The endangered thick-shelled river mussel (<Emphasis Type="Italic">Unio crassus</Emphasis>): a new host species for the European bitterling (<Emphasis Type="Italic">Rhodeus amarus</Emphasis>)

Large freshwater mussels (Unionoida) are declining throughout the world. The European bitterling Rhodeus amarus (Bloch, 1782) female spawns its eggs inside the unionids’ shells, where fertilisation and further embryonic development take place; thus its reproduction depends fully on the presence of large freshwater mussels. Unio crassus, previously regarded as one of the most numerous unionids in Europe, is now listed in the IUCN Red Data List as being globally endangered. Despite its previous prevalence, it was never reported as a host for the bitterling. A large population of U. crassus was studied in small river at the ?wi?tokrzyskie Mts (Poland), where also electrofishing was conducted. In each bitterling territory located on the study plots, we found individuals of U. crassus, with the bitterling eggs or larvae developing on mussel’s gills. That proves that this species can be also used by the bitterling for reproduction. We suggest that this relationship has not been reported to date due to the mussels’ rarity and ongoing decline. However, it is also possible that the endangered mussel is a novel host for the bitterling, which is expanding its range throughout Europe.     

Phenotypic plasticity and genetic isolation-by-distance in the freshwater mussel <Emphasis Type="Italic">Unio pictorum</Emphasis> (Mollusca: Unionoida)

Freshwater mussels (Unionoida) show high intraspecific morphological variability, and some shell morphological traits are believed to be associated with habitat conditions. It is not known whether and which of these ecophenotypic differences reflect underlying genetic differentiation or are the result of phenotypic plasticity. Using 103 amplified fragment length polymorphism (AFLP) markers, we studied population genetics of three paired Unio pictorum populations sampled from two different habitat types (marina and river) along the River Thames. We found genetic differences along the Thames which were consistent with a pattern of isolation by distance and probably reflect limited dispersal via host fish species upon which unionoid larvae are obligate parasites. No consistent genetic differences were found between the two different habitat types suggesting that morphological differences in the degree of shell elongation and the shape of dorso-posterior margin are caused by phenotypic plasticity. Our study provides the first good evidence for phenotypic plasticity of shell shape in a European unionoid and illustrates the need to include genetic data in order properly to interpret geographic patterns of morphological variation.     

Overland transport of recreational boats as a spreading vector of zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis>

In aquatic ecosystems invasive species are among the most important threats to biodiversity worldwide. Understanding the dispersal mechanisms of aquatic invaders is very important for protection and management of vulnerable water bodies. Here we ask how recreational boats that are transported overland could contribute to the dispersal of invasive zebra mussels among lakes in Switzerland. Using a questionnaire sent to registered boat owners, we surveyed properties of transported boats and collected information on self-reported mussel fouling and transport activities of boat owners. We also sampled boat hulls at launching ramps and harbors for biofouling invertebrates. Boats that were kept seasonally or year-round in water were found to have high vector potential with mussel fouling rates of more than 40 %. However, only about 6 % of boats belonging to these groups were transported overland to other water bodies. Considering that approximately 100,000 recreational boats are registered in Switzerland, we estimated that every year around 1400 boats fouled with mussels are transported overland. Such boats pose a high risk of distributing zebra mussels between water bodies. Our results suggest that there is a considerable risk that recreational boats may spread new fouling species to all navigable water bodies within the study area. We speculate that one such species could be the quagga mussel, which has not yet invaded lakes in Switzerland. On a more positive note, our study has identified the group of high-risk boats so that possible control measures would only affect a relatively small number of boat owners.     

Natural hybridization of two mussel species <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas, 1771) and <Emphasis Type="Italic">Dreissena bugensis</Emphasis> (Andrusov, 1897)

Dreissenids display a high diversity of shell morphology, and it is frequently difficult to ascribe some individuals from mixed populations to one of the two species, Dreissena polymorpha (Pallas, 1771) or D. bugensis (Andrusov, 1897). Presumably, such individuals may be interspecific hybrids. We have analyzed species-specific allozyme loci of the typical representatives of these two mussel species and putative interspecific hybrids. A natural interspecific hybrid between D. polymorpha and D. bugensis was discovered for the first time by genetic methods. It has been demonstrated that D. bugensis was a maternal parent.     

The effectiveness of the induced anti-predator behaviour of zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> in the presence of molluscivorous roach <Emphasis Type="Italic">Rutilus rutilus</Emphasis>

We checked whether the induced anti-predator defences of zebra mussels are able to affect the predation success of roach, being one of the most efficient zebra mussel predators in Europe. Previously, several anti-predator defences of mussels have been observed in the presence of roach, including stronger attachment, aggregation forming and inhibition of upward movement. However, the actual efficiency of these responses to reduce the mussel vulnerability to predation was unknown. To check the effectiveness of attachment strength, we exposed mussels for 6 (strong attachment), 1 (weak attachment) or 0 (unattached) days in ceramic trays and then presented the trays to fish in an experimental tank. To test the effectiveness of aggregation, we glued mussels to the trays in groups of three (touching one another) or singly using denture glue and exposed them to fish. To check the effect of the vertical position, we glued mussels with denture glue to the bottom and 10, 20 and 30 cm above the bottom of the tank with fish. After 1-h exposure, we determined the percentages of consumed mussels. Roach predation rate was lowest on strongly attached mussels, intermediate on weakly attached mussels and highest on unattached mussels. Aggregated mussels were less frequently consumed than singletons. Conversely, the vertical position of mussels did not affect the roach predation success. Our study demonstrates that the behavioural defences exhibited by zebra mussels can increase their survival in the presence of predators and thus emphasizes the importance of the anti-predator behaviour of this species.     

Zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>) affects the feeding ecology of early stage striped bass (<Emphasis Type="Italic">Morone saxatilis</Emphasis>) in the Hudson River estuary

Variability in the feeding ecology of young fishes over short and long time scales in estuaries is likely to affect population dynamics. We studied 14 years of early stage Striped Bass feeding ecology in the Hudson River Estuary over a 25-year time span, including years in which invasive zebra mussels markedly altered energy flow within the estuary. We predicted that feeding success would be low and that diet composition would be altered during years of high zebra mussel impact, particularly in upriver locations where mussels occur. Feeding success in the short term was indicated by volume of gut contents and in the long term by dry mass at length, i.e. condition; these measures were positively intercorrelated and varied significantly year to year. We tested for associations between condition and multiple biotic and abiotic environmental variables. There was a strong negative effect of zebra mussel grazing rate on condition in upriver locations and a weak positive effect in downriver locations. In upriver locations, condition was 33% higher when local salinity was high and zebra mussel grazing rates were low, whereas in downriver locations, condition was 35% higher when zebra mussel grazing rates and copepod abundance were high and local dissolved oxygen was low. Copepods, amphipods, mysids, and Leptodora constituted the highest prey-specific index of relative importance throughout the estuary. There was no evident effect of the zebra mussel invasion on diet composition. This long-term study corroborates the inferences of earlier studies that zebra mussels reduced early-stage striped bass growth rate.     

Density effects on the clearance rate of the zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis>: flume study results

Zebra mussel filtration rates and regulating factors have been addressed earlier in a number of studies. Still, only a few of them have taken into consideration the refiltration phenomenon, and therefore the direct extrapolation of experimental results may only give the potential filtering capacity, and hence, over- or underestimate the actual amount of seston being removed by zebra mussels in an ecosystem. The current experimental study aimed to gain insight into the refiltration effect on the clearance rate of the zebra mussels at relatively high seston concentrations, and its potential role in controlling the filtration efficiency of the zebra mussel population. The experiment was conducted in a laboratory flume following the Latin squares design with one fixed (mussel density) and three random factors (initial total particulate matter (TPM) concentration, flume “wall effect” and distance from the flume inflow area) considered. The results showed the significant effects of mussel density and the TPM concentration on the effective clearance rate (ECR) of zebra mussels. The higher ECR values were obtained at denser mussel clumps and lower TPM concentrations. The flume “wall effect” had no significant effect on the ECR, whereas the distance from the flume inflow area appeared to have a significant impact. A positive relationship between ECR and the zebra mussel density was most evident in the proximity of the TPM source. Based on the results, we assume that at high TPM concentration, refiltration may assert itself by the elevated net clearance rate of mussels within dense clumps compared to that of mussels at relatively low individual densities. This should be taken into consideration while modelling and assessing the role of the zebra mussel in energy flow and redistribution of organic matter in an ecosystem.     

The role of environmental factors in the induction of oxidative stress in zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>)

The aim of this study was to investigate the influence of specific environmental factors, such as temperature, pH, oxygen concentration, and phosphate, nitrate, chloride, sodium, potassium, sulphate, magnesium and calcium ions concentration, as well as microcystins, on the seasonal variations in the activity of the antioxidant system of the zebra mussel. We examined changes in lipid peroxidation (LPO) levels, glutathione content and the catalase activity of mussels inhabiting the two ecosystems, which differ due to their trophic structure and the presence of toxic cyanobacteria. The results show a relationship between the activity of the antioxidant system of zebra mussels and the seasonal fluctuations of environmental parameters: the symptoms of oxidative stress were generally the highest during spring and the lowest during summer in both ecosystems. Our study also revealed that regardless of the study area the most important factors determining the activity of the antioxidant defences of mussels were the mineral composition (particularly magnesium and calcium ions concentrations) and physical parameters of the water (oxygen concentration and pH). However, factors resulting from the trophic status of studied ecosystems, such as limitations in food resources or high concentration of microcystins during cyanobacterial blooms, were periodically responsible for increased level of LPO in the tissues of zebra mussel. These findings may indicate a limited tolerance of the zebra mussel to the local environmental conditions.     

Towards a ground pattern reconstruction of bivalve nervous systems: neurogenesis in the zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis>

Bivalvia is a taxon of aquatic mollusks that includes clams, oysters, mussels, and scallops. Within heterodont bivalves, Dreissena polymorpha is a small, mytiliform, freshwater mussel that develops indirectly via a planktotrophic veliger larva. Currently, only a few studies on bivalve neurogenesis are available, impeding the reconstruction of a ground pattern in Bivalvia. In order to inject novel data into this discussion, we describe herein the development of the serotonin-like and α-tubulin-like immunoreactive (lir) neuronal components of D. polymorpha from the early trochophore to the late veliger stage. Neurogenesis starts in the early trochophore stage at the apical pole with the appearance of one flask-shaped serotonin-lir cell. When larvae reach the veliger stage, four flask-shaped serotonin-lir cells are present in the apical organ. At the same time, the anlagen of the cerebral ganglia start to form at the base of the apical organ. From the apical organ, one pair of cerebro-visceral connectives projects posteriorly and connects to a posterior larval sensory organ that contains serotonin- and α-tubulin-like flask-shaped cells. Additional, paired serotonin-lir neurites originate from the apical organ and project into the velum. One unpaired stomatogastric serotonin-lir cell develops ventrally to the stomach at the veliger stage. The low number of serotonin-lir cells in the apical organ of bivalve veligers is shared with larvae of basally branching gastropods and scaphopods and is thus considered a feature of the last common ancestor of Conchifera, while the overall simplicity of the larval neural architecture appears to be a specific trait of Bivalvia.     

Comparison of nutrition range in <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> and <Emphasis Type="Italic">Dreissena bugensis</Emphasis> mussels by biochemical markers

Based on biochemical markers, we studied the nutrition ranges of populations of Dreissena polymorpha and Dreissena bugensis mussels that inhabit the Volga reach of the Rybinsk reservoir and differ in the long-term population dynamics. Features of the nutrition ranges of mussels are regarded as the probable cause of changes in the number of mollusca.     

Feeding,development, and growth of juvenile perch <Emphasis Type="Italic">perca fluviatilis</Emphasis> in mesocosms in the presence of filter-feeding zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> pallas

Quantitative and qualitative changes in the feeding spectra and growth patterns are studied in the larvae and juveniles of perch in artificial water ecosystems (mesocosms) in the presence of a filter-feeding zebra mussel. At a stocking density of 0.75 kg/m², the presence of a zebra mussel leads to a change in the feeding conditions of zooplankton, to a decrease in its abundance in regards to critical values for fish feeding, to an increase in the abundance of organisms of macrobenthos in the food, and to the rapid transition of the fish to feeding on chironomids. As a result of these changes, the growth rate of perch larvae decreases, their development at step D ₁ is delayed, the differentiation of the juveniles by size is accelerated, their size and weight variability increases, and individual predators (cannibals) appear.     

Development of an in vitro culture method for cells and tissues from the zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>)

Despite the successful transfer of mammalian in vitro techniques for use with fish and other vertebrates, little progress has been made in the area of invertebrate tissue culture. This paper describes the development of an in vitro technique for the culture of both cells in suspension and tissue explants from the gill, digestive gland and mantle of the zebra mussel (Dreissena polymorpha) and their successful maintenance in culture for up to 14 days. Cell suspensions from the gills and digestive gland were the most successful technique developed with viability >80% maintained for up to 8 days in culture, suitable for use in short term toxicity tests. Tissue explants from the mantle were also maintained in culture for up to 14 days. This paper describes the challenges involved in the development of a novel in vitro culture technique for aquatic invertebrates.     

Preferences of invasive Ponto-Caspian and native European gammarids for zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>, Bivalvia) shell habitat

The migratory behavior and swimming patterns of anadromous upstream migratory fish have been poorly described in the Shibetsu River in eastern Hokkaido, Japan. In this 2004 study, we used electromyogram (EMG) transmitters and depth/ temperature (DT) loggers to compare the upstream migratory behavior of adult male chum salmon (Oncorhynchus keta) and pink salmon (O. gorbuscha) in the canalized and reconstructed segments of the Shibetsu River, where a part of canalized section was preliminary reconstructed meander to restore a more natural section. The EMG transmitter and DT logger were externally attached to the left side of the body, below the front edge of the dorsal fin. Fish of both species often migrated along the riverbanks and near the bottom of the water column, sometimes engaged in holding behavior, which was defined as cessation of swimming during their upstream migration for 5 minutes. Modal swimming depth calculated by DT loggers for chum salmon (0.2–0.4 m) was shallower than pink salmon (0.6–0.8 m). Further, modal swimming speeds measured by calibrated EMG for chum salmon (0.2–0.4 BL s⁻¹) were slower than pink salmon (1.2–1.4 BL s⁻¹). Pink salmon swam faster as well as in relatively deeper than chum salmon, suggesting that they expend more energy than chum salmon in the reconstructed segment. Based on these results, it seemed likely that the upstream migration behavior of chum and pink salmon was different with species-specific strategies.     

Effect of over-expression of <Emphasis Type="Italic">Linum usitatissimum</Emphasis> PINORESINOL LARICIRESINOL REDUCTASE (<Emphasis Type="Italic">LuPLR</Emphasis>) gene in transgenic <Emphasis Type="Italic">Phyllanthus amarus</Emphasis>

Shoot tip explants of Phyllanthus amarus were cocultivated with Agrobacterium tumefaciens strain LBA 4404 carrying plasmid pCAMBIA 2301 harbouring genes coding for betaglucuronidase (gus), kanamycin (kan), and neomycin phosphotransferase II (nptII) along with a gene coding for Linum usitatissimum PINORESINOL LARICIRESINOL REDUCTASE (Lu-PLR). Transformed shoot tip explants were maintained in a Murashige and Skoog (MS) medium containing TDZ 1.54 mg l^?1, kan 50 mg l^?1 and cephotaxime 62.5 mg l^?1. The optimum medium for regeneration of multiple shoots was MS supplemented with TDZ 1.54 mg l^?1, kan 50 mg l^?1. Efficient and effective rooting of plantlets was achieved by culturing the in vitro regenerated shoots on liquid ½ MS medium containing 0.7 mg l^?1 indole 3-butyric acid (IBA) and 5 mg l^?1 kan. Rooted plants were acclimatized in the mixtures of vermiculite and soil. The transformation of kan-resistant plantlets regenerated from shoot-tip explants was confirmed by GUS and polymerase chain reaction (PCR) analysis. Southern blot and reverse transcribed PCR (RT-PCR) analysis confirmed successful integration and expression of Lu-PLR gene. Quantitative analysis of phyllanthin performed on transgenic and wild plants using high-performance liquid chromatography (HPLC) revealed that transgenic lines contained higher phyllanthin content (0.3–0.81% w/w) than wild plants (0.09% w/w). The highest yield of phyllanthin was detected in transgenic lines was up to 1.16, 1.22 and 1.23 folds higher than that of wild plant. This report highlights the transgenic approach to enhance the contents of phyllanthin and hypophyllanthin.     

Effects of increasing temperatures on population dynamics of the zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis>: implications from an individual-based model

Zebra mussels (Dreissena polymorpha, Pallas, 1771) have had unprecedented success in colonizing European and North American waters under strongly differing temperature regimes. Thus, the mussel is an excellent model of a species which is able to cope with increasing water temperatures expected under global change. We study three principle scenarios for successful survival of the mussel under rising temperatures: (1) no adaptation to future thermal conditions is needed, existing performance is great enough; (2) a shift (adaptation) towards higher temperatures is required; or (3) a broadening of the range of tolerated temperatures (adaptation) is needed. We developed a stochastic individual-based model which describes the demographic growth of D. polymorpha to determine which of the alternative scenarios might enable future survival. It is a day-degree model which is determined by ambient water temperature. Daily temperatures are generated based on long-term data of the River Rhine. Predictions under temperature conditions as recently observed for this river that are made for the phenology of reproduction, the age distribution and the shell length distribution conform with field observations. Our simulations show that temporal patterns in the life cycle of the mussel will be altered under rising temperatures. In all scenarios spawning started earlier in the year and the total reproductive output of a population was dominated by the events later in the spawning period. For maximum temperatures between 20 and 26°C no thermal adaptation of the mussel is required. No extinctions and stable age distributions over generations were observed in scenario 2 for all maximum temperatures studied. In contrast, no population with a fixed range of tolerated temperatures survived in scenario 3 with high maximum temperatures (28, 30, 32°C). Age distributions showed an excess of 0+ individuals which resulted in an extinction of the population for several thermal ranges investigated. Priority programme of the German Research Foundation—contribution 14.     

<Emphasis Type="Italic">STAYGREEN</Emphasis> (<Emphasis Type="Italic">CsSGR</Emphasis>) is a candidate for the anthracnose (<Emphasis Type="Italic">Colletotrichum orbiculare</Emphasis>) resistance locus <Emphasis Type="Italic">cla</Emphasis> in Gy14 cucumber

Key message

Map-based cloning identified a candidate gene for resistance to the anthracnose fungal pathogen Colletotrichum orbiculare in cucumber, which reveals a novel function for the highly conserved STAYGREEN family genes for host disease resistance in plants.

Abstract

Colletotrichum orbiculare is a hemibiotrophic fungal pathogen that causes anthracnose disease in cucumber and other cucurbit crops. No host resistance genes against the anthracnose pathogens have been cloned in crop plants. Here, we reported fine mapping and cloning of a resistance gene to the race 1 anthracnose pathogen in cucumber inbred lines Gy14 and WI 2757. Phenotypic and QTL analysis in multiple populations revealed that a single recessive gene, cla, was underlying anthracnose resistance in both lines, but WI2757 carried an additional minor-effect QTL. Fine mapping using 150 Gy14?×?9930 recombinant inbred lines and 1043 F₂ individuals delimited the cla locus into a 32 kb region in cucumber Chromosome 5 with three predicted genes. Multiple lines of evidence suggested that the cucumber STAYGREEN (CsSGR) gene is a candidate for the anthracnose resistance locus. A single nucleotide mutation in the third exon of CsSGR resulted in the substitution of Glutamine in 9930 to Arginine in Gy14 in CsSGR protein which seems responsible for the differential anthracnose inoculation responses between Gy14 and 9930. Quantitative real-time PCR analysis indicated that CsSGR was significantly upregulated upon anthracnose pathogen inoculation in the susceptible 9930, while its expression was much lower in the resistant Gy14. Investigation of allelic diversities in natural cucumber populations revealed that the resistance allele in almost all improved cultivars or breeding lines of the U.S. origin was derived from PI 197087. This work reveals an unknown function for the highly conserved STAYGREEN (SGR) family genes for host disease resistance in plants.

     

Habitat engineering by the invasive zebra mussel <Emphasis Type="Italic">Dreissena polymorpha</Emphasis> (Pallas) in a boreal coastal lagoon: impact on biodiversity

Habitat engineering role of the invasive zebra mussel Dreissena polymorpha (Pallas) was studied in the Curonian lagoon, a shallow water body in the SE Baltic. Impacts of live zebra mussel clumps and its shell deposits on benthic biodiversity were differentiated and referred to unmodified (bare) sediments. Zebra mussel bed was distinguished from other habitat types by higher benthic invertebrate biomass, abundance, and species richness. The impact of live mussels on biodiversity was more pronounced than the effect of shell deposits. The structure of macrofaunal community in the habitats with >10³ g/m² of shell deposits devoid of live mussels was similar to that found within the zebra mussel bed. There was a continuous shift in species composition and abundance along the gradient ‘bare sediments—shell deposits—zebra mussel bed’. The engineering impact of zebra mussel on the benthic community became apparent both in individual patches and landscape-level analyses.     

Actinomycetemcomitin: a new bacteriocin produced by <Emphasis Type="Italic">Aggregatibacter</Emphasis> (<Emphasis Type="Italic">Actinobacillus</Emphasis>) <Emphasis Type="Italic">actinomycetemcomitans</Emphasis>

Aggregatibacter (Actinobacillus) actinomycetemcomitans P_7–20 strain isolated from a periodontally diseased patient has produced a bacteriocin (named as actinomycetemcomitin) that is active against Peptostreptococcus anaerobius ATCC 27337. Actinomycetemcomitin was produced during exponential and stationary growth phases, and its amount decreased until it disappeared during the decline growth phase. It was purified by ammonium sulphate precipitation (30–60% saturation), and further by FPLC (mono-Q ionic exchange and Phenyl Superose hydrophobic interaction) and HPLC (C-18 reversed-phase). This bacteriocin loses its activity after incubation at a pH below 7.0 or above 8.0, following heating for 30 min at 45°C, and after treatment with proteolytic enzymes such as trypsin, α-chymotrypsin, and papain. Actinomycetemcomitin has a molecular mass of 20.3 KDa and it represents a new bacteriocin from A. actinomycetemcomitans.