A Review of the Biology and Ecology of the Quagga Mussel (Dreissena bugensis), a Second Species of Freshwater Dreissenid Introduced to North America

SYNOPSIS. North America's Great Lakes have recently been invadedby two genetically and morphologically distinct species of Dreissena.The zebra mussel (Dreissena polymorpha) became established inLake St. Clair of the Laurentian Great Lakes in 1986 and spreadthroughout eastern North America. The second dreissenid, termedthe quagga mussel, has been identified as Dreissena bugensisAndrusov, 1897. The quagga occurs in the Dnieper River drainageof Ukraine and now in the lower Great Lakes of North America.In the Dnieper River, populations of D. polymorpha have beenlargely replaced by D. bugensis; anecdotal evidence indicatesthat similar trends may be occurring in the lower LaurentianGreat Lakes. Dreissena bugensis occurs as deep as 130 m in theGreat Lakes, but in Ukraine is known from only 0–28 m.Dreissena bugensis is more abundant than D. polymorpha in deeperwaters in Dneiper River reservoirs. The conclusion that NorthAmerican quagga mussels have a lower thermal maximum than zebramussels is not supported by observations made of populationsin Ukraine. In the Dnieper River drainage, quagga mussels areless tolerant of salinity than zebra mussels, yet both dreissenidshave acclimated to salinities higher than North American populations;eventual colonization into estuarine and coastal areas of NorthAmerica cannot be ignored.     

Origin of Spanish invasion by the zebra mussel, Dreissena polymorpha (Pallas, 1771) revealed by amplified fragment length polymorphism (AFLP) fingerprinting

The zebra mussel, Dreissena polymorpha is an aquatic nuisance invasive species originally native to the Ponto-Caspian region where it is found in lakes and delta areas of large rivers draining into the Black and Caspian seas. The dispersal of D. polymorpha began at the end of the 18th century, at a time when shipping trade become increasingly important and many canals were built for linking different navigable river systems in Europe. Over the past 200 years, zebra mussels spread to most of the lakes, rivers and waterways in Europe by a combination of natural and anthropogenic dispersal mechanisms. D. polymorpha invaded Spain around 2001, being found for the first time in the Riba-roja reservoir at the lower part of the Ebro River, North-East Spain. The relatively late invasion of Spain was most likely caused by the presence of the Pyrenees, which isolated the Iberian Peninsula from the rest of the European continent, and acted as a barrier to the dispersal of D. polymorpha. In recent studies, molecular genetic methods have successfully been used to determine phylo-geographic relationships, which may reflect invasion corridors and can help retrace source populations. Zebra mussels from populations in Great Britain, The Netherlands, Belgium, France, Germany, Spain, Italy, Romania and North America were analyzed using PCR based amplified fragment length polymorphism (AFLP)-fingerprinting to determine the source population of D. polymorpha in Spain. The phylogenetic analyses and pair-wise genetic distances revealed that the recent invasion of zebra mussels in Spain is most likely from France.     

ENDOSYMBIONTS OF DREISSENA POLYMORPHA IN IRELAND: EVIDENCE FOR THE INTRODUCTION OF ADULT MUSSELS

Although zebra mussels (Dreissena polymorpha) have invaded watersacross Europe for over 200 years, they colonized Ireland onlywithin the past decade. To test the hypothesis that Irelandwas colonized by adult D. polymorpha, we examined mussels fromdifferent sites along the Lower Shannon River system in Irelandfor the presence of host specific and generalist endosymbionts.Withinthe mantle cavity and/or associated with zebra mussel tissueswe found species specific-ciliates (Conchophthirus acuminatusand Ophryoglena hemophaga) and generalist symbionts (the ciliateAncistrumina limnica, nematodes, oligochaetes and chironomids).We found a significant difference in the prevalence of symbiontsamong sites, but all mussels at all sites harboured one specialistspecies C. acuminatus, and all of the mussels at three of thefour sites also had the second specialist, O. hemophaga. Thus,with the introduction of D. polymorpha into Ireland, at leasttwo additional species, their host-specific symbionts C. acuminatusand O. hemophaga, have also been introduced. The presence ofthese symbionts in Ireland supports the hypothesis that adultzebra mussels were introduced into Ireland, rather than larvalstages. This contrasts with the introduction of zebra musselsto North America, where adult zebra mussels are devoid of host-specificsymbionts. (Received 8 June 2005; accepted 7 November 2005)     

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.     

Effects of temperature and temperature acclimation on survival of zebra mussels (Dreissena polymorpha) and Asian clams (Corbicula fluminea) under extreme hypoxia

Following acclimation to 5°, 15° or 25°C for 14days, samples of 30 Dreissena polymorpha (zebra mussels) andCorbicula fluminea (Asian clams) were held in either aerated(control) or extremely hypoxic N₂ gassed water (PO2 < 3%of full air saturation). Mortality was negligible in all aeratedcontrols. Mean hypoxia tolerance in D. polymorpha ranged from3–4 days at 25°C to 38–42 days at 5°C. Hypoxiatolerance time of zebra mussels increased significantly withdeclining test temperature (P < 0.001) and increasing acclimationtemperature (P < 0.001). Larger zebra mussels were more tolerantthan smaller individuals. Asian clams were 2–7 times moretolerant of hypoxia than zebra mussels, surviving a mean of11.8 and 35.1 days at 25°C and 15°C, respectively, andwithout mortality for 84 days at 5°C, and were not influencedby temperature acclimation. At 25°C, larger specimens ofAsian clams were less tolerant of hypoxia than smaller individuals.Both species are amongst the least hypoxia tolerant freshwaterbivalve molluscs, reflecting their prevalence in well-oxygenatedshallow water habitats. Prolonged exposure to extreme hypoxiamay provide an efficacious control strategy, particularly forD. polymorpha (Received 12 January 1998; accepted 30 September 1998)     

Genetic variability and phylogeographical patterns of a nonindigenous species invasion: a comparison of exotic vs. native zebra and quagga mussel populations

There have been few investigations of the number of founding sources and amount of genetic variability that lead to a successful nonindigenous species invasion, although genetic diversity is believed to play a central role. In the present study, population genetic structure, diversity and divergence patterns were analysed for the zebra mussel Dreissena polymorpha [n=280 samples and 63 putative randomly amplified polymorphic DNA (RAPDs) gene loci] and the quagga mussel D. bugensis (n=136 and 52 loci) from 10 nonindigenous North American and six Eurasian sampling sites, representing their present‐day ranges. Results showed that exotic populations of zebra and quagga mussels had surprisingly high genetic variability, similar to those in the Eurasian populations, suggesting large numbers of founding individuals and consistent with the hypothesis of multiple colonizations. Patterns of genetic relationships indicate that the North American populations of D. polymorpha likely were founded by multiple source populations from north‐western and northcentral Europe, but not from southcentral or eastern Europe. Sampling areas within North America also were significantly divergent, having levels of gene flow and migration about twice those separating long‐established Eurasian populations. Samples of D. bugensis in Lakes Erie and Ontario were significantly different, with the former being more closely related to a native population from the Dnieper River, Ukraine. No evidence for a founder effect was discerned for either species.     

Fouling of European freshwater bivalves (Unionidae) by the invasive zebra mussel (Dreissena polymorpha)

1. The zebra mussel (Dreissena polymorpha) is well known for its invasive success and its ecological and economic impacts. Of particular concern has been the regional extinction of North American freshwater mussels (Order Unionoida) on whose exposed shells the zebra mussels settle. Surprisingly, relatively little attention has been given to the fouling of European unionoids. 2. We investigated interspecific patterns in fouling at six United Kingdom localities between 1998 and 2008. To quantify the effect on two pan‐European unionoids (Anodonta anatina and Unio pictorum), we used two measures of physiological status: tissue mass : shell mass and tissue glycogen content. 3. The proportion of fouled mussels increased between 1998 and 2008, reflecting the recent, rapid increase in zebra mussels in the U.K. Anodonta anatina was consistently more heavily fouled than U. pictorum and had a greater surface area of shell exposed in the water column. 4. Fouled mussels had a lower physiological condition than unfouled mussels. Unlike tissue mass : shell mass ratio, tissue glycogen content was independent of mussel size, making it a particularly useful measure of condition. Unio pictorum showed a stronger decline in glycogen with increasing zebra mussel load, but had a broadly higher condition than A. anatina at the time of study (July). 5. Given the high conservation status and important ecological roles of unionoids, the increased spatial distribution and fouling rates by D. polymorpha in Europe should receive more attention.     

European populations of Diabrotica virgifera virgifera are resistant to aldrin,but not to methyl‐parathion

The western corn rootworm, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae), is a major pest of cultivated corn in North America and has recently begun to invade Europe. In addition to crop rotation, chemical control is an important option for D. v. virgifera management. However, resistance to chemical insecticides has evolved repeatedly in the USA. In Europe, chemical control strategies have yet to be harmonized and no surveys of insecticide resistance have been carried out. We investigated the resistance to methyl‐parathion and aldrin of samples from nine D. v. virgifera field populations originating from two European outbreaks thought to have originated from two independent introductions from North America. Diagnostic concentration bioassays revealed that all nine D. v. virgifera field populations were resistant to aldrin but susceptible to methyl‐parathion. Aldrin resistance was probably introduced independently, at least twice, from North America into Europe, as there is no evident selection pressure to account for an increase of frequency of aldrin resistance in each of the invasive outbreaks in Europe. Our results suggest that organophosphates, such as methyl‐parathion, may still provide effective control of both larval and adult D. v. virgifera in the European invasive outbreaks studied.     

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.     

Trinucleotide microsatellite loci for the zebra mussel Dreissena polymorpha,an invasive species in Europe and North America

The high mutation rate at microsatellite loci can supply important demographic information on founder events and range expansion in an invasive species such as the zebra mussel Dreissena polymorpha, following its initial introduction. In order to facilitate studies into the colonization patterns of this species in new habitats in Europe and North America, five trinucleotide microsatellite loci were isolated from a partial DNA library. Allelic diversity at all described loci was high, ranging from 20 to 35 alleles per locus. Homologous loci were not amplified in a second related invasive species, Dreisenna bugensis, using the primers developed here.     

Grazing on colonial and filamentous, toxic and non-toxic cyanobacteria by the zebra mussel Dreissena polymorpha

Colony forming and toxic cyanobacteria form a problem in surfacewaters of shallow lakes, both for recreation and wildlife. Zebramussels, Dreissena polymorpha, have been employed to help torestore shallow lakes in the Netherlands, dominated by cyanobacteria,to their former clear state. Zebra mussels have been presentin these lakes since they were created in the 19th century bythe excavation of peat and are usually not considered to bean invasive species. Most grazing experiments using Dreissenahave been performed with uni-cellular phytoplankton laboratorystrains and information on grazing of larger phytoplankton taxahardly exists. To gain more insight in to whether D. polymorphais indeed able to decrease cyanobacteria in the phytoplankton,we therefore performed grazing experiments with zebra musselsand two species of cyanobacteria, that greatly differ in shape:colony forming strains of Microcystis aeruginosa and the filamentousspecies Planktothrix agardhii. For both species a toxic anda non-toxic strain was selected. We found that zebra musselscleared toxic Planktothrix at a higher rate than non-toxic Planktothrix,toxic or non-toxic Microcystis. Clearance rates between theother strains were not significantly different. Both phytoplanktonspecies, regardless of toxicity, size and shape, were foundin equal amounts (based on chlorophyll concentrations) in theexcreted products of the mussels (pseudofaeces). The resultsshow that zebra mussels are capable of removing colonial andfilamentous cyanobacteria from the water, regardless of whetherthe cyanobacteria are toxic or not. This implies that the musselsmay be used as a biofilter for the removal of harmful cyanobacterialblooms in shallow (Dutch) lakes where the mussels are alreadypresent and not a nuisance. Providing more suitable substratefor zebra mussel attachment may lead to appropriate mussel densitiescapable of filtering large quantities of cyanobacteria.     

Osmotic and Ionic Regulation of North American Zebra Mussels (Dreissena polymorpha)

SYNOPSIS. Unlike other freshwater bivalves that survive formonths in deionized water, Dreissena polymorpha requires minimalconcentrations of Na, K, Mg, and Cl in the bathing medium forlong-term survival. Although ion transport rates are higherin D. polymorpha compared to other freshwater bivalves, theytend to have lower blood solute concentrations. D. polymorphahas an unusually "leaky" epithelium with a high paracellularpermeability to solutes. Thus, even with high transport rates,it may not be possible for zebra mussels to retain higher bloodsolutes because of the extensive passive loss of ions. Undera hyperosmotic stress, D. polymorpha will rapidly osmoconform(about 12 hr) due primarily to the diffusion of solutes andpartially to the osmotic loss of water. D. polymorpha is notcapable of surviving an imbalance of Na/K in the external medium.In the absence of K the cells will tend to lose volume to achieveisosmotic balance with the blood, but the animals usually diewithin a few days. If D. polymorpha is exposed to excess K inthe environment (1 mM), they will accumulate K in the blood.If the K enters the cells, cellular volume would expand dueto increase in osmolyte concentration, yet, if K remains inthe blood, there will be an electrochemical imbalance. In eithercase, the animal cannot survive much longer than a day. WhenNa and K are present in the medium in a balanced combinationapproximated by artificial seawater (ASW), D. polymorpha willsurvive an acute transfer to 100 mosm ASW indefinitely (months).Our preliminary studies have shown that D. polymorpha will toleratestep-wise acclimation to solutions >250 mosm provided thechanges in salinity do not exceed 50–100 mosm. Freshwaterbivalves, unlike the marine bivalves, have limited free aminoacids in their body fluids and must rely on inorganic ions forosmotic regulation. The free amino acids serve as an importantosmolyte buffer for volume regulation when an animal experiencesan environment of changing salinity. The inability of Dreissena,and perhaps other freshwater bivalves, to tolerate hyperosmoticallyinduced dehydration may be due, in part, to the inability toaccumulate or retain sufficient intracellular K to facilitateregulatory volume adjustments.     

Invasion history, distribution, and relative abundances of Dreissena bugensis in the old world: a synthesis of data

We examined trends in expansion patterns and relative abundances of Dreissena bugensis in reservoirs and major river systems in eastern Europe. Based on our own data and data from the literature, it is apparent that trends were variable across river basins and not easily related to environmental conditions. In some cases these did not conform to the patterns typically found for dreissenids. In the early period of expansion beyond its native range in the Dnieper-Bug delta and estuary, D. bugensis rapidly replaced Dreissena polymorpha in the upper Dnieper River system, but increased only gradually and over time became less abundant relative to D. polymorpha in the Don-Manych River system. Contrary to the Dnieper and Don River systems, in the Volga River system considerable spatial variability in relative abundances was apparent, particularly in northern reservoirs. Moreover, even though D. bugensis usually displaces D. polymorpha as the dominant dreissenid, the latter can remain dominant in certain types of habitats where conditions are less favourable for the former. Suggested factors that may be responsible for differences in invasion patterns in the river systems may include differential responses to temperature, or to some other factor(s) associated with geographical latitude, the level of water mineralization, and selective predation by molluscivorous fish. In particular, the northward expansion of D. bugensis seems to be limited by temperature. The lack of long-term data on appropriate scales precludes linking these differences to specific features within the environment, but our comparisons indicate that the expansion of D. bugensis relative to D. polymorpha is more complex than previously believed.     

Examining the genetic diversity of the orange blossom wheat midge,Sitodiplosis mosellana (Géhin), across North America

The orange blossom wheat midge, Sitodiplosis mosellana (Géhin) (Diptera: Cecidomyiidae), is a significant pest of wheat (Triticum spp.) grown in the Northern Hemisphere. It was accidently introduced to North America over 200 years ago and has subsequently spread throughout the northern Great Plains. Since 2010, several Canadian spring wheat varieties containing the resistance gene Sm1 have been released. Due to the potential of wheat midge populations to evolve virulent biotypes to Sm1, cultivars containing Sm1 are grown with a susceptible cultivar in an interspersed refuge. An understanding of the genetic diversity of wheat midge populations could provide important information on the potential development of resistance to Sm1. In the current study, we used two mitochondrial genes (CO1 and ND4) from wheat midge collected across the northern Great Plains and Québec in North America to assess population structure and genetic diversity. We found limited genetic diversity and population structure across the sampled North American populations. We also assessed North American haplotype similarity to wheat midge collected from Europe and China and found high similarity between North American and European populations, although sampling in Europe was limited. This supports the hypothesis that North American populations originated from Europe.     

Changes in the distribution and abundance of Dreissena polymorpha within lakes through time

Dreissena polymorpha population densities and biomass were followed in three Belarusian lakes with different trophic status over a 12-year period subsequent to initial colonization. In all three lakes zebra mussel population densities did not change once they reached a maximum. Application of the Ramcharan et al. [1992. Canadian Journal of Fisheries and Aquatic Sciences 49: 2611–2620] model for predicting population dynamics of zebra mussels was accurate for two of the three lakes studied. Population density appears to depend on the time since initial colonization, relative abundance of substrate available for colonization, lake morphometry and trophic type. Zebra mussel distribution within lakes was highly patchy, but the degree of dispersion decreased over time after initial colonization, which may be a result of saturation of suitable substrates by zebra mussels as populations increase and reach carrying capacity. In lakes where submerged macrophytes are the dominant substrate for zebra mussel attachment, populations may be less stable than in lakes with a variety of substrates, which will have a more balanced age distribution, and be less impacted by year to year variation in recruitment. Dreissena polymorpha usually reach maximum population density 7–12 years after initial introduction. However, the timing of initial introduction is often very difficult to determine. Both European and North American data suggest that zebra mussels reach maximum density in about 2–3 years after populations are large enough to be detected.     

Zebra mussels (Dreissena polymorpha) in Ireland, AFLP-fingerprinting and boat traffic both indicate an origin from Britain

1. The zebra mussel (Dreissena polymorpha) is an aquatic nuisance species that invaded Ireland around 1994. We studied the invasion of the zebra mussel combining field surveys and genetic studies, to determine the origin of invasion and the vector of introduction. 2. Field surveys showed that live zebra mussels, attached to the hulls of pleasure boats, were transported from Britain to Ireland. These boats were lifted from British waters onto trailers, transported to Ireland by ferry and lifted into Irish waters within a day. Length‐frequency distributions of dead and living mussels on one vessel imported 3 months earlier revealed a traumatic occurrence caused by the overland, air‐exposed transportation. Results show that a large number of individuals survived after re‐immersion in Irish waters and continued to grow. 3. Zebra mussels from populations in Ireland, Great Britain, the Netherlands, France and North America, were analysed using amplified fragment length polymorphisms (AFLP)‐fingerprinting to determine the origin of the Irish invasion. Phylogenetic analysis revealed that Irish and British mussels clustered closely together, suggesting an introduction from Britain. 4. Ireland remained un‐invaded by the zebra mussel for more than 150 year. The introduction of the zebra mussel to Ireland occurred following the abolition of value added tax in January 1993 on imported second‐hand boats from the European Union (UK and continental Europe). This, together with a favourable monetary exchange rate at that time, may have increased the risk of invasion of the zebra mussel.     

Habitat Shift in Invading Species: Zebra and Quagga Mussel Population Characteristics on Shallow Soft Substrates

Unexpected habitat innovations among invading species are illustrated by the expansion of dreissenid mussels across sedimentary environments in shallow water unlike the hard substrates where they are conventionally known. In this note, records of population characteristics of invading zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels from 1994 through 1998 are reported from shallow (less than 20m) sedimentary habitats in western Lake Erie. Haphazard SCUBA collections of these invading species indicated that combined densities of zebra and quagga mussels ranged from 0 to 32,500 individuals per square meter between 1994 and 1998, with D. polymorpha comprising 75–100% of the assemblages. These mixed mussel populations, which were attached by byssal threads to each other and underlying sand-grain sediments, had size–frequency distributions that were typical of colonizing populations on hard substrates. Moreover, the presence of two mussel cohorts within the 1994 samples indicated that these species began expanding onto soft substrates not later than 1992, within 4 years of their initial invasion in western Lake Erie. Such historical data provide baselines for interpreting adaptive innovations, ecological interactions and habitat shifts among the two invading dreissenid mussel species in North America.     

Biogeographic position and body size jointly set lower thermal limits of wandering spiders

Most species encounter large variations in abiotic conditions along their distribution range. The physiological responses of most terrestrial ectotherms (such as insects and spiders) to clinal gradients of climate, and in particular gradients of temperature, can be the product of both phenotypic plasticity and local adaptation. This study aimed to determine how the biogeographic position of populations and the body size of individuals set the limits of cold (freezing) resistance of Dolomedes fimbriatus. We compared D. fimbriatus to its sister species Dolomedes plantarius under harsher climatic conditions in their distribution range. Using an ad hoc design, we sampled individuals from four populations of Dolomedes fimbriatus originating from contrasting climatic areas (temperate and continental climate) and one population of the sister species D. plantarius from continental climate, and compared their supercooling ability as an indicator of cold resistance. Results for D. fimbriatus indicated that spiders from northern (continental) populations had higher cold resistance than spiders from southern (temperate) populations. Larger spiders had a lower supercooling ability in northern populations. The red‐listed and rarest D. plantarius was slightly less cold tolerant than the more common D. fimbriatus, and this might be of importance in a context of climate change that could imply colder overwintering habitats in the north due to reduced snow cover protection. The lowest cold resistance might put D. plantarius at risk of extinction in the future, and this should be considered in conservation plan.     

Invasive mollusc faunas of the River Thames exemplify biostratigraphical characterization of the Anthropocene

Profound changes to the species configuration of ecosystems globally during the 19th to 21st centuries, resulting from the introduction of neobiota, have produced a distinctive palaeontological signature in sedimentary deposits, here exemplified by those of the River Thames. Coring near Teddington Lock (ca. 4.3 m above sea level, ca. 89 km upstream from the mouth of the Thames estuary) yielded dense assemblages of shells of the invasive Asian clam Corbicula fluminea (recently invaded in 2004) and the zebra mussel Dreissena polymorpha (invaded 1824), which together accounted for 96% of individuals sampled. Population densities of C. fluminea of over 6000 individuals per m² were maintained for a depth of 1 m indicating that the Asian clam is an important biostratigraphical marker in the Thames for sedimentary deposits accumulating since 2004. The first modern European occurrence of C. fluminea was in Portugal in 1980. In 1987, the first occurrence of C. fluminea on the northern coast of South America was observed in the Caripe River, Venezuela. The non-native range of D. polymorpha was restricted to continental Europe for over 200 years until it appeared in the Great Lakes, USA, in 1986 having been transported in ballast water. Within three years, it reached populations of over 750,000 individuals per m² and it is presently recorded in 35 states. Therefore, the pan-Atlantic range expansion of D. polymorpha, coupled with the recent invasion history of C. fluminea in Venezuela and Portugal, identifies a biostratigraphical interval in sedimentary deposits forming from the early 1980s that can be correlated between Europe and the Americas.     

Linking foraging behavior to lifetime reproductive success for an insect parasitoid: adaptation to host distributions

European and American populations of the parasitoid Cotesiaglomerata show pronounced differences in foraging behavior acrossplants and leaves. This variation in spatial aspects of foragingbehavior was observed about 350 generations after the introductionof C. glomerata from Europe to North America. We used a simulationmodel to study how these behavioral differences affect lifetimereproductive success in environments that differ in the spatialdistribution of hosts. The preferred gregarious host Pierisbrassicae occurs in rare large clusters in Europe but is absentin North America. The solitary caterpillars of Pieris rapaeare negative binomially distributed across plants during summerin North America, whereas they are Poisson-distributed in Europe,and early and late in the season in North America. Simulationsshowed that the foraging strategy of American C. glomerata resultedin a higher lifetime reproductive success than did the strategyof European C. glomerata on a Poisson P. rapae distribution,but did not differ on the more clustered negative binomial distribution.American parasitoids spend less time on exploration flights,focusing on the exploitation of P. rapae patches. This suggeststhat C. glomerata has adapted to the North American environmentthrough the loss of exploration traits necessary for the locationof rare clusters of P. brassicae. Lifetime reproductive successof the European strategy was most sensitive to an increase inthe giving up time on infested leaves. This behavioral parameterwas more than twice as high in the American parasitoids comparedwith their European conspecifics.