring recently published by (Corander et al., 2013, Molecular Ecology, 2931-2940), and show that there are many more fixed loci than expected in the absence of genetic structure. However, we show through coalescent simulations that the degree of population structure required to explain the fraction of alternatively fixed SNPs is extraordinarily high and that the surplus of fixed loci is more likely a consequence of limited representation of individual gene copies in the pooled samples, than it is of population structure. Our analysis signals that the use of NGS on pooled samples to identify divergent SNPs warrants caution. With pooled samples, it is hard to diagnose when an NGS experiment has gone awry; especially when NGS data on pooled samples are of low read depth with a limited number of individuals, it may be worthwhile to temper claims of unexpected population differentiation from pooled samples, pending verification with more reliable methods or stricter adherence to recommended sampling designs for pooled sequencing e.g. Futschik & Schlötterer 2010, Genetics, 186, 207; Gautier et al., 2013a, Molecular Ecology, 3766-3779). Analysis of the data and diagnosis of problems is easier and more reliable (and can be less costly) with individually barcoded samples. Consequently, for some scenarios, individual barcoding may be preferable to pooling of samples.

Genetic variability of the neogregarine Apicystis bombi, an etiological agent of an emergent bumblebee disease.

The worldwide spread of diseases is considered a major threat to biodiversity and a possible driver of the decline of pollinator populations, particularly when novel species or strains of parasites emerge. Previous studies have suggested that populations of introduced European honeybee (Apis mellifera) and bumblebee species (Bombus terrestris and Bombus ruderatus) in Argentina share the neogregarine parasite Apicystis bombi with the native bumblebee (Bombus dahlbomii). In this study we investigated whether A. bombi is acting as an emergent parasite in the non-native populations. Specifically, we asked whether A. bombi, recently identified in Argentina, was introduced by European, non-native bees. Using ITS1 and ITS2 to assess the parasite’s intraspecific genetic variation in bees from Argentina and Europe, we found a largely unstructured parasite population, with only 15% of the genetic variation being explained by geographic location. The most abundant haplotype in Argentina (found in all 9 specimens of non-native species) was identical to the most abundant haplotype in Europe (found in 6 out of 8 specimens). Similarly, there was no evidence of structuring by host species, with this factor explaining only 17% of the genetic variation. Interestingly, parasites in native Bombus ephippiatus from Mexico were genetically distant from the Argentine and European samples, suggesting that sufficient variability does exist in the ITS region to identify continent-level genetic structure in the parasite. Thus, the data suggest that A. bombi from Argentina and Europe share a common, relatively recent origin. Although our data did not provide information on the direction of transfer, the absence of genetic structure across space and host species suggests that A. bombi may be acting as an emergent infectious disease across bee taxa and continents.

A mechanism that maintains alternative life histories in a loggerhead sea turtle population

Intrapopulation variation in habitat use is commonly seen among mobile animals, yet the mechanisms maintaining it have rarely been researched among untrackable species. To investigate how alternative life histories are maintained in a population of the loggerhead sea turtle (Caretta caretta), cumulative reproductive output was evaluated and compared between small planktivores inhabiting oceanic areas (with water depths > 200 m) and large benthivores inhabiting neritic areas (depths < 200 m) that sympatrically nested at Yakushima Island, Japan, from 1986 to 2011. In total, 362 nesting females sampled in three different years were classified into the two foraging groups based on stable isotope ratios in egg yolks. There were significant differences between the two foraging groups in most recorded life history parameters (clutch size, clutch frequency, breeding frequency, and remigration intervals), with the exception of emergence success. We did not find evidence of life history trade-offs, nor age-related changes in fecundity. Over the 26-year study period, we calculated a 2.4-fold greater reproductive output for neritic foragers than for oceanic ones, accounting for breeding and clutch frequency. Temporal consistencies in stable isotope ratios and remigration intervals within females suggested that female Japanese loggerheads show fidelity to respective foraging habitats throughout the adult stage. The large difference in productivity between the two groups was unlikely to be offset by the difference in survival during the period from aboveground emergence to first reproduction, suggesting that oceanic foragers have a lower level of fitness than neritic ones. Together with an absence of genetic structure between foraging groups, we infer that alternative life histories in a loggerhead turtle population are maintained by a conditional strategy.

Population demography and genetic structure of the fat greenling (Hexagrammos otakii) inferred from mtDNA control region sequence analyses

Pleistocene ice ages in addition to geographical and geological modifications have affected the natural range and habitat of marine organisms in Northwestern Pacific. The effects of glacial events have left a genomic signature, resulting in concordant phylogeographical structures among many species. To investigate the effects of Quaternary climatic changes on the evolution in H. otakii, fragments of 471 bp at the 5′ end of mitochondrial DNA control region were sequenced for 275 individuals from 10 localities in the Northern China and Japan. Both mismatch distribution analyses and neutrality tests suggested recent population expansion (64,000–227,000 years ago). Although estimated value of pairwise population differentiation (FST) was low, half (23 of 45) of the comparisons showed statistically significant. Coalescent-based estimates show that gene flow was asymmetric or directional, most of all comparisons (57 of 65) among populations showed low evaluation value of Nm (Nm < 10). Analysis of molecular variance (AMOVA) showed genetic structuring among groups when the data was partitioned into six groups in this study. The defined pattern of genetic variation suggested a crucial role of habitat requirement, marine current, marine gyres and history process. Absence of genetic structure over hundreds of kilometers between AO and assemblage of QD, RZ and GY might imply the common coalescent other than current gene flow. Specific exchange mechanism and fine scale genetic structure need further research using faster evolution molecular markers (microsatellite markers) and further sampling.

Lack of genetic structure among Eurasian populations of the tick Ixodesricinus contrasts with marked divergence from north-African populations

Host–parasite interactions may select for significant novel mutations with major evolutionary consequences for both partners. In poor active dispersers such as ticks, their population structures are shaped by their host movements. Here, we use population genetics and phylogeography to investigate the evolutionary history of the most common tick in Europe, Ixodes ricinus, a vector of pathogenic agents causing diseases in humans and animals. Two mitochondrial and four nuclear genes were sequenced for 60 individuals collected on four geographical scales (local, regional, Eurasian and western Palearctic scales). The overall level of nucleotide diversity was low and the variability did not differ at the local, regional or Eurasian scales but increased two fold for the western Palearctic scale. Moreover, the phylogenetic trees indicated an absence of genetic structure among Eurasian ticks, contrasting with a strong differentiation of the north-African ticks which formed a divergent clade. The homogeneity in Eurasian ticks may be explained by gene flows due to passive dispersal of ticks by hosts within a continuous population and recent range expansion of I. ricinus as shown by the fit of the observed frequency distribution of numbers of mismatches between pairwise sequences with the demographic expansion model (Harpending raggedness index, P=0.74). The genetic divergence of the north-African populations could be explained by genetic drift in these small populations that are geographically isolated and/or selection pressures due to different ecological conditions (seasonal activity, pathogenic agents and hosts communities). The consequences of these results on the epidemiology of vector-borne diseases are discussed.