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Acknowledgements The authors acknowledge the two anonymous reviewers for their useful comments that improved the manuscript. Financial support for the excavations in Neumark‐Nord 2 was provided by the Lausitzer Mitteldeutsche Braunkohlengesellschaft mbH, the Landesamt fur Denkmalpflege und Archaologie Sachsen‐Anhalt (Harald Meller, Susanne Friederich), the Romisch‐Germanisches Zentralmuseum Mainz, the Leids Universiteits Fonds ‘Campagne voor Leiden’ program and the Netherlands Organization for Scientific Research (N.W.O.).

The first in-depth revision of a lacustrine freshwater mollusc fauna of the Serbian Lake System (SLS) is carried out. We describe and discuss well-preserved faunas from two localities in central and southern Serbia (Mađere and Medoševac), along with the reinvestigation of type material of several species described in the late nineteenth and early twentieth centuries. Our revision yields 14 species of gastropods, with the families Hydrobiidae (six species) and Planorbidae (four species) being most abundant, along with one species each of Neritidae, Melanopsidae, Bithyniidae and Bulinidae, as well as two dreissenid bivalve species. Three of the hydrobiid gastropods are new to science, Prososthenia milosevici sp. nov., Prososthenia? naissensis sp. nov., and Prososthenia rundici sp. nov., and so is the bivalve Trigonipraxis madjerensis sp. nov. The present study results in 12 lectotype designations, 10 new generic combinations, and 10 new junior synonyms. About four-fifths (81.3%) of the species are endemic to the SLS, which is slightly higher than the overall SLS endemism (71.4%). The composition at the genus and family level overlaps strongly with the slightly older faunas of the Dinaride Lake System in Croatia and Bosnia and Herzegovina, as well as that of the late Miocene Lake Pannon. Its stratigraphically intermediate position and geographical proximity suggest that the SLS was a stepping stone for many of the mollusc lineages, some of which are found only in those systems.

Glycogen is a primary metabolic reserve in bivalves and can be suitable for the evaluation of bivalve condition and health status, but the use of glycogen as a diagnostic tool in aquaculture and biomonitoring is still relatively rare. A tissue biopsy combined with a simplified phenol-sulfuric acid method was used in this study to evaluate the inter- and intraindividual variation in the glycogen concentrations among several tissues (foot, mantle, gills, adductor muscle) of the unionid bivalve, the duck mussel Anodonta anatina. This short report documents that individual bivalves differ in the spatial distribution of glycogen among tissues. Sampling of different types of tissues can cause distinct results in the evaluation of energetic reserves at the individual level. At the same time, spatial variability in glycogen content has the potential to provide a more detailed evaluation of physiological conditions based on tissue-specific glycogen storage. The results obtained and the simplified methodology provide a new opportunity for researching the energetic reserves and health status of freshwater mussels in various applications.

The effects of invasive alien species (IAS) on host–affiliate relationships are often subtle and remain unnoticed or insufficiently quantified. The global decline of freshwater unionid mussel species has been attributed to many causes, but little is known about the interactions of IAS, with their complex life cycle, which includes an obligatory parasitic stage (the glochidium) that develops on fishes. The capacity of a European freshwater mussel, Anodonta anatina, to develop on its widespread fish host, Squalius cephalus was tested experimentally, after previous infestations by the IAS, Sinanodonta (Anodonta) woodiana. The initial attachment of glochidia, the length of the parasitic period, and the metamorphosis success rate of A. anatina glochidia were compared among treatments of different priming infestation intensities. The metamorphosis success rate of the native A. anatina glochidia was strongly reduced (Wilcoxon Signed-Rank Test, P < 0.001) and declined by 42.1 and 45.4% on fish hosts that were previously exposed to S. woodiana by single and multiple priming infestations, respectively, in comparison with the control group. Such cross-resistance is expected to decrease significantly the quality of the host resources available to native mussels. This study provides the first evidence of the host-mediated adverse impact of invasive S. woodiana on native mussel species. These results also highlight the importance of potential competition for hosts between threatened groups of affiliate species and their invasive counterparts, which should be reflected in conservation strategies., Czech Science Foundation, Grant/Award Number: 13-05872S, info:eu-repo/semantics/publishedVersion

The effects of location and density on the growth and survival of juvenile freshwater pearl mussel, Chamberlainia hainesiana, 150–360 d after metamorphosis were investigated to determine the optimal ranges for commercial farming in Thailand. Juveniles were reared outdoors in two locations (the Mae Klong Reservoir and the Khwae Yai River, Kanchanaburi Province). Three density levels (25, 50, and 100 mussels/basket) were established at each location, with three replicates per density level. Phytoplankton from the water column in the natural habitats served as feed; no supplemental feed was provided. The mussels cultured in the reservoir had significantly higher growth rates than those cultured in the river (P 0.05), but both showed significant differences in growth from the density level of 100 mussels/basket (P

The study was supported financially by the Hungarian Scientific Research Fund under the contract No. OTKA T/046180 and No. CNK80140. Ronaldo Sousa acknowledges the financial support provided by the Portuguese Foundation for Science and Technology (FCT) and COMPETE funds — project ECO-IAS (Contract:PTDC/AAC-AMB/116685/2010).

The diminutive, extinct longirostrine dolphin Parapontoporia is one of the most abundantly represented late Neogene odontocetes from the eastern North Pacific and is widely known from numerous marine strata of late Miocene and Pliocene age in California, Baja California and possibly Japan. Parapontoporia has been identified as the sister taxon of the recently extinct Chinese river dolphin (Lipotes vexillifer); unlike Lipotes, which exclusively inhabited freshwater, the depositional context of Parapontoporia suggests it was marine. A newly identified petrosal of Parapontoporia sp. was preserved alongside terrestrial vertebrates in the nonmarine Tulare Formation (upper Pliocene to Pleistocene, 2.2–0.6 Ma), California, which was deposited under lacustrine and fluviodeltaic conditions. Abundantly preserved freshwater molluscs and rare marine taxa suggest predominantly freshwater settings with intermittent periods of estuarine conditions. This occurrence of Parapontoporia indicates its presence in the San Joaquin basin after the retreat of the inland sea and suggests that this extinct odontocete may have been freshwater tolerant and an inhabitant of marine and freshwater settings, heralding the exclusively freshwater existence of its Recent sister taxon Lipotes vexillifer.

Aim: Ecological theory predicts that invasive ecosystem engineers like the American beaver (Castor canadensis) in Tierra del Fuego (TDF) affect landscape-level biodiversity and ecosystem function (BEF) when engineered habitats are novel or extensive. We tested these hypotheses on freshwater BEF, sampling benthic habitat and macroinvertebrates in natural lotic (forest and grassland streams) and natural lentic habitats (bogs, lakes) and beaver-modified lentic ecosystems (active and abandoned ponds). Location: Tierra del Fuego Archipelago (Chile and Argentina). Methods: To determine effects on patch-scale BEF, we assessed two drivers: substrate diversity (H′) and benthic organic matter standing crop (BOM, g m-2). Extent of impact was estimated as relative stream length (%) for each patch type in four 1000 ha images. Results: The freshwater landscape was 56% free-flowing streams (natural lotic), 13% bogs and lakes (natural lentic) and 31% active and abandoned beaver ponds (beaver lentic). While engineering significantly modified lotic habitats (converting them to ponds), the beaver ponds were largely similar to natural lentic systems, but engineered lentic patches retained more BOM. While benthic biodiversity in beaver ponds was less than streams, the assemblage contained no habitat-specific taxa and was a subset of the natural lentic community. Main conclusions: Invasive beavers engineer habitats whose biodiversity is similar to the landscape's natural lentic habitats, but by increasing the surface area and unit area retention of BOM via its impoundments, this invasion augments carbon standing stock approximately 72% in watersheds. While this invasion is considered the largest alteration to TDF's forested biome in the Holocene, here we discover that its impact is to ecosystem function, rather than biodiversity in the aquatic landscape. Fil: Anderson, Christopher Brian. Universidad Nacional de Tierra del Fuego. Instituto de Ciencias Polares, Recursos Naturales y Ambiente; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Omora Sub-Antarctic Research Alliance; Estados Unidos Fil: Lencinas, María Vanessa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Wallem, Petra K.. Bioamerica Consultores; Chile Fil: Valenzuela, Alejandro Eduardo Jorge. Administración de Parques Nacionales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Simanonok, Michael P.. State University Of Montana; Estados Unidos Fil: Martínez Pastur, Guillermo José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina

Each year, hundreds of aquatic migratory birds migrate from northern hemisphere to the Mazandaran Province, northern Iran. Little information is available on prevalence and density of schistosomes in water birds in Iran and around the world. The objectives of this study were to determine definitive and intermediate hosts of avian schistosomes as well as to assess human cercarial dermatitis (HCD) in a wildlife refuge in Mazandaran Province. Of 1106 examined people, 589 (53.2%) had maculopapular rashes mainly on feet but also on hand. The majority of cases were adults and local residents. Of 260 ducks, 41 (15.8%) were found to be infected with Trichobilharzia spp. eggs or adult worms. Prevalence was highest in Anas clypeata and Anas platyrhynchos, 79% and 18.9%, respectively. A total of 1.2% snails, examined by both shedding and crushing methods, were infected with furcocercariae belonging to avian schistosomes. The most frequently infected snail was Lymnaea gedrosiana (5.9%). Our results showed that cercarial dermatitis and avian schistosomiasis is a common and yet neglected disease in this area. Anas clypeata played the most important role in exposing snails to miracidia in ponds and paddy fields. Moreover, because of the high prevalence in ducks and high prevalence of HCD in the region, it is considered as a new endemic focus in Iran.

The aim of this study was to assess the invasion risk of freshwater habitats and determine the environmental variables that are most favorable for the establishment of alien amphipods, isopods, gastropods, and bivalves. A total of 981 sites located in streams and rivers in Germany. Therefore we analyzed presence–absence data of alien and indigenous amphipods, isopods, gastropods, and bivalves from 981 sites located in small to large rivers in Germany with regard to eight environmental variables: chloride, ammonium, nitrate, oxygen, orthophosphate, distance to the next navigable waterway, and maximum and minimum temperature. Degraded sites close to navigable waters were exposed to an increased invasion risk by all major groups of alien species. Moreover, invaded sites by all four groups of alien species were similar, whereas the sites where indigenous members of the four groups occurred were more variable. Increased temperature and chloride concentration as well as decreased oxygen concentration were identified as major factors for the invasibility of a site. Species-specific analyses showed that chloride was among the three most predictive environmental variables determining species assemblage in all four taxonomic groups. Also distance to the next navigable waterways was similarly important. Additionally, the minimum temperature was among the most important variables for amphipods, isopods, and bivalves. The bias in the occurrence patterns of alien species toward similarly degraded habitats suggests that the members of all four major groups of freshwater alien species are a non-random, more tolerant set of species. Their common tolerance to salinity, high temperature, and oxygen depletion may reflect that most alien species were spread in ballast water tanks, where strong selective pressures, particularly temperature fluctuations, oxygen depletion, and increased salinity may create a bottleneck for successful invasion. Knowledge on the major factors that influence the invasion risk of a habitat is needed to develop strategies to limit the spread of invasive species.

The transition from marine to freshwater habitats is one of the major steps in the evolution of life. In the decapod crustaceans, four groups have colonized fresh water at different geological times since the Triassic, the freshwater shrimps, freshwater crayfish, freshwater crabs and freshwater anomurans. Some families have even colonized terrestrial habitats via the freshwater route or directly via the sea shore. Since none of these taxa has ever reinvaded its environment of origin the Decapoda appear particularly suitable to investigate life-history adaptations to fresh water. Evolutionary comparison of marine, freshwater and terrestrial decapods suggests that the reduction of egg number, abbreviation of larval development, extension of brood care and lecithotrophy of the first posthatching life stages are key adaptations to fresh water. Marine decapods usually have high numbers of small eggs and develop through a prolonged planktonic larval cycle, whereas the production of small numbers of large eggs, direct development and extended brood care until the juvenile stage is the rule in freshwater crayfish, primary freshwater crabs and aeglid anomurans. The amphidromous freshwater shrimp and freshwater crab species and all terrestrial decapods that invaded land via the sea shore have retained ocean-type planktonic development. Abbreviation of larval development and extension of brood care are interpreted as adaptations to the particularly strong variations of hydrodynamic parameters, physico-chemical factors and phytoplankton availability in freshwater habitats. These life-history changes increase fitness of the offspring and are obviously favoured by natural selection, explaining their multiple origins in fresh water. There is no evidence for their early evolution in the marine ancestors of the extant freshwater groups and a preadaptive role for the conquest of fresh water. The costs of the shift from relative r- to K-strategy in freshwater decapods are traded-off against fecundity, future reproduction and growth of females and perhaps against size of species but not against longevity of species. Direct development and extension of brood care is associated with the reduction of dispersal and gene flow among populations, which may explain the high degree of speciation and endemism in directly developing freshwater decapods. Direct development and extended brood care also favour the evolution of social systems, which in freshwater decapods range from simple subsocial organization to eusociality. Hermaphroditism and parthenogenesis, which have evolved in some terrestrial crayfish burrowers and invasive open water crayfish, respectively, may enable populations to adapt to restrictive or new environments by spatio-temporal alteration of their socio-ecological characteristics. Under conditions of rapid habitat loss, environmental pollution and global warming, the reduced dispersal ability of direct developers may turn into a severe disadvantage, posing a higher threat of extinction to freshwater crayfish, primary freshwater crabs, aeglids and landlocked freshwater shrimps as compared to amphidromous freshwater shrimps and secondary freshwater crabs.

The authors tested the efficacy of elevated partial pressures of CO2 to kill invasive New Zealand mudsnails. The New Zealand mudsnails were exposed to 100 kPa at three water temperatures, and the survival was modeled versus dose as cumulative °C-h. We estimated an LD50 of 59.4°C-h for adult and juvenile New Zealand mudsnails. The results suggest that CO2 may be an effective and inexpensive lethal tool to treat substrates, tanks, or materials infested with New Zealand mudsnails. Environ. Toxicol. Chem. 2012; 31: 1838–1842. © 2012 SETAC

Freshwater mussels are in decline throughout their range. The lack of natural recruitment in freshwater pearl mussel populations and other freshwater molluscs has led to controversies about the usefulness and applicability of captive breeding techniques for their conservation. The current state of rearing and culturing programmes for freshwater mussels in Europe and North America is reviewed here with a focus on the endangered freshwater pearl mussel (Margaritifera margaritifera). Different strategies of propagation and the key factors of success are addressed and conservation management decisions are discussed with respect to risk reduction and the intensity of the culturing system. Based on the rearing techniques applied for multiple species in North America, and for the genus Margaritifera in European countries, sufficient numbers of juveniles can be produced to sustain selected populations. However, captive breeding and stocking should be carefully documented and must not replace the restoration of functional stream habitats. From a conservation point of view, captive breeding of endangered mussel species can be a last-minute rescue tool in order to retain the evolutionary potential of priority populations which would not persist long enough to benefit from habitat restoration practices. Copyright © 2011 John Wiley & Sons, Ltd.

The fresh and saline lakes of Ounianga Kebir and Serir in northeastern Chad are among the very few permanent aquatic ecosystems currently existing in the hyper-arid core of the Sahara desert. The confirmed modern fauna of aquatic molluscs at Ounianga comprises three widespread species (Melanoides tuberculata, Biomphalaria pfeifferi and Lymnaea natalensis), of which only the first appears to maintain a thriving population. We recovered seven more species of gastropods, among which one is new to science (Gabbiella ouniangaensis), and one bivalve species from early Holocene outcrops of diatomaceous limestone at Ounianga Serir. All species except one are known to be commonly spread between lake and river systems by birds, and in its entirety this species-rich fossil mollusc fauna of Ounianga Serir resembles that of other Saharan lake sites known to have been hydrologically isolated during the early Holocene. The impoverished modern mollusc fauna, which lacks even the widespread and opportunistic species Bulinus truncatus, may have become established relatively recently through new colonisation events, following eradication of the early Holocene mollusc fauna during a later episode of high salinity or desiccation. Copyright # 2011 John Wiley & Sons, Ltd.

SUMMARY 1. Birds and snails are suitable hosts for many parasites, including helminths in general and trematodes in particular. Among trematodes, members of the family Schistosomatidae with two-host life cycles (snails as intermediate hosts and birds as definitive hosts) are successful and abundant pathogens. Their transmission between birds and snails in nature can be influenced by many abiotic and biotic factors. 2. In snails, the prevalence of schistosome infections and production of cercariae can be influenced by host immunological susceptibility ⁄ physiological suitability, snail age ⁄ size, interspecific competition of trematode larvae, etc. Schistosomes are able to survive in overwintering snails, serving as a source of infection in spring. 3. Birds may also differ in susceptibility to and prevalence rates of schistosome infections. They are long-range vectors of schistosomes. 4. Climate changes influence behaviour of migratory birds, lead to shifts in season- or temperature-dependent processes in snails and schistosomes, and influence the frequency of schistosome transmission and intensity of infection. Also, eutrophication can increase the growth of snail populations and transmission of bird schistosomes. 5. Dispersal of bird schistosomes to new regions and an increased availability (local abundance) of the snail hosts, together with the use of new water reservoirs (e.g., in higher latitudes) for recreational purposes, may contribute to a higher number of outbreaks of cercarial dermatitis.

SUMMARY 1. Freshwater ecosystems, including ponds, lakes, streams and rivers, represent an interaction nexus between environmental change and a wide variety of infectious diseases, including human malaria, salmonid whirling disease, amphibian chytridiomycosis, crayfish plague and many others. However, few studies have explicitly examined patterns of disease in fresh waters and how they are changing over time. 2. Freshwater environments can function as transmission foci for pathogens because of (i) the importance of fresh water for organism survival, (ii) the aquatic life histories of many vectors and intermediate hosts, (iii) the concentrated aggregations of species – both freshwater and terrestrial – in and around freshwater habitats and (iv) the highly altered condition of freshwater ecosystems, which can affect species interactions and disease pathology. 3. To determine whether water-related diseases in wildlife are increasing, we used generalised additive models to quantitatively assess trends in the scientific literature (1970–2009) for major freshwater groups, including amphibians, molluscs, crayfishes, fishes, mammals, reptiles and birds. We further examined what types of pathogens were primarily responsible for observed patterns and whether recurrent groups or transmission modes could be identified. 4. After correcting for research effort and temporal autocorrelation, we find that reports of disease varied over time and across freshwater taxa, with significant increases in amphibians, fishes and crayfishes, a significant decrease in molluscs, and no significant change in freshwater reptiles, birds or mammals. The types and diversity of pathogens varied considerably among groups. Reports of infection in amphibians were dominated by helminths and a chytridiomycete, in crayfishes by viruses and fungi, in molluscs by digenetic trematodes, in birds, fishes and mammals by viruses, protists and helminths and in reptiles by helminths and bacteria. 5. These results provide some of the first quantitative evidence indicative of a long-term increase in disease-related research for freshwater taxa. Managing freshwater ecosystems to reduce or minimise human and wildlife disease risk – arguably one of the most significant ecosystem services – will require enhanced incorporation of ecological approaches alongside medical and veterinary tools.

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 f ...

Population genetic perturbations of intermediate hosts, often a consequence of human pressure on environmental resources, can precipitate unexpectedly severe disease outbreaks. Such disturbances are set to become increasingly common following range changes concomitant with climate shifts, dwindling natural resources and major infrastructure changes such as hydroprojects. Construction of the Diama dam in the Senegal River Basin (SRB) reduced river salinity, enabling the freshwater snail intermediate host Biomphalaria pfeifferi to rapidly expand its distribution. A serious public health problem ensued, with an epidemic of intestinal schistosomiasis occurring in the previously schistosome-free Richard-Toll region within 2 years. The current study aimed to assess the population variability of B. pfeifferi in the SRB, and speculate upon its subsequent impact on host-parasite interactions following such engineered ecological change. Genetic variation at nine polymorphic microsatellite loci revealed little population differentiation in SRB snails compared with those from natural habitats in Zimbabwe, where Schistosoma mansoni transmission is much lower. 'Open' SRB habitats are associated with greater water contact, smaller population sizes and less genetic diversity, with sites downstream of Richard-Toll showing greater inter- and intrapopulation variation, concomitant with less frequent human contact. These observations may be explained by rapid expansion into pristine habitat selecting for high fecundity genotypes at the expense of schistosome resistance, presenting S. mansoni with genetically homogenous highly fecund susceptible populations around the focal point, promoting development of a highly compatible host-parasite relationship. Longitudinal study of such systems may prove important in predicting public health risks engendered by future environmental engineering projects.

Recent studies have used carbon and nitrogen stable isotope ratios of preserved soft tissues to examine historical changes in trophic patterns of aquatic ecosystems. A limitation in this application is the difficulty in finding specimens for primary consumers, which can act as a surrogate for basal food sources in determining the trophic status of higher consumers. The availability of preserved soft tissues of invertebrate primary consumers is often limited in museum and archival collections; hard parts such as mollusc shells, however, are often abundant because of their ease of storage. We used stable isotope ratios of carbon and nitrogen to determine if there was a relationship between the isotopic composition of the periostracum of the shell and soft body tissue of freshwater molluscs. We found a significant correlation between (1) periostracum and tissue of freshly collected freshwater mussels, (2) ethanol-preserved adductor muscle tissue and dry-preserved mussels from museum collections, and (3) ethanol-preserved tissue and periostracum of gastropods from museum collections. The predictability of these relationships enhances the capacity to track changes in trophic complexity over time and responses of food webs to natural and anthropogenic environmental perturbations.

The digenetic trematode Bolbophorus damnificus has been associated with mortalities in commercial channel catfish Ictalurus punctatus in the Mississippi Delta. In the life cycle of B. damnificus, the only confirmed first intermediate host is the ram's horn snail Planorbella trivolvis. Recently, the exotic snail Biomphalaria havanensis has been isolated in several channel catfish ponds in the Mississippi Delta. The aim of this study was to determine whether this invasive snail species could also serve as a first intermediate host in the B. damnificus life cycle. Bolbophorus damnificus ova were collected from an American white pelican Pelecanus erythrorhynchos that had been artificially infected with B. damnificus metacercariae; the ova were then introduced into an aquarium with parasite-negative B. havanensis. Bolbophorus damnificus cercariae (confirmed by polymerase chain reaction) were detected in B. havanensis 45 d after exposure to B. damnificus ova. The snails continued to shed B. damnificus ...

Freshwater mollusks are highly imperiled, with 70% of the North American species extinct, endangered, or at risk of extinction. Impoundments and other human impacts on the Coosa River of Alabama, Georgia and Tennessee of the southeastern USA alone are believed to have caused 50 mollusk species extinctions, but uncertainty over boundaries among several putatively closely related species makes this number preliminary. Our examination of freshwater mussels collected during an extensive survey of the upper-drainage basin, DNA barcoding and molecular phylogenetic analyses confirm the rediscovery of four morphospecies in the genus Pleurobema (Unionidae) previously thought to be extinct from the upper Coosa basin. A fifth ‘extinct’ form was found in an adjoining basin. Molecular data show that the Coosa morphologies represent at least three species-level taxa: Pleurobema decisum, P. hanleyianum and P. stabile . Endemism is higher than currently recognized, both at the species level and for multispecies clades. Prompt conservation efforts may preserve some of these taxa and their ecosystem.

The most efficient way to reduce future damages from nonindigenous species is to prevent the introduction of harmful species. Although ecologists have long sought to predict the identity of such species, recent methodological advances promise success where previous attempts failed. We applied recently developed risk assessment approaches to nonindigenous freshwater molluscs at two geographic scales: the Laurentian Great Lakes basin and the 48 contiguous states of the United States. We used data on natural history and biogeography to discriminate between established freshwater molluscs that are benign and those that constitute nuisances (i.e., cause environmental and/or economic damage). Two statistical techniques, logistic regression and categorical tree analysis, showed that nuisance status was positively associated with fecundity. Other aspects of natural history and biogeography did not significantly affect likelihood of becoming a nuisance. We then used the derived statistical models to predict the chance that 15 mollusc species not yet in natural ecosystems would cause damage if they become established. We also tested whether time since establishment is related to the likelihood that nonindigenous mollusc species in the Great Lakes and United States would cause negative impacts. No significant relationship was evident at the U.S. scale, but recently established molluscs within the Great Lakes were more likely to cause negative impacts. This may reflect changing environmental conditions, changing patterns of trade, or may be an indication of “invasional meltdown.” Our quantitative analyses could be extended to other taxa and ecosystems and offer a number of improvements over the qualitative risk assessments currently used by U.S. (and other) government agencies. Resumen: La prevencion de la introduccion de especies perjudiciales es la manera mas eficiente de reducir los danos futuros ocasionados por especies no nativas. Aunque los ecologos han buscado predecir la identidad de tales especies durante mucho tiempo, avances metodologicos actuales prometen exito en donde han fallado intentos anteriores. Aplicamos metodos de evaluacion de riesgo, desarrollados recientemente, en moluscos dulceacuicolas en dos escalas regionales: la cuenca Laurentian de Grandes Lagos y los 48 estados contiguos de los Estados Unidos. Utilizamos datos de historia natural y biogeografia para discriminar moluscos dulceacuicolas establecidos que son beneficos de los que son perjudiciales (i.e., causan dano ambiental y/o economico). Dos tecnicas estadisticas, regresion logistica y analisis de arbol categorico, mostraron que el estatus perjudicial estaba asociado positivamente con la fecundidad. Otros aspectos de la historia natural y biogeografia no alteraron la probabilidad de convertirse en perjudicial. Posteriormente utilizamos los modelos estadisticos derivados para predecir la probabilidad de que 15 especies de moluscos que aun no estan en ecosistemas naturales pudieran causar danos en caso de establecerse. Tambien probamos si el tiempo transcurrido desde el establecimiento esta relacionado con la probabilidad de que especies de moluscos no nativos en los Grandes Lagos y en Estados Unidos pudieran causar impactos negativos. No hubo relacion significativa evidente en la escala de E. U. A., pero los moluscos recientemente establecidos en los Grandes Lagos tuvieron mayor probabilidad de provocar impactos negativos. Esto puede ser reflejo de condiciones ambientales cambiantes, de patrones de comercio cambiantes o puede ser un indicador de una “fundicion invasiva.” Nuestros analisis cuantitativos podrian ser extendidos a otros taxa y ecosistemas y ofrecen numerosas mejorias de las evaluaciones de riesgo cualitativas que actualmente son utilizadas por agencias gubernamentales de E.U.A (y otros paises).

Introduced species provide an opportunity to examine responses to novel ecological conditions, in particular to the absence of co-evolved enemies. Introduced populations could evolve lower investment in resistance or could down-regulate their immune system as a plastic response to enemy absence. The response might have consequences for the success of introduced species. Assuming a trade-off between resistance and traits related to demographic success, an evolved change or reallocation from resistance could increase the chances of invasions. On the other hand, introduced populations could have increased resistance as a correlate of greater vigour and competitive ability among successful invaders [Sampling Bias hypothesis (SBH)]. These hypotheses make different predictions about investment in resistance in introduced populations. Using a New Zealand clonal snail (Potamopyrgus antipodarum), we examined the resistance of three introduced genotypes (one from the US and two from Europe) to several populations of a native range parasite (Microphallus sp.). One genotype (Euro A) was resistant to all native range parasite populations, consistent with the SBH. However, two remaining genotypes (Euro C and US 1) were less susceptible to parasite populations that were allopatric to their source populations. Furthermore, resistance of one genotype (US 1) collected from the introduced range was indistinguishable from its resistance when collected from the range of the parasite. Hence, there was no evidence for decreased resistance in the absence of native enemies, which is inconsistent with hypotheses that envision reduced allocation to resistance or a trade-off between competitive ability and resistance.

Calcium is an essential requirement for the successful growth and development of gastropod molluscs. Data for British freshwater gastropods were used to examine the relationship between environmental calcium requirements and British and European range sizes. At both spatial scales calciphile species, which require a high level of environmental calcium, had significantly smaller range sizes than species able to exploit a wide range of environmental calcium levels. However, at least in Britain, range size may also be influenced by the availability of suitable habitat. British and European range sizes were significantly correlated. This study provides evidence for niche-based explanations of range size variation, and suggests that both niche breadth and niche availability are important in determining range size.

Genotoxic effects were evaluated in the somatic and gonadal cells of five bivalve and gastropod mollusc species inhabiting various sites of Klaipe˙da port area, differing by ecotoxic impacts. Aneuploidy, polyploidy of cells, meiotic injures, centromere dissociation and fragmented polyploid nuclei were assessed as cytogenetic disturbances. The highest level of environmental genotoxicity was observed in the cells of Lymnaea ovata snails inhabiting Malkų Bay in 1995 and 1996. Dredging and removal of contamined sediments from Malkų Bay resulted in marked decrease of cytogenetic damage in molluscs, which were studied in 1997 and 1998. In 1997 the aneugenic effects were more frequent in the tissues of Bithynia tentaculata from Smelte River than those collected from Malkų Bay and Klaipeda passage. The level of cytogenetic damage in molluscs from Vilhelmo Channel was increasing from 1995 to 1998.

The mollusc record from Lago d'Averno, central southern Italy, provides a detailed 1600-yr record of changes in water quality in response to bradyseismic movements and salinity fluctuations. Bradyseismic vertical land movements and human impact in Roman times led to several transgressions from the Mediterranean Sea, 1 km distant, making the lake a valuable resource for documenting the effect of episodic marine transgressions of a freshwater lake. Low-oxygen-tolerant freshwater molluscs suggest that, at around 900–500 bc the lake had a slowly decreasing medium freshwater quality, resulting from contamination of volcanic origin. Disappearance of the obligate freshwater snails and transgression of low-salinity-tolerant marine species indicate that, after 500 bc, continuous subsidence resulted in episodic marine transgressions from the nearby sea. The construction of a canal that connected the lake with the sea, in 37 bc, is marked by a considerable increase in the number of shells and by arrival of brackish-water-intolerant marine species. Species diversity increased considerably when the area was partly depopulated towards the end of the Roman Empire around ad 400. When the land was slightly uplifted around ad 600–750, the water quality of the lake became less favourable for marine molluscs. Copyright © 2000 John Wiley & Sons, Ltd.

This study examines the direct and indirect effects of atrazine on two grazer species— Physa acuta and Ancylus fluviatilis —as assessed by changes in mortality rates, biomass, searching behaviour and histological properties. No direct effects were observed in the acute toxicity test (48 h) with 0.02, 0.2, 2, 10 and 20 mg l−1 of atrazine. A chronic toxicity test (18 days) performed in six experimental channels with 15 μg l−1 of atrazine showed significant changes in grazer behaviour, increased searching velocity and different movement patterns in animals exposed to herbicide. No significant effects were observed in rates of mortality and biomass. Kidney cells of Physa acuta displayed an important cell lysis when animals were exposed to 0.1 mg l−1 of atrazine for 10 days, and this effect was not reversed after a decontamination process. These results provide evidence of behavioural and structural changes in freshwater molluscs due to a subacute atrazine concentration. Copyright © 1999 John Wiley & Sons, Ltd.

Marine molluscs have long been recognised as potential records of palaeoclimate change using the patterns and differences in the stable isotopic composition of the carbonate shells. The aim of this study is to improve the robustness of this approach for aragonitic molluscs by completing the first experimental calibration of the fractionation between water and biogenic aragonite. Fractionation factors were calibrated by growing specimens of the freshwater mollusc Lymnaea peregra under controlled conditions of water temperature and isotopic composition. Fifteen populations of L. peregra were maintained at constant temperature and isotopic conditions for five months (at five different temperatures and using three different water compositions). Water samples and temperature measurements were taken regularly throughout the experiment. The temperature dependence of the fractionation factor, between 8 and 24 degrees C, is given by: 1000 ln alpha=16.74x(1000T(-1))-26.39 (T in Kelvin) and the relationship between temperature (T), delta(18)O(carb) and delta(18)O(wat) is given by: T=21.36-4.83xdelta(+ degrees )O(carb)-delta(+ degrees )O(wat) (T is in degrees C, delta(18)O(carb) is with respect to Vienna Pee Dee Belemnite (PDB), the International Atomic Energy Agency (IAEA) replacement standard for PDB, and delta(18)O(wat) is with respect to Vienna standard mean ocean water (VSMOW)) The outcome of the controlled experiment is compared with previous studies on synthetic, and biogenic, calcite and aragonite from field and laboratory investigations. These comparisons suggest that although a vital offset exists between the fractionation of isotopes in synthetic and biogenic aragonite for molluscs in general, there is no vital effect that is specific either to freshwater, or to individual, genera. Therefore, the calibrated relationship may be used for any freshwater or marine mollusc to derive palaeotemperatures providing the isotopic composition of the environmental water can be reliably constrained. Copyright 1999 John Wiley & Sons, Ltd.

1. Twelve biogeographical zones for freshwater habitats in Great Britain were derived, using detrended canonical correspondence analysis of data on climate, relief, geology, soils and land use, in conjunction with occurrence data for more than 300 native freshwater species. 2. The taxonomic groups used were aquatic macrophytes, dragonflies, freshwater molluscs, amphibians and selected leeches, water beetles and crustaceans. The computer database of the Institute of Terrestrial Ecology's Biological Records Centre was used as the principal source of species data. 3. Within each of the 12 biogeographical zones, 10×10 km square ‘hotspots’ for species richness and rarity were identified. 4. The significance of this work for the conservation of freshwater habitats and species in Great Britain is discussed. Copyright © 1999 John Wiley & Sons, Ltd.

Two hundred roach and over 400 molluscs were examined over a one year period to investigate the occurrence and life history of Asymphylodora kubanicum in the Worcester-Birmingham canal. Larval stages, infective to the fish definitive host, were present in molluscs throughout the year but did not show a seasonal fluctuation in numbers. Parasites in the intestine of the roach showed a marked annual cycle of occurrence and maturation: low winter infection levels preceded a dramatic increase in infection during the spring and summer. Maturation of the parasite population was rapid during the spring and summer and in late summer and early autumn the parasites laid their eggs and subsequently died. The death of parasites after egg-laying resulted in the low winter infection level during which time little recruitment occurred. Roach became infected mainly in their third year when molluscs become a dominant component of their diet. Thereafter the older fishes (

The complex patterns of geographic variation exhibited by many groups of freshwater molluscs present some extremely difficult evolutionary and taxonomic problems. A common pattern among members of the gastropod family Pleuroceridae (Mesogastropoda) is the downstream replacement of a relatively smooth-shelled form or species by a more sculptured form or species (Adams, 1915; Goodrich, 1934, 1935; Rosewater, 1960). This pattern is displayed by the pleurocerid species Goniobasis fioridensis (Reeve) and Goniobasis dickinsoni Clench and Turner in the Chipola River drainage and Holmes Creek: two adjacent streams that occur in different river basins in the Florida panhandle. The Chipola River is in the Apalachicola River Basin, and Holmes Creek is in the Choctawhatchee River Basin. Goniobasis dickinsoni occurs in the upper reaches of the Chipola River and some upper tributaries of the Choctawhatchee River Basin, including Holmes Creek. Goniobasis fioridensis occurs in lower reaches of Holmes Creek and the Chipola River as well as in most Florida river systems lying to the east (Clench and Turner, 1956). The shells of G. dickinsoni are smooth or have faint to moderate ribs on the whorls. Goniobasis fioridensis shells are heavily sculptured with ribs intersecting spiral cords to form nodules (Fig. 1). These "species" intergrade where their ranges overlap within the Chipola River drainage. Adult shells with sculpture patterns varying between those of G. dickinsoni and G. floridensis are found in this intergrade zone; which, following the terminology of Woodruff (1973), may be called a zone of widespread sympatric hybridization. These species do not intergrade in shell sculpture where their ranges overlap in Holmes Creek. An electrophoretic analysis of 18 allozyme loci (Chambers, 1980) indicated little divergence between these species in the Choctawhatchee and Apalachicola river basins. Genetic distance values, as measured by the genetic distance index (D) of Nei (1972), between samples of these different species ranged from 0.008 to 0.068. Genetic distances between samples of G. dickinsoni from the two different basins were 0.057 and 0.072. Genetic distances between G. floridensis samples from these different basins were 0.046 and 0.060. These values are comparable to the average values calculated for conspecific populations of other animal species (Ayala, 1975). Since nearly all common alleles were shared by populations of the two species, there is little or no allozyme evidence for reproductive isolation between them. The present study was undertaken to determine if chromosomal differences might explain the different relationships of the two forms within the two different river basins. The results of the karyotypic analysis indicate that, although there is no evidence for chromosomal involvement in divergence between forms, there is chromosomal divergence between populations from Holmes Creek and the Chipola River drainage that suggests the parallel evolution of similar shell sculpture patterns.