Deciphering the worldwide invasion of the Asian long‐horned beetle: A recurrent invasion process from the native area together with a bridgehead effect

Retracing introduction routes is crucial for understanding the evolutionary processes involved in an invasion, as well as for highlighting the invasion history of a species at the global scale. The Asian long‐horned beetle (ALB) Anoplophora glabripennis is a xylophagous pest native to Asia and invasive in North America and Europe. It is responsible for severe losses of urban trees, in both its native and invaded ranges. Based on historical and genetic data, several hypotheses have been formulated concerning its invasion history, including the possibility of multiple introductions from the native zone and secondary dispersal within the invaded areas, but none have been formally tested. In this study, we characterized the genetic structure of ALB in both its native and invaded ranges using microsatellites. In order to test different invasion scenarios, we used an approximate Bayesian “random forest” algorithm together with traditional population genetics approaches. The strong population differentiation observed in the native area was not geographically structured, suggesting complex migration events that were probably human‐mediated. Both native and invasive populations had low genetic diversity, but this characteristic did not prevent the success of the ALB invasions. Our results highlight the complexity of invasion pathways for insect pests. Specifically, our findings indicate that invasive species might be repeatedly introduced from their native range, and they emphasize the importance of multiple, human‐mediated introductions in successful invasions. Finally, our results demonstrate that invasive species can spread across continents following a bridgehead path, in which an invasive population may have acted as a source for another invasion.     

Genomic footprints of a biological invasion: Introduction from Asia and dispersal in Europe of the topmouth gudgeon (Pseudorasbora parva)

Facilitated by the intensification of global trading, the introduction and dispersal of species to areas in which they are historically non‐native is nowadays common. From an evolutionary standpoint, invasions are paradoxical: not only non‐native environments could be different from native ones for which introduced individuals would be ill‐adapted, but also small founding population size should be associated with reduced adaptive potential. As such, biological invasions are considered valuable real‐time evolutionary experiments. Here, we investigated the population structure and adaptive potential of the highly invasive topmouth gudgeon (Pseudorasbora parva) across Europe and East Asia. We RAD‐sequenced 301 specimens from sixteen populations and three distinct within‐catchment invaded regions as well as two locations in the native range. With 13,785 single nucleotide polymorphisms, we provide conclusive evidence for a genome‐wide signature of two distinct invasion events, in Slovakia and Turkey, each originating from a specific area in the native range. A third invaded area, in France, appears to be the result of dispersal within the invasive range. Few loci showed signs of selection, the vast majority of which being identified in the Slovakian region. Functional annotation suggests that faster early stage development, resistance to pollution and immunocompetence contribute to the invasion success of the local habitats. By showing that populations in the invasive range have different evolutionary histories, our study reinforces the idea that populations, rather than species, are the units to consider in invasion biology.     

Human‐aided admixture may fuel ecosystem transformation during biological invasions: theoretical and experimental evidence

Biological invasions can transform our understanding of how the interplay of historical isolation and contemporary (human‐aided) dispersal affects the structure of intraspecific diversity in functional traits, and in turn, how changes in functional traits affect other scales of biological organization such as communities and ecosystems. Because biological invasions frequently involve the admixture of previously isolated lineages as a result of human‐aided dispersal, studies of invasive populations can reveal how admixture results in novel genotypes and shifts in functional trait variation within populations. Further, because invasive species can be ecosystem engineers within invaded ecosystems, admixture‐induced shifts in the functional traits of invaders can affect the composition of native biodiversity and alter the flow of resources through the system. Thus, invasions represent promising yet under‐investigated examples of how the effects of short‐term evolutionary changes can cascade across biological scales of diversity. Here, we propose a conceptual framework that admixture between divergent source populations during biological invasions can reorganize the genetic variation underlying key functional traits, leading to shifts in the mean and variance of functional traits within invasive populations. Changes in the mean or variance of key traits can initiate new ecological feedback mechanisms that result in a critical transition from a native ecosystem to a novel invasive ecosystem. We illustrate the application of this framework with reference to a well‐studied plant model system in invasion biology and show how a combination of quantitative genetic experiments, functional trait studies, whole ecosystem field studies and modeling can be used to explore the dynamics predicted to trigger these critical transitions.     

RAD sequencing reveals genomewide divergence between independent invasions of the European green crab (Carcinus maenas) in the Northwest Atlantic

Genomic studies of invasive species can reveal both invasive pathways and functional differences underpinning patterns of colonization success. The European green crab (Carcinus maenas) was initially introduced to eastern North America nearly 200 years ago where it expanded northwards to eastern Nova Scotia. A subsequent invasion to Nova Scotia from a northern European source allowed further range expansion, providing a unique opportunity to study the invasion genomics of a species with multiple invasions. Here, we use restriction‐site‐associated DNA sequencing‐derived SNPs to explore fine‐scale genomewide differentiation between these two invasions. We identified 9137 loci from green crab sampled from 11 locations along eastern North America and compared spatial variation to mitochondrial COI sequence variation used previously to characterize these invasions. Overall spatial divergence among invasions was high (pairwise F_ST ~0.001 to 0.15) and spread across many loci, with a mean F_ST ~0.052 and 52% of loci examined characterized by F_ST values >0.05. The majority of the most divergent loci (i.e., outliers, ~1.2%) displayed latitudinal clines in allele frequency highlighting extensive genomic divergence among the invasions. Discriminant analysis of principal components (both neutral and outlier loci) clearly resolved the two invasions spatially and was highly correlated with mitochondrial divergence. Our results reveal extensive cryptic intraspecific genomic diversity associated with differing patterns of colonization success and demonstrates clear utility for genomic approaches to delineating the distribution and colonization success of aquatic invasive species.     

Multiple introductions and population structure during the rapid expansion of the invasive Sahara mustard (Brassica tournefortii)

The specific mechanisms that result in the success of any species invasion case are difficult to document. Reproductive strategies are often cited as a primary driver of invasive success, with human activities further facilitating invasions by, for example, acting as seed vectors for dispersal via road, train, air, and marine traffic, and by producing efficient corridors for movement including canals, drainages, and roadways. Sahara mustard (Brassica tournefortii) is a facultative autogamous annual native to Eurasia that has rapidly invaded the southwestern United States within the past century, displacing natives, and altering water‐limited landscapes in the southwest. We used a genotyping‐by‐sequencing approach to study the population structure and spatial geography of Sahara mustard from 744 individuals from 52 sites across the range of the species’ invasion. We also used herbaria records to model range expansion since its initial introduction in the 1920s. We found that Sahara mustard occurs as three populations in the United States unstructured by geography, identified three introduction sites, and combined herbaria records with genomic analyses to map the spread of the species. Low genetic diversity and linkage disequilibrium are consistent with self‐fertilization, which likely promoted rapid invasive spread. Overall, we found that Sahara mustard experienced atypical expansion patterns, with a relatively constant rate of expansion and without the lag phase that is typical of many invasive species.     

Congener diversity,topographic heterogeneity and human‐assisted dispersal predict spread rates of alien herpetofauna at a global scale

Understanding the factors that determine rates of range expansion is not only crucial for developing risk assessment schemes and management strategies for invasive species, but also provides important insight into the ability of species to disperse in response to climate change. However, there is little knowledge on why some invasions spread faster than others at large spatiotemporal scales. Here, we examine the effects of human activities, species traits and characteristics of the invaded range on spread rates using a global sample of alien reptile and amphibian introductions. We show that spread rates vary remarkably among invaded locations within a species, and differ across biogeographical realms. Spread rates are positively related to the richness of native congeneric species and human‐assisted dispersal in the invaded range but are negatively correlated with topographic heterogeneity. Our findings highlight the importance of environmental characteristics and human‐assisted dispersal in developing robust frameworks for predicting species' range shifts.     

Niche conservatism and spread of seaweed invasive lineages with different residence time in the Mediterranean Sea

Marine algae invasions attract a lot of interest as they are altering the structure of marine ecosystems. However, niche dynamics and risk predictions of marine invasions integrating phylogeographic structure in the analyses have not yet been investigated. In this study, we perform a comprehensive analysis of two invasive lineages of Caulerpa taxifolia with different residence time in the Mediterranean Sea for a better understanding of their invasive processes. We performed lineage-based and species-based niche models to assess the risk of invasion, the spatial overlap, and the variables delimiting the distribution of the two lineages. We also compared the effect of using different extents on niche overlap and niche shift analyses. Intraspecific models with pooled occurrences accurately found two separate regions susceptible of invasion for each invasive lineage in the Mediterranean, while species-based predictions underestimated invaded regions. The invasive lineages spread across colder coastal areas than the species. Altogether, we provide evidence that different invasive lineages of algae show dissimilar environmental responses and invasive ranges that are not detectable by species-based analyses. Moreover, niche overlap and niche shift analyses seem to depend greatly on the geographical extent used. According to the most appropriate extent (worldwide), the invaded range did not show niche shift, and thus, no evidence of a post-introduction adaptation scenario was found as both lineages invaded habitats similar to their Australian native locations. Actions to prevent further spreading of the most recent invasive lineage are needed.     

Invasion success of alien plants: do habitat affinities in the native distribution range matter?

Aim To assess how habitat affinities in the native distribution range influence the invasion success of 282 central European neophytes (alien plants introduced after ad 1500). Location Czech Republic. Methods Classification trees were used to determine which native habitats donate the most alien species, the correspondence between habitats occupied by species in their native and invaded distribution ranges, and invasion success of species originating from different habitats. Results The species most likely to naturalize in Central Europe are those associated with thermophile woodland fringes in their native range (81%), cultivated areas of gardens and parks (75%) and broad‐leaved deciduous woodlands (72%). The largest proportions of invasive species recruit from those that occur on riverine terraces and eroded slopes, or grow in both deciduous woodland and riverine scrub. When the relative role of habitats in the native range is assessed as a determinant of the probability that a species will become invasive in concert with other factors (the species’ residence time, life history, region of origin), the direct effect of habitat is negligible. However, the effect of native habitats on patterns of invasions observed in central Europe is manifested by large differences in the numbers of species they supply to the invaded region. More than 50 neophytes were recruited from each of the following habitats: dry grasslands, ruderal habitats, deciduous woodland, inland cliffs, rock pavements and outcrops, and tall‐herb fringes and meadows. Main conclusions Casual species recruit from a wider range of habitats in their native range than they occupy in the invaded range; naturalized but not invasive species inhabit a comparable spectrum of habitats in both ranges, and successful invaders occupy a wider range of habitats in the invaded than in the native range. This supports the idea that the invasive phase of the process is associated with changes in biological features that allow for extension of the spectrum of habitats invaded.     

Modelling the introduction and spread of non‐native species: international trade and climate change drive ragweed invasion

Biological invasions are a major driver of global change, for which models can attribute causes, assess impacts and guide management. However, invasion models typically focus on spread from known introduction points or non‐native distributions and ignore the transport processes by which species arrive. Here, we developed a simulation model to understand and describe plant invasion at a continental scale, integrating repeated transport through trade pathways, unintentional release events and the population dynamics and local anthropogenic dispersal that drive subsequent spread. We used the model to simulate the invasion of Europe by common ragweed (Ambrosia artemisiifolia), a globally invasive plant that causes serious harm as an aeroallergen and crop weed. Simulations starting in 1950 accurately reproduced ragweed's current distribution, including the presence of records in climatically unsuitable areas as a result of repeated introduction. Furthermore, the model outputs were strongly correlated with spatial and temporal patterns of ragweed pollen concentrations, which are fully independent of the calibration data. The model suggests that recent trends for warmer summers and increased volumes of international trade have accelerated the ragweed invasion. For the latter, long distance dispersal because of trade within the invaded continent is highlighted as a key invasion process, in addition to import from the native range. Biosecurity simulations, whereby transport through trade pathways is halted, showed that effective control is only achieved by early action targeting all relevant pathways. We conclude that invasion models would benefit from integrating introduction processes (transport and release) with spread dynamics, to better represent propagule pressure from native sources as well as mechanisms for long‐distance dispersal within invaded continents. Ultimately, such integration may facilitate better prediction of spatial and temporal variation in invasion risk and provide useful guidance for management strategies to reduce the impacts of invasion.     

Patterns of niche filling and expansion across the invaded ranges of an Australian lizard

Studies of realized niche shifts in alien species typically ignore the potential effects of intraspecific niche variation and different invaded‐range environments on niche lability. We incorporate our detailed knowledge of the native‐range source populations and global introduction history of the delicate skink Lampropholis delicata to examine intraspecific variation in realized niche expansion and unfilling, and investigate how alternative niche modelling approaches are affected by that variation. We analyzed the realized niche dynamics of L. delicata using an ordination method, ecological niche models (ENMs), and occurrence records from 1) Australia (native range), 2) New Zealand, 3) Hawaii, 4) the two distinct native‐range clades that were the sources for the New Zealand and Hawaii introductions, and 5) the species’ global range (including Lord Howe Island, Australia). We found a gradient of realized niche change across the invaded ranges of L. delicata: niche stasis on Lord Howe Island, niche unfilling in New Zealand (16%), and niche unfilling (87%) and expansion (14%) in Hawaii. ENMs fitted to native‐range data generally identified suitable climatic conditions at sites where the species has established non‐native populations, whereas ENMs based on native‐range source clades and non‐native populations had lower spatial transferability. Our results suggest that the extent to which realized niches are maintained during invasion does not depend on species‐level traits. When realized niche shifts are predominately due to niche unfilling, fully capturing species’ responses along climatic gradients by basing ENMs on native distributions may be more important for accurate invasion forecasts than incorporating phylogenetic differentiation, or integrating niche changes in the invaded range.     

Molecular genetic approaches to elucidate the ecological and evolutionary issues associated with biological invasions

Biological invasions may cause serious damage to the native environments and threaten the native biodiversity. Molecular genetic approaches have been found to be powerful tools for investigating the ecological and evolutionary aspects of biological invasions because the genetic structure and level of genetic variation of an invasive species are changed following its invasion. The present article reviews the use of molecular markers in addressing various aspects of invasive species. The application of these techniques has shown that many invasive species are actually "cryptic" species – species whose uniqueness is only recognizable at the genetic level. An estimation of the actual number of invasive species is essential when evaluating its ecological and economic impacts. Molecular genetic approaches have also enabled the source populations of invasive species to be identified. Reconstructions of invasion histories are crucial to preventing future invasions and conserving the native biodiversity, while comparisons of genetic variations between the native and introduced populations provide valuable opportunities to elucidate the mechanisms of rapid adaptation demonstrated by many invasive species.     

动物入侵的行为机制

行为特征可在外来动物建立种群和扩张过程中发挥重要作用,因此,要正确理解动物入侵,常常需要仔细研究其行为机制。20世纪80年代以来,随着动物入侵规模在世界各地的迅速加剧,有关其行为机制的研究也受到了广泛关注。最近一些研究表明,一些入侵动物种内攻击和觅食等行为具有可塑性,因此它们能够灵活应对多变的环境条件,这对于种群的建立和维持至关重要;入侵动物与土著物种发生行为互作时,往往占据优势,从而取代土著物种,并有助于其地域扩张;入侵动物长距离扩散可以提高其地域扩张速度,许多行为可与扩散行为结合进一步促进扩张。今后需要加强对入侵动物的行为分析,使之全面地融合到生物入侵的研究之中。这不仅可以提高对外来物种入侵的预警和治理能力,而且为探索动物行为的奥秘以及动物间行为互作在物种进化中的意义提供了独特的机会。     

Thermogeography predicts the potential global range of the invasive European green crab (Carcinus maenas)

Aim The highly adaptable estuarine crab (Carcinus maenas) has successfully invaded five temperate geographic regions outside of its native Europe. Here, we determine which environmental factors predict the current distribution of C. maenas and what the potential geographic range of this species might be. We also investigated whether the invasion potential of C. maenas differs with respect to the origin of a native subpopulation. Location Models were developed using global observation records of C. maenas. Methods Boosted regression trees were used to model observations from the (1) native, (2) invasive, (3) southern European, (4) northern European and (5) the combined native and invasive geographic ranges of C. maenas. Results Most established invasions were predicted mainly based on temperature. Interestingly, the environment encountered by established invasions failed to predict the majority of northern European populations; suggesting that invasion potential may differ between distinct native populations. Supporting this suggestion, a model of northern European populations, distinguished from southern European populations based on genetic structure, only predicted established invasions south of Nova Scotia. By contrast, a model of southern European populations predicted most established invasions. Main conclusions These results suggest that invasion potential depends on the European origin of an invasive population and that most invasions have arisen from southern Europe. Finally, a model based on combined native and invasive ranges of C. maenas identified potential geographic range extension along many currently invaded coastlines and the potential invasion of countries like Chile, China, Russia, Namibia and New Zealand.     

Population genomics of the Asian tiger mosquito,Aedes albopictus: insights into the recent worldwide invasion

Aedes albopictus, the “Asian tiger mosquito,” is an aggressive biting mosquito native to Asia that has colonized all continents except Antarctica during the last ~30–40 years. The species is of great public health concern as it can transmit at least 26 arboviruses, including dengue, chikungunya, and Zika viruses. In this study, using double‐digest Restriction site‐Associated DNA (ddRAD) sequencing, we developed a panel of ~58,000 single nucleotide polymorphisms (SNPs) based on 20 worldwide Ae. albopictus populations representing both the invasive and the native range. We used this genomic‐based approach to study the genetic structure and the differentiation of Ae. albopictus populations and to understand origin(s) and dynamics of the recent invasions. Our analyses indicated the existence of two major genetically differentiated population clusters, each one including both native and invasive populations. The detection of additional genetic structure within each major cluster supports that these SNPs can detect differentiation at a global and local scale, while the similar levels of genomic diversity between native and invasive range populations support the scenario of multiple invasions or colonization by a large number of propagules. Finally, our results revealed the possible source(s) of the recent invasion in Americas, Europe, and Africa, a finding with important implications for vector‐control strategies.     

基于分子生物学方法的外来入侵物种入侵历史重构

生物入侵是一个世界性的问题。全球每年因生物入侵造成的损失超过1万亿美元。探究入侵物种在入侵地的入侵历史对了解生物入侵的生物生态学机制、制定阻截及防除措施有重要意义。分子标记方法的兴起和大规模应用打开了入侵生物入侵历史研究的新天地。采用分子标记的方法可鉴定入侵物种的种类、追溯其来源地、回溯其扩散路径、分析扩散模式及探究物种入侵过程中对入侵种群本身的变化及其对生态系统所造成的各种影响。分子标记的应用使得多个入侵物种的入侵历史得以重现。由于分子标记方法重构的入侵历史受采样范围、采用的分子标记的种类及数量等因素的影响,该方法呈现入侵历史是否是真实发生的入侵过程还存在争议。     

Overlooking the smallest matter: viruses impact biological invasions

Parasites and pathogens have recently received considerable attention for their ability to affect biological invasions, however, researchers have largely overlooked the distinct role of viruses afforded by their unique ability to rapidly mutate and adapt to new hosts. With high mutation and genomic substitution rates, RNA and single‐stranded DNA (ssDNA) viruses may be important constituents of invaded ecosystems, and could potentially behave quite differently from other pathogens. We review evidence suggesting that rapidly evolving viruses impact invasion dynamics in three key ways: (1) Rapidly evolving viruses may prevent exotic species from establishing self‐sustaining populations. (2) Viruses can cause population collapses of exotic species in the introduced range. (3) Viruses can alter the consequences of biological invasions by causing population collapses and extinctions of native species. The ubiquity and frequent host shifting of viruses make their ability to influence invasion events likely. Eludicating the viral ecology of biological invasions will lead to an improved understanding of the causes and consequences of invasions, particularly as regards establishment success and changes to community structure that cannot be explained by direct interspecific interactions among native and exotic species.     

Reduced genetic diversity, increased isolation and multiple introductions of invasive giant hogweed in the western Swiss Alps

The giant hogweed ( Heracleum mantegazzianum ) has successfully invaded 19 European countries as well as parts of North America. It has become a problematic species due to its ability to displace native flora and to cause public health hazards. Applying population genetics to species invasion can help reconstruct invasion history and may promote more efficient management practice. We thus analysed levels of genetic variation and population genetic structure of H. mantegazzianum in an invaded area of the western Swiss Alps as well as in its native range (the Caucasus), using eight nuclear microsatellite loci together with plastid DNA markers and sequences. On both nuclear and plastid genomes, native populations exhibited significantly higher levels of genetic diversity compared to invasive populations, confirming an important founder event during the invasion process. Invasive populations were also significantly more differentiated than native populations. Bayesian clustering analysis identified five clusters in the native range that corresponded to geographically and ecologically separated groups. In the invaded range, 10 clusters occurred. Unlike native populations, invasive clusters were characterized by a mosaic pattern in the landscape, possibly caused by anthropogenic dispersal of the species via roads and direct collection for ornamental purposes. Lastly, our analyses revealed four main divergent groups in the western Swiss Alps, likely as a consequence of multiple independent establishments of H. mantegazzianum .     

Biogeographical contrasts to assess local and regional patterns of invasion: a case study with two reciprocally introduced exotic maple trees

Quantitative comparisons of distribution and abundance of exotic species in their native and non‐native ranges represent a first step when studying invaders. However, this approach is rarely applied 2 particularly to tree species. Using biogeographical contrasts coupled with regional dispersal surveys, we assessed whether two exotic maple tree species, Acer negundo and Acer platanoides, can be classified as invasive in the non‐native regions surveyed. We also examined the importance of biogeography in determining the degree of invasion by exotic species using this reciprocal approach. Local‐scale surveys were conducted in a total of 34 forests to compare density, relative abundance, age structure of native and introduced populations, and whether the two introduced maple species negatively affected native tree species density. Regional‐scale surveys of a total of 136 forests were then conducted to assess distribution in the introduced regions. Introduced populations of A. negundo were denser than populations measured in their native range and negatively related to native tree species density. Age structure did not differ between regions for this species. At the regional scale, this species has invaded most of the riparian corridors sampled in France. Conversely, the density of A. platanoides introduced populations was similar to that of native populations and was not related to native tree species density. Although seedling recruitment was higher away than at home, this species has invaded only 9% of the forests sampled in southern Ontario, Canada. Although reported invasive, these two exotic maple species differed in their relative demographic parameters and regional spread. Acer negundo is currently invasive in southern France while A. platanoides is not aggressively invasive in southern Ontario. Importantly, this study effectively demonstrates that biogeography through structured contrasts provide a direct means to infer invasion of exotic species.     

Standing genetic diversity and selection at functional gene loci are associated with differential invasion success in two non‐native fish species

Invasive species are expected to experience a unique combination of high genetic drift due to demographic factors while also experiencing strong selective pressures. The paradigm that reduced genetic diversity should limit the evolutionary potential of invasive species, and thus, their potential for range expansion has received little empirical support, possibly due to the choice of genetic markers. Our goal was to test for effects of genetic drift and selection at functional genetic markers as they relate to the invasion success of two paired invasive goby species, one widespread (successful) and one with limited range expansion (less successful). We genotyped fish using two marker types: single nucleotide polymorphisms (SNPs) in known‐function, protein‐coding genes and microsatellites to contrast the effects of neutral genetic processes. We identified reduced allelic variation in the invaded range for the less successful tubenose goby. SNPs putatively under selection were responsible for the observed differences in population structure between marker types for round goby (successful) but not tubenose goby (less successful). A higher proportion of functional loci experienced divergent selection for round goby, suggesting increased evolutionary potential in invaded ranges may be associated with round goby's greater invasion success. Genes involved in thermal tolerance were divergent for round goby populations but not tubenose goby, consistent with the hypothesis that invasion success for fish in temperate regions is influenced by capacity for thermal tolerance. Our results highlight the need to incorporate functional genetic markers in studies to better assess evolutionary potential for the improved conservation and management of species.