The relationship between the freshwater pearl mussel (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis>) and its hosts

Endangered freshwater pearl mussels Margaritifera margaritifera reveal a complex life cycle with an obligate host-dependent phase. Only two species, Atlantic salmon Salmo salar and brown trout S. trutta, are important hosts in Europe, indicating a high degree of specialization. Whilst freshwater pearl mussels with their filtering activity can provide important ecosystem services and indirectly improve the habitat quality for their salmonid hosts, their direct effects on physiological stress, reduced swimming performance, and increased mortality at high rates of infestation all support a parasitic character of the mussel during its hostdependent phase. From an evolutionary perspective, both the much greater generation time of the parasite compared to the host, as well as the great distribution ranges of M. margaritifera and its hosts should favour local adaptation patterns. The variable suitability of different salmonid strains and species as hosts for M. margaritifera and the resulting differences in the performance of larvae during the host-dependent phase indicate that host-management strategies should focus on maintaining high quality hosts at a regional scale to avoid selection or genetic drift effects which could erode the genetic and evolutionary potential for adaptation to changing environmental conditions.     

Variation in the <Emphasis Type="Italic">COI</Emphasis> gene of the freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> from River Vuokkijoki

The freshwater pearl mussel Margaritifera margaritifera L. is one of the most endangered freshwater mussels in the world. Effective conservation of threatened species requires not only ecological, but also genetic information from the target species and populations. Since low genetic diversity can reduce the ability of a species to adapt to environmental changes, maintaining genetic diversity has been identified as one of the key elements in successful conservation programs. We examined genetic variation of the freshwater pearl mussel from the River Vuokkijoki, Karelia, Russia. We sequenced a fragment of the cytochrome c oxidase subunit I gene (COI) from 22 individuals and compared the data to 32 previously published COI sequences available in GenBank. We identified 10 different COI haplotypes in the sequenced samples, three of which had not been previously reported. Our results show that the River Vuokkijoki has high genetic diversity and suggest that the colonization of this northern freshwater pearl mussel population might have occurred from multiple and even distant refugia. Therefore, the freshwater pearl mussel population of the River Vuokkijoki is valuable for the conservation of the whole species.     

Regional monitoring of freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> in the County of Norrbotten,Sweden

A total of 16 freshwater pearl mussel Margaritifera margaritifera rivers out of 64 known freshwater pearl mussel rivers are included in the Administrative County of Norrbotten regional monitoring program. First surveys were done in 1994 and the results show that only three rivers have viable populations according to national criteria despite little visible human impact and that juvenile mussels (<50 mm in length) have been found in all rivers at every occasion. The results also indicate that there might be “missing years” for juvenile recruitment suggesting that freshwater pearl mussel populations at the extreme end of the species range might be dependent on “golden moments” in order to keep up viable populations. Deeper knowledge and better tools for determining viable populations might be necessary in order to make the right decisions on how to manage the rivers and the freshwater pearl mussel populations.     

Some biochemical parameters of the transformation of xenobiotics in the freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis>

We determined the concentration of glutathione (GSH) and the activity of glutathione S-transferase (GST) in the gills and hepatopancreas of the freshwater pearl mussel Margaritifera margaritifera L. It was found that the concentration of GSH in the gills decreases with a decrease in temperature, which indicates that metabolic processes in these ectothermic animals are decelerated. It was also found that changes in the concentration of GSH and in the activity of GST do not depend on age; thus, these biochemical markers can be used as bioindicators regardless of age. No substrate-specific activity of GST was observed, which means that freshwater pearl mussels have limited ability to metabolize compounds with different chemical structures.     

The freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> L.: Metamorphosis,growth, and development dynamics of encysted glochidia

The growth and morphogenesis of glochidia of the freshwater pearl mussel Margaritifera margaritifera on the gills of the Atlantic salmon Salmo salar in the Syuskyuyanyoki River (Karelia) are studied. Comparative analysis of histological features of glochidia depending on the age of the cyst is made, and the results of studies of the relationship and the influence of seasonal changes in water temperature on growth and morphogenesis of glochidia, which is essential for adaptation of living organisms and ensuring the sustainability of the participants of the parasite–host relationship, are presented.     

Threatened freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> L. in NW Spain: low and very structured genetic variation in southern peripheral populations assessed using microsatellite markers

A genetic analysis of freshwater pearl mussel Margaritifera margaritifera populations from NW Spain, a peripheral area of its European distribution, was carried out using microsatellite markers. These populations were formerly reported as genetically differentiated on the basis of growth and longevity studies. Ten loci previously characterized in populations from central Europe were used to comparatively analyze the genetic variability at the southern edge of the species’ range. Iberian pearl mussel populations showed very low genetic variability and significant high genetic differentiation. Half of the total genetic diversity observed appeared to be distributed between populations, which suggested a highly structured adaptive potential in pearl mussel at the southern peripheral distribution of the species. Population distinctiveness was evidenced by assignment tests, which revealed a high accuracy of individual assignments to their population of origin. All data suggested low effective population size and major effects of genetic drift on population genetic structure. In order to avoid further loss of genetic variation in biologically distinctive populations from NW Spain, prioritization of genetic resources of this species is required for conservation and management.     

Using genetic monitoring to inform best practice in a captive breeding programme: inbreeding and potential genetic rescue in the freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis>

Freshwater pearl mussel (Margaritifera margaritifera) populations are declining in Northern Ireland to the extent that a captive breeding programme was established on the Upper Ballinderry river in 1998. Previous genetic analysis of the hatchery broodstock and their first cohort of offspring showed significant levels of inbreeding (F _IS  = 0.166). The broodstock, which currently numbers ca. 90 individuals, was supplemented with new individual mussels, whilst in 2013, a previously unknown population was discovered on the Lower Ballinderry river. The aim of the present study was to determine whether the rotation of the broodstock has led to a decrease in the levels of inbreeding in the second cohort of juveniles, and to determine whether the new population found in the Lower Ballinderry was genetically distinct from the captive bred population and populations from the Upper Ballinderry, which represent the source of the hatchery broodstock. Genotyping using eight microsatellite markers indicated that levels of inbreeding in the second cohort of captive-bred mussels were high, (F _IS  = 0.629), and were comparable to those sampled from the original cohort and the hatchery broodstock (F _IS  = 0.527 and 0.636 respectively). Bayesian analysis of population structure indicated that the newly discovered Lower Ballinderry population was genetically distinct from the broodstock and its source populations on the Upper Ballinderry. The observed differentiation was primarily due to differences in allele frequencies, and was most likely a result of genetic drift. The occurrence of ten alleles, albeit at low frequency, in the Lower Ballinderry population, including four private alleles, suggests that this new population could be incorporated into the broodstock with the aim of decreasing levels of inbreeding in the future.     

Strategies for the conservation of endangered freshwater pearl mussels (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> L.): a synthesis of Conservation Genetics and Ecology

Freshwater pearl mussels (Margartifera margaritifera L.) are among the most critically threatened freshwater bivalves worldwide. The pearl mussel simultaneously fulfils criteria of indicator, flagship, keystone and umbrella species and can thus be considered an ideal target species for the process conservation of aquatic ecosystem functioning. The development of conservation strategies for freshwater pearl mussels and for other bivalve species faces many challenges, including the selection of priority populations for conservation and strategic decisions on habitat restoration and/or captive breeding. This article summarises the current information about the species’ systematics and phylogeny, its distribution and status as well as about its life history strategy and genetic population structure. Based on this information, integrative conservation strategies for freshwater mollusc species which combine genetic and ecological information are discussed. Holistic conservation strategies for pearl mussels require the integration of Conservation Genetics and Conservation Ecology actions at various spatial scales, from the individual and population level to global biodiversity conservation strategies. The availability of high resolution genetic markers for the species and the knowledge of the critical stages in the life cycle, particularly of the most sensitive post-parasitic phase, are important prerequisites for conservation. Effective adaptive conservation management also requires an evaluation of previous actions and management decisions. As with other freshwater bivalves, an integrative conservation approach that identifies and sustains ecological processes and evolutionary lineages is urgently needed to protect and manage freshwater pearl mussel diversity. Such research is important for the conservation of free-living populations, as well as for artificial culturing and breeding techniques, which have recently been or which are currently being established for freshwater pearl mussels in several countries.     

The populations of the freshwater pearl mussel, <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> (Linnaeus, 1758), and the thick shelled river mussel, <Emphasis Type="Italic">Unio crassus</Emphasis> Philipsson, 1788, in Latvia

The populations of two endangered species—the freshwater pearl mussel Margaritifera margaritifera and the thick shelled river mussel Unio crassus in Latvia were studied. The specimens were counted, measured, population density and age structure were calculated. The possible host fish presence was found.     

Ontogenetic morphometrics of individual freshwater pearl mussels (<Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> (L.)) reconstructed from geometric conchology and trigonometric sclerochronology

This study bridges two conchological approaches to model the growth characteristics of freshwater pearl mussel shell: size-at-age and sclerochronology. We demonstrate a simple numerical model that transfers sclerochronological data into realistic estimates of ontogenetic shell sizing. This model was constructed for a subset of shell growth data dealing with morphometrics and annual shell growth increments. Further, validation of the model was performed using a dataset that was withheld from the calibration. Both subsets of data showed significant correlations between the observed (measured by vernier callipers) and reconstructed size-at-age data, indicating a successful model. The practical applicability of the model was exemplified for the studied Finnish freshwater pearl mussel populations. In accordance with the previously set theory about the plasticity of life history traits of the species, the southern mussels showed higher growth rates than the northern mussels. Handling editor: K. Martens     

Drainage-independent genetic structure and high genetic diversity of endangered freshwater pearl mussels (<Emphasis Type=Italic>Margaritifera margaritifera</Emphasis>) in northern Europe

Freshwater pearl mussels (Margaritifera margaritifera) are among the most critically threatened bivalve molluscs worldwide. An understanding of spatial patterns of genetic diversity is crucial for the development of integrative conservation strategies. We used microsatellites to study the genetic diversity and differentiation of 14 populations of M. margaritifera in central Sweden, an area which was described as a major secondary contact zone in postglacial colonisation for other species. Genetic diversity of Swedish pearl mussel populations was much greater than in central and southern Europe but similar to the genetic diversity observed in the northeastern portion of their European range. Genetic differentiation among populations was pronounced but to a large extent independent from present-day drainage systems. The complex patterns of genetic diversity and differentiation in pearl mussel seem to be strongly influenced by the species’ high degree of specialisation and extraordinary life history strategy which involves facultative hermaphrodism and an obligatory encystment stage on a host fish. Genetic drift effects and anthropogenic disturbances resulting in reduction of population size and loss of connectivity are less pronounced in northern pearl mussel populations compared to those in central and southern Europe.     

The status of the freshwater pearl mussel <Emphasis Type="Italic">Margaritifera margaritifera</Emphasis> in Scotland: extent of change since 1990s,threats and management implications

All known rivers in Scotland with recent records of freshwater pearl mussels Margaritifera margaritifera were surveyed in 2013–2015 using a standard methodology. Freshwater pearl mussel populations were classed as: (i) apparently extinct in 11 rivers, (ii) not successfully recruiting in 44 rivers, and (iii) evidence of recent successful recruitment in 71 rivers. On a regional basis, a high proportion of extant populations were located in North and West Scotland. In all regions extant populations were characterised by low pearl mussel densities, with 97 of 115 extant Scottish populations defined as ‘rare’ (0.1–0.9 mussels per 1 m ²) or ‘scarce’ (1.0–9.9 mussels per 1 m ²). Only 18 Scottish rivers now hold pearl mussel populations in densities that are considered to be ‘common’ (10–19.9 mussels per 1 m ²) or ‘abundant’ (>20 mussels per 1 m ²). Based on survey evidence, the number of apparently extinct pearl mussel populations in Scottish rivers is now 73. The decline is particularly pronounced in the West Highlands and Western Isles strongholds. The key threats are: (i) pearl fishing, (ii) low host fish densities, (iii) pollution/water quality, (iv) climate change and habitat loss, (v) hydrological management/river engineering and (vi) ‘other factors’, such as non-native invasive species. Over the last 100 years this endangered species has been lost from much of its former Holarctic range. Scotland’s extant M. margaritifera populations continue to be of international importance, but their continued decline since the first national survey in 1998 is of great concern.     

The zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>) impacts European bitterling (<Emphasis Type="Italic">Rhodeus amarus</Emphasis>) load in a host freshwater mussel (<Emphasis Type="Italic">Unio pictorum</Emphasis>)

The European bitterling, Rhodeus amarus, is a non-indigenous fish species in British fresh waters. It lays its eggs in unionid mussels which themselves are vulnerable to fouling by the non-indigenous zebra mussel, Dreissena polymorpha. Observations from an unmanipulated natural system showed that only 27% of zebra mussel-fouled Unio pictorum hosted bitterling, while 47% of unfouled U. pictorum hosted bitterling. We conducted a field experiment in the River Great Ouse catchment, Cambridgeshire, England in May–June 2007 and 2008 to quantify the impact of zebra mussels on bitterling load in host mussels. Zebra mussel-fouled unionids were significantly less likely to host bitterling than unfouled unionids. The number of unionids hosting bitterling did not differ significantly whether the zebra mussels fouling the unionid were alive or dead. Bitterling appeared to discriminate against zebra mussel-fouled unionids less as the 2007 breeding season advanced, potentially because preferred unfouled unionids had a higher bitterling load, and were therefore relatively lower quality hosts than at the start of the breeding season.     

Host-dependent genetic variation in freshwater pearl mussel (Margaritifera margaritifera L.)

Freshwater fishes are vulnerable to changes in water quality, physical habitat and connectivity resulting from drought, particularly in regulated rivers. When adequate river flows return, the recovery of populations might depend on the duration and consequences of drought. Rivers of the highly regulated Murray–Darling Basin in south-eastern Australia terminate at two large, shallow lakes that are separated from the estuary by tidal barrages. Over-abstraction of water and widespread prolonged drought (1997–2010) placed the lakes under severe environmental stress, culminating in critical water level recession from 2007 to 2010. Concurrently, most freshwater fish populations collapsed. We investigate shifts in fish assemblages resulting from habitat inundation in the lakes following the drought. The inundation and re-connection of the lakes and fringing habitats led to a substantial reduction of salinity throughout the region, and aquatic vegetation shifted from salt-tolerant to freshwater species. Fish assemblages became increasingly characterized by common freshwater taxa (ecological generalists), including high proportions of alien species. There were no indications of population recovery for three threatened species. The findings emphasize that short-lived fishes with specialized habitat requirements are vulnerable to severe population declines during prolonged drought in regulated rivers, which might restrict their recovery when adequate flows return.     

Distinct diversity patterns of <Emphasis Type="Italic">Planctomycetes</Emphasis> associated with the freshwater macrophyte <Emphasis Type="Italic">Nuphar lutea</Emphasis> (L.) Smith

Members of the phylum Planctomycetes were originally described as freshwater bacteria. Most recent studies, however, address planctomycete diversity in other environments colonized by these microorganisms, including marine and terrestrial ecosystems. This study was initiated in order to revisit the specific patterns of planctomycete diversity in freshwater habitats using cultivation-independent approaches. The specific focus was made on planctomycetes associated with Nuphar lutea (L.) Smith, an emergent macrophyte with floating leaves, which is widespread in the Holarctic. As revealed by Illumina pair-end sequencing of 16S rRNA gene fragments, the bacterial assemblages colonizing floating leaf blades of waterlilies sampled from two different boreal lakes displayed similar composition but were distinct from the planktonic bacterial communities. 16S rRNA gene fragments from the Planctomycetes comprised 0.1–1 and 1–2.2% of total 16S rRNA gene reads retrieved from water samples and plant leaves, respectively. Planktonic planctomycetes were mostly affiliated with the class Planctomycetaceae (77–97%), while members of the Phycisphaerae were less abundant (3–22%). The relative proportion of the latter group, however, increased by 13–45% on leaves of N. lutea. The Phycisphaera-related group WD2101, Pirellula-like planctomycetes, as well as Gemmata, Zavarzinella and Planctopirus species were the most abundant groups of planctomycetes associated with plant leaves, which may suggest their involvement in the degradation of plant-derived organic matter.     

Temporal trends of genetic diversity in European barley cultivars (<Emphasis Type="Italic">Hordeum vulgare</Emphasis> L.)

The changes of genetic diversity over time were monitored in 504 European barley cultivars released during the 20th century by genotyping with 35 genomic microsatellites. For analysis, the following four temporal groups were distinguished: 1900–1929 (TG1 with 19 cultivars), 1930–1949 (TG2 with 40 cultivars), 1950–1979 (237 cultivars as TG3), and 1980–2000 (TG4 consisting of 208 cultivars). After rarefaction of allelic diversity data to the comparable sample size of 18 varieties, of the 159 alleles found in the first group (TG1) 134 were retained in the last group (TG4) resulting in a loss of only 15.7% of alleles. On the other hand 51 novel alleles were discovered in the group representing the last investigated time period (TG4) in comparison with the TG1. Novel alleles appeared evenly distributed over the genome, almost at all investigated genomic loci, with up to five such novel alleles per locus. Alleles specific for a temporal group were discovered for all investigated time periods, however analysis of molecular variance (AMOVA) did not reveal any significant population structure attributable to temporal decadal grouping. Only 2.77% of the total observed variance was due to differences between the four temporal groups and 1.42% between individual decades of the same temporal group, while 95.81% of the variance was due to variation within temporal groups. The distinction between two-rowed and six-rowed genetic types accounted for 19.5% of the total observed variance by AMOVA, whereas the comparison between ‘winter’ and ‘spring’ types accounted for 17% of the total observed variation. The analysis of linkage disequilibrium did not reveal statistically significant differences between the temporal groups. The results indicated that the impact of breeding effort and variety delivery systems did not result in any significant quantitative losses of genetic diversity in the representative set of barley cultivars over the four time periods.     

Assessment of genetic diversity of <Emphasis Type="Italic">Saltol</Emphasis> QTL among the rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) genotypes

Eight Saltol quantitative trait locus (QTL) linked simple sequence repeat (SSR) markers of rice (Oryza sativa L.) were used to study the polymorphism of this QTL in 142 diverse rice genotypes that comprised salt tolerant as well as sensitive genotypes. The SSR profiles of the eight markers generated 99 alleles including 20rare alleles and 16 null alleles. RM8094 showed the highest number (13) of alleles followed by RM3412 (12), RM562 (11), RM493 (9) and RM1287 (8) while as, RM10764 and RM10745 showed the lowest number (6) of alleles. Based on the highest number of alleles and PIC value (0.991), we identified RM8094 as suitable marker for discerning salt tolerant genotypes from the sensitive ones. Based upon the haplotype analysis using FL478 as a reference (salt tolerant genotypes containing Saltol QTL), we short listed 68 rice genotypes that may have at least one allele of FL478 haplotype. Further study may confirm that some of these genotypes might have Saltol QTL and can be used as alternative donors in salt tolerant rice breeding programmes.     

Assessment of genetic diversity among Syrian durum (<Emphasis Type="Italic">Triticum</Emphasis> ssp. <Emphasis Type="Italic">durum</Emphasis>) and bread wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) using SSR markers

Genetic diversity among 49 wheat varieties (37 durum and 12 bread wheat) was assayed using 32 microsatellites representing 34 loci covering almost the whole wheat genome. The polymorphic information content (PIC) across the tested loci ranged from 0 to 0.88 with average values of 0.57 and 0.65 for durum and bread wheat respectively. B-genome had the highest mean number of alleles (10.91) followed by A genome (8.3) whereas D genome had the lowest number (4.73). The correlation between PIC and allele number was significant in all genome groups accounting for 0.87, 074 and 0.84 for A, B and D genomes respectively, and over all genomes, the correlation was higher in tetraploid (0.8) than in hexaploid wheat varieties (0.5). The cluster analysis discriminated all varieties and clearly divided the two ploidy levels into two separate clusters that reflect the differences in genetic diversity within each cluster. This study demonstrates that microsatellites markers have unique advantages compared to other molecular and biochemical fingerprinting techniques in revealing the genetic diversity in Syrian wheat varieties that is crucial for wheat improvement.     

Ectopic expression of cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) <Emphasis Type="Italic">CsTIR</Emphasis>/<Emphasis Type="Italic">AFB</Emphasis> genes enhance salt tolerance in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis>

Auxin receptors TIR1/AFBs play an essential role in a series of signaling network cascades. These F-box proteins have also been identified to participate in different stress responses via the auxin signaling pathway in Arabidopsis. Cucumber (Cucumis sativus L.) is one of the most important crops worldwide, which is also a model plant for research. In the study herein, two cucumber homologous auxin receptor F-box genes CsTIR and CsAFB were cloned and studied for the first time. The deduced amino acid sequences showed a 78% identity between CsTIR and AtTIR1 and 76% between CsAFB and AtAFB2. All these proteins share similar characteristics of an F-box domain near the N-terminus, and several Leucine-rich repeat regions in the middle. Arabidopsis plants ectopically overexpressing CsTIR or CsAFB were obtained and verified. Shorter primary roots and more lateral roots were found in these transgenic lines with auxin signaling amplified. Results showed that expression of CsTIR/AFB genes in Arabidopsis could lead to higher seeds germination rates and plant survival rates than wild-type under salt stress. The enhanced salt tolerance in transgenic plants is probably caused by maintaining root growth and controlling water loss in seedlings, and by stabilizing life-sustaining substances as well as accumulating endogenous osmoregulation substances. We proposed that CsTIR/AFB-involved auxin signal regulation might trigger auxin mediated stress adaptation response and enhance the plant salt stress resistance by osmoregulation.