A sensitive environmental DNA (eDNA) assay leads to new insights on Ruffe (<Emphasis Type="Italic">Gymnocephalus cernua</Emphasis>) spread in North America

Detection of invasive species before or soon after they establish in novel environments is critical to prevent widespread ecological and economic impacts. Environmental DNA (eDNA) surveillance and monitoring is an approach to improve early detection efforts. Here we describe a large-scale conservation application of a quantitative polymerase chain reaction assay with a case study for surveillance of a federally listed nuisance species (Ruffe, Gymnocephalus cernua) in the Laurentian Great Lakes. Using current Ruffe distribution data and predictions of future Ruffe spread derived from a recently developed model of ballast-mediated dispersal in US waters of the Great Lakes, we designed an eDNA surveillance study to target Ruffe at the putative leading edge of the invasion. We report a much more advanced invasion front for Ruffe than has been indicated by conventional surveillance methods and we quantify rates of false negative detections (i.e. failure to detect DNA when it is present in a sample). Our results highlight the important role of eDNA surveillance as a sensitive tool to improve early detection efforts for aquatic invasive species and draw attention to the need for an improved understanding of detection errors. Based on axes that reflect the weight of eDNA evidence of species presence and the likelihood of secondary spread, we suggest a two-dimensional conceptual model that management agencies might find useful in considering responses to eDNA detections.     

Patterns of invasion in the Laurentian Great Lakes in relation to changes in vector activity

The Laurentian Great Lakes basin has been invaded by at least 182 non-indigenous species. A new invader is discovered every 28 weeks, which is the highest rate recorded for a freshwater ecosystem. Over the past century, invasions have occurred in phases linked to changes in the dominant vectors. The number of ship-vectored invaders recorded per decade is correlated with the intensity of vessel traffic within the basin. Ballast water release from ocean vessels is the putative vector for 65% of all invasions recorded since the opening of the St. Lawrence Seaway in 1959. As a preventive measure, ocean vessels have been required since 1993 to exchange their freshwater or estuarine ballast with highly saline ocean water prior to entering the Great Lakes. However, this procedure has not prevented ship-vectored species introductions. Most ships visiting the Great Lakes declare 'no ballast on board' (NOBOB) and are exempt from the regulation, even though they carry residual water that is discharged into the Great Lakes during their activities of off-loading inbound cargo and loading outbound cargo. Recently introduced species consist predominantly of benthic invertebrates with broad salinity tolerance. Such species are most likely to survive in a ballast tank following ballast water exchange, as well as transport in the residual water and tank sediments of NOBOB ships. Thus, the Great Lakes remain at risk of being invaded by dozens of euryhaline invertebrates that have spread into Eurasian ports from whence originates the bulk of foreign ships visiting the basin.     

Recent mass invasion of the North American Great Lakes by Ponto-Caspian species

The North American Great Lakes have been invaded and dramatically altered by more than 145 alien species. Many invasions have occurred during the past few decades because of the release of Eurasian ballast water from transoceanic ships. Current regulations require ships to exchange foreign ballast with highly saline water before entering the Great Lakes; this procedure should prevent colonization by strictly freshwater species, but species with broad salinity tolerance might survive transport in exchanged water. A recent series of invasions by euryhaline organisms from the Black and Caspian Seas region signals a new phase in the transformation of the Great Lakes - one that supports the concept of an 'invasional meltdown'.     

Domestic ships as a potential pathway of nonindigenous species from the Saint Lawrence River to the Great Lakes

Ballast water moved by transoceanic vessels has been recognized globally as a predominant vector for the introduction of aquatic nonindigenous species (NIS). In contrast, domestic ships operating within confined geographic areas have been viewed as low risk for invasions, and are exempt from regulation in consequence. We examined if the St. Lawrence River could serve as a source of NIS for the Laurentian Great Lakes by surveying ballast water carried by domestic vessels and comparing biological composition in predominant St. Lawrence River—Great Lakes port-pairs in order to determine the likelihood that NIS could be transported to, and survive in, the Great Lakes. Thirteen potential invaders were sampled from ballast water, while 26 taxa sampled from St. Lawrence River ports are not reported from the Great Lakes. The majority of NIS recorded in samples are marine species with low potential for survival in the Great Lakes, however two euryhaline species (copepod Oithona similis, and amphipod Gammarus palustris) and two taxa reported from brackish waters (copepod Microsetella norvegica and decapod Cancer irroratus) may pose a risk for invasion. In addition, four marine NIS were collected in freshwater samples indicating that at least a subset of marine species have potential as new invaders to the Great Lakes. Based on results from this study, the ports of Montreal, Sorel, Tracy and Trois Rivières appear to pose the highest risk for new ballast-mediated NIS from the St. Lawrence River to the Great Lakes.     

Modeling the secondary spread of viral hemorrhagic septicemia virus (VHSV) by commercial shipping in the Laurentian Great Lakes

Researchers have only begun to study the role of shipping in the spread of invasive species in the Laurentian Great Lakes despite a well-documented history of introductions in these lakes due to ballast water release. Here, we determine whether ballast water discharge was a likely vector of spread of the fish disease, viral hemorrhagic septicemia virus genotype IVb (VHSV-IVb), throughout the Great Lakes and St. Lawrence Seaway. Three models were developed to assess whether the spread of VHSV was due to (1) chance (random model), or (2) ballast water discharge (location model), and whether (3) increased propagule pressure, as measured by the number of visitations by ships carrying ballast water from VHSV infected areas, increased the likelihood of a discharge location becoming infected with VHSV (propagule pressure model). The third model was also used to assess the probable point of initial introduction of VHSV. Presence and absence accuracies and weighted Cohen’s kappa were calculated to determine which models best predicted observed presences and absences of VHSV. Location models explain the patterns of VHSV detections better than random models, and inclusion of “propagule pressure” often improved model fit; however, the relationship is weak likely because of a long lag time between introduction and detection, a high rate of false negatives in reporting, and the possible contribution of other vectors of spread. Montreal was also identified as the more likely introduction site of VHSV, rather than Lake St. Clair, the site where the virus was first detected.     

Transport of the Harmful Bloom Alga Aureococcus anophagefferens by Oceangoing Ships and Coastal Boats

It is well established that cyst-forming phytoplankton species are transported in ships' ballast tanks. However, there is increasing evidence that other phytoplankton species which do not encyst are also capable of surviving ballast transit. These species have alternative modes of nutrition (hetero- or mixotrophy) and/or are able to survive long-term darkness. In our studies of no-ballast-on-board vessels arriving in the Great Lakes, we tested for the presence of the harmful algal bloom species Aureococcus anophagefferens (brown tide) in residual (i.e., unpumpable) ballast water using methods based on the PCR. During 2001, the brown tide organism was detected in 7 of 18 ballast water tanks in commercial ships following transit from foreign ports. Furthermore, it was detected after 10 days of ballast tank confinement during a vessel transit in the Great Lakes, a significant result given the large disparity between the salinity tolerance for active growth of Aureococcus (>22 ppt) and the low salinity of the residual ballast water (~2 ppt). We also investigated the potential for smaller, recreational vessels to transport and distribute Aureococcus. During the summer of 2002, 11 trailered boats from the inland bays of Delaware and coastal bays of Maryland were sampled. Brown tide was detected in the bilge water in the bottoms of eight boats, as well as in one live-well sample. Commercial ships and small recreational boats are therefore implicated as potential vectors for long-distance transport and local-scale dispersal of Aureococcus.     

Molecular detection of invasive species in heterogeneous mixtures using a microfluidic carbon nanotube platform

Screening methods to prevent introductions of invasive species are critical for the protection of environmental and economic benefits provided by native species and uninvaded ecosystems. Coastal ecosystems worldwide remain vulnerable to damage from aquatic species introductions, particularly via ballast water discharge from ships. Because current ballast management practices are not completely effective, rapid and sensitive screening methods are needed for on-site testing of ships in transit. Here, we describe a detection technology based on a microfluidic chip containing DNA oligonucleotide functionalized carbon nanotubes. We demonstrate the efficacy of the chip using three ballast-transported species either established (Dreissena bugensis) or of potential threat (Eriocheir sinensis and Limnoperna fortuneii) to the Laurentian Great Lakes. With further refinement for on-board application, the technology could lead to real-time ballast water screening to improve ship-specific management and control decisions.     

Transoceanic ships as vectors for nonindigenous freshwater bryozoans

Aim The transport of organisms in ships’ ballast tanks is a dominant vector for aquatic invasions worldwide. Until recently, efforts to manage this vector have overlooked the potential transport of invertebrate resting stages in the residual waters and sediments within emptied ballast tanks, i.e. NOBOB (‘No Ballast On Board’) tanks. The resting stages (statoblasts) of freshwater bryozoans are often buoyant and locally abundant and thus can be taken up easily during ballasting operations. They are also resistant to extreme environmental conditions and can generate new colonies after being dormant for decades; as such, they would likely remain viable propagules after lengthy transport in ship ballast tanks. This study quantified the occurrence of freshwater bryozoan statoblasts in ballast tank sediments of transoceanic ships. Location North American Great Lakes. Methods We quantified the frequency of occurrence, abundance and diversity of bryozoans (as statoblasts) in residual sediment samples taken from 51 NOBOB tanks of 33 transoceanic ships visiting the Great Lakes from 2000 to 2002. Results Our study identified 11 species, comprising nearly 12% of the total number of freshwater bryozoans known worldwide. These include two exotic species unrecorded in the Great Lakes (Fredericella sultana and Lophopus crystallinus), an exotic species already established in the region (Lophopodella carteri) and three cosmopolitan species (Plumatella casmiana, P. fungosa and P. repens). Our estimates suggest that a ship with NOBOB tanks may carry up to 10⁶ statoblasts. Main conclusions The discovery of species unrecorded in the Great Lakes and the potentially large numbers of statoblasts being transported in ship ballast tanks indicate a significant risk of new species introductions. Furthermore, the presence of cosmopolitan species and an exotic species already established in the Great Lakes suggests the strong possibility of cryptic invasions via the introduction of exotic genotypes.     

Dynamics and short-term survival of toxic cyanobacteria species in ballast water from NOBOB vessels transiting the Great Lakes—implications for HAB invasions

We measured the presence, viability and potential toxicity of cyanobacteria in ships’ ballast tanks during three domestic voyages through the North American Great Lakes. Using molecular methods, the toxin-producing forms of Microcystis and Anabaena were monitored in ballast water after ships’ ballast tanks were filled at their first port of call, and at subsequent ports as ships transited the Great Lakes. Microcystis was detected in ballast water at intermediate and final ports of call in all three experiments, but the presence of Anabaena was more variable, suggesting low abundance or patchy distribution in ballast tanks. Both species were detected in ballast water up to 11 days old. Detection of the microcystin synthetase gene, mcyE, in ballast tanks indicated entrained cells were capable of producing microcystin, and further analyses of RNA indicated the toxin was being expressed by Microcystis, even after 11 days in dark transit. These data demonstrate within-basin transport and delivery of planktonic harmful algal bloom (HAB) species to distant ports in the world's largest freshwater reservoir, with potential implications for drinking water quality. These implications are discussed with respect to management of microbial invasions and the fate of introduced phytoplankton in their receiving environment.     

Potential changes to the biology and challenges to the management of invasive sea lamprey Petromyzon marinus in the Laurentian Great Lakes due to climate change

Control programs are implemented to mitigate the damage caused by invasive species worldwide. In the highly invaded Great Lakes, the climate is expected to become warmer with more extreme weather and variable precipitation, resulting in shorter iced‐over periods and variable tributary flows as well as changes to pH and river hydrology and hydrogeomorphology. We review how climate change influences physiology, behavior, and demography of a damaging invasive species, sea lamprey (Petromyzon marinus), in the Great Lakes, and the consequences for sea lamprey control efforts. Sea lamprey control relies on surveys to monitor abundance of larval sea lamprey in Great Lakes tributaries. The abundance of parasitic, juvenile sea lampreys in the lakes is calculated by surveying wounding rates on lake trout (Salvelinus namaycush), and trap surveys are used to enumerate adult spawning runs. Chemical control using lampricides (i.e., lamprey pesticides) to target larval sea lamprey and barriers to prevent adult lamprey from reaching spawning grounds are the most important tools used for sea lamprey population control. We describe how climate change could affect larval survival in rivers, growth and maturation in lakes, phenology and the spawning migration as adults return to rivers, and the overall abundance and distribution of sea lamprey in the Great Lakes. Our review suggests that Great Lakes sea lamprey may benefit from climate change with longer growing seasons, more rapid growth, and greater access to spawning habitat, but uncertainties remain about the future availability and suitability of larval habitats. Consideration of the biology of invasive species and adaptation of the timing, intensity, and frequency of control efforts is critical to the management of biological invasions in a changing world, such as sea lamprey in the Great Lakes.     

Salinity tolerance of Great Lakes invaders

1. The Laurentian Great Lakes are among the most invaded freshwater ecosystems in the world. Historically, the major vector for the introduction of non‐indigenous species (NIS) has been the release of contaminated ballast water via transoceanic ships. Despite regulations implemented in 1993, requiring vessels carrying fresh ballast water to exchange this water with saline ocean water, new reports of invasions have continued. 2. NIS often have a wide environmental tolerance allowing them to adapt to and invade a variety of habitats. It has been hypothesized that NIS with broad salinity tolerance may be able to survive ballast water exchange (BWE) and continue to pose an invasion risk to the Great Lakes. 3. We tested the short‐term salinity tolerance of eight recent invaders to the Great Lakes, specifically three cladocera (Bosmina coregoni, Bythotrephes longimanus, Cercopagis pengoi), two molluscs (Dreissena polymorpha, Dreissena rostriformis bugensis), and one species each of the families Gammaridae, Mysidae and Gobidae (Echinogammarus ischnus, Hemimysis anomala, Neogobius melanostomus) to determine if they could have survived salinities associated with BWE. 4. Overall, short‐term exposure to highly saline water dramatically reduced survival of all species. Two different methods of BWE tested, simultaneous and sequential, were equally effective in reducing survival. Species that survived the longest in highly saline water either possess behavioural characteristics that reduce exposure to adverse environments (valve closure; both Dreissena species) or are reported to have some degree of salinity tolerance in their native region (Echinogammarus). Given that exposure in our trials lasted a maximum of 48 h, and that species in ballast tanks would typically be exposed to saline water for c. 5 days, it appears that BWE is an effective method to reduce the survival of these NIS. These results provide impetus for tightening policy and monitoring of BWE, in particular for ships entering the Great Lakes from freshwater ports.     

Salinity tolerance of diapausing eggs of freshwater zooplankton

1. Many freshwater zooplankton produce diapausing eggs capable of withstanding periods of adverse environmental conditions, such as anoxia, drought and extreme temperature. These eggs may also allow oligostenohaline species to survive increased salinity during periods of tidal flux or evaporation, and here we test the ability of diapause eggs to withstand such conditions. 2. Salinity tolerance may also enable organisms to invade new environments. The increased rate of introduction of non‐indigenous species to the Laurentian Great Lakes since 1989, when ballast water exchange regulations (to replace fresh/brackish water at sea with full seawater) were first implemented for transoceanic vessels, has stimulated studies that explore mechanisms of introduction, other than of active animals, in ballast water. One hypothesis proposes that freshwater organisms transported in ballast tanks as diapausing eggs may be partially responsible for the increased rate of species introduction, as these eggs may tolerate a wide array of adverse environmental conditions, including exposure to saline water. 3. We collected ballast sediments from transoceanic vessels entering the Great Lakes, isolated diapausing eggs of three species (Bosmina liederi, Daphnia longiremis and Brachionus calyciflorus), and measured the effect of salinity on hatching rate. In general, exposure to salinity significantly reduced the hatching rate of diapausing eggs. However, as non‐indigenous species can establish from a small founding population, it is unclear whether salinity exposure will be effective as a management tool.     

Comparative Biology of Zebra Mussels in Europe and North America: An Overview

SYNOPSIS. Since the discovery of the zebra mussel, Dreissenapolymorpha, in the Great Lakes in 1988 comparisons have beenmade with mussel populations in Europe and the former SovietUnion. These comparisons include: Population dynamics, growthand mortality rates, ecological tolerances and requirements,dispersal rates and patterns, and ecological impacts. NorthAmerican studies, mostly on the zebra mussel and a few on asecond introduced species, the quagga mussel, Dreissena bugensis,have revealed some similarities and some differences. To dateit appears that North American populations of zebra musselsare similar to European populations in their basic biologicalcharacteristics, population growth and mortality rates, anddispersal mechanisms and rates. Relative to European populationsdifferences have been demonstrated for: (1) individual growthrates; (2) life spans; (3) calcium and pH tolerances and requirements;(4) potential distribution limits; and (5) population densitiesof veligers and adults. In addition, studies on the occurrenceof the two dreissenid species in the Great Lakes are showingdifferences in their modes of life, depth distributions, andgrowth rates. As both species spread throughout North America,comparisons between species and waterbodies will enhance ourability to more effectively control these troublesome species.     

Predicting habitat use and trophic interactions of Eurasian ruffe,round gobies,and zebra mussels in nearshore areas of the Great Lakes

The Laurentian Great Lakes have been subject to numerous introductions of nonindigenous species, including two recent benthic fish invaders, Eurasian ruffe (Gymnocephalus cernuus) and round gobies (Neogobius melanostomus), as well as the benthic bivalve, zebra mussel (Dreissena polymorpha). These three exotic species, or “exotic triad,” may impact nearshore benthic communities due to their locally high abundances and expanding distributions. Laboratory experiments were conducted to determine (1) whether ruffe and gobies may compete for habitat and invertebrate food in benthic environments, and (2) if zebra mussels can alter those competitive relationships by serving as an alternate food source for gobies. In laboratory mesocosms, both gobies and ruffe preferred cobble and macrophyte areas to open sand either when alone or in sympatry. In a 9-week goby–ruffe competition experiment simulating an invasion scenario with a limited food base, gobies grew faster than did ruffe, suggesting that gobies may be competitively superior at low resource levels. When zebra mussels were added in a short-term experiment, the presence or absence of mussels did not affect goby or ruffe growth, as few zebra mussels were consumed. This finding, along with other laboratory evidence, suggests that gobies may prefer soft-bodied invertebrate prey over zebra mussels. Studies of interactions among the “exotic triad”, combined with continued surveillance, may help Great Lakes fisheries managers to predict future population sizes and distributions of these invasive fish, evaluate their impacts on native food webs, and direct possible control measures to appropriate species.     

Invasion Genetics of Ponto-Caspian Gobies in the Great Lakes: A ‘Cryptic’ Species, Absence of Founder Effects, and Comparative Risk Analysis

Genetic variability and structure of nonindigenous vs native populations are compared for the Eurasian round goby Neogobius melanostomus and the tubenose goby Proterorhinus marmoratus, which both invaded Lake St. Clair of the North American Great Lakes about 1990. The round goby spread rapidly to all of the Great Lakes and the tubenose goby largely has been restricted to Lake St. Clair, with some recent range extension into western Lake Erie. Risk analyses may indicate whether genetic variability of colonizers is predictive of their relative invasive and establishment successes. The present investigation examined DNA sequence variation across the left domain of the mitochondrial DNA cytochrome b gene in round and tubenose gobies from Eurasian and Great Lakes locations. We also sequenced six additional Neogobius species (including the monkey N.␣fluviatilis, racer N. gymnotrachelus, and bigheadN. kessleri gobies that have been ‘on the move’ in Europe) and the knout goby Mesogobius batrachocephalus from the Black Sea in order to develop diagnostic genetic characters to identify them in case of future and/or undetected invasions and to delineate their phylogenetic relationships. Results show that a diverse number of haplotypes characterize round and tubenose goby populations from both North America and Eurasian sites, fitting a risk analysis prediction of high genetic variability in their successful introductions. Phylogenetic results indicate that the current genus Neogobius is paraphyletic and that the subgenusApollonia thus should be elevated to the level of genus, containingApollonia (N.) melanostomus (the round goby) andA. (N.) fluviatilis (the monkey goby). In addition, there appear to be two separate species of Proterorhinus marmoratus, a marine P. marmoratus Pallas 1814 in the Black Sea (matching the original type locality), and a ‘cryptic’ freshwater species in the Danube and Dnieper Rivers and probably other Eurasian freshwater habitats, as well as invasive in the Great Lakes. We suggest resurrecting the name P. semilunaris Heckel 1837 for the freshwater species (a taxon that was originally described from rivers draining into the Aegean Sea and the Danube River, but was later placed in synonymy with P. marmoratus). An erratum to this article is available at .     

Recreational boats as a vector of secondary spread for aquatic invasive species and native crustacean zooplankton

Recreational boats in tow between lakes are a known vector of the spread of aquatic invading species (AIS), but we have no test of the hypothesis that recreational boats are also a vector of secondary spread of AIS among freshwater ecosystems via in-water transport i.e., while boating between interconnected waterways. In this study, we surveyed recreational boaters travelling into Lake Simcoe (44°25′N, 79°20′W), Ontario, Canada, on their recreational activities, boat maintenance, and travel destinations, measured the degree of vessel fouling, and sampled all standing water and attached macrophytes associated with their vessels. A total of 321 zooplankton individuals comprising 15 different species were collected from the standing water in vessels, including veligers of the invasive zebra mussel Dreissena. The volume of water collected within the vessels significantly increased the number of zooplankton transported. Zooplankton species from pelagic habitats or with planktonic life stages were collected more frequently than species that occupy littoral or benthic habitats, likely reflecting the recreational activities of boaters. Patterns of boater activities, movements and hygiene habits, suggest recreational boating in the Lake Simcoe region is contributing to the spread of native and invasive species into nearby waterways. Our study validates the widespread assumption that recreational boats are an important in-water vector for the secondary spread of both native and invasive zooplankton species. Future management strategies to reduce the spread of AIS should be aimed at increasing awareness of boater hygiene practices, particularly the frequent draining of standing water.     

Estimating the financial costs of freshwater invasive species in Great Britain: a standardized approach to invasive species costing

Both ecological and economic impacts factor into invasive alien species (IAS) management considerations; however, economic impacts are often difficult to assess, much less quantify. Studies frequently aggregate identified financial costs as a proxy for IAS economic impacts, but these aggregate figures are often generated in an ad hoc fashion. Such estimates typically sum disparate costs, which might vary with respect to precision, accuracy, and scope. A standardized approach for IAS costing would better enable the comparison of cost estimates between taxa and across studies by controlling for surveying and scaling inconsistencies. This study develops a simple, survey-based approach to generate economic cost estimates for non-native freshwater invasive species (FIS) in Great Britain. The approach scales an average cost for each species by a ratio of management effort, thereby estimating the actual, annual expenditures incurred by a variety of stakeholders. The Great Britain-wide cost of controlling FIS is estimated to be approximately ￡26.5 million year⁻¹; however, the costs of control could total ￡43.5 million year⁻¹ if management efforts were undertaken at all FIS infested locations. Cost estimates are highest for Canadian pondweed (Elodea canadensis), a particularly widespread species, and for the zebra mussel (Dreissena polymorpha), which adversely impacts both industrial water users and boaters. This assessment of the relative economic impacts between species provides policy-makers with a monetary basis for rank-ordering species’ economic impacts and prioritizing management efforts. In addition, the cost assessment approach developed in this study could serve as a model for IAS economic impact assessments elsewhere.     

A review of Ruffe (<Emphasis Type="Italic">Gymnocephalus cernua</Emphasis>) life history in its native versus non-native range

Invasive Ruffe (Gymnocephalus cernua) has caused substantial ecological damage in North America, parts of Western Europe, Scandinavian countries, and the United Kingdom. The objectives of this review are to define Ruffe’s native and non-native range, examine life history requirements, explore the life cycle, and differentiate between life stages. We compare data from its native and non-native ranges to determine if there are any differences in habitat, size, age, genotype, or seasonal migration. Literature from both the native and non-native ranges of Ruffe, with some rare, translated literature, is used. In each life stage, Ruffe exhibit plasticity with regard to chemical, physical, biological, and habitat requirements. Adult Ruffe has characteristics that allow them to adapt to a range of environments, including rapid maturation, relatively long life and large size (allowing them to reproduce many times in large batches), batch spawning, genotype and phenotype (having plasticity in their genetic expression), tolerance to a wide range of water quality, broad diet, and multiple dispersal periods. There is, however, variability among these characteristics between the native, non-native North American, and European non-native populations, which presents a challenge to managing populations based on life history characteristics. Monitoring and preventative strategies are important because, based on Ruffe’s variable life history strategies and its recent range expansion, all of the Laurentian Great Lakes and many other water bodies in the UK, Europe, and Norway are vulnerable to Ruffe establishment.     

Invasion genetics of the Eurasian round goby in North America: tracing sources and spread patterns

The Eurasian round goby Neogobius melanostomus ( Apollonia melanostoma ) invaded the North American Great Lakes in 1990 through ballast water, spread rapidly, and now is widely distributed and moving through adjacent tributaries. We analyse its genetic diversity and divergence patterns among 25 North American ( N  = 744) and 22 Eurasian ( N  = 414) locations using mitochondrial DNA cytochrome b gene sequences and seven nuclear microsatellite loci in order to: (i) identify the invasion's founding source(s), (ii) test for founder effects, (iii) evaluate whether the invasive range is genetically heterogeneous, and (iv) determine whether fringe and central areas differ in genetic diversity. Tests include F _ST analogues, neighbour-joining trees, haplotype networks, Bayesian assignment, Monmonier barrier analysis, and three-dimensional factorial correspondence analysis. We recovered 13 cytochrome b haplotypes and 232 microsatellite alleles in North America and compared these to variation we previously described across Eurasia. Results show: (i) the southern Dnieper River population was the primary Eurasian donor source for the round goby's invasion of North America, likely supplemented by some alleles from the Dniester and Southern Bug rivers, (ii) the overall invasion has high genetic diversity and experienced no founder effect, (iii) there is significant genetic structuring across North America, and (iv) some expansion areas show reduced numbers of alleles, whereas others appear to reflect secondary colonization. Sampling sites in Lake Huron's Saginaw Bay and Lake Ontario significantly differ from all others, having unique alleles that apparently originated from separate introductions. Substantial genetic variation, multiple founding sources, large number of propagules, and population structure thus likely aided the goby's ecological success.     

Population genetic history of the dreissenid mussel invasions: expansion patterns across North America

This study tests population genetic patterns across the Eurasian dreissenid mussel invasions of North America—encompassing the zebra mussel Dreissena polymorpha (1986 detection) and the quagga mussel D. rostriformis bugensis (detected in 1990, which now has largely displaced the former in the Great Lakes). We evaluate their source-spread relationships and invasion genetics using 9–11 nuclear microsatellite loci for 583 zebra mussels (21 sites) and 269 quagga mussels (12 sites) from Eurasian and North American range locations, with the latter including the Great Lakes, Mississippi River basin, Atlantic coastal waterways, Colorado River system, and California reservoirs. Additionally, mtDNA cytochrome b gene sequences are used to verify species identity. Our results indicate that North American zebra mussels originate from multiple non-native northern European populations, whereas North American quagga mussels trace to native estuaries in the Southern Bug and Dnieper Rivers. Invasive populations of both species show considerable genetic diversity and structure (zebra F _ST = 0.006–0.263, quagga F _ST = 0.008–0.267), without founder effects. Most newer zebra mussel populations have appreciable genetic diversity, whereas quagga mussel populations from the Colorado River and California show some founder effects. The population genetic composition of both species changed over time at given sites; with some adding alleles from adjacent populations, some losing them, and all retaining closest similarity to their original composition. Zebra mussels from Kansas and California appear genetically similar and assign to a possible origin from the St. Lawrence River, whereas quagga mussels from Nevada and California assign to a possible origin from Lake Ontario. These assignments suggest that overland colonization pathways via recreational boats do not necessarily reflect the most proximate connections. In conclusion, our microsatellite results comprise a valuable baseline for resolving present and future dreissenid mussel invasion pathways.