Molecular data provide strong evidence of natural hybridization between native and introduced lineages of <Emphasis Type="Italic">Phragmites australis</Emphasis> in North America

Hybridization, both within and between taxa, can be an important evolutionary stimulus for bioinvasions. Novel intra-taxon hybridizations may arise either between formerly allopatric introduced lineages, or between native and introduced lineages. The latter can occur following a cryptic invasion of a non-native lineage, such as the nineteenth century introduction to North America of a European lineage of the common reed Phragmites australis. Previous studies found no evidence of natural hybridization between native and introduced lineages of P. australis, but produced some F₁ hybrids under experimental conditions when the seed parent was native and the pollen parent was introduced. In this study we used microsatellite data to compare genotypes of P. australis along a transect of approximately 2,000 km in eastern North America. Although hybridization appears uncommon, simulations and principle component analysis of genetic data provided strong evidence for natural hybridization at two sites adjacent to Lake Erie in which native and introduced lineages were sympatric. The seed parent was the native lineage in some cases, and the introduced lineage in other cases. There is now the potential for P. australis hybrids to become increasingly invasive, and managers should consider as a priority the removal of introduced stands from sites where they co-exist with native stands.     

Common reed (Phragmites australis) invasion and amphibian distribution in freshwater wetlands

Invasive plants can substantially modify wetland structure and animal distribution patterns. In eastern North America, a Eurasian haplotype of the common reed (Phragmites australis, haplotype M) is invading wetlands. We studied the invasion of common reed in freshwater wetlands of an urbanized landscape and its effects on the distribution of amphibians at different life stages. Specifically, we hypothesized that the probability of reed invasion would be greatest in wetlands near anthropic disturbances. We predicted that the probability of desiccation at sampling stations increases with reed cover. Furthermore, we expected that wetlands invaded by common reed would have lower amphibian abundances, apparent survival, and rates of recruitment. We conducted trapping surveys to compare anuran assemblages of tadpoles, juveniles, and adults in 50 wetlands during two field seasons. The probability of reed invasion in wetlands increased with the cover of heavily-managed areas within 1,000 m and the distance to the nearest forest, but decreased with the length of roads within 1,000 m. The probability of station desiccation increased with reed cover. We found no evidence of a negative effect of reed presence on anuran population parameters, at any life stage. Landscape variables, such as the percent cover of forest or heavily-managed areas within a given radius from each wetland, influenced the abundance or the apparent survival of juvenile frogs and the abundance of ranid tadpoles. Our results show that amphibian patterns depend more strongly on the structure of the landscape surrounding wetlands than on exotic reed invasion in wetlands.     

Preadaptation and post‐introduction evolution facilitate the invasion of Phragmites australis in North America

Compared with non‐invasive species, invasive plant species may benefit from certain advantageous traits, for example, higher photosynthesis capacity and resource/energy‐use efficiency. These traits can be preadapted prior to introduction, but can also be acquired through evolution following introduction to the new range. Disentangling the origins of these advantageous traits is a fundamental and emerging question in invasion ecology. We conducted a multiple comparative experiment under identical environmental condition with the invasive haplotype M lineage of the wetland grass Phragmites australis and compared the ecophysiological traits of this invasive haplotype M in North America with those of the European ancestor and the conspecific North American native haplotype E lineage, P. australis ssp. americanus. The invasive haplotype M differed significantly from the native North American conspecific haplotype E in several ecophysiological and morphological traits, and the European haplotype M had a more efficient photosynthetic apparatus than the native North American P. australis ssp. americanus. Within the haplotype M lineage, the introduced North American P. australis exhibited different biomass allocation patterns and resource/energy‐use strategies compared to its European ancestor group. A discriminant analysis of principal components separated the haplotype M and the haplotype E lineages completely along the first canonical axis, highly related to photosynthetic gas‐exchange parameters, photosynthetic energy‐use efficiency and payback time. The second canonical axis, highly related to photosynthetic nitrogen use efficiency and construction costs, significantly separated the introduced P. australis in North America from its European ancestor. Synthesis. We conclude that the European P. australis lineage was preadapted to be invasive prior to its introduction, and that the invasion in North America is further stimulated by rapid post‐introduction evolution in several advantageous traits. The multicomparison approach used in this study could be an effective approach for distinguishing preadaptation and post‐introduction evolution of invasive species. Further research is needed to link the observed changes in invasive traits to the genetic variation and the interaction with the environment.     

Heteroplasmy due to chloroplast paternal leakage: another insight into <Emphasis Type="Italic">Phragmites</Emphasis> haplotypic diversity in North America

Chloroplasts contain several copies of their DNA, and intra-individual haplotypic variation (heteroplasmy) is common in plants, but unexplored in the cosmopolitan genus Phragmites. The aims of this study were to assess if heteroplasmy due to paternal leakage of the chloroplast occurs in Phragmites and which new insights into the evolutionary history of Phragmites australis in North America can be identified from the heteroplasmic variation. Eight non-native P. australis haplotypes occur in North America and can interbreed with P. australis ssp. americanus and P. australis var. berlandieri, creating opportunities for biparental inheritance of distinctive haplotypes. The polymorphism in the trnT-trnL sequence length revealed seventeen cases of heteroplasmy worldwide, in contact zones of distantly related haplotypes and in known hybrid populations, nine of which occurred in North America. In America, the cloned sequences, combined with nuclear markers, identified recombined haplotypes between native P. australis ssp. americanus and invasive P. australis haplotype M, and between the species P. mauritianus and P. australis, due to chloroplast paternal leakage. The occurrence of heteroplasmy and recombined haplotypes suggest a local origin for some of the rare non-native haplotypes occurring in North America, and plastid leakage events in the evolutionary histories of P. australis ssp. americanus and P. australis var. berlandieri.     

Invasive and Non-Invasive Congeners Show Similar Trait Shifts between Their Same Native and Non-Native Ranges

Differences in morphological or ecological traits expressed by exotic species between their native and non-native ranges are often interpreted as evidence for adaptation to new conditions in the non-native ranges. In turn this adaptation is often hypothesized to contribute to the successful invasion of these species. There is good evidence for rapid evolution by many exotic invasives, but the extent to which these evolutionary changes actually drive invasiveness is unclear. One approach to resolving the relationship between adaptive responses and successful invasion is to compare traits between populations from the native and non-native ranges for both exotic invaders and congeners that are exotic but not invasive. We compared a suite of morphological traits that are commonly tested in the literature in the context of invasion for three very closely related species of Centaurea, all of which are sympatric in the same native and non-native ranges in Europe and North America. Of these, C. solstitialis is highly invasive whereas C. calcitrapa and C. sulphurea are not. For all three species, plants from non-native populations showed similar shifts in key traits that have been identified in other studies as important putative adaptive responses to post-introduction invasion. For example, for all three species plants from populations in non-native ranges were (i) larger and (ii) produced seeds that germinated at higher rates. In fact, the non-invasive C. calcitrapa showed the strongest trait shift between ranges. Centaurea solstitialis was the only species for which plants from the non-native range increased allocation to defensive spines, and allocated proportionally less resources to reproduction, patterns contrary to what would be predicted by theory and other empirical studies to enhance invasion. Our results suggest caution when interpreting the commonly observed increase in size and reproductive capacity as factors that cause exotics to become invaders.     

Seeds contribute strongly to the spread of the invasive genotype of the common reed (<Emphasis Type="Italic">Phragmites australis</Emphasis>)

The introduced subspecies of the common reed (Phragmites australis (Cav.) Trin. ex Steud. subsp. australis; Poaceae) is considered one of the most invasive plants in North American wetlands. Given its relatively low seed set and its tremendous capacity to spread via stolons or rhizomes, it has generally been thought that the spread of vegetative diaspores was responsible for the establishment of new populations. To test this hypothesis, we sampled a single plant from each of 345 visually-distinct common reed stands located along the shores of Lake St. François (southern Quebec, Canada). With a set of six nuclear microsatellite markers, we distinguished 134 different genotypes. The number of individuals sharing the same genotype ranged from one to 16, and averaged 2.1. Most genotypes were encountered only once. We examined the spatial distribution of the most frequent genotypes and found little evidence of clusters along the lakeshore. These data contradict the hypothesis that a common reed invasion is initiated by the introduction of vegetative diaspores from a few clones. Rather, they clearly support the alternative hypothesis that seeds were the primary diaspores responsible for the establishment of common reed populations.     

Genetic and epigenetic changes during the invasion of a cosmopolitan species (Phragmites australis)

While many introduced invasive species can increase genetic diversity through multiple introductions and/or hybridization to colonize successfully in new environments, others with low genetic diversity have to persist by alternative mechanisms such as epigenetic variation. Given that Phragmites australis is a cosmopolitan reed growing in a wide range of habitats and its invasion history, especially in North America, has been relatively well studied, it provides an ideal system for studying the role and relationship of genetic and epigenetic variation in biological invasions. We used amplified fragment length polymorphism (AFLP) and methylation‐sensitive (MS) AFLP methods to evaluate genetic and epigenetic diversity and structure in groups of the common reed across its range in the world. Evidence from analysis of molecular variance (AMOVA) based on AFLP and MS‐AFLP data supported the previous conclusion that the invasive introduced populations of P. australis in North America were from European and Mediterranean regions. In the Gulf Coast region, the introduced group harbored a high level of genetic variation relative to originating group from its native location, and it showed epigenetic diversity equal to that of the native group, if not higher, while the introduced group held lower genetic diversity than the native. In the Great Lakes region, the native group displayed very low genetic and epigenetic variation, and the introduced one showed slightly lower genetic and epigenetic diversity than the original one. Unexpectedly, AMOVA and principal component analysis did not demonstrate any epigenetic convergence between native and introduced groups before genetic convergence. Our results suggested that intertwined changes in genetic and epigenetic variation were involved in the invasion success in North America. Although our study did not provide strong evidence proving the importance of epigenetic variation prior to genetic, it implied the similar role of stable epigenetic diversity to genetic diversity in the adaptation of P. australis to local environment.     

Replacement of estuarine communities by an exotic shrub: distribution and invasion history of Baccharis halimifolia in Europe

Baccharis halimifolia L. (Asteraceae) is a shrub native to North America which is invading estuarine communities in Europe. We report the invasion history and the distribution limits of B. halimifolia in Europe, with particular emphasis on the frequency of its presence in estuarine communities in Spain. B. halimifolia has been cultivated in Europe since the 17th century to present. It was first recorded as naturalized in the Bay of Biscay in 1906, where it forms currently stable and locally abundant populations in almost all the estuaries of Northern Spain and Western France. The ongoing invasion to the west could reach well conserved estuarine communities in Galicia (Spain). B. halimifolia also forms scattered populations in Northern and Southern France, Belgium, Netherlands, United Kingdom and Italy. In these countries it has experienced a rapid expansion during the last years. In Northern Spain, subhalophilous communities dominated by rush (Juncus maritimus) and/or sea couch (Elytrigia atherica), common reed stands (Phragmites australis) and ungrazed wet meadows are the most vulnerable to invasion. The subhalophilous communities are part of natural habitats of community interest according to the habitats directive 92/43/EEC. In some areas of Northern Spain these communities have been totally replaced by monospecific stands of B. halimifolia. In contrast, halophilous communities of the low marsh are resistant to invasion, suggesting that the survival of B. halimifolia may be limited by threshold values of salinity and waterlogging. With this study we want to raise awareness about the risk of replacement of estuarine subhalophilous communities by the ongoing invasion of B. halimifolia in Europe.     

Slipping through the Cracks: The Taxonomic Impediment Conceals the Origin and Dispersal of Haminoea japonica,an Invasive Species with Impacts to Human Health

Haminoea japonica is a species of opisthobranch sea slug native to Japan and Korea. Non-native populations have spread unnoticed for decades due to difficulties in the taxonomy of Haminoea species. Haminoea japonica is associated with a schistosome parasite in San Francisco Bay, thus further spread could have consequence to human health and economies. Anecdotal evidence suggests that H. japonica has displaced native species of Haminoea in North America and Europe, becoming locally dominant in estuaries and coastal lagoons. In this paper we study the population genetics of native and non-native populations of H. japonica based on mt-DNA data including newly discovered populations in Italy and France. The conclusions of this study further corroborate a Northeastern Japan origin for the non-native populations and suggest possible independent introductions into North America and Europe. Additionally, the data obtained revealed possible secondary introductions within Japan. Although non-native populations have experienced severe genetic bottlenecks they have colonized different regions with a broad range of water temperatures and other environmental conditions. The environmental tolerance of this species, along with its ability to become dominant in invaded areas and its association with a schistosome parasite, suggest H. japonica could be a dangerous invasive species.     

Living in two worlds: Evolutionary mechanisms act differently in the native and introduced ranges of an invasive plant

Identifying the factors that influence spatial genetic structure among populations can provide insights into the evolution of invasive plants. In this study, we used the common reed (Phragmites australis), a grass native in Europe and invading North America, to examine the relative importance of geographic, environmental (represented by climate here), and human effects on population genetic structure and its changes during invasion. We collected samples of P. australis from both the invaded North American and native European ranges and used molecular markers to investigate the population genetic structure within and between ranges. We used path analysis to identify the contributions of each of the three factors—geographic, environmental, and human‐related—to the formation of spatial genetic patterns. Genetic differentiation was observed between the introduced and native populations, and their genetic structure in the native and introduced ranges was different. There were strong effects of geography and environment on the genetic structure of populations in the native range, but the human‐related factors manifested through colonization of anthropogenic habitats in the introduced range counteracted the effects of environment. The between‐range genetic differences among populations were mainly explained by the heterogeneous environment between the ranges, with the coefficient 2.6 times higher for the environment than that explained by the geographic distance. Human activities were the primary contributor to the genetic structure of the introduced populations. The significant environmental divergence between ranges and the strong contribution of human activities to the genetic structure in the introduced range suggest that invasive populations of P. australis have evolved to adapt to a different climate and to human‐made habitats in North America.     

Jack-and-Master Trait Responses to Elevated CO2 and N: A Comparison of Native and Introduced Phragmites australis

Global change is predicted to promote plant invasions world-wide, reducing biodiversity and ecosystem function. Phenotypic plasticity may influence the ability of introduced plant species to invade and dominate extant communities. However, interpreting differences in plasticity can be confounded by phylogenetic differences in morphology and physiology. Here we present a novel case investigating the role of fitness trait values and phenotypic plasticity to global change factors between conspecific lineages of Phragmites australis. We hypothesized that due to observed differences in the competitive success of North American-native and Eurasian-introduced P. australis genotypes, Eurasian-introduced P. australis would exhibit greater fitness in response to global change factors. Plasticity and plant performance to ambient and predicted levels of carbon dioxide and nitrogen pollution were investigated to understand how invasion pressure may change in North America under a realistic global change scenario. We found that the introduced Eurasian genotype expressed greater mean trait values in nearly every ecophysiological trait measured – aboveground and belowground – to elevated CO₂ and nitrogen, outperforming the native North American conspecific by a factor of two to three under every global change scenario. This response is consistent with “jack and master” phenotypic plasticity. We suggest that differences in plant nitrogen productivity, specific leaf area, belowground biomass allocation, and inherently higher relative growth rate are the plant traits that may enhance invasion of Eurasian Phragmites in North America. Given the high degree of genotypic variability within this species, and our limited number of genotypes, our results must be interpreted cautiously. Our study is the first to demonstrate the potential importance of jack-and-master phenotypic plasticity in plant invasions when facing imminent global change conditions. We suggest that jack-and-master invasive genotypes and/or species similar to introduced P. australis will have an increased ecological fitness, facilitating their invasion in both stressful and resource rich environments.     

Condition status and parasite infection of Neogobius kessleri and N. melanostomus (Gobiidae) in their native and non-native area of distribution of the Danube River

The success of introduced species is often facilitated by escape from the effects of natural predators and parasites. Introduced species can profit from this favourable situation, attaining higher population densities and greater individual sizes in novel areas. In this study, somatic condition and parasite infection were compared between native and non-native populations of Neogobius kessleri Günther; introduced only within the interconnected Danube and Rhine River system, and N. melanostomus (Pallas); widely introduced throughout several river systems in Europe and North America. Higher values of Fulton’s condition factor were observed in non-native populations of both goby species. Neogobius melanostomus attained higher gonadosomatic index values in non-native populations, indicating potential increased investment in reproduction in its new area. A lower splenosomatic index was observed in non-native populations, especially in N. melanostomus. Parasite infracommunity richness and mean abundance were higher in N. kessleri in both native and non-native populations, suggesting higher susceptibility of N. kessleri to these parasites. Non-native populations of both hosts showed higher infra-community richness as a result of acquiring parasites native to the new area, but lower parasite abundance. Differences in success of the introduction and establishment in new areas between the two fish species may be associated with a relatively low parasite infection rate and a higher gonadosomatic index in non-native populations of N. melanostomus in comparison to N. kessleri.     

Changes inPhragmites australis in south-eastern Australia: A habitat assessment

The status of common reed (Phragmites australis) in south-eastern Australia was assessed by considering its physical habitat.Phragmites habitats were categorized into three types — wetland, riverine and estuarine and all three showed negative change (loss, degradation) since European settlement. However, there were also instances of positive (new, re-establishment) changes. Integrating these negative and positive changes at the catchment scale for the Murrumbidgee River, suggests a re-distribution ofPhragmites is occurring, and this may be true for other rivers managed for irrigation. Agriculture appears to be the principal cause ofPhragmites australis losses in eastern Australia. There is no evidence to date of reed decline in Australia like that in parts of Europe, nor of expansion as in the coastal wetlands of the United States of America. The habitat approach used here was qualitative but this was necessary due to the lack of historical data onPhragmites and to the limited number of case studies. However, quantitative studies are needed, in order to understand how river health and aquatic biodiversity are being affected.     

Haplotype diversity of mt<Emphasis Type="Italic">COI</Emphasis> in the fall webworm <Emphasis Type="Italic">Hyphantria cunea</Emphasis> (Lepidoptera: Arctiidae) in introduced regions in China,Iran, Japan,Korea, and its homeland,the United States

Hyphantria cunea (Drury) has colonized many countries outside its native range of North America and has become a model species for studies of the colonization and subsequent adaptation of agricultural pests. Molecular genetic analyses can clarify the origin and subsequent adaptations to non-native habitats. Using the mitochondrial COI gene, we examined the genetic relationships between invasive populations (China, Iran, Japan, and Korea) and native populations (i.e., the United States). The Jilin (China) and Guilan (Iran) populations showed nine previously unknown haplotypes that differed from those found in the south–central United States, suggesting multiple colonization events and different regions of invasion. A dominant mtDNA haplotype in populations in the United States was shared by all of the populations investigated, suggesting that H. cunea with that haplotype have successfully colonized China, Iran, Japan, and Korea.     

Fungal endophytes of invasive Phagramites australis populations vary in species composition and fungicide susceptibility

Phragmites australis subsp. australis (Poaceae) is an aggressively invasive reed that threatens both freshwater and saltwater ecosystems in North America. We sampled P.a. australis plants for fungal endophytes at seven sites across a short geographic range near a freshwater lake in Michigan. Compared to previous studies, our data reveal novel variation in the diversity and abundance of fungal endophytes within P.a. australis. Within each sampling site we observed 4–10 morphologically unique, culturable fungi. Since fungal endophytes can confer significant benefits to their plant host, we hypothesized that fungal endophytes are important for mediating plant invasions. To test this hypothesis we first had to establish a protocol to experimentally control fungal endophytes within P.a. australis, which does not easily grow from sterile seed. We therefore investigated the effect of fungicides as a potential method for eliminating fungi from living plant tissue such as rhizomes. We selected the ten most abundant fungi isolated from P.a. australis and tested their susceptibility to three commonly available fungicides. Response to the fungicides varied across fungal isolates, demonstrating physiological variation and fungicide-resistant phenotypes.     

Diversity,migration routes,and worldwide population genetic structure of Lecanosticta acicola,the causal agent of brown spot needle blight

Lecanosticta acicola is a pine needle pathogen causing brown spot needle blight that results in premature needle shedding with considerable damage described in North America, Europe, and Asia. Microsatellite and mating type markers were used to study the population genetics, migration history, and reproduction mode of the pathogen, based on a collection of 650 isolates from 27 countries and 26 hosts across the range of L. acicola. The presence of L. acicola in Georgia was confirmed in this study. Migration analyses indicate there have been several introduction events from North America into Europe. However, some of the source populations still appear to remain unknown. The populations in Croatia and western Asia appear to originate from genetically similar populations in North America. Intercontinental movement of the pathogen was reflected in an identical haplotype occurring on two continents, in North America (Canada) and Europe (Germany). Several shared haplotypes between European populations further suggests more local pathogen movement between countries. Moreover, migration analyses indicate that the populations in northern Europe originate from more established populations in central Europe. Overall, the highest genetic diversity was observed in south‐eastern USA. In Europe, the highest diversity was observed in France, where the presence of both known pathogen lineages was recorded. Less than half of the observed populations contained mating types in equal proportions. Although there is evidence of some sexual reproduction taking place, the pathogen spreads predominantly asexually and through anthropogenic activity.     

Putative source of the invasive Sirex noctilio fungal symbiont, Amylostereum areolatum, in the eastern United States and its association with native siricid woodwasps

Two genotypes of the fungal symbiont Amylostereum areolatum are associated with the invasive woodwasp Sirex noctilio first found in North America in 2004. S. noctilio is native to Europe but has been introduced to Australasia, South America and Africa where it has caused enormous losses in pine plantations. Based on nucleotide sequence data from the intergenic spacer region (IGS) of the nuclear ribosomal DNA, the A. areolatum genotypes found in North America are most similar to genotypes found in Europe, and not to genotypes from the southern hemisphere. Although two IGS strains of A. areolatum were found in North America it cannot be stated whether A. areolatum was introduced to North America from Europe once or twice based on our study. Genetic groupings formed by sequencing data were in most cases supported by vegetative compatibility groups (VCGs). Other siricid woodwasp species in the genus Sirex are native to North America. The North American native Sirex edwardsii emerging from the same tree as S. noctilio carried the same strain of A. areolatum as S. noctilio. The North American native Sirex sp. ‘nitidus’ collected outside the geographical range of S. noctilio carried a unique strain within A. areolatum. Our findings of A. areolatum in the native North American species, S. sp. ‘nitidus’, contrast with the previous view that A. areolatum was not present in North America before the accidental invasion of S. noctilio.     

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.     

Genetic diversity and population structure identify the potential source of the invasive red clover casebearer moth, <Emphasis Type="Italic">Coleophora deauratella</Emphasis>, in North America

The red clover casebearer, Coleophora deauratella, is an invasive pest of red clover grown for seed in North America. In 2006, an outbreak in Alberta, Canada was discovered that resulted in significant seed losses, while further invasion threatens the world’s largest red clover forage seed production region in Oregon, USA. Prior to the recent outbreak, C. deauratella was thought to be restricted to eastern North America in its invasive range. We sequenced a 615-bp fragment of the mitochondrial cytochrome c oxidase subunit 1 gene, and developed three microsatellite markers to assess the genetic diversity and population structure of C. deauratella in North America and its native range in Europe. We observed signatures of a founder effect in North American populations and a further loss of genetic diversity within Alberta populations. Most genetic differentiation was found between continents, with no evidence of isolation-by-distance within each continent. From the limited number of European populations sampled, a single introduction from Switzerland is the most probable source of North American populations based on similar mitochondrial diversity and lack of population differentiation. Within North America, based on increased genetic diversity compared to the rest of the continent, the first North American record from Ithaca, NY, and the first documented outbreak in southern Ontario in 1989, the initial C. deauratella invasion most likely occurred in southern Ontario, Canada or adjacent states in the USA, followed by transport throughout the continent. This study provides insight into the phylogeographic history of C. deauratella in North America and Europe and may help to identify a regional source of future classical biological control agents.     

Changes in pathways and vectors of biological invasions in Northwest Europe

We assessed how establishment patterns of non-native freshwater, marine and terrestrial species into Northwest Europe (using Great Britain, France, Belgium and the Netherlands as the study countries) have changed over time, and identified the prevalent pathways and vectors of recent arrivals. Data were extracted from 33 sources on (a) presence/absence and (b) first year of observation in the wild in each country, and (c) continent(s) of origin, (d) invasion pathway(s), (e) invasion vector(s) and (f) environment(s) for 359 species, comprising all non-native Mollusca, Osteichthyes (bony fish), Anseriformes (wildfowl) and Mammalia, and non-native invasive Angiospermae present in the area. Molluscs, fish and wildfowl, particularly those originating from South America, arrived more recently into Northwest Europe than other groups, particularly mammals, invasive plants and species originating from North America. Non-deliberate introductions, those of aquatic species and those from elsewhere in Europe and/or Asia increased strongly in importance after the year 2000 and were responsible for 69, 83 and 89 % of new introductions between 2001 and 2015, respectively. Non-deliberate introductions and those from Asia and North America contributed significantly more to introductions of invasive species in comparison to other non-native species. From the 1960s, ornamental trade has increased in importance relative to other vectors and was responsible for all deliberate introductions of study groups since 2001. Non-deliberate introductions of freshwater and marine species originating from Southeast Europe and Asia represent an increasingly important ecological and economic threat to Northwest Europe. Invertebrates such as molluscs may be particularly dangerous due to their small size and difficulties in detection. Prevention of future invasions in this respect will require intensive screening of stowaways on boats and raising of public awareness.