Premature refutation of a human-mediated marine species introduction: the case history of the marine snail <Emphasis Type="Italic">Littorina littorea</Emphasis> in the Northwestern Atlantic

The closely documented spread of the European periwinkle snail, Littorina littorea from Pictou, Nova Scotia in 1840 to New Jersey by 1870, its near absence in pre-European fossil deposits, and its close association with human mechanisms of transport from Europe, are among the clearest evidence of a human-mediated marine introduction ever reported. Genetic data were recently proposed as evidence that North American L. littorea predate European contact and thus, are not introduced. Review of these genetic data and all other data reveals that the simplest explanation of the modern occurrence of this snail in North America is by human introduction.     

How to Use Genetic Data to Distinguish Between Natural and Human-Mediated Introduction of <Emphasis Type="Italic">Littorina littorea</Emphasis> to North America

The rapid range southward expansion of the periwinkle Littorina littorea from the Canadian maritimes has fueled a long-running debate over whether this species was introduced to North America by human activity. A reappraisal of the mitochondrial DNA sequence evidence finds considerable endemic allelic diversity in the American population. The degree of endemic genetic diversity is higher than expected from human-mediated colonization, but not so much to suggest that it survived the last glacial maximum in America. Coalescent estimates of population divergence agree that colonization of America preceded European contact. A reappraisal of the ITS nuclear sequence data finds extensive recombination. Taking this recombination into account strengthens the genetic case against human-mediated introduction. Finally, a reappraisal of conflicting allozyme studies from the 1970’s supports a claim of limited divergence between American and European populations. This is consistent with post-glacial colonization, but the allozyme data cannot distinguish between natural or human-mediated colonization. Taken as a whole, the DNA sequence data supports the many sub-fossil reports of an American L. littorea population in the Canadian maritimes that preceded even the first visits by the Vikings.     

Global population genetic structure of the starlet anemone <Emphasis Type="Italic">Nematostella vectensis</Emphasis>: multiple introductions and implications for conservation policy

Distinguishing natural versus anthropogenic dispersal of organisms is essential for determining the native range of a species and implementing an effective conservation strategy. For cryptogenic species with limited historical records, molecular data can help to identify introductions. Nematostella vectensis is a small, burrowing estuarine sea anemone found in tidally restricted salt marsh pools. This species’ current distribution extends over three coast lines: (i) the Atlantic coast of North America from Nova Scotia to Georgia, (ii) the Pacific coast of North America from Washington to central California, and (iii) the southeast coast of England. The 1996 IUCN Red List designates N. vectensis as “vulnerable” in England. Amplified fragment length polymorphism (AFLP) fingerprinting of 516 individuals from 24 N. vectensis populations throughout its range and mtDNA sequencing of a subsample of these individuals strongly suggest that anthropogenic dispersal has played a significant role in its current distribution. Certain western Atlantic populations of N. vectensis exhibit greater genetic similarity to Pacific populations or English populations than to other western Atlantic populations. At the same time, F-statistics showing high degrees of genetic differentiation between geographically proximate populations support a low likelihood for natural dispersal between salt marshes. Furthermore, the western Atlantic harbors greater genetic diversity than either England or the eastern Pacific. Collectively, these data clearly imply that N. vectensis is native to the Atlantic coast of North America and that populations along the Pacific coast and in England are cases of successful introduction.     

Parsimony dictates a human introduction: on the use of genetic and other data to distinguish between the natural and human-mediated invasion of the European snail Littorina littorea in North America

Two centuries of historical, archaeological, paleontological, geological, oceanographical and biological data conclusively indicate that the periwinkle snail Littorina littorea was introduced to North America from Europe either by Norse explorers 1000 years ago or by European colonists after 1840. Available genetic data do not indicate ancient divergence of North American and European L. littorea and thus do not challenge all other evidence that it was introduced from Europe by humans.     

First report of the oriental shrimp <Emphasis Type="Italic">Palaemon macrodactylus</Emphasis> Rathbun, 1902 (Decapoda,Caridea, Palaemonidae) from German waters

The native East Asian shrimp Palaemon macrodactylus has become a common inhabitant of estuaries along the Pacific coast of North America. More recently (documented since 1999), the species has also been colonising European waters and has been reported from Spain, England, Belgium and the Netherlands. In this study, we present a chronology of the reported introductions of this species and provide the first detailed report of its occurrence in German waters. P. macrodactylus was found in the Geeste river mouth (Weser Estuary) as well as in Hooksiel, north of Wilhelmshaven between 2004 and 2005. We assume its presence in other estuarine habitats of the North Sea and predict its introduction into the Baltic Sea.     

Invasion by a Japanese marine microorganism in western North America

The earliest record in western North America of Trochammina hadai Uchio, a benthic foraminifer common in Japanese estuaries, is from sediment collected in Puget Sound in 1971. It was first found in San Francisco Bay in sediment samples taken in 1983, and since 1986 has been collected at 91% of the sampled sites in the Bay, constituting up to 93% of the foraminiferal assemblage at individual sites. The species is also present in recent sediment samples from 12 other sites along the west coast of North America. The evidence indicates that T. hadai is a recent introduction to San Francisco Bay, and is probably also not native to the other North American sites. Trochammina hadai was probably transported from Japan in ships' ballast tanks, in mud associated with anchors, or in sediments associated with oysters imported for mariculture. Its remarkable invasion of San Francisco Bay suggests the potential for massive, rapid invasions by other marine microorganisms.     

Rapid colonization of Belgian breakwaters by the direct developer,Littorina saxatilis (Olivi) (Prosobranchia,Mollusca)

The Belgian coast has no natural rocky sites but a number of man-made constructions are colonized by rocky shore organisms. The rough periwinkle, Littorina saxatilis (Olivi), lacks a planktonic larval stage but is found on most breakwaters along the Belgian coast, a few built as recently as 1986. This indicates a good potential of dispersal along this sandy shallow coast, nearly as good as for the planktonic developer Littorina littorea (L.) which is found on generally the same sites in Belgium. The breakwater populations of L. saxatilis, however, tend to be somewhat less variable (level of heterozygosity about 10% less) than non-Belgian L. saxatilis populations of natural sites. This suggests that the breakwater populations have passed through bottlenecks when founded, but probably restored population sizes fairly rapidly afterwards. No relationship is found between geographic and genetic distances between populations of L. saxatilis.     

Genetic analyses of the Asian longhorned beetle (Coleoptera,Cerambycidae, <Emphasis Type="Italic">Anoplophora glabripennis</Emphasis>), in North America,Europe and Asia

The Asian longhorned beetle, (Coleoptera, Cerambycidae, Anoplophora glabripennis (Motschulsky)), is endemic to China and Korea and an important invasive insect in North America and Europe. We analyzed mitochondrial DNA sequence data of invasive populations of A. glabripennis in North America and Europe, and microsatellite allele frequency data of beetles from North America. We show that populations in New York City and Long Island NY; New Jersey, Chicago, IL, and Toronto, Canada have limited genetic diversity compared to populations in China. In addition, the data suggest that separate introduction events were responsible for many of the populations in North America and for European populations in Austria, France, Germany and Italy. Populations on Long Island, NY are suspected to have been initiated by the transport of cut wood from New York City. A. glabripennis beetles found in Jersey City, NJ appear to be derived from an expansion of the New York City, NY population, whereas beetles found in Linden, NJ are an expansion from the Carteret, NJ population. Limited genetic diversity did not stop this invasive insect from establishing damaging populations in North America. Founders of introduced A. glabripennis populations in North America and Europe are likely derived from populations in China that are themselves invasive, rendering difficult the identification of source populations. Invasiveness in an insect’s natural range could be an important predictor of potential pest status of introduced populations.     

Potential Impacts of a Western Pacific Grapsid Crab on Intertidal Communities of the Northwestern Atlantic Ocean

Population density and size distribution, salinity tolerance, and feeding activity were examined in a western Pacific grapsid crab, Hemigrapsus sanguineus, that was recently introduced to the mid-Atlantic coast of North America. Seasonal abundance on a boulder/cobble shore (Crane Neck Pt.) in central Long Island Sound, New York, USA, during 1997–1998, ranged from 7 to 10 crabs m⁻² averaged over the entire intertidal zone. Crabs occurred throughout the intertidal during summer and fall, but appeared to move from high to low elevations during winter. In laboratory experiments, H. sanguineus tolerated salinity down to 10 ppt for 7 d, but showed significant preference for 20 or 27 ppt over 10 ppt. The crabs readily consumed juvenile snails (Littorina littorea) and mussels (Mytilus edulis), as well as other common species of macroalgae and invertebrates occurring at Crane Neck Pt. High feeding rates and the ability to consume littorine snails up to 13 mm in height and mussels up to 20 mm in length suggest that this nonindigenous species has the potential to significantly affect the structure of rocky intertidal communities in the northwestern Atlantic Ocean; however, rigorous field studies are needed to accurately determine the impact of this recent introduction. This revised version was published online in July 2006 with corrections to the Cover Date.     

When invasion increases population genetic structure: a study with <Emphasis Type="Italic">Centaurea diffusa</Emphasis>

Biological invasions offer excellent systems to study the evolutionary processes involved in introductions of species to new ranges. Molecular markers can reveal invasion histories and the effects of introductions on amounts and structuring of genetic variation. We used five polymorphic microsatellite loci to elucidate genetic diversity and population structure between native range and introduced range populations of a prominent North American rangeland weed, Centaurea diffusa (Asteraceae). We found that the total number of alleles and the number of private alleles was slightly higher in the native Eurasian range, and that allelic richness did not differ between the ranges, indicating overall levels of diversity were similar in Eurasia and North America. It therefore seems unlikely that this invasion has been affected by genetic bottlenecks or founder effects. Indeed, results of assignment tests suggest that multiple introductions have contributed to North America’s C. diffusa invasion. Additionally, assignment tests show that both Eurasian and North American sites had a strong pattern of mixed genetic ancestry. This mixed assignment corresponded to a lack of geographic population structure among Eurasian samples. The lack of population structure in the native range conflicts with general expectations and findings to date for invasion genetics, and cautions that even species’ native ranges may show signs of recent ecological upheaval. Despite the mixed assignments, North American samples showed strong population structure, suggesting that the invasion has been characterized by long-range dispersal of genetically distinct propagules across the introduced range.     

Observations on the morphology of some North American nemertines with consequent taxonomic changes and a reassessment of the architectonics of the phylum

A majority of the nemertine species from the western North Atlantic were originally described from life in the nineteenth century. Many of these were established by A. E. Verrill who had ‘an eye for species’ no matter which phylum he was working with, and thus when living nemertines which he described are encountered, they can usually be recognized. The morphology of most of these species has never been reported; some may prove to be species described earlier from the eastern North Atlantic. Morphological observations on the nemertine species from the North East coast of the Pacific are inadequate and have prevented satisfactory comparison with species from Japan and eastern Russia. The morphology of some species collected in the Gulf of Maine and from Cape Cod, as well as a re-examination of some of the slides of type specimens of species from the west coast of North America, indicates that their generic placement must be re-examined. The architectonic plan of the heteronemertines postulated over 100 years ago can not be substantiated and is redescribed. Three new heteronemertean genera are described: Tenuilineus gen.n. Parvicirrus gen.n., Tarrhomyos gen.n.     

Reconstructing past biological invasions: niche shifts in response to invasive predators and competitors

Studying historic invasions can provide insight into the ongoing invasions that threaten global biodiversity. In this study, we reconsider the impacts of Littorina littorea and Carcinus maenas on the rocky intertidal community of the Gulf of Maine. Past research using invader-removal experiments demonstrated strong top-down effects of L. littorea on algal community structure; however, such removal experiments may overlook the long-term effects of niche shifts and local extinctions caused by invasive species. We considered how a niche-shift in the native littorine, Littorina saxatilis, may change the interpretation of L. littorea impacts. Using a factorial experiment crossing predator presence/absence with L. littorea presence/absence, we found that L. saxatilis is able to exert top-down control on ephemeral algae similar to that exerted by L.␣littorea and that both competition by L. littorea and predation by C. maenas have strong, negative impacts on L. saxatilis. We also found higher predation rates on protected shores and at lower tidal heights and preferential predation on L.␣saxatilis compared to L. littorea. While movement experiments demonstrate that behavioral response to tidal height is the proximate cause of L. saxatilis exclusion from the lower intertidal, our study suggests that the ultimate causes are the additive effects of competition from and predation by invasive species.     

Home and Away: Comparisons of Resource Utilization by a Marine Species in Native and Invaded Habitats

The exotic Asian shore crab, Hemigrapsus sanguineus, was recently introduced to the northeastern coast of North America and during the 1990's breeding populations were established throughout southern New England. In 1997–1998, ecological studies of several co-occurring brachyuran crabs were conducted and in native (Tanabe Bay, Japan) and invaded (Long Island Sound, USA) habitats of H. sanguineus. Standardized comparisons of H. sanguineus were made between the 2 habitats using data on crab sizes, utilization of space, and food habits. Results revealed that (1) the resource use of H. sanguineus was quite different from that of other resident species in its invaded habitat, and (2) there were no substantial changes in resource utilization by H. sanguineus after it became established in the invaded habitat (relative to native Tanabe Bay). Differing patterns of resource use by H. sanguineus and other crabs in the invaded habitat, the lack of restriction in resource use by H. sanguineus following its introduction, and the climatological and physical similarities between native and invaded regions likely contributed to the successful invasion of H. sanguineus into rocky intertidal habitats in southern New England.     

Refuting a controversial case of a human-mediated marine species introduction

Human activities have strongly impacted natural communities through the introduction of non-native species in historical times. A frequently cited marine example is Littorina littorea , a common intertidal gastropod that was first reported in North America in 1840. The seemingly sudden appearance and rapid geographical spread of this species southward from Nova Scotia has led many researchers to consider L. littorea a human-mediated species introduction. This is despite allozyme and subfossil evidence that the `European periwinkle' was in North America long before 1840. Our mitochondrial and nuclear DNA sequence data confirm that L. littorea has been in continuous residence in North America for at least 8000 years. It appears most likely that ecological interactions, rather than oceanographic or climatic forces, maintained the limited geographical distribution of L. littorea prior to the 19th century.     

European green crabs (Carcinus maenas) in the northeastern Pacific: genetic evidence for high population connectivity and current-mediated expansion from a single introduced source population

Aim The European green crab (Carcinus maenas) expanded dramatically after its introduction to the west coast of North America, spreading over 1000 km in < 10 years. We use samples of Carcinus maenas collected over time and space to investigate the genetic patterns underlying the species’ initial establishment and spread, and discuss our findings in the context of the species’ life history characteristics and demography. Location The central west coast of North America, encompassing California, Oregon, and Washington (USA) and British Columbia (Canada). Methods We collected 1040 total samples from 21 sites representing the major episodes of population establishment and expansion along the west coast of North America. Microsatellite markers were used to assess genetic diversity and structure at different time points in the species’ spread, to investigate connectivity between embayments and to estimate both short‐term effective population sizes and the number of original founders. Assignment testing was performed to determine the likely source of the introduction. Results Carcinus maenas in western North America likely derived from a single introduction of a small number of founders to San Francisco Bay, CA from the east coast of North America. Throughout its western North American range, the species experiences periodic migration between embayments, resulting in a minor loss of genetic diversity in more recently established populations versus the populations in the area of initial establishment. Main conclusions Low genetic diversity has not precluded the ability of C. maenas to successfully establish and spread on the west coast of North America. An efficient oceanographic transport mechanism combined with highly conducive life history traits are likely the major drivers of C. maenas spread. Evidence for a single introduction underscores the potential utility of early detection and eradication of high‐risk invasive species.     

Characterization of microsatellite loci in the widely introduced estuarine anemone Nematostella vectensis

We characterized 10 polymorphic microsatellite loci from Nematostella vectensis, a burrowing anemone recently introduced to estuaries along the Pacific coast of North America and the southeast coast of England. Preliminary results indicate high variability and significant departures from Hardy–Weinberg equilibrium, the latter likely the result of population genetic structure and reproductive plasticity. Both results are consistent with earlier genetic analyses. These markers will be useful for resolving global patterns of introduction and for describing spatio‐temporal genetic structure at local and regional scales.     

Population structure and genetic diversity in Swainson’s Hawks (Buteo swainsoni): implications for conservation

Swainson’s Hawks (Buteo swainsoni) are large raptors with a breeding distribution extending across much of western North America where they were historically considered one of the most abundant raptors. Swainson’s Hawks have declined precipitously in many parts of their range during the 20th century, and the historical range in California has been much reduced. In the Central Valley of California (CV), Swainson’s Hawks exhibit behavioral and morphological characteristics apparently different from other regions. To describe the genetic diversity and population structure of Swainson’s Hawks throughout their range, 19 microsatellite loci and 416 base pairs of the mitochondrial control region were analyzed. Microsatellite diversity appears high throughout the contemporary range. A Bayesian model-based analysis of microsatellite genotypes revealed clusters associated with the CV and the Great Basin/Great Plains region of North America (GBGP) with overlap between regions. F _ST estimates suggest limited differentiation among Swainson’s Hawks with isolation by distance. A heterozygote excess indicated a recent reduction in effective population size of Swainson’s Hawks across all regions. Control region data revealed no population structure and provided evidence of historic population expansion in the GBGP. In the CV a weaker signature of population expansion was detected, possibly altered by recent declines. While genetic data suggests recent gene-flow across regions, apparent differences between the CV and GBGP in traits with potential fitness consequences (migratory behavior and morphology) along with marked decline in numbers in California call for careful conservation, management, and monitoring of Swainson’s Hawks in the CV.     

Population structure of the butternut canker fungus,Ophiognomonia clavigignenti‐juglandacearum,in North American forests

The occurrence of multiple introduction events, or sudden emergence from a host jump, of forest pathogens may be an important factor in successful establishment in a novel environment or on a new host; however, few studies have focused on the introduction and emergence of fungal pathogens in forest ecosystems. While Ophiognomonia clavigignenti‐juglandacearum (Oc‐j), the butternut canker fungus, has caused range‐wide mortality of butternut trees in North America since its first observation in 1967, the history of its emergence and spread across the United States and Canada remains unresolved. Using 17 single nucleotide polymorphic loci, we investigated the genetic population structure of 101 isolates of Oc‐j from across North America. Clustering analysis revealed that the Oc‐j population in North America is made up of three differentiated genetic clusters of isolates, and these genetic clusters were found to have a strong clonal structure. These results, in combination with the geographic distribution of the populations, suggest that Oc‐j was introduced or has emerged in North America on more than one occasion, and these clonal lineages have since proliferated across much of the range of butternut. No evidence of genetic recombination was observed in the linkage analysis, and conservation of the distinct genetic clusters in regions where isolates from two or more genetic clusters are present, would indicate a very minimal or non‐existent role of sexual recombination in populations of Oc‐j in North America.     

Origin, taxonomy and population structure of the allopolyploid peat mossSphagnum majus

The polyploid peat mossSphagnum majus shows considerable phenotypic plasticity along ecological gradients in mires. It is considered taxonomically heterogeneous, and two subspecies have been described. Isozyme analyses were carried out on populations ofS. majus from Central Norway and from eastern coast of North America in order to assess the origin, taxonomy and population structure of this species. High levels of fixed heterozygosity in the populations demonstrate thatS. majus is a genetic allopolyploid. At all loci screened, extant populations ofS. cuspidatum shared enzyme bands withS. majus. The other most likely progenitor based on morphology,S. annulatum, was fixed for enzyme bands not found inS. majus. The progenitor genotype ofS. annulatum may have been missed because of inadequate sampling or extinction. Alternatively, another extinct or undetected taxon may constitute the second progenitor. The observed patterns of genetic variation and linkage disequilibria were uncorrelated with the previously proposed subspecific classification ofS. majus. Lack of genetic divergence between continents suggests that the origins ofS. majus in Europe and North America were not independent. Low mutation rates and large effective population sizes may be important causing populations to diverge slowly, and may explain the observed patterns without hypothesising frequent long-distance dispersal.