Molecular resolution of the family Dreissenidae (Mollusca: Bivalvia) with emphasis on Ponto-Caspian species, including first report of Mytilopsis leucophaeata in the Black Sea basin

An impact of non-native species invasions on the Caspian Sea biota

The Caspian Sea is a large inland brackish basin, vulnerable to invaders due to its long isolation and considerable endemism among its native biota. A brief description of Caspian biota evolution until its modern state is given. The pathways and vectors of invasion and the ways of establishment of non-native species since the early 20th century are summarized. The newly established species are euryphilic, with high ecological plasticity, able to adapt to new environments and to affect their biodiversity. This review is based on unpublished field data, collected in 1999-2019 in the Northern, Middle and Southern Caspian, and on relevant published information. The arrival of non-native species occurred in three periods: (1) in the 1930s, deliberate introductions aimed at enriching commercial stocks and edible resources, (2) since 1952, the construction of the Volga-Don Canal led to the arrival of benthic foulers and macrophytes from ships; (3) since the early 1980s to present, ballast water tanks were mounted on ships, favoring the arrival of phyto- and zooplankton species. Most established non-native species reached the Caspian Sea via the Black Sea. They include both Black Sea native species and non-native species from the North Atlantic areas, which first arrived and established in the Black Sea. Few established non-native species came from brackish water; fresh water fishes were deliberately introduced to develop aquaculture. Though not numerous, these species became dominant in both benthos and plankton communities, where they replaced native Caspian species. Among them, the invading ctenophore Mnemiopsis leidyi, which had no predators, continues to thrive in the Caspian ecosystem, impoverishing its biodiversity and bio-resources. However, lately its natural predator, the ctenophore Beroe ovata, arrived and established in the Southern and Middle Caspian providing a chance for ecosystem recovery, as has already happened in the Black Sea.

What we know and don't know about the invasive zebra (Dreissena polymorpha) and quagga (Dreissena rostriformis bugensis) mussels

We summarized existing knowledge on Dreissena polymorpha (the zebra mussel) and D. r. bugensis (the quagga mussel), including data on their taxonomy, systematics, evolution, life cycle, reproduction, feeding, growth and longevity, population dynamics, interspecific competition, habitat requirements, and distribution within and among waterbodies. We analyzed the history of spread of both species and the major pathways and vectors of their spread in Europe and North America. Special consideration was given to their ecological and economic impacts and their natural enemies, like waterfowl, fishes, and parasites, as well as the prevention of their introduction, early detection, control, and containment. We also outlined the most salient ecosystem services provided by zebra and quagga mussels, including water purification, nutrient recycling, culling the effects of eutrophication, biomonitoring, and their role as a food resource for fish and waterfowl. Finally, we identified major knowledge gaps and key studies needed to better understand the biology, ecology, and impacts of these aggressive freshwater invaders. Our review indicates that much crucial information on the quagga mussel is still missing, including key life history parameters, like spawning cues, fecundity, and longevity, particularly for the profundal zone of deep lakes.

DISTRIBUTION OF ALIEN ZOOBENTHIC SPECIES ON THE SHELF OF THE BLACK SEA

The number of alien species in the zoobenthos of the Black Sea increased up to 65 species. Depending on the scale of their distribution in the Black Sea, non-native zoobenthos species are combined into three groups: 1) 5 species have spread in the entire sea, 2) 35 species were found in several areas, and 3) 25 species were found only in one of the areas of the sea. Six areas of the Black Sea shelf have been identified (Varna - Burgas, Danube, Northwestern, Crimean, Caucasian and Anatolian) in accordance with the seasonal and annual values of the thermohaline characteristics. The zoobenthos differed not only in quantity, but also in the composition of non-native species between the six areas of the shelf. The results of multivariate statistical analysis revealed a low level of similarity between these areas of the Black Sea shelf. The greatest similarity in the composition of alien species of zoobenthos was observed for the Danube region with the Varna and Burgas bays, which border each other. The species composition of the alien species of the Caucasian shelf was more similar to the Varna - Burgas and Danube areas than to the neighboring Crimean and Anatolian areas. Spatial gradients of temperature and salinity form hydrological fronts of water masses, which are a kind of ecological barriers and can limit the natural exchange of alien species between shelf areas.

Social network analysis and the implications for Pontocaspian biodiversity conservation in Romania and Ukraine: A comparative study

Romania and Ukraine share the Black Sea coastline, the Danube Delta and associated habitats, which harbor the endemic, aquatic Pontocaspian biota. Currently, this biota is diminishing both in numbers of species and their abundance because of human activities, and its future persistence strongly depends on the adequacy of conservation measures. Romania and Ukraine have a common responsibility to address the conservation of Pontocaspian biodiversity. The two countries, however have different socio-political and legal conservation frameworks, which may result in differences in the social network structure of stakeholder institutions with different implications for Pontocaspian biodiversity conservation. Here, we study the social network structure of stakeholder organizations involved in conservation of Pontocaspian biodiversity in Romania and the implications of network structure for conservation outcomes. Then we compare the findings from Romania to an earlier similar study from Ukraine. We apply a mix of qualitative and quantitative social network analysis methods to combine the content and context of the interactions with relational measures. We show that Pontocaspian biodiversity plays a minor and mostly incidental role in the inter-organizational interactions in Romania. Furthermore, there is room for improvement in the network structure through e.g. more involvement of governmental and nongovernmental organizations and increased motivation of central stakeholders to initiate conservation actions. Social variables, such as lack of funding, hierarchical, non-inclusive system of conservation governance and continuous institutional reforms in the public sector are consequential for the network relations and structure. Social network of stakeholders in Ukraine is more connected and central stakeholders utilize their favorable positions. However, neither in Ukraine is the Pontocaspian biodiversity a driver of organizational interactions. Consequently, both networks translate into sub-optimal conservation actions and the roads to optimal conservation are different. We end with sketching out conservation implications and recommendations for improved national and cross-border conservation efforts.

The quagga mussel genome and the evolution of freshwater tolerance

Freshwater dreissenid mussels evolved from marine ancestors during the Miocene ∼30 million years ago and today include some of the most successful and destructive invasive species of freshwater environments. Here, we sequenced the genome of the quagga mussel Dreissena rostriformis to identify adaptations involved in embryonic osmoregulation. We provide evidence that a lophotrochozoan-specific aquaporin water channel, a vacuolar ATPase subunit and a sodium/hydrogen exchanger are involved in osmoregulation throughout early cleavage, during which time large intercellular fluid-filled 'cleavage cavities' repeatedly form, coalesce and collapse, expelling excess water to the exterior. Independent expansions of aquaporins coinciding with at least five freshwater colonization events confirm their role in freshwater adaptation. Repeated aquaporin expansions and the evolution of membrane-bound fluid-filled osmoregulatory structures in diverse freshwater taxa point to a fundamental principle guiding the evolution of freshwater tolerance and provide a framework for future species control efforts.

Environmental transcriptomes of invasive dreissena, a model species in ecotoxicology and invasion biology

Dreissenids are established model species for ecological and ecotoxicological studies, since they are sessile and filter feeder organisms and reflect in situ freshwater quality. Despite this strong interest for hydrosystem biomonitoring, omics data are still scarce. In the present study, we achieved full de novo assembly transcriptomes of digestive glands to gain insight into Dreissena polymorpha and D. rostriformis bugensis molecular knowledge. Transcriptomes were obtained by Illumina RNA sequencing of seventy-nine organisms issued from fifteen populations inhabiting sites that exhibits multiple freshwater contamination levels and different hydrosystem topographies (open or closed systems). Based on a recent de novo assembly algorithm, we carried out a complete, quality-checked and annotated transcriptomes. The power of the present study lies in the completeness of transcriptomes gathering multipopulational organisms sequencing and its full availability through an open access interface that gives a friendly and ready-to-use access to data. The use of such data for proteogenomic and targeted biological pathway investigations purpose is promising as they are first full transcriptomes for this two Dreissena species.

Mollusc species from the Pontocaspian region - an expert opinion list

Defining and recording the loss of species diversity is a daunting task, especially if identities of species under threat are not fully resolved. An example is the Pontocaspian biota. The mostly endemic invertebrate faunas that evolved in the Black Sea - Caspian Sea - Aral Sea region and live under variable salinity conditions are undergoing strong change, yet within several groups species boundaries are not well established. Collection efforts in the past decade have failed to produce living material of various species groups whose taxonomic status is unclear. This lack of data precludes an integrated taxonomic assessment to clarify species identities and estimate species richness of Pontocaspian biota combining morphological, ecological, genetic, and distribution data. In this paper, we present an expert-working list of Pontocaspian and invasive mollusc species associated to Pontocaspian habitats. This list is based on published and unpublished data on morphology, ecology, anatomy, and molecular biology. It allows us to (1) document Pontocaspian mollusc species, (2) make species richness estimates, and (3) identify and discuss taxonomic uncertainties. The endemic Pontocaspian mollusc species richness is estimated between 55 and 99 species, but there are several groups that may harbour cryptic species. Even though the conservation status of most of the species is not assessed or data deficient, our observations point to deterioration for many of the Pontocaspian species.

Multilocus phylogeny of the zebra mussel family Dreissenidae (Mollusca: Bivalvia) reveals a fourth Neotropical genus sister to all other genera

Dreissenidae is one of the most economically and ecologically important families of freshwater and estuarine mollusks. Fourteen extant species and three genera are currently recognized: Congeria contains three species from karst caves along the eastern Adriatic coast and one from the Orinoco River of Venezuela, Dreissena contains six species native to Eastern European rivers and estuaries, and Mytilopsis contains three species from the Gulf of Mexico, Caribbean, and northwestern coast of South America and one from the Tocantins River of Brazil. Previous molecular phylogenetic studies have examined all species except those from South American rivers, and found each genus to be monophyletic with Congeria and Mytilopsis forming a clade sister to Dreissena. We present the first multilocus phylogeny of Dreissenidae inclusive of South American riverine species. Bayesian and maximum likelihood analyses of a 3085 bp alignment consisting of mitochondrial (COI and 16S) and nuclear (18S and 28S) gene regions found Neotropical species to be consistently and strongly supported as sister to all other dreissenids, although incomplete sequencing of the single Orinoco specimen obscured Neotropical monophyly. Our intergeneric relationships are inconsistent with an extensive fossil record suggesting that dreissenids originated in Europe approximately 30 My before dispersing to the Western Hemisphere. Fossil-calibrated analyses indicated that Neotropical dreissenids diverged from European lineages in the mid to late Eocene (∼39.3 Ma), and Brazilian and Guiana shield populations diversified during the Oligocene to Miocene. We erect the new genus Rheodreissena for all Neotropical freshwater dreissenids and present haplotype data indicative of at least three species. Widespread anthropogenic alteration of the middle Xingu River and lower Amazon threatens the persistence of these endemic, poorly studied mussels and may facilitate introduction beyond their native range.

A late Pleistocene gastropod fauna from the northern Caspian Sea with implications for Pontocaspian gastropod taxonomy

The present paper details a very diverse non-marine gastropod fauna retrieved from Caspian Pleistocene deposits along the Volga River north of Astrakhan (Russia). During time of deposition (early Late Pleistocene, late Khazarian regional substage), the area was situated in shallow water of the greatly expanded Caspian Sea. The fauna contains 24 species, of which 16 are endemic to the Pontocaspian region and 15 to the Caspian Sea. The majority of the species (13) belongs to the Pyrgulinae (Hydrobiidae), a group famous for its huge morphological variability in the Pontocaspian region. The phenotypic diversity has led to an inflation of genus and species names in the literature. New concepts are proposed for many of the genera and species found in the present material, with implications for the systematics and taxonomy of the entire Pontocaspian gastropod fauna. Laevicaspiavinarskiisp. n. is described as a new species. This contribution is considered a first step in revising the Pontocaspian gastropod fauna.

The Shell of the Invasive Bivalve Species Dreissena polymorpha: Biochemical, Elemental and Textural Investigations

The zebra mussel Dreissena polymorpha is a well-established invasive model organism. Although extensively used in environmental sciences, virtually nothing is known of the molecular process of its shell calcification. By describing the microstructure, geochemistry and biochemistry/proteomics of the shell, the present study aims at promoting this species as a model organism in biomineralization studies, in order to establish a bridge with ecotoxicology, while sketching evolutionary conclusions. The shell of D. polymorpha exhibits the classical crossed-lamellar/complex crossed lamellar combination found in several heterodont bivalves, in addition to an external thin layer, the characteristics of which differ from what was described in earlier publication. We show that the shell selectively concentrates some heavy metals, in particular uranium, which predisposes D. polymorpha to local bioremediation of this pollutant. We establish the biochemical signature of the shell matrix, demonstrating that it interacts with the in vitro precipitation of calcium carbonate and inhibits calcium carbonate crystal formation, but these two properties are not strongly expressed. This matrix, although overall weakly glycosylated, contains a set of putatively calcium-binding proteins and a set of acidic sulphated proteins. 2D-gels reveal more than fifty proteins, twenty of which we identify by MS-MS analysis. We tentatively link the shell protein profile of D. polymorpha and the peculiar recent evolution of this invasive species of Ponto-Caspian origin, which has spread all across Europe in the last three centuries.

Vodné mäkkýše ochranársky významných lokalít na Podunajskej nížine [Freshwater molluscs of water bodies with a high conservation value in the Danubian lowland (SW Slovakia)]

In the autumn of 2014, we conducted a malacological survey at 23 freshwater bodies in the Danubian lowland, SW Slovakia. We aimed to conduct a malacological inventory of semi-natural sites of a high conservation value. During the fieldwork, we used conventional methods of sampling; mostly sweeping by a hemispherical metal kitchen strainer from both natant and submerged vegetation and also from bottom sediments. At each site, ten people have collected molluscs for 60 to 90 minutes (except site No. 3, 5 and 15 – 1 person/2 hrs.). During the sampling we did not use any destructive methods. A total of 67 species were found in the whole surveyed territory (43 gastropods, 24 bivalves), which is the complete current species richness of the aquatic mollusc fauna in the Danubian lowland. The most species rich sites include the Číčovské rameno Oxbow lake (36 species, No. 2), Klátovské rameno Side arm (32 spp., No. 10) and Parížske močiare Swamp (24 spp., No. 11). Bithynia tentaculata and Planorbarius corneus were the most frequent species (i.e. found at +65% of sites) and the following eight species were recorded at 44–52% of sites (i.e. 10–12 individual sites; given in a descending order): Anisus vortex, Lymnaea stagnalis, Planorbis planorbis, Anisus vorticulus, Bithynia leachii, Stagnicola palustris, Viviparus acerosus and V. contectus. In contrast, Bithynia transsilvanica, Gyraulus riparius, Pisidium personatum, Planorbis carinatus, Sphaerium nucleus and Valvata macrostoma were found at only one site (species recorded only in flood debris of the Danube River were not considered).

Grazing rate of zebra mussel in a shallow eutrophicated bay of the Baltic Sea

Benthic suspension feeding is an important process in coastal ecosystems. Among all the World's oceans, coastal ecosystems are the most modified by human impact and changing at accelerating pace. It is complicated to understand, how various environmental factors affect feeding rates of suspension feeders in their natural habitats. Thus, shapes of such relationships are poorly described for several intersections of environmental gradients. In this study, relationships between grazing rates of an invasive bivalve Dreissena polymorpha and ambient environmental factors were investigated in a turbid eutrophic bay of the central Baltic Sea using a novel modelling method of Boosted Regression Trees (BRT), a statistical tool able to handle non-normal distributions, complex relationships, and interactive effects. Feeding rates of mussels were derived from field populations by measuring the content of algal pigments in specimens collected from their natural habitat. The content of pigments was converted to feeding rate separately each time using field experiments measuring simultaneously the content of pigments and biodeposition of mussels. The results suggest that feeding rates of D. polymorpha are related to several environmental factors which gradients outreach the optimal range for the local mussel population. All the observed effects were non-linear with complex shapes. Variability along the resource gradient was the most important predictor of mussel feeding, followed by salinity and disturbance caused by wind. The most important interaction occurred between disturbance and resource gradient, while feeding function showed more plasticity along the latter. Mapping of environmental tipping points with the aid of machine learning methods may enable to concentrate the most relevant information about ecological functions worldwide.

Diversification of Ponto-Caspian aquatic fauna: morphology and molecules retrieve congruent evolutionary relationships in Pontogammarus maeoticus (Amphipoda: Pontogammaridae)

The geological history of the Ponto-Caspian region, with alternating cycles of isolation and reconnection among the three main basins (Black and Azov Seas, and the more distant Caspian Sea) as well as between them and the Mediterranean Sea, profoundly affected the diversification of its aquatic fauna, leading to a high degree of endemism. Two alternative hypotheses on the origin of this amazing biodiversity have been proposed, corresponding to phases of allopatric separation of aquatic fauna among sea basins: a Late Miocene origin (10-6 MYA) vs. a more recent Pleistocene ancestry (<2 MYA). Both hypotheses support a vicariant origin of (1) Black+Azov Sea lineages on the one hand, and (2) Caspian Sea lineages on the other. Here, we present a study on the Ponto-Caspian endemic amphipod Pontogammarus maeoticus. We assessed patterns of divergence based on (a) two mitochondrial and one nuclear gene, and (b) a morphometric analysis of 23 morphological traits in 16 populations from South and West Caspian Sea, South Azov Sea and North-West Black Sea. Genetic data indicate a long and independent evolutionary history, dating back from the late Miocene to early Pleistocene (6.6-1.6 MYA), for an unexpected, major split between (i) a Black Sea clade and (ii) a well-supported clade grouping individuals from the Caspian and Azov Seas. Absence of shared haplotypes argues against either recent or human-mediated exchanges between Caspian and Azov Seas. A mismatch distribution analysis supports more stable population demography in the Caspian than in the Black Sea populations. Morphological divergence largely followed patterns of genetic divergence: our analyses grouped samples according to the basin of origin and corroborated the close phylogenetic affinity between Caspian and Azov Sea lineages. Altogether, our results highlight the necessity of careful (group-specific) evaluation of evolutionary trajectories in marine taxa that should certainly not be inferred from the current geographical proximity of sea basins alone.

Genetic diversity in introduced golden mussel populations corresponds to vector activity

We explored possible links between vector activity and genetic diversity in introduced populations of Limnoperna fortunei by characterizing the genetic structure in native and introduced ranges in Asia and South America. We surveyed 24 populations: ten in Asia and 14 in South America using the mitochondrial cytochrome c oxidase subunit I (COI) gene, as well as eight polymorphic microsatellite markers. We performed population genetics and phylogenetic analyses to investigate population genetic structure across native and introduced regions. Introduced populations in Asia exhibit higher genetic diversity (H(E) = 0.667-0.746) than those in South America (H(E) =  0.519-0.575), suggesting higher introduction effort for the former populations. We observed pronounced geographical structuring in introduced regions, as indicated by both mitochondrial and nuclear markers based on multiple genetic analyses including pairwise Ф(ST), F(ST), bayesian clustering method, and three-dimensional factorial correspondence analyses. Pairwise F(ST) values within both Asia (F(ST) = 0.017-0.126, P = 0.000-0.009) and South America (F(ST) =0.004-0.107, P = 0.000-0.721) were lower than those between continents (F(ST) = 0.180-0.319, P = 0.000). Fine-scale genetic structuring was also apparent among introduced populations in both Asia and South America, suggesting either multiple introductions of distinct propagules or strong post-introduction selection and demographic stochasticity. Higher genetic diversity in Asia as compared to South America is likely due to more frequent propagule transfers associated with higher shipping activities between source and donor regions within Asia. This study suggests that the intensity of human-mediated introduction vectors influences patterns of genetic diversity in non-indigenous species.

Survey of PAH in low density residential stormwater ponds in coastal South Carolina: false dark mussels (Mytilopsis leucophaeata) as potential biomonitors

The distribution of PAHs was studied in sediment and false dark mussels, Mytilopsis leucophaeata, of three brackish stormwater retention ponds on Kiawah Island, a gated residential community and golf resort. Impervious surface in pond watersheds ranged from 5 to 30%. Sediment concentrations were lower than those found in other studies of suburban residential areas, and there were no significant differences among ponds or seasons. Mean summation PAH16 values for sediments in Ponds 67, 100, and 37 were 184.7+/-101.3ng g(-1), 67.5+/-26.0ng g(-1), and 84.3+/-75.5ng g(-1), respectively. Mussel summation PAH16 concentrations from Pond 67 in August (mean 734.5+/-148.1ng g(-1)), and from Pond 37 in December (mean 1115.1+/-87.7ng g(-1)), were significantly higher than other ponds. Mean summation PAH16 values for mussels in Ponds 67, 100, and, 37 were 555.9+/-219.7ng g(-1), 312.5+/-99.1ng g(-1) and 737.8+/-419.8ng g(-1), respectively. The mean biota-to-sediment ratio was 7.6+/-8.1. Isomer ratios generally suggested pyrogenic sources. False dark mussels are a promising indicator species for PAH contamination because they are abundant, easy to sample, bioaccumulate PAH profiles representative of the time-integrated sediment profiles, and their PAH levels are less variable than either stormwater or sediment samples.

Comparative phylogeography of Ponto-Caspian mysid crustaceans: isolation and exchange among dynamic inland sea basins

The distributions of many endemic Ponto-Caspian brackish-water taxa are subdivided among the Black, Azov and Caspian Sea basins and further among river estuaries. Of the two alternative views to explain the distributions, the relict school has claimed Tertiary fragmentation of the once contiguous range by emerging geographical and salinity barriers, whereas the immigration view has suggested recolonization of the westerly populations from the Caspian Sea after extirpation during Late Pleistocene environmental perturbations. A study of mitochondrial (COI) phylogeography of seven mysid crustacean taxa from the genera Limnomysis and Paramysis showed that both scenarios can be valid for different species. Four taxa had distinct lineages related to the major basin subdivision, but the lineage distributions and depths of divergence were not concordant. The data do not support a hypothesis of Late Miocene (10-5 Myr) vicariance; rather, range subdivisions and dispersal from and to the Caspian Sea seem to have occurred at different times throughout the Pleistocene. For example, in Paramysis lacustris each basin had an endemic clade 2-5% diverged from the others, whereas Paramysis kessleri from the southern Caspian and the western Black Sea were nearly identical. Species-specific ecological characteristics such as vagility and salinity tolerance seem to have played important roles in shaping the phylogeographic patterns. The mitochondrial data also suggested recent, human-mediated cryptic invasions of P. lacustris and Limnomysis benedeni from the Caspian to the Sea of Azov basin via the Volga-Don canal. Cryptic species-level subdivisions were recorded in populations attributed to Paramysis baeri, and possibly in P. lacustris.

Molecular Phylogeny of Silk Producing Insects Based on Internal Transcribed Spacer DNA1

Silk moths are the best studied silk secreting insects and belong to the families Bombycidae and Saturniidae. The phylogenetic relationship between eleven silk producing insects was analyzed using the complete DNA sequence of the internal transcribed spacer DNA 1 locus. The PCR amplification and sequence analysis showed variation in length ranging from 138 bp (Antheraea polyphemus) to 911 bp (Hyalopora cecropia). Microsatellite sequences were found and was be used to distinguish Saturniidae and Bombycidae members. The nucleotide sequences were aligned manually and used for construction of phylogenetic trees based on Maximum parsimony and Maximum likelihood methods. The topology in both the approaches yielded a similar tree that supports the ancestral position of the Antheraea assama.

Bathymetric and geographic population structure in the pan-Atlantic deep-sea bivalve Deminucula atacellana (Schenck, 1939)

The deep-sea soft-sediment environment hosts a diverse and highly endemic fauna of uncertain origin. We know little about how this fauna evolved because geographic patterns of genetic variation, the essential information for inferring patterns of population differentiation and speciation are poorly understood. Using formalin-fixed specimens from archival collections, we quantify patterns of genetic variation in the protobranch bivalve Deminucula atacellana, a species widespread throughout the Atlantic Ocean at bathyal and abyssal depths. Samples were taken from 18 localities in the North American, West European and Argentine basins. A hypervariable region of mitochondrial 16S rDNA was amplified by polymerase chain reaction (PCR) and sequenced from 130 individuals revealing 21 haplotypes. Except for several important exceptions, haplotypes are unique to each basin. Overall gene diversity is high (h = 0.73) with pronounced population structure (Phi(ST) = 0.877) and highly significant geographic associations (P < 0.0001). Sequences cluster into four major clades corresponding to differences in geography and depth. Genetic divergence was much greater among populations at different depths within the same basin, than among those at similar depths but separated by thousands of kilometres. Isolation by distance probably explains much of the interbasin variation. Depth-related divergence may reflect historical patterns of colonization or strong environmental selective gradients. Broadly distributed deep-sea organisms can possess highly genetically divergent populations, despite the lack of any morphological divergence.

Phylogeography and systematics of zebra mussels and related species

The genus Dreissena includes two widespread and aggressive aquatic invaders, the zebra mussel, Dreissena polymorpha, and the quagga mussel, Dreissena bugensis. This genus evolved in the Ponto-Caspian Sea basin, characterized by dynamic instability over multiple timescales and a unique evolutionary environment that may predispose to invasiveness. The objectives of this study were to gain insights into the demographic history of Dreissena species in their endemic range, to reconstruct intraspecific phylogeographic relationships among populations, and to clarify systematics of the genus, using DNA sequences from the mitochondrial cytochrome oxidase I (COI) gene. We found four deeply diverged clades within this genus, with a basal split that approximately coincided with the Cretaceous-Tertiary boundary. Divergence events within the four base clades were much more recent, corresponding to geographically disjunct sets of populations, which might represent species complexes. Across all taxa, populations of Dreissena shared a common pattern of genetic signatures indicating historical population bottlenecks and expansions. Haplotype diversity was relatively low in Ponto-Caspian drainages relative to more stable tectonic lakes in Greece, Macedonia, and Turkey. The phylogeographic and demographic patterns in the endemic range of Dreissena might have resulted from vicariance events, habitat instability, and the high fecundity and passive dispersal of these organisms.

Growth patterns of Mytilopsis leucophaeata, an invasive biofouling bivalve in Europe

For the first time, growth of Mytilopsis leucophaeata, an important European fouling species, was investigated. By means of growth cages, individual shell growth of three cohorts, with, respectively, initial shell lengths of < or =5 mm, 10 mm and 15 mm, was monitored in the harbour of Antwerp, Belgium, during 2003 - 2004. M. leucophaeata followed an oscillatory growth pattern with a single summer growing period per year (May to August). Growth decreased during wintertime, but never ceased completely. M. leucophaeata has an average growth rate of < 3-6 mm year- 1. Temperature was found to be the main environmental factor affecting growth. The von Bertalanffy growth function was used to model growth of individuals < or =5 mm, resulting in Linfinity = 16.7 mm and K= 0.56. Based on a combination of growth of all three cohorts, the hypothetical growth of an average individual mussel could be modelled over a 5-year period, resulting in a maximum length > 19 mm with a growth rate of 0.41. Its longevity (more than 5 years) and the positive effect of higher water temperatures on growth, combined with its high resistance to chlorination, provides M. leucophaeata with a high potential for severe and long-lasting biofouling

Upper temperature tolerances of exotic brackish-water mussel, Mytilopsis leucophaeata (Conrad): an experimental study

The dark false mussel, Mytilopsis leucophaeata is an important mussel colonising the brackish-water systems of temperate and subtropical regions. Of late it has earned notoriety as a biofouling species in industrial cooling water systems. However, there are no published data on the temperature tolerance of this species. This paper presents data on the upper temperature tolerance of this mussel from the view point of biofouling control using thermal methods. In addition to mortality, response of physiological activities such as oxygen consumption, filtration rate, foot activity and byssus thread production were also studied at temperatures varying from 5 to 35 degrees C. Experiments were also carried out to understand the effect of mussel size, breeding condition, nutritional status and acclimation conditions (temperature and salinity) on the mortality pattern. The physiological activities were significantly reduced at temperatures beyond 27.5 degrees C and ceased at 35 degrees C. In 20 mm size group mussels exposed to 37 degrees C, 50% mortality was observed after 85 min and 100% mortality after 113 min. The effect of mussel size on mortality at different temperatures was significant, with the larger size group mussels showing greater resistance. M. leucophaeata collected during the non-breeding season (December-April) were more tolerant to temperature than those collected during the breeding season (June-October). Nutritional status of the mussel had no significant influence on the thermal tolerance of the mussel: fed and starved (non-fed) mussels succumbed to temperature at comparable rates. The effect of acclimation temperature and acclimation salinity on M. leucophaeata mortality at different temperatures was significant. Survival time increased with increasing acclimation temperature and decreased with increasing salinity. In comparison with other co-occurring species such as Mytilus edulis and Dreissena polymorpha, M. leucophaeata appears to be more tolerant to high temperature stress.

Invasion genetics of a freshwater mussel (Dreissena rostriformis bugensis) in eastern Europe: high gene flow and multiple introductions

In recent years, the quagga mussel, Dreissena rostriformis bugensis, native to the Dnieper and Bug Limans of the northern Black Sea, has been dispersed by human activities across the basin, throughout much of the Volga River system, and to the Laurentian Great Lakes. We used six published microsatellite markers to survey populations throughout its native and introduced range to identify relationships among potential source populations and introduced ones. Mussels from 12 sites in Eurasia, including the central Caspian Sea and one in North America (Lake Erie), were sampled. Field surveys in the Volga River basin suggested that the species first colonized the middle reach of the river near Kubyshev Reservoir, and thereafter spread both upstream and downstream. Evidence of considerable gene flow among populations was observed and genetic diversity was consistent with a larger, metapopulation that has not experienced bottlenecks or founder effects. We propose that high gene flow, possibly due to multiple invasions, has facilitated establishment of quagga mussel populations in the Volga River system. The Caspian Sea population (D. rostriformis rostriformis (=distincta)) was genetically more distinct than other populations, a finding that may be related to habitat differences. The geographical pattern of genetic divergence is not characteristic of isolation-by-distance but, rather, of long-distance dispersal, most likely mediated by commercial ships' ballast water transfer.