Effects of admixture in native and invasive populations of <Emphasis Type="Italic">Lythrum salicaria</Emphasis>

Intraspecific hybridization between diverged populations can enhance fitness via various genetic mechanisms. The benefits of such admixture have been proposed to be particularly relevant in biological invasions, when invasive populations originating from different source populations are found sympatrically. However, it remains poorly understood if admixture is an important contributor to plant invasive success and how admixture effects compare between invasive and native ranges. Here, we used experimental crosses in Lythrum salicaria, a species with well-established history of multiple introductions to Eastern North America, to quantify and compare admixture effects in native European and invasive North American populations. We observed heterosis in between-population crosses both in native and invasive ranges. However, invasive-range heterosis was restricted to crosses between two different Eastern and Western invasion fronts, whereas heterosis was absent in geographically distant crosses within a single large invasion front. Our results suggest that multiple introductions have led to already-admixed invasion fronts, such that experimental crosses do not further increase performance, but that contact between different invasion fronts further enhances fitness after admixture. Thus, intra-continental movement of invasive plants in their introduced range has the potential to boost invasiveness even in well-established and successfully spreading invasive species.     

Bridgehead Effect in the Worldwide Invasion of the Biocontrol Harlequin Ladybird

Recent studies of the routes of worldwide introductions of alien organisms suggest that many widespread invasions could have stemmed not from the native range, but from a particularly successful invasive population, which serves as the source of colonists for remote new territories. We call here this phenomenon the invasive bridgehead effect. Evaluating the likelihood of such a scenario is heuristically challenging. We solved this problem by using approximate Bayesian computation methods to quantitatively compare complex invasion scenarios based on the analysis of population genetics (microsatellite variation) and historical (first observation dates) data. We applied this approach to the Harlequin ladybird Harmonia axyridis (HA), a coccinellid native to Asia that was repeatedly introduced as a biocontrol agent without becoming established for decades. We show that the recent burst of worldwide invasions of HA followed a bridgehead scenario, in which an invasive population in eastern North America acted as the source of the colonists that invaded the European, South American and African continents, with some admixture with a biocontrol strain in Europe. This demonstration of a mechanism of invasion via a bridgehead has important implications both for invasion theory (i.e., a single evolutionary shift in the bridgehead population versus multiple changes in case of introduced populations becoming invasive independently) and for ongoing efforts to manage invasions by alien organisms (i.e., heightened vigilance against invasive bridgeheads).     

A layover in Europe: Reconstructing the invasion route of asexual lineages of a New Zealand snail to North America

Non‐native invasive species are threatening ecosystems and biodiversity worldwide. High genetic variation is thought to be a critical factor for invasion success. Accordingly, the global invasion of a few clonal lineages of the gastropod Potamopyrgus antipodarum is thus both puzzling and has the potential to help illuminate why some invasions succeed while others fail. Here, we used SNP markers and a geographically broad sampling scheme (N = 1617) including native New Zealand populations and invasive North American and European populations to provide the first widescale population genetic assessment of the relationships between and among native and invasive P. antipodarum. We used a combination of traditional and Bayesian molecular analyses to demonstrate that New Zealand populations harbour very high diversity relative to the invasive populations and are the source of the two main European genetic lineages. One of these two European lineages was in turn the source of at least one of the two main North American genetic clusters of invasive P. antipodarum, located in Lake Ontario. The other widespread North American group had a more complex origin that included the other European lineage and two New Zealand clusters. Altogether, our analyses suggest that just a small handful of clonal lineages of P. antipodarum were responsible for invasion across continents. Our findings provide critical information for prevention of additional invasions and control of existing invasive populations and are of broader relevance towards understanding the establishment and evolution of asexual populations and the forces driving biological invasion.     

Inferring the origin of populations introduced from a genetically structured native range by approximate Bayesian computation: case study of the invasive ladybird Harmonia axyridis

Correct identification of the source population of an invasive species is a prerequisite for testing hypotheses concerning the factors responsible for biological invasions. The native area of invasive species may be large, poorly known and/or genetically structured. Because the actual source population may not have been sampled, studies based on molecular markers may generate incorrect conclusions about the origin of introduced populations. In this study, we characterized the genetic structure of the invasive ladybird Harmonia axyridis in its native area using various population genetic statistics and methods. We found that native area of H. axyridis most probably consisted of two geographically distinct genetic clusters located in eastern and western Asia. We then performed approximate Bayesian computation (ABC) analyses on controlled simulated microsatellite data sets to evaluate (i) the risk of selecting incorrect introduction scenarios, including admixture between sources, when the populations of the native area are genetically structured and sampling is incomplete and (ii) the ability of ABC analysis to minimize such risks by explicitly including unsampled populations in the scenarios compared. Finally, we performed additional ABC analyses on real microsatellite data sets to retrace the origin of biocontrol and invasive populations of H. axyridis, taking into account the possibility that the structured native area may have been incompletely sampled. We found that the invasive population in eastern North America, which has served as the bridgehead for worldwide invasion by H. axyridis, was probably formed by an admixture between the eastern and western native clusters. This admixture may have facilitated adaptation of the bridgehead population.     

Does intraspecific hybridization contribute to the evolution of invasiveness?: an experimental test

One of the major objectives of research on invasive species is to determine the relative importance of different evolutionary and ecological forces in the invasion process. It was recently suggested that post-introduction intraspecific hybridization between previously isolated genotypes could produce novel and/or heterotic progeny that might express enhanced invasiveness. We tested this hypothesis with Silene latifolia, a European native that has successfully invaded North America and has previously been shown to have undergone genetic change since its introduction. In a common garden experiment we compared the performance of plants derived from within and between population crosses from eight European and 18 North American populations. Results showed that there was no significant effect of crossing distance on progeny phenotype. Furthermore, progeny from within or between population crosses did not differ in size, reproductive output or survival. Collectively, these results suggest that the invasive phenotype of S. latifolia is likely the result of natural selection and/or genetic drift rather than intraspecific hybridization.     

Multiple introductions,admixture and bridgehead invasion characterize the introduction history of Ambrosia artemisiifolia in Europe and Australia

Admixture between differentiated populations is considered to be a powerful mechanism stimulating the invasive success of some introduced species. It is generally facilitated through multiple introductions; however, the importance of admixture prior to introduction has rarely been considered. We assess the likelihood that the invasive Ambrosia artemisiifolia populations of Europe and Australia developed through multiple introductions or were sourced from a historical admixture zone within native North America. To do this, we combine large genomic and sampling data sets analysed with approximate Bayesian computation and random forest scenario evaluation to compare single and multiple invasion scenarios with pre‐ and postintroduction admixture simultaneously. We show the historical admixture zone within native North America originated before global invasion of this weed and could act as a potential source of introduced populations. We provide evidence supporting the hypothesis that the invasive populations established through multiple introductions from the native range into Europe and subsequent bridgehead invasion into Australia. We discuss the evolutionary mechanisms that could promote invasiveness and evolutionary potential of alien species from bridgehead invasions and admixed source populations.     

Changes in genetic structure of North American Bythotrephes populations following invasion from Lake Ladoga, Russia

1. We used allozyme electrophoresis to compare Bythotrephes longimanus (Crustacea: Onychopoda: Cercopagididae) from recently founded North American populations with those from native European populations, and to examine changes in genetic structure of North American populations over time.
2. The genetic structure of North American populations in 1996 was similar to that of European populations, because of the disappearance of founder effects which distinguished North American from European populations in 1989.
3. The Lake Ladoga, Russia population was more closely related to North American populations than to other European populations, consistent with non-genetic evidence implicating Lake Ladoga as the source of North American populations.
4. Our results provide additional evidence of the presence of an invasion corridor that allows Urasian and Ponto-Caspian species to be introduced into North American freshwater ecosystems, and show that founder effects can erode over time following establishment of invasive species.     

Patterns of Admixture and Population Structure in Native Populations of Northwest North America

The initial contact of European populations with indigenous populations of the Americas produced diverse admixture processes across North, Central, and South America. Recent studies have examined the genetic structure of indigenous populations of Latin America and the Caribbean and their admixed descendants, reporting on the genomic impact of the history of admixture with colonizing populations of European and African ancestry. However, relatively little genomic research has been conducted on admixture in indigenous North American populations. In this study, we analyze genomic data at 475,109 single-nucleotide polymorphisms sampled in indigenous peoples of the Pacific Northwest in British Columbia and Southeast Alaska, populations with a well-documented history of contact with European and Asian traders, fishermen, and contract laborers. We find that the indigenous populations of the Pacific Northwest have higher gene diversity than Latin American indigenous populations. Among the Pacific Northwest populations, interior groups provide more evidence for East Asian admixture, whereas coastal groups have higher levels of European admixture. In contrast with many Latin American indigenous populations, the variance of admixture is high in each of the Pacific Northwest indigenous populations, as expected for recent and ongoing admixture processes. The results reveal some similarities but notable differences between admixture patterns in the Pacific Northwest and those in Latin America, contributing to a more detailed understanding of the genomic consequences of European colonization events throughout the Americas.     

Testing the role of genetic factors across multiple independent invasions of the shrub Scotch broom (Cytisus scoparius)

Knowledge of the introduction history of invasive plants informs on theories of invasiveness and assists in the invasives management. For the highly successful invasive shrub Scotch broom, Cytisus scoparius, we analysed a combination of nuclear and chloroplast microsatellites for eight native source regions and eight independent invasion events in four countries across three continents. We found that two exotic Australian populations came from different sources, one of which was derived from multiple native populations, as was an invasive sample from California. An invasive population from New Zealand appeared to be predominantly sourced from a single population, either from the native or exotic ranges. Four invasive populations from Chile were genetically differentiated from the native range samples analysed here and so their source of introduction could not be confirmed, but high levels of differentiation between the Chilean populations suggested a combination of different sources. This extensive global data set of replicated introductions also enabled tests of key theories of invasiveness in relation to genetic diversity. We conclude that invasive populations have similar levels of high genetic diversity to native ranges; levels of admixture may vary across invasive populations so admixture does not appear to have been an essential requirement for invasion; invasive and native populations exhibit similar level of genetic structure indicating similar gene flow dynamics for both types of populations. High levels of diversity and multiple source populations for invasive populations observed here discount founder effects or drift as likely explanations for previously observed seed size differences between ranges. The high levels of genetic diversity, differential and source admixture identified for most exotic populations are likely to limit the ability to source biocontrol agents from the native region of origin of invasive populations.     

Recent admixture generates heterozygosity–fitness correlations during the range expansion of an invading species

Admixture, the mixing of historically isolated gene pools, can have immediate consequences for the genetic architecture of fitness traits. Admixture may be especially important for newly colonized populations, such as during range expansion and species invasions, by generating heterozygosity that can boost fitness through heterosis. Despite widespread evidence for admixture during species invasions, few studies have examined the demographic history leading to admixture, how admixture affects the heterozygosity and fitness of invasive genotypes, and whether such fitness effects are maintained through time. We address these questions using the invasive plant Silene vulgaris, which shows evidence of admixture in both its native Europe and in North America where it has invaded. Using multilocus genotype data in conjunction with approximate Bayesian computation analysis of demographic history, we showed that admixture during the invasion of North America was independent from and much younger than admixture in the native range of Europe. We tested for fitness consequences of admixture in each range and detected a significant positive heterozygosity–fitness correlation (HFC) in North America; in contrast, no HFC was present in Europe. The lack of HFC in Europe may reflect the longer time since admixture in the native range, dissipating associations between heterozygosity at markers and fitness loci. Our results support a key short‐term role for admixture during the early stages of invasion by generating HFCs that carry populations past the threat of extinction from inbreeding and demographic stochasticity.     

An experimental study of the reproductive biology and hybridization in the European and North American species of Equisetum

Sporophytc production was investigated in the eleven North American and European species of Equisetum by means of fertilization experiments on both intact and subcultured gametophytes. Comparison of intra- and inter-gametophytic selfing with intergametophytic crossing failed to reveal any evidence of recessive sporophytic lethals, leaky lethals or deleterious recessive genes. Fertilization in Equisetum depends solely on the availability of ripe archegonia. Despite the absence of detectable genetic load in Equisetum , intergametophytic mating is ensured by gametophyte dioecism in the wild. All populations tested were freely interfcrtile indicating a high degree oi genetic con-specihcity, even between North America and Europe. Low sporophyte frequencies in European E. scirpoides are attributed to defective spermatozoids. Polyembryony occurs. Cessation in gametophyte development is mediated by allelopathic compounds liberated from the young sporophytes.
Reciprocal crosses resulted in the synthesis of 12 hybrids (six in subgenus Equisetum and six in subgenus Hippochaete plus abortive zygotes in the cross E. ramosissimum female x E. scirpoides male), 11 of which had previously been reported in nature. No intersubgeneric hybrids were produced, indicating that both subgenera are natural groups only distantly related to one another. The putative wild combinations E. pratense x E. atvense and E. variegatum x E. scirpoides were not synthesized, but a new hybrid from the allopatric E. ramosissimum and E. laevigatum arose. Reciprocal crosses within the subgenus Hippochaete usually yielded equal frequencies of hybrids, but in the subgenus Equisetum the majority of successful crosses were unidirectional. All taxa oi Hippochaete are linked by hybrids whereas in subgenus Equisetum, E. pratense and E. sylvatkum form an isolated pair, Hybridization studies, and evidence from gametophyte morphology support the traditional sectional classification of Equisetum.     

Genetic variation within and among domesticated Atlantic salmon broodstocks in British Columbia, Canada

Atlantic salmon have been reared in the British Columbia, Canada aquaculture industry since the early 1980s. No breeding programmes spanned the entire production period and pedigree records were not kept for broodstocks prior to or since importation. Of the three recognized industry strains, two are of European ancestry ('Mowi' from Norway and 'McConnell' from Scotland) and one is of North American heritage ('Cascade' from Gaspe, Quebec). We evaluated the amount and distribution of genetic variation within industry broodstocks by surveying microsatellite variation at 11 loci in 20 broodstock groups sampled from major production facilities. Allelic richness averaged 10.9 (range 5.8-13.8), compared with a value of 20.3 obtained for a North American wild population. Pairwise genetic distances (D(S)) between samples within strains were generally less than those between strains, with samples attributed to the same strain clustering together in a neighbour-joining dendrogram. Nevertheless, average distances between samples within the European strains were high (0.41 for Mowi; 0.71 for McConnell) but lower (0.06) for the Cascade strain. The reduced intra-sample and increased intra-strain genetic variation observed for the BC domesticated samples compared with wild populations was similar to observations for European domesticated Atlantic salmon. Evidence of introgression of the Cascade strain into European broodstocks was provided by the presence of large Ssa202 alleles (confined to North America in wild populations) in some Mowi and McConnell samples. Introgression likely also contributed to the decreased intercontinental genetic distance for the domesticated samples of this study compared with that observed for wild populations.     

Invasion genetics of the Eurasian spiny waterflea: evidence for bottlenecks and gene flow using microsatellites

The Eurasian spiny waterflea (Bythotrephes longimanus) is a predacious zooplankter that has increased its range in Europe and is rapidly invading inland water-bodies throughout North America's Great Lakes region. To examine the genetics of these invasions, we isolated five microsatellite DNA loci with between 5 and 19 alleles per locus. We sampled three populations where B. longimanus has been historically present (Switzerland, Italy, and Finland) as well as an introduced European population (the Netherlands) and three North American populations (Lakes Erie, Superior, Shebandowan). Consistent with a bottleneck during colonization (i.e. founder effect), average heterozygosities of the four European populations ranged from 0.310 to 0.599, and were higher than that of three North American populations (0.151-0.220). Pairwise F(ST) estimates among North American populations (0.002-0.063) were not significantly different from zero and were much lower than among European populations (0.208-0.474). This is consistent with a scenario of high gene flow among North American populations relative to that of European ones. Contrary to an invasion bottleneck, however, Erie and Superior populations contained similar numbers of rare alleles as European populations. Assignment tests identified several migrant genotypes in all introduced populations (the Netherlands, Erie, Superior, Shebandowan), but rarely in native ones (Switzerland, Italy and Finland). A large number of genotypes from North America were assigned to our Italian population suggesting a second, previously unidentified, invasion source somewhere in the region of northern Italy. Together, our results support an invasion bottleneck for North American populations that has been largely offset by gene flow from multiple native sources, as well as gene flow among introduced populations.     

The lack of genetic bottleneck in invasive Tansy ragwort populations suggests multiple source populations.

Jacobaea vulgaris (Asteraceae) is a species of Eurasian origin that has become a serious non-indigenous weed in Australia, New Zealand, and North America. We used neutral molecular markers to (1) test for genetic bottlenecks in invasive populations and (2) to investigate the invasion pathways. It is for the first time that molecular markers were used to unravel the process of introduction in this species.The genetic variation of 15 native populations from Europe and 16 invasive populations from Australia, New Zealand and North America were compared using the amplified fragment length polymorphisms (AFLP's). An analysis of molecular variance showed that a significant part (10%) of the total genetic variations between all individuals could be explained by native or invasive origin.Significant among-population differentiation was detected only in the native range, whereas populations from the invasive areas did not significantly differ from each other; nor did the Australian, New Zealand and North American regions differ within the invasive range. The result that native populations differed significantly from each other and that the amount of genetic variation, measured as the number of polymorphic bands, did not differ between the native and invasive area, strongly suggests that introductions from multiple source populations have occurred. The lack of differentiation between invasive regions suggests that either introductions may have occurred from the same native sources in all invasive regions or subsequent introductions took place from one into another invasive region and the same mix of genotypes was subsequently introduced into all invasive regions.An assignment test showed that European populations from Ireland, the Netherlands and the United Kingdom most resembled the invasive populations.     

A new strain group of common carp: The genetic differences and admixture events between Cyprinus carpio breeds

Common carp (Cyprinus carpio) has an outstanding economic importance in freshwater aquaculture due to its high adaptive capacity to both food and environment. In fact, it is the third most farmed fish species worldwide according to the Food and Agriculture Organization. More than four million tons of common carp are produced annually in aquaculture, and more than a hundred thousand tons are caught from the wild. Historically, the common carp was also the first fish species to be domesticated in ancient China, and now, there is a huge variety of domestic carp strains worldwide. In the present study, we used double digestion restriction site‐associated DNA sequencing to genotype several European common carp strains and showed that they are divided into two distinct groups. One of them includes central European common carp strains as well as Ponto–Caspian wild common carp populations, whereas the other group contains several common carp strains that originated in the Soviet Union, mostly as cold‐resistant strains. We believe that breeding with wild Amur carp and subsequent selection of the hybrids for resistance to adverse environmental conditions was the attribute of the second group. We assessed the contribution of wild Amur carp inheritance to the common carp strains and discovered discriminating genes, which differed in allele frequencies between groups. Taken together, our results improve our current understanding of the genetic variability of common carp, namely the structure of natural and artificial carp populations, and the contribution of wild carp traits to domestic strains.     

The population genomic basis of geographic differentiation in North American common ragweed (Ambrosia artemisiifolia L.)

Common ragweed (Ambrosia artemisiifolia L.) is an invasive, wind‐pollinated plant nearly ubiquitous in disturbed sites in its eastern North American native range and present across growing portions of Europe, Africa, Asia, and Australia. Phenotypic divergence between European and native‐range populations has been described as rapid evolution. However, a recent study demonstrated major human‐mediated shifts in ragweed genetic structure before introduction to Europe and suggested that native‐range genetic structure and local adaptation might fully explain accelerated growth and other invasive characteristics of introduced populations. Genomic differentiation that potentially influenced this structure has not yet been investigated, and it remains unclear whether substantial admixture during historical disturbance of the native range contributed to the development of invasiveness in introduced European ragweed populations. To investigate fine‐scale population genetic structure across the species' native range, we characterized diallelic SNP loci via a reduced‐representation genotyping‐by‐sequencing (GBS) approach. We corroborate phylogeographic domains previously discovered using traditional sequencing methods, while demonstrating increased power to resolve weak genetic structure in this highly admixed plant species. By identifying exome polymorphisms underlying genetic differentiation, we suggest that geographic differentiation of this important invasive species has occurred more often within pathways that regulate growth and response to defense and stress, which may be associated with survival in North America's diverse climatic regions.     

Invasion history of North American Canada thistle,Cirsium arvense

Aim Canada thistle (Cirsium arvense– Cardueae, Asteraceae) is one of the worst invasive plants world‐wide. Native to Eurasia, its unintentional introduction into North America now threatens the native flora and is responsible for enormous agricultural losses. The goals of this study are to: (1) reconstruct the evolutionary history of C. arvense and estimate how often it may have colonized North America, (2) compare the genetic diversity between European and North American populations to detect signs of demographic bottlenecks and/or patterns of population admixture, and (3) conduct bioclimatic comparisons to infer eventual niche shifts following this species’ introduction into North America. Location Europe and North America. Methods A total of 1522 individuals from 58 populations were investigated with six microsatellite markers. Estimates of heterozygosity (H_E) and allelic richness (R_S) were quantified for each population, and population structure was inferred via analyses of molecular variance (AMOVAs), principal components analyses (PCAs), Mantel tests and Bayesian clustering analyses. Climatic niche spaces were based on 19 bioclimatic variables extracted from approximately 32,000 locations covering the entire range, and compared using PCA and hierarchical cluster analysis. Results Although there is evidence of multiple introductions from divergent European lineages, North American populations of C. arvense exhibited significantly lower levels of genetic diversity than their putative ancestors. Bioclimatic comparisons pointed to a high degree of niche conservatism during invasion, but indicated that genotypes from the former USSR and Central European mountain chains were probably best adapted to invade North America upon entry into the continent. Main conclusions Genetic and historical data suggest that C. arvense first entered North America from Western Europe with the first European settlers, and was later introduced from Eastern Europe into the prairie states during the agricultural boom. The species went through a significant bottleneck following its introduction into the New World, but the level of genetic diversity remained high owing to admixture between genetically differentiated lineages and to a highly efficient outcrossing breeding system.     

Evidence for multiple introductions of Centaurea stoebe micranthos (spotted knapweed,Asteraceae) to North America

Invasive species’ success may depend strongly on the genetic resources they maintain through the invasion process. We ask how many introductions have occurred in the North American weed Centaurea stoebe micranthos (Asteraceae), and explore whether genetic diversity and population structure have changed as a result of introduction. We surveyed individuals from 15 European native range sites and 11 North American introduced range sites at six polymorphic microsatellite loci. No significant difference existed in the total number of alleles or in the number of private alleles found in each range. Shannon–Weaver diversity of phenotype frequencies was also not significantly different between the ranges, while expected heterozygosity was significantly higher in the invasive range. Population structure was similar between the native range and the invasive range, and isolation by distance was not significant in either range. Traditional assignment methods did not allocate any North American individuals to the sampled European populations, while Bayesian assignment methods grouped individuals into nine genetic clusters, with three of them shared between North America and Europe. Invasive individuals tended to have genetically admixed profiles, while natives tended to assign more strongly to a single cluster. Many North American individuals share assignment with Romania and Bulgaria, suggesting two separate invasions that have undergone gene flow in North America. Samples from three other invasive range sites were genetically distinct, possibly representing three other unique introductions. Multiple introductions and the maintenance of high genetic diversity through the introduction process may be partially responsible for the invasive success of C. stoebe micranthos.     

Reduced anti-predator responses in multi-generational hybrids of farmed and wild Atlantic salmon (<Emphasis Type="Italic">Salmo salar</Emphasis> L.)

Cultured organisms undergo genetically-based behavioural changes that may reduce their ability to survive in the wild. This has raised concerns that interbreeding between escaped cultured and wild organisms will generate hybrids exhibiting maladaptive behaviours which may ultimately reduce the fitness of the wild counterpart. We compared anti-predator responses in Atlantic salmon (Salmo salar) from two wild North American populations, the major farmed strain used in regional aquaculture, and their wild-farmed hybrids (F₁, F₂, and wild backcross). Anti-predator responses of fry (age 0+ parr) were measured under common environmental conditions, using a model of a natural predator (belted kingfisher, Ceryle alcyon). Farmed fry exhibited significantly reduced anti-predator responses relative to fry from both wild populations. The anti-predator responses of wild-farmed hybrid fry were intermediate to those of the parental populations (pure farmed or wild). The magnitude by which wild-farmed hybrids differed in anti-predator responses from pure wild fish also depended on the wild population. These results suggest that: (1) the observed behavioural differences have a genetic basis; (2) wild-farmed hybrids have, on average, reduced anti-predator responses relative to wild fish; and that (3) the effects of wild-farmed interbreeding on anti-predator responses will differ between wild populations. Our study is consistent with the general hypothesis that continual farmed-wild interbreeding may have detrimental effects on the fitness of wild organisms.     

Phylogeography and population genetics of introduced Silver Carp (<Emphasis Type="Italic">Hypophthalmichthys molitrix</Emphasis>) and Bighead Carp (<Emphasis Type="Italic">H. nobilis</Emphasis>) in North America

The success of a biological invasion and the ability to control an invader may partially depend on the genetic diversity of the invasive species and the amount of dispersal and gene flow occurring throughout its introduced range. Here, we used nuclear microsatellites to analyze genetic diversity and structure and whole mitogenomic sequences to analyze the phylogeography of Silver Carp (SC; Hypophthalmichthys molitrix) and Bighead Carp (BHC; H. nobilis) across their North American ranges. Our objectives were to assess: (1) the number of mitochondrial haplotypes that were introduced and how they are distributed in North America, which may provide insight into the history of the invasion, (2) how genetic diversity compares between the native Asian and introduced North American populations, (3) how genetic variation is structured across the North American ranges of SC and BHC as well as between the two species, and (4) whether patterns of genetic diversity and structure are likely to affect success of environmental DNA programs for monitoring these species. In both species, we found relatively few mitochondrial haplotypes, and most were present throughout the range. For both SC and BHC, unique haplotypes were found only in a portion of the species’ range, possibly indicating the location of additional, more recent introductions. In both species, genetic diversity was moderately lower in North American populations (i.e., 75–90% of that found in Asian populations), but genetic diversity still remained high. We found very little population genetic structure, consistent with a rapidly spreading invasive species, and did not find evidence of cryptic interspecific hybrids. The markers developed for eDNA monitoring will be effective for detecting the majority of individuals of these species in North America. The relatively high level of genetic variation and lack of population structure of SC and BHC in North America indicate that genetic diversity likely will not limit their persistence and that high connectivity will likely complicate efforts to control these invasive species.