Expansion Front Research Articles

First regional evaluation of nuclear genetic diversity and population structure in northeastern coyotes ( Canis latrans).

Previous genetic studies of eastern coyotes ( Canis latrans) are based on one of two strategies: sampling many individuals using one or very few molecular markers, or sampling very few individuals using many genomic markers. Thus, a regional analysis of genetic diversity and population structure in eastern coyotes using many samples and several molecular markers is lacking. I evaluated genetic diversity and population structure in 385 northeastern coyotes using 16 common single nucleotide polymorphisms (SNPs). A region-wide analysis of population structure revealed three primary genetic populations, but these do not correspond to the same three subdivisions inferred in a previous analysis of mitochondrial DNA sequences. More focused geographic analyses of population structure indicated that ample genetic structure occurs in coyotes from an intermediate contact zone where two range expansion fronts meet. These results demonstrate that genotyping several highly heterozygous SNPs in a large, geographically dense sample is an effective way to detect cryptic population genetic structure. The importance of SNPs in studies of population and wildlife genomics is rapidly increasing; this study adds to the growing body of recent literature that demonstrates the utility of SNPs ascertained from a model organism for evolutionary inference in closely related species.

First regional evaluation of nuclear genetic diversity and population structure in northeastern coyotes (Canis latrans)

Previous genetic studies of eastern coyotes ( Canis latrans ) are based on one of two strategies: sampling many individuals using one or very few molecular markers, or sampling very few individuals using many genomic markers. Thus, a regional analysis of genetic diversity and population structure in eastern coyotes using many samples and several molecular markers is lacking. I evaluated genetic diversity and population structure in 385 northeastern coyotes using 16 common single nucleotide polymorphisms (SNPs). A region-wide analysis of population structure revealed three primary genetic populations, but these do not correspond to the same three subdivisions inferred in a previous analysis of mitochondrial DNA sequences. More focused geographic analyses of population structure indicated that ample genetic structure occurs in coyotes from an intermediate contact zone where two range expansion fronts meet. These results demonstrate that genotyping several highly heterozygous SNPs in a large, geographically dense sample is an effective way to detect cryptic population genetic structure. The importance of SNPs in studies of population and wildlife genomics is rapidly increasing; this study adds to the growing body of recent literature that demonstrates the utility of SNPs ascertained from a model organism for evolutionary inference in closely related species.

Increased activity and growth rate in the non‐dispersive aquatic larval stage of a damselfly at an expanding range edge

Summary While evolutionary changes in adult traits during range expansion have been recorded in many species, similar changes in the non‐dispersive larval stage have only rarely been documented. Increased activity in the non‐dispersive larval stage is an important ecologically relevant trait in aquatic communities that may be expected to evolve in the edge populations (i) as a result of the combination of spatial sorting in dispersal‐related adult activity and a coupling between adult and larval behaviour and (ii) to meet higher energy demands to allow higher growth rates and a higher investment in costly dispersal‐related traits. We specifically address whether activity is higher in the larval non‐dispersive aquatic stage at an expanding range front by comparing larvae of replicated core and edge populations of the damselfly Coenagrion scitulum in three common garden experiments where larvae were reared from the egg stage. As expected, activity in the non‐dispersive larval stage was consistently higher in the edge populations. Although changes in larval activity probably have consequences for ecological interactions, the higher activity was not associated with increased predation rates by dragonfly larvae, potentially because of associated compensatory changes in other antipredator mechanisms. We documented one of the few cases of a positive coupling of activity in the larval and adult stages. Yet, contrary to larval activity, adult activity did not differ between core and edge populations. This indicates that the higher larval activity we documented is not shaped by a coupling with adult activity. Instead, our results are consistent with the hypothesis that a higher energy need in edge populations shaped the higher larval activity. Edge larvae showed a higher growth rate which is expected to evolve at the initial low population densities in newly founded edge populations. Moreover, higher growth rate showed the expected positive covariation with larval activity. Increases in activity in the non‐dispersive stage in edge populations at an expansion front should be included in the ongoing debate whether evolutionary changes at invasion fronts are driven by adaptive versus non‐adaptive evolution. Moreover, they may have the potential to affect ecological interactions at expanding range fronts.

Diabrotica virgifera virgifera LeConte wing shape variation reveals multiple populations across the European expansion front

Unterschiedliche Flugelauspragungen bei Diabrotica virgifera virgifera LeConte offenbaren das Vorhandensein multipler Populationen entlang der europaischen Ausbreitungsfront

The effects of chemical interactions and culture history on the colonization of structured habitats by competing bacterial populations

BackgroundBacterial habitats, such as soil and the gut, are structured at the micrometer scale. Important aspects of microbial life in such spatial ecosystems are migration and colonization. Here we explore the colonization of a structured ecosystem by two neutrally labeled strains of Escherichia coli. Using time-lapse microscopy we studied the colonization of one-dimensional arrays of habitat patches linked by connectors, which were invaded by the two E. coli strains from opposite sides.ResultsThe two strains colonize a habitat from opposite sides by a series of traveling waves followed by an expansion front. When population waves collide, they branch into a continuing traveling wave, a reflected wave and a stationary population. When the two strains invade the landscape from opposite sides, they remain segregated in space and often one population will displace the other from most of the habitat. However, when the strains are co-cultured before entering the habitats, they colonize the habitat together and do not separate spatially. Using physically separated, but diffusionally coupled, habitats we show that colonization waves and expansion fronts interact trough diffusible molecules, and not by direct competition for space. Furthermore, we found that colonization outcome is influenced by a culture’s history, as the culture with the longest doubling time in bulk conditions tends to take over the largest fraction of the habitat. Finally, we observed that population distributions in parallel habitats located on the same device and inoculated with cells from the same overnight culture are significantly more similar to each other than to patterns in identical habitats located on different devices inoculated with cells from different overnight cultures, even tough all cultures were started from the same −80°C frozen stock.ConclusionsWe found that the colonization of spatially structure habitats by two interacting populations can lead to the formation of complex, but reproducible, spatiotemporal patterns. Furthermore, we showed that chemical interactions between two populations cause them to remain spatially segregated while they compete for habitat space. Finally, we observed that growth properties in bulk conditions correlate with the outcome of habitat colonization. Together, our data show the crucial roles of chemical interactions between populations and a culture’s history in determining the outcome of habitat colonization.

崇明东滩盐沼植被扩散格局及其形成机制研究

长江河口盐沼植被的形成和演化是生物与其生长环境相互作用的结果。以崇明东滩盐沼植被典型扩散前沿为研究对象，2011至2012年期间调查了盐沼植被扩散前沿实生苗扩散、定居以及形成的扩散格局，同时测定了盐沼植被扩散前沿的潮滩冲淤动态和水文动力条件。研究结果表明，崇明东滩盐沼植被在扩散前沿形成了互花米草-光滩（<em>Spartina alterniflora </em>-Mudflat，SM）和互花米草-海三棱藨草-光滩（<em>Spartina alterniflora</em>-<em>Scirpus mariqueter </em>-Mudflat，SSM）两种典型的扩散格局。冲淤动态和水文动力条件是影响盐沼植被扩散格局的重要因子，尤其是在4-6月盐沼植物实生苗传播和定居的关键阶段。在此基础上，分析了东滩盐沼植被扩散前沿的生物-物理相互作用以及盐沼植被扩散格局的形成机制。研究结果不仅有助于理解长江河口地区盐沼植被扩散的生物物理过程，并对全球气候变化和海平面上升条件下滨海生态系统动态预测与湿地保护与管理具有重要的意义。;The range expansion of saltmarshes in the Yangtze Estuary depends on accretion of dynamic mudflats resulting from the large amount of silt brought down the Yangtze River. The formation and succession of saltmarsh vegetation is a result of the interaction between saltmarsh plants and their living environment. Over the last 15 years, rapid invasion of large areas of the saltmarshes of Chongming Dongtan by an exotic plant<em> Spartina alterniflora</em> has occurred. Two types of advancing fronts are found: the <em>S. alterniflora</em>-mudflat (SM) front and the <em>S. alterniflora</em>-<em>Scirpus mariqueter </em>-mudflat (SSM) front. The dynamic and natural characteristics of the coastal wetlands at Chongming Dongtan, both in terms of sediment deposition, salt marsh succession and biological invasion, make it an ideal place for studying the interaction between the range expansion of saltmarsh vegetation and the hydrodynamic regimes. In this study, we invested the seedling dispersal, establishment and formation of expansion pattern at the advancing fronts during the years of 2011 and 2012. At the same time, the accretion/erosion regime and hydrodynamic conditions at the saltmarsh expansion fronts were measured. The research aims were to: 1) test whether and how the hydrodynamic regimes govern the spatial structure of range expansion of saltmarshes at these two advancing fronts; 2) determine the interactions between the range expansion of saltmarsh and hydrodynamic regimes, and 3) understand the mechanisms underlying the range expansion of saltmarshes and their implications for the spatial structure of tidal saltmarshes. The results showed that the accretion/erosion regime and hydrodynamic condition, especially in the critical stage of seedling establishment during April-June, were the most important factors responsible for the formation of these two typical expansion patterns. The rate of range expansion at the SM front was much faster than the SSM front. The different colonization behaviors at these two types of advancing fronts could be related to the differences in hydrodynamic regimes. At the site with a regime of autumn/winter erosion and spring/summer accretion, the sediment accretion and seedling recruitment of <em>S. alterniflora</em> were much higher, while the wave energy and current velocity were relatively gentle during the critical period of seedling establishment. At such site, the original pioneer species of <em>S. mariqueter</em> was replaced by<em> S. alterniflora</em> and a SM pattern of range expansion developed. In contrast, at the site with a relatively stable autumn/winter accretion regime and relatively strong wave energy and current velocity during the critical period of seedling establishment, the original pioneer species of <em>S. mariqueter</em> could remain within the advancing front and a SSM pattern of range expansion developed. Based on these results, the impact of abiotic and biotic factors governing the range expansion of and its implications on the spatial structure of tidal saltmarshes are discussed. The results from this study can provide a valuable insight into the bio-physical interactions on the formation of expansion patterns and the mechanisms underlying the range expansion of saltmarshes in the Yangtze Estuary, which could be important for the maintenance of coastal saltmarsh resource and biodiversity as well as the dynamics prediction of coastal saltmarshes under the impact of climate change.

Patterns of genetic diversity reveal multiple introductions and recurrent founder effects during range expansion in invasive populations of Geranium carolinianum (Geraniaceae)

Genetic diversity, and thus the adaptive potential of invasive populations, is largely based on three factors: patterns of genetic diversity in the species' native range, the number and location of introductions and the number of founding individuals per introduction. Specifically, reductions in genetic diversity ('founder effects') should be stronger for species with low within-population diversity in their native range and few introductions of few individuals to the invasive range. We test these predictions with Geranium carolinianum, a winter annual herb native to North America and invasive in China. We measure the extent of founder effects using allozymes and microsatellites, and ask whether this is consistent with its colonization history and patterns of diversity in the native range. In the native range, genetic diversity is higher and structure is lower than expected based on life history traits. In China, our results provide evidence for multiple introductions near Nanjing, Jiangsu province, with subsequent range expansion to the west and south. Patterns of genetic diversity across China reveal weak founder effects that are driven largely by low-diversity populations at the expansion front, away from the introduction location. This suggests that reduced diversity in China has resulted from successive founder events during range expansion, and that the loss of genetic diversity in the Nanjing area was mitigated by multiple introductions from diverse source populations. This has implications for the future of G. carolinianum in China, as continued gene flow among populations should eventually increase genetic diversity within the more recently founded populations.

Rapid evolution of larval life history, adult immune function and flight muscles in a poleward‐moving damselfly

Although a growing number of studies have documented the evolution of adult dispersal-related traits at the range edge of poleward-expanding species, we know little about evolutionary changes in immune function or traits expressed by nondispersing larvae. We investigated differentiation in larval (growth and development) and adult traits (immune function and flight-related traits) between replicated core and edge populations of the poleward-moving damselfly Coenagrion scitulum. These traits were measured on individuals reared in a common garden experiment at two different food levels, as allocation trade-offs may be easier to detect under energy shortage. Edge individuals had a faster larval life history (growth and development rates), a higher adult immune function and a nearly significant higher relative flight muscle mass. Most of the differentiation between core and edge populations remained and edge populations had a higher relative flight muscle mass when corrected for latitude-specific thermal regimes, and hence could likely be attributed to the range expansion process per se. We here for the first time document a higher immune function in individuals at the expansion front of a poleward-expanding species and documented the rarely investigated evolution of faster life histories during range expansion. The rapid multivariate evolution in these ecological relevant traits between edge and core populations is expected to translate into changed ecological interactions and therefore has the potential to generate novel eco-evolutionary dynamics at the expansion front.

First Preliminary Results From U.S. Round-Robin Tests

The first preliminary results are reported from the U.S. Round-Robin Test on Plasma Expansion Speed. The tests were performed at the NASA Glenn Research Center on two coupons (six strings) of International Space Station (ISS) solar cell arrays, with a separate small array to obtain arcs (because it is so difficult to get ISS arrays to arc). ISS arrays were used because they have no exposed interconnects to act as bare current collectors and confuse the experimental results. The preconstructed ISS strings were laid out approximately parallel to the plasma expansion velocity to allow for the best test of the simple plasma expansion front current waveform model. Several Langmuir probes were arranged above and to the sides of the sample to allow for measurement of the plasma propagation speed. In the initial set of tests, primary arcs and the consequent current waveforms were measured in a Low Earth Orbit-type plasma. In a second set of tests, two electron guns with diffusers were used to provide an approximately uniform Geosynchronous Earth Orbit-type environment, and primary arcs and current waveforms were obtained. The objective of this and other round-robin tests is to characterize primary arc waveforms in terms of speed and degree of discharge of arc plasmas produced by primary arcs, and their dependences on environment, capacitance per unit area, arc voltage, temperature, and so on. The final goal is to allow engineering estimates of arc current peaks and half-widths to allow confident design and construction of space solar arrays, and to allow mitigation techniques to be evaluated. This is the first in an extended series of tests to be performed at six different U.S. facilities, and with participation from ten different U.S. organizations.

Long‐distance dispersal maximizes evolutionary potential during rapid geographic range expansion

Conventional wisdom predicts that sequential founder events will cause genetic diversity to erode in species with expanding geographic ranges, limiting evolutionary potential at the range margin. Here, we show that invasive European starlings (Sturnus vulgaris) in South Africa preserve genetic diversity during range expansion, possibly as a result of frequent long-distance dispersal events. We further show that unfavourable environmental conditions trigger enhanced dispersal, as indicated by signatures of selection detected across the expanding range. This brings genetic variation to the expansion front, counterbalancing the cumulative effects of sequential founding events and optimizing standing genetic diversity and thus evolutionary potential at range margins during spread. Therefore, dispersal strategies should be highlighted as key determinants of the ecological and evolutionary performances of species in novel environments and in response to global environmental change.

Cliff Swallow Breeding Range Expansion Along the Great Pee Dee River Corridor in the Carolinas

Petrochelidon pyrrhonota (Cliff Swallow) initially expanded its breeding range to the Great Pee Dee River corridor of the Carolinas in the early 1980s. In 2012, I documented approximately 1700 active nests of the Cliff Swallow at 20 colony sites in the Lower Piedmont of North Carolina and Coastal Plain of South Carolina along this river corridor. Cliff Swallows nested primarily at bridges and other water-based sites but also bred at several land-based sites, including the first colony documented at a highway overpass in the Carolinas. Compared to colony sizes in the early 1980s and mid-1990s at 3 major sites in North Carolina, numbers in 2012 were approximately 1500% and 400% higher, respectively. Before this study, Cliff Swallows nesting along the Great Pee Dee River was documented only as far as Cheraw, at the Fall Line. This study demonstrates that breeding now occurs 145 km farther south along this corridor at 6 sites, including 2 sites in the tidewater region of South Carolina. Several bridges along this corridor with favorable structural characteristics for breeding are still unoccupied. The breeding range expansion front of interior populations along and near the Great Pee Dee River has moved slowly (≈3.25 km/yr), in an apparently stepwise manner. However, the gap between expanding interior and coastal populations is confounding the pattern of range expansion in the Lower Coastal Plain of South Carolina.

Historical and Contemporary Population Genetics of the Invasive Western Corn Rootworm (Coleoptera: Chrysomelidae) in Croatia

Classical population genetic analyses were used to investigate populations of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in Croatia in 1996 and 2009. The number of alleles was low in both 1996 and 2009; however, more alleles were found in the putative populations surveyed in 2009. Croatia had only 51% of the alleles recorded from the United States and 69% from Europe. However, 10 private (unique) alleles were found in Croatia, which were not found previously in Europe. Most populations were out of Hardy-Weinberg equilibrium, although no linkage disequilibrium was found. Low to no genetic differentiation was found between population pairwise comparisons in 1996, with a greater level of differentiation found between populations sampled in 2009. Using the program STRUCTURE, a single genetic cluster was found for populations sampled in 1996 and 2009. However, two genetic clusters were detected when the 1996 and 2009 data were combined, indicating significant temporal differentiation. Isolation by distance pattern of gene flow characterized populations sampled in 2009 only when the most distant population of Ogulin (the head of the expansion front) was included in the analysis. When Ogluin was excluded from the 2009 analysis no isolation by distance pattern was found. The possible impact that control practices have had on the population genetics of D. v. virgifera in Croatia from 1996 to 2009 are discussed in light of the temporal genetics differences found.

A process-based grid model for the simulation of range expansion of Spartina alterniflora on the coastal saltmarshes in the Yangtze Estuary

Spartina alterniflora has been widely introduced to many coastal and estuarine regions of the world as a species for ecological engineering and this species has been spreading rapidly and widely along the Chinese coastline for the past 30 years. Based on four years of field measurements at the Chongming Dongtan wetland in the Yangtze Estuary, a process-based grid model of spatio-temporal range expansion for S. alterniflora was developed. The model incorporated the seasonal patterns of seed bank dynamics, seedling establishment, clonal propagation and vegetative growth, while also considering the effects of hydrodynamic conditions on the range expansion of S. alterniflora in the coastal saltmarshes. Modelling of a survey strip over a single year on the Dongtan wetland showed that the simulated spread pattern agreed with the actual pattern recorded during the growing season (March–September) with an accuracy of 90–95%, based on the estimations of seed bank dynamics and seedling establishment. On a wider spatio-temporal scale, an 8 year simulation showed that the patterns of range expansion of S. alterniflora are amenable to spatially-explicit modelling that takes spatio-temporal processes into account, mainly due to the aggregation effects of clonal integration in patches. Hydrodynamic conditions and niche availability were the most important factors controlling the expansion rate of S. alterniflora on the seaward expansion front. However, the actual expansion rate of S. alterniflora has slowed down in recent years due to the reduction in the sediment load of the Yangtze River following the completion of the Three Gorges Dam Project. There remain several uncertain issues relating to the model setup and its predictive capacity in terms of environmental variability and the stochasticity that is inherent in the modelling of the reproduction, dispersal and survival of S. alterniflora. Furthermore, an update of the model is needed linked to the sediment dynamics seasonality of hydrodynamic conditions in the Yangtze Estuary. In conclusion, this modelling approach provided valuable insights into the life-cycle mechanisms and range expansion processes of S. alterniflora under the current conditions. We suggest the potential application of this model in comparing various control strategies.

Rapid range expansion increases genetic differentiation while causing limited reduction in genetic diversity in a damselfly

Many ectothermic species are currently expanding their geographic range due to global warming. This can modify the population genetic diversity and structure of these species because of genetic drift during the colonization of new areas. Although the genetic signatures of historical range expansions have been investigated in an array of species, the genetic consequences of natural, contemporary range expansions have received little attention, with the only studies available focusing on range expansions along a narrow front. We investigate the genetic consequences of a natural range expansion in the Mediterranean damselfly Coenagrion scitulum, which is currently rapidly expanding along a broad front in different directions. We assessed genetic diversity and genetic structure using 12 microsatellite markers in five centrally located populations and five recently established populations at the edge of the geographic distribution. Our results suggest that, although a marginal significant decrease in the allelic richness was found in the edge populations, genetic diversity has been preserved during the range expansion of this species. Nevertheless, edge populations were genetically more differentiated compared with core populations, suggesting genetic drift during the range expansion. The smaller effective population sizes of the edge populations compared with central populations also suggest a contribution of genetic drift after colonization. We argue and document that range expansion along multiple axes of a broad expansion front generates little reduction in genetic diversity, yet stronger differentiation of the edge populations.

Quaternary range and demographic expansion of Liolaemus darwinii (Squamata: Liolaemidae) in the Monte Desert of Central Argentina using Bayesian phylogeography and ecological niche modelling

Until recently, most phylogeographic approaches have been unable to distinguish between demographic and range expansion processes, making it difficult to test for the possibility of range expansion without population growth and vice versa. In this study, we applied a Bayesian phylogeographic approach to reconstruct both demographic and range expansion in the lizard Liolaemus darwinii of the Monte Desert in Central Argentina, during the Late Quaternary. Based on analysis of 14 anonymous nuclear loci and the cytochrome b mitochondrial DNA gene, we detected signals of demographic expansion starting at ~55ka based on Bayesian Skyline and Skyride Plots. In contrast, Bayesian relaxed models of spatial diffusion suggested that range expansion occurred only between ~95 and 55ka, and more recently, diffusion rates were very low during demographic expansion. The possibility of population growth without substantial range expansion could account for the shared patterns of demographic expansion during the Last Glacial Maxima (OIS 2 and 4) in fish, small mammals and other lizards of the Monte Desert. We found substantial variation in diffusion rates over time, and very high rates during the range expansion phase, consistent with a rapidly advancing expansion front towards the southeast shown by palaeo-distribution models. Furthermore, the estimated diffusion rates are congruent with observed dispersal rates of lizards in field conditions and therefore provide additional confidence to the temporal scale of inferred phylogeographic patterns. Our study highlights how the integration of phylogeography with palaeo-distribution models can shed light on both demographic and range expansion processes and their potential causes.

The supernova remnant W51C: a plausible source of galactic cosmic rays?

Supernova remnants are a probable site of acceleration of particles via diffusive shock processes. High energies carried by electrons or protons are radiated into photons detectable from radio to γ rays. MAGIC has recently observed W51C, one of the most luminous galactic supernova remnants, and completed its spectrum between 50 GeV and 5 TeV. We modelled different processes for high energy photon emission of this source, and compared the predictions with the measured spectral energy distribution. It is plausible that hadrons are accelerated in the expansion front of this source, in interaction with the surrounding molecular cloud, and photons are produced in the decay of neutral mesons created in hadronic collisions.

Behavior of substorm auroral arcs and Pi2 waves: implication for the kinetic ballooning instability

Abstract. We present synoptic observations of the 21 December 2006 substorm event by the THEMIS ground-based All-Sky-Imagers, the ISUAL CCD Imager aboard the FORMOSAT-2 satellite, the geosynchronous satellites and the ground-based magnetometers, and discuss the implication of the observations. There are three subsequent arc breakups with time separation of &lt;1 min during the substorm expansion phase. In particular, we investigated the mode number of the substorm arc bead-like structure and the concurrent behavior of the arc intensity, the westward electroject intensity, and the ground Pi2 pulsation amplitude. Prior to each arc breakup there was a clear azimuthally-spaced bright spot structure along the arc with high mode number (~140–180) and the arc intensity increased together with the westward electrojet and the ground Pi2 pulsation amplitude under the arc. The Pi1 perturbations observed under the arc appeared at or after the arc breakup started. This suggests that the Pi2 pulsation is related to the arc formation. The Pi2 pulsation may be caused by the kinetic ballooning instability (KBI) that is excited in the strong cross-tail current region. The longitudinal extent of the earthward expansion front of the substorm dipolarization region at the geosynchronous orbit is estimated from timings of the energetic proton and electron injections and is roughly located between ~19.50 MLT and ~23.00 MLT, which is consistent with the corresponding longitudinal extent of the auroral substorm activity.

Exploring neutral and adaptive processes in expanding populations of gilthead sea bream, Sparus aurata L., in the North-East Atlantic.

Recent studies in empirical population genetics have highlighted the importance of taking into account both neutral and adaptive genetic variation in characterizing microevolutionary dynamics. Here, we explore the genetic population structure and the footprints of selection in four populations of the warm-temperate coastal fish, the gilthead sea bream (Sparus aurata), whose recent northward expansion has been linked to climate change. Samples were collected at four Atlantic locations, including Spain, Portugal, France and the South of Ireland, and genetically assayed using a suite of species-specific markers, including 15 putatively neutral microsatellites and 23 expressed sequence tag-linked markers, as well as a portion of the mitochondrial DNA (mtDNA) control region. Two of the putatively neutral markers, Bld-10 and Ad-10, bore signatures of strong directional selection, particularly in the newly established Irish population, although the potential 'surfing effect' of rare alleles at the edge of the expansion front was also considered. Analyses after the removal of these loci suggest low but significant population structure likely affected by some degree of gene flow counteracting random genetic drift. No signal of historic divergence was detected at mtDNA. BLAST searches conducted with all 38 markers used failed to identify specific genomic regions associated to adaptive functions. However, the availability of genomic resources for this commercially valuable species is rapidly increasing, bringing us closer to the understanding of the interplay between selective and neutral evolutionary forces, shaping population divergence of an expanding species in a heterogeneous milieu.

THE 2011 FEBRUARY 15 X2 FLARE, RIBBONS, CORONAL FRONT, AND MASS EJECTION: INTERPRETING THE THREE-DIMENSIONAL VIEWS FROM THESOLAR DYNAMICS OBSERVATORYANDSTEREOGUIDED BY MAGNETOHYDRODYNAMIC FLUX-ROPE MODELING

The 2011 February 15 X2.2 flare and associated Earth-directed halo coronal mass ejection were observed in unprecedented detail with high resolution in spatial, temporal, and thermal dimensions by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory, as well as by instruments on the two STEREO spacecraft, then at near-quadrature relative to the Sun-Earth line. These observations enable us to see expanding loops from a flux-rope-like structure over the shearing polarity-inversion line between the central δ-spot groups of AR 11158, developing a propagating coronal front (EIT wave), and eventually forming the coronal mass ejection moving into the inner heliosphere. The observations support the interpretation that all of these features, including the EIT wave, are signatures of an expanding volume traced by loops (much larger than the flux rope only), surrounded by a moving front rather than predominantly wave-like perturbations; this interpretation is supported by previously published MHD models for active-region and global scales. The lateral expansion of the eruption is limited to the local helmet-streamer structure and halts at the edges of a large-scale domain of connectivity (in the process exciting loop oscillations at the edge of the southern polar coronal hole). The AIA observations reveal that plasma warming occurs within the expansion front as it propagates over quiet Sun areas. This warming causes dimming in the 171 A (Fe IX and Fe X) channel and brightening in the 193 and 211 A (Fe XII-XIV) channels along the entire front, while there is weak 131 A (Fe VIII and Fe XXI) emission in some directions. An analysis of the AIA response functions shows that sections of the front running over the quiet Sun are consistent with adiabatic warming; other sections may require additional heating which MHD modeling suggests could be caused by Joule dissipation. Although for the events studied here the effects of volumetric expansion are much more obvious than true wave phenomena, we discuss how different magnetic environments within and around the erupting region can lead to the signatures of either or both of these aspects.

Dispersal in the course of an invasion

Invasive species receive attention as manifestations of global ecological change and because of the effects that they may have on other organisms. They are commonly discussed in the context of the ecological perturbations or the human activities that permitted the invasion. There is also evidence, that there is an intrinsic component to biological invasions in that evolutionary changes of the invaders themselves can facilitate or limit invasions (Lee 2002; Urban et al. 2007; Van Bocxlaer et al. 2010). Hence, teasing apart whether environmental change or changes of the organism foster invasions is an interesting field of research. Ample evidence for plants and animals documents that ecological change and human activities trigger range expansions and invasions, but questions regarding evolutionary change of invaders remain less explored although there are several reasons to believe it matters. Firstly, rapid evolutionary change is possible in time-frames relevant for contemporary biological invasions(Hendry et al. 2007). Furthermore, population genetic modelling suggests that there are circumstances where the range expansion and colonization of empty spaces in the course of an invasion can induce evolutionary change in a way that is specific to invaders: the process of repeated founding out of marginal populations in the course of a range expansion can shift allele frequencies and has been referred to as allele surfing, which not only affects neutral genetic variance, but also fitness relevant traits (Klopfstein et al. 2006; Travis et al. 2007; Burton & Travis 2008). Importantly, this process poses a null model for evolutionary inference in invasive populations. It predicts conspicuous allele frequency changes in an expanding metapopulation unless migration homogenizes the gene pool. Despite this relevance, ideas about allele surfing rely heavily on modelling although some experimental evidence comes from studies that document the segregation of genetic variants in growing plaques of bacteria (Hallatschek et al. 2007). To date, little empirical data is available that would reveal the migration processes that affect the establishment of gene pools at invasion fronts in natural systems. This aspect sets the study of Bronnenhuber et al. (2011) apart. They quantify migration behind the expansion front of an invading fish and thus provide important baseline data for the interpretation of the emerging patterns of genetic differentiation.