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Freshwater mussel populations are in sharp decline and are considered to be one of the most imperilled groups globally. Consequently, the number of captive breeding programmes has increased rapidly in recent years, coupled with subsequent reintroductions/population reinforcements to reverse these declines. The outcomes of mussel conservation translocations are seldom reported in the primary literature, hindering opportunities for learning and for population recovery at pace. Here, we describe the methods employed to carry out a successful conservation translocation of the freshwater pearl mussel (Margaritifera margaritifera) in a declining population in northwest England. Following a small-scale pilot release in 2017, four release sites were identified for a population reinforcement of over 1300 tagged mussels in 2021. Monitoring during 2022 showed high levels of retention of juveniles at three out of the four release sites, despite the occurrence of a significant flood event during October 2021. Subsequent releases of 1100 juveniles were carried out across the three successful sites in 2023. Ongoing and regular monitoring is essential in order to provide data on the longer-term fate of propagated juveniles in the wild. This will allow for adaptive management of release activities in this river. These data will be useful to design conservation translocation strategies for other imperilled pearl mussel populations in the UK and throughout Europe. [ABSTRACT FROM AUTHOR]

Freshwater pearl mussels (FPMs, Margaritifera margaritifera, Linnaeus, 1758) are endangered and particularly vulnerable to climate change. To create effective conservation strategies, we studied their thermal tolerance and the impact of elevated water temperatures on growth and survival. Our experiments included field mesocosm studies in five FPM-streams in the Vogtland region (Germany) (2016 to 2020), as well as laboratory experiments at temperatures ranging from 1 to 26 °C. Growth of juvenile FPMs increased significantly within a temperature gradient from 12 to 21 °C. In the streams, maximum growth was 8.9 µm/d in surface water and 6.5 µm/d in the interstitial. The upper thermal tolerance for the mussels ranged from 22.1 to 22.9 °C, resulting in low survival during hot summer periods in 2018 and 2019. Warming during winter (+5 °C) did not significantly affect growth and survival, but survival during winter increased with the pre-overwintering shell length. Exceeding a shell length of about 1100 µm in December indicating gill development corelated to 50% survival. Shell length in December is primarily controlled by growth depending on water temperatures during summer. These findings define the thermal niche of juvenile FPMs (average summer temperatures of 14.5–21 °C) and have implications for water management, conservation strategies, and site selection for releasing captive-breeding mussels. [ABSTRACT FROM AUTHOR]

Margaritifera margaritifera is a critically threatened species in Europe. Metal pollution may be one of the reasons for its decline, but the influence of this factor remains insufficiently studied. Zn, Cu, Ni, Cd, and Pb were determined in the foot tissue of the freshwater pearl mussel Margaritifera margaritifera (bivalvia, margaritiferidae) from Green Belt rivers of Fennoscandia [the Murmansk region (Kola Peninsula) and Karelia (northern part)] and the accumulation of the metals was shown to be variable; however, their levels in the molluscs, being quite long-lived aquatic organisms, do not exceed the established standards of the Russian Federation. The recorded levels of the metals in the foot tissue of the Margaritifera margaritifera can be considered indicators of the background levels of geologic and anthropogenic metal concentrations in the environment influencing the distribution and development of this protected species in the lake-river systems of the Green Belt of Fennoscandia. [ABSTRACT FROM AUTHOR]

The freshwater pearl mussel Margaritifera margaritifera is considered to be the most rapidly declining species of freshwater bivalve, whereas its colonies in rivers of the White Sea Basin remain the most numerous in the world. The lipid profiles of mantle, muscle (foot), and digestive gland tissues of the freshwater pearl mussel from the Kem, Ukhta, and Vozhma Rivers in autumn (end of September, early October) were studied using high performance thin-layer chromatography. The highest total lipid [TL] content was found in the digestive gland. Cholesterol esters, non-esterified fatty acids, phospholipids, and cholesterol were the dominant lipids in all studied tissues. The reduced triacylglycerol content in the mussels was associated with its utilization during the spawning period. The colony of the freshwater pearl mussel inhabiting the Vozhma River was distinguished by higher TL content in the mantle and digestive gland. Data on the size-age characteristics of mollusks from the Kem, Ukhta, and Vozhma Rivers and the relationship between the structural and storage lipid content and size-age parameters are discussed. The results are important for different conservation strategies of endangered species, such as the freshwater pearl mussel, especially in ecological monitoring based on evaluation of the physiological and biochemical state of mollusks and rare natural colonies. [ABSTRACT FROM AUTHOR]

Triangle sail mussel (Hyriopsis cumingii , Lea 1852) is the most important freshwater pearl mussel in China. Growth traits of host mussels and inner shell color traits of donor mussels are critical determinants for pearl size and color. In this study, we performed GWAS analysis to explore the genetic architecture of growth and inner shell color traits. Using genotype by sequencing (GBS) technique, we obtained 80,562 SNPs from a total dataset of 463 mussels, based on these data, we found weak genetic relationship (−0.1–0.4) and rapid LD decay rate among the population. Moreover, GWAS analysis identified 12 growth-related significant SNPs and 29 inner shell color related significant SNPs. Five of the 12 SNPs linked to growth traits were validated to be credible SNPs in a new population. Cyclin , SNF , PMP22 , CPED1 , F-box and APC/C genes were found to be significantly associated with growth traits, which may influence the growth and development of H. cumingii by regulating cell mitosis, mantle epithelial tissue activity, and Ca2+ absorption and transport capacity. Notably, redness a* showed an obvious aggregation peak in chromosome 17, indicating that this region may be closely related to the inner shell color. Furthermore, three causal genes in chromosome 17, HSP78 , MAS and PKS are inferred to be the key genes on color formation of purple inner shell. These results provide some new insights into the genetic basis and physiological regulation mechanism of growth and inner shell color traits in H. cumingii. However, detailed functional identification and regulation mechanism analysis merits more investigation. • The first genome-wide association study (GWAS) for growth and inner shell color traits in freshwater pearl mussel. • 12 growth-related significant SNPs and 29 inner shell color related significant SNPs were detected. • Five SNPs were validated to be credible SNPs for growth traits. • Candidate genes PKS and MAS are closely related to purple inner shell color. [ABSTRACT FROM AUTHOR]

The freshwater pearl mussel Margaritifera margaritifera has been suffering major population declines in Europe. This endangered species is a host specialist and exclusively requires salmonid species (Salmo trutta and Salmo salar) to complete its life cycle. In theory, obligatory biotic interactions should deserve special conservation attention, because the loss or massive decline of fish hosts may elicit the extirpation of their affiliated species. While many threats disturbing M. margaritifera are similarly affecting salmonids, climate change is particularly alarming, with the potential to significantly change the fish‐mussel dynamics.To evaluate the importance of including the occurrence of fish hosts for predicting the distribution of M. margaritifera in Europe, three datasets were used to build species distribution models (SDMs) with a maximum entropy (MaxEnt) approach: (1) environmental variables (ENV); (2) probability of fish hosts occurrence (FH); and (3) environmental variables and probability of fish hosts occurrence (ENV + FH). We identified the environmental variables that better explain M. margaritifera distribution and modelled its current and future distribution under a suite of climate change scenarios. Furthermore, projections were used to evaluate the adequacy of current networks of European protected areas in covering the suitable habitats for M. margaritifera.Results showed that incorporating data about fish hosts into M. margaritifera SDMs avoided the overprediction of geographical projections and, to a minor extent, improved model performance (area under the curve: ENV = 0.851; FH = 0.848; ENV + FH = 0.867). The distribution range of M. margaritifera in Europe is expected to contract in all future timeframes and emission scenarios considered. Forecasts point to large contractions particularly in central and southern Europe and lowland regions. The European network of protected areas fails to protect 69% of the current and 66%–67% of the future predicted M. margaritifera distribution.This study clearly illustrates the importance of including mussel–fish hosts interactions for accurately predicting M. margaritifera's distribution. The response of M. margaritifera to environmental variables highlights its vulnerability to the higher temperatures, particularly in southern Europe. While predictions indicate large contractions in M. margaritifera's distribution as a result of future climate change, the current European network of protected areas fails to safeguard M. margaritifera.This work provides strong evidence for proposing the generalised use of biotic information about hosts in addition to purely environmental variables to model the distribution of freshwater mussels, as well as for other species with obligatory biotic interactions. Building SDMs such as those discussed here can inform political decision‐making about the likely scenarios for species occurrence in future decades, the requirements needed for an effective conservation strategy, and the regions where conservation should be a priority. [ABSTRACT FROM AUTHOR]

The freshwater pearl mussel Margaritifera margaritifera is a benthic organism sensitive to hydrological regime alterations and habitat degradation driven by excessive fine bed material deposit (FBMD). Both issues are potentially exacerbated by climate change. Understanding how climate change affects future mussel habitats and the dispersal among them (dependent on the brown trout as fish host) can support the planning of effective conservation actions.To project the impacts of climate change on the mussel, a semi‐mechanistic modelling cascade was implemented for the Aist catchment in Austria (630 km2), including a hydrological model, a hydraulic model, Random Forest Models for FBMD accumulation risk and Species Distribution Models. Two climate change models (RCPs 4.5 and 8.5) for two future horizons (2060 and 2090) were considered. A graph‐based assessment of the structural connectivity was used to measure the probability of successful dispersal.Results show a reduction of peak discharge that cascades into a widespread reduction in shear stresses during high flow. The mussel's habitats, defined by hydraulics (i.e. patches with low shear stresses during high flow), are predicted to be stable over the simulated scenarios.The pressure of FBMDs over the delineated habitat patches is predicted to increase in the future due to the reduced stream transport capacity, reducing up to 25% of the available patches in 2090 for RCP 8.5. Consequently, the mussel's dispersal probability decreases to 44.3%–75.6% of the maximum theoretical value, with the highest drops for short dispersal distances, impacting metapopulation dynamics.Synthesis and applications. The widespread issue of fine sediment deposition in the streambed will be exacerbated for those catchments where climate change reduces the stream transport capacity. The impacts on the freshwater pearl mussel include habitat loss due to the formation of a new unsuitable substrate, and a decrease in the potential dispersal among the residual habitats. Thus, conservation plans that aim to protect the mussel in the future should focus on the mitigation of fine bed material deposits, prioritizing those subreaches that offer the highest potential for preserving connectivity among suitable habitats. [ABSTRACT FROM AUTHOR]

During the conservation aquaculture of the freshwater mussel Margaritifera margaritifera, fish health has become a concern due to the need of mussel larvae (glochidia) to parasitize the salmonid gills and metamorphose into juveniles. However, there is a lack of information about the impact on fish during the juvenile detachment and the subsequent gill healing. To evaluate the morphopathological changes and gill recovery after the parasitism of M. margaritifera, 51 Atlantic salmon fry (Salmo salar), infested with around 22 larvae/fish g, were necropsied during the synchronized detachment of the mussel juveniles, and gills were assessed by stereomicroscopy and by light and scanning electron microscopy. Salmon showed no clinical signs during the trial and gills recovered their normal morphology almost completely in a short time, suggesting a minimal impact on fish health after glochidiosis. In this sense, the non‐erosive droplet detachment and the goblet cell hyperplasia favoured an effective gill remodelling mediated by apoptosis, polarization and cell shedding of the gill epithelia, providing insights to the defence, clearing and healing mechanisms of the gill. These morphopathological techniques could also be implemented to preserve fish welfare and to optimize the artificial breeding programmes of endangered freshwater mussels. [ABSTRACT FROM AUTHOR]

Conservation of the endangered freshwater pearl mussel (FPM) includes artificially rearing juveniles, but the pulsed flow-through (PFT) method, enabling the continuous renewal of water and food in culture containers, has not been applied to FPM. This study tested the PFT method in culture of FPM juveniles, and the effect of water source (tap vs well water) and food concentration (mixture of commercial phytoplankton products) on the survival and growth of juveniles. Beaker-specific survival rates varied from 0 to 100% (mean: 34%) and from 0 to 58% (mean: 16%) in the 1st (2-week) and 2nd (10-week) experiment, respectively. In the 1st experiment, juveniles attained statistically significantly bigger sizes and more than two times higher survival in well water than they did in tap water. In both experiments, the food concentration of 0.250 µl/l resulted in the highest survival (compared to other concentrations ranging from 0.125 to 0.500 µl/l). However, food concentration did not have a significant effect on size of juvenile FPM in either of the experiments. Results indicate that the PFT system is suitable for FPM rearing experiments, but its applicability to mass culture of FPM juveniles requires further investigation. [ABSTRACT FROM AUTHOR]

In China, the freshwater pearl mussel aquaculture plays an important role in agricultural production. The freshwater pearl mussel’s growth process does not harm the environment, but the traditional aquaculture model has caused problems such as serious water pollution, eutrophication, and ecological environment destruction. Facing such a situation, it’s necessary to develop a new model for freshwater pearl aquaculture. This study showed a new industrialized circulating water aquaculture model (using multi-layer dimensional cages and feed pearl mussel with high-quality microalgae). Due to the high density of aquaculture, this model had very high requirements for water quality, so it was particularly important to monitor the circulating water quality. This study developed a distributed monitoring system for the water quality monitoring based on ZigBee wireless sensor network. The system used the three-layer architecture of the field sensing layer, transmission layer and application layer, and mainly included the following 4 parts: water quality monitoring subsystem, meteorological monitoring subsystem, equipment control subsystem, and monitoring data center. The system used the ZigBee module to set up the wireless transmission network, the advantage of this method was flexible networking and easy operation, and it simplified the installation and maintenance work. In the field scene, we set up multiple monitoring points in different places, multi-parameter water quality sensors were used to monitor key circulating water quality parameters (including temperature, pH value, dissolved oxygen, ammonia nitrogen, calcium concentration, and algae concentration), and meteorological parameters (such as temperature, humidity, barometric pressure, illumination, wind direction, and wind speed) were collected at meteorological station. All the sensors sent real-time detection data to their related ZigBee routers by RS485 protocol, and through the ZigBee wireless communication network, the data (including water quality and meteorological parameters) would be gathered in the ZigBee coordinator. The ZigBee coordinator was the center of the wireless communication network, it was also connected to the PLC controller by RS485 protocol, so the PLC controller could collect real-time detection data from basic monitoring points. At the same time, the PLC controller and MCGS touch screen communicated through the serial port, so the water quality and meteorological parameters monitoring information could be displayed on the MCGS touch screen. According to the designed procedure, the MCGS touch screen displayed the water quality data change curve, and users could also issue equipment control commands at the screen, such as controlling the circulating water treatment equipment (including arc screen separator, microfiltration filter, protein separator, sand filter, and disinfection pool) and the algae feeding system device. By using the PLC controller, the study designed a program to control the start and stop status of aquaculture equipment and adopted a two-position control strategy for the algae feeding system. Besides, the PLC controller communicated with the host computer via the CP243-1 Ethernet communication module, so all the monitoring data was uploaded to the host computer in the monitoring center house. On the host computer, MCGS (network version) software and SQL Server database software were used to build a database to save the water quality data, and this database could provide a decision basis for scientific aquaculture. Through the practical test, the communication success rate of the whole system was more than 98%, and the average relative errors of dissolved oxygen, temperature, pH, and ammonia nitrogen were ±0.3 mg/L, ±0.4 ℃, ±0.3 and ±0.04 mg/L, respectively. It could be seen that this system met the monitoring needs of freshwater pearl mussel aquaculture. This system was conducive to solve the previous shortcomings and ensure the growth of production, it was very worthy of promotion and application, and it would open up a new situation for the establishment of a new environment-friendly and efficient aquaculture mode of freshwater pearl mussel. [ABSTRACT FROM AUTHOR]

Freshwater mussels of the order Unionida encyst into the fish mucosa to metamorphose and complete their life cycle, causing a parasitic disease known as glochidiosis. This parasitic stage represents a bottleneck for the survival of naiads, particularly for critically endangered species as Margaritifera margaritifera; however, little is known about the events occurring during this critical stage. Therefore, this study aimed to histologically characterize the development of M. margaritifera glochidiosis in Atlantic salmon to get insight into the pathogenesis of this interaction. Fish exposed to glochidia were sampled during the first 44 days post‐exposure, and organs were observed by stereomicroscopy and light microscopy. Glochidia attached to the gills by pinching the lamellar epithelium, whereupon an acute proliferative branchitis engulfed most of the larvae. However, during the first 14 days, a severe detachment of unviable glochidia occurred, associated with the presence of pleomorphic inflammatory infiltrate and epithelial degeneration. In the cases where larvae remained attached, a chronification of the lesions with none to scarce inflammation was observed. These results provide key information to better understand the complex host–parasite interaction during the early stages of glochidiosis and provide valuable information to optimize artificial rearing of naiads in conservation of threatened freshwater mussel populations. [ABSTRACT FROM AUTHOR]

Abstract The Freshwater Pearl Mussel (Margaritifera margaritifera) is an endangered organism across its entire range. It has a complex life cycle and stringent habitat requirements and is therefore an indicator species for the general ecosystem health of host rivers. Whereas historical intensive pearl fishing contributed to population declines, excess nutrient and sediment loss associated with current land use pressures in host river catchments, including modern intensive farming practices, are now highlighted as primary contributory factors. Accordingly, this study investigated the sources and dynamics of fine-grained sediment sampled in the mussel beds of the River Torridge, SW England. Sediment source fingerprinting using a combination of colorimetric and radiometric tracers to construct different composite signatures revealed the importance of roads both as a sediment source and delivery pathway for fine-grained sediment mobilised from fields predominantly supporting lowland livestock farming. Grassland fields with evidence of soil poaching were highlighted as important sediment sources, but equally, riparian woodland was also identified as important, especially during the latter stages of consecutive runoff events when its rainfall buffering capacity was exceeded. Bed sediment storage levels (median up to 393 g m−2) were found to be low (41st percentile) compared to typical values reported by a recent strategic scale survey across England and Wales, whereas elevated turbidity peaks were shown to be long duration (days) in conjunction with consecutive days of rainfall and corresponding runoff events. Hysteresis patterns varied but were generally clockwise during the largest runoff events associated with consecutive rain days; again, suggesting mobilisation of sediment from proximal woodland sources following exceedance of rainfall buffering capacity. In combination, the data assembled by this study provides a basis for planning sediment control measures for protecting the Freshwater Pearl Mussel (FPM) beds from excessive fine-grained sediment inputs associated with the intensive use of primarily grazing land. Graphical abstract Unlabelled Image Highlights • Fine sediment is degrading Freshwater Pearl Mussel habitats in the River Torridge. • Roads, woodland, channel banks and agriculture were all major sediment sources. • Bank erosion contributed more to bed sediment than suspended sediment. • Turbidity was high in storm events and dominant sediment sources change over time. • High turbidity peaks were elongated in duration. [ABSTRACT FROM AUTHOR]

A 74‐day experiment was conducted to evaluate the production performance and water quality variation in three types of farming system for largemouth bass Micropterus salmoides. The tested aquaculture models included monoculture of largemouth bass (MC), polyculture of largemouth bass, gibel carp Carassius auratus gibelio and silver carp Hypophthalmichthys molitrix (PC), and integrated culture of largemouth bass, gibel carp, silver carp and freshwater pearl mussel Hyriopsis cumingii (IC). The ratio of largemouth bass, gibel carp and silver carp was 30:2:1 in the PC model, and the ratio of largemouth bass, gibel carp, silver carp and mussel was 30:2:1:5 in the IC model. The largemouth bass were fed with formulated feed twice daily. No significant differences were found in weight gain and yield of largemouth bass, total fish yield, nitrogen (N) and phosphorus (P) utilization efficiencies, N and P wastes, pH, nitrite, nitrate, reactive phosphate, total nitrogen, total phosphorus, total organic carbon, chemical oxygen demand, 5‐day biochemical oxygen demand, chlorophyll a, primary productivity among the MC, PC and IC models. The ammonia was lower, while the dissolved oxygen was higher in the PC tanks than in the MC tanks. These results suggest that the environment situation was better in the PC tanks relative to that in the MC tanks. The present study reveals that the PC model should be a way to optimize the aquaculture model for commercial largemouth bass farming. [ABSTRACT FROM AUTHOR]

Parasites alter their host behaviour and vice versa as a result of mutual adaptations in the evolutionary arms race. One of these adaptations involves changes in host thermoregulation, which has the potential to harm the parasite and thereby act as a defence mechanism.We used a model of the brown trout (Salmo trutta) experimentally parasitised with glochidia ectoparasitic larvae from the endangered freshwater pearl mussel (Margaritifera margaritifera) to reveal whether parasitisation alters fish behavioural thermoregulation. A study using radiotelemetry temperature sensors was performed during almost one year of the M. margaritifera parasitic stage. Glochidia-infested S. trutta altered their thermoregulation through active searching for habitats with different thermal regimes. The general preference for temperatures in infested fish varied and was either above or below the temperature preferred by uninfested individuals. Infested fish also preferred different temperatures across localities, whereas uninfested fish maintained their thermal preference no matter which stream they inhabited. Glochidia further induced the expression of a behavioural syndrome among S. trutta personality traits, suggesting that it might increase the probability that the fish host would occur in the glochidia temperature optimum. Our findings present the first evidence that thermoregulation plays a fundamental role in the relationship of affiliated mussels and their fish hosts. Incorporating thermoregulation as a factor in the study of this relationship can help to interpret results from previous behavioural studies, as well as to optimise management measures related to endangered mussels. [ABSTRACT FROM AUTHOR]

Preinfection by one parasitic species may facilitate or by contrast hamper the subsequent penetration and/or establishment of other parasites in a host. The biology of interacting species, timing of preinfection, and dosage of subsequent parasite exposure are likely important variables in this multiparasite dynamic infection process. The increased vulnerability to subsequent infection can be an important and often overlooked factor influencing parasite virulence. We investigated how the preinfection by freshwater pearl mussel Margaritifera margaritifera glochidia could influence the success of subsequent infection by the common trematode Diplostomum pseudospathaceum in brown trout Salmo trutta and vice versa whether preinfection by the trematode made fish more susceptible to glochidia infection. The first experiment was repeated twice with different (low and high) exposure doses to initiate the subsequent trematode infection, while in the second experiment we varied the timing of the preinfection with trematodes. The preinfection with glochidia made fish more vulnerable to subsequent infection with trematodes. Since the trematodes penetrate through the gills, we suggest that increased host vulnerability was most likely the result of increased respiration caused by the freshwater pearl mussel glochidia encysted on gills. In turn, brown trout preinfected with trematodes were more vulnerable to the subsequent glochidial infection, but only if they were preinfected shortly before the subsequent infection (20 hr). Fish preinfected with trematodes earlier (2 weeks before the subsequent infection) did not differ in their vulnerability to glochidia. These effects were observed at moderate intensities of infections similar to those that occur in nature. Our study demonstrates how the timing and sequence of exposure to parasitic species can influence infection success in a host–multiparasite system. It indicates that the negative influence of glochidia on host fitness is likely to be underestimated and that this should be taken into consideration when organizing freshwater pearl mussel restoration procedures. Freshwater pearl mussels's parasitic stage (glochidia) is usually considered to be not very harmful to their host, brown trout. However, even a small damage to fish gills caused by this parasite can make its host more vulnerable to subsequent infections. We demonstrate that the glochidia infection predispose fish to the infection by common trematode. Interestingly, fish preinfected with trematode was also more vulnerable to infection with glochidia, but only, if preinfection happened shortly before the second infection. [ABSTRACT FROM AUTHOR]

Information on the genetic diversity and population genetic structure of threatened species is important for guiding management decisions. Margaritifera margaritifera (freshwater pearl mussel) occurs across western Russia, north and central Europe, and Atlantic drainages of north-eastern North America (NA). European populations of M. margaritifera are considered endangered, whereas NA populations are thought to be relatively secure. As such, the population genetics of M. margaritifera occurring in European rivers is relatively well studied while that of NA populations is not known. In this study, we investigated the genetic diversity and differentiation of M. margaritifera in Canada and the USA. Genetic diversity indices calculated from nine microsatellite loci were relatively high in the NA population. Analyses of genetic structure indicated that a single panmictic population exists for M. margaritifera in NA. However, there was evidence of substructure in some tributaries of the St. Lawrence River in Québec, Canada. The NA population of M. margaritifera has low genetic differentiation and high diversity, possibly resulting from large population size and high gene flow. Consequently, conservation of this species should focus primarily on maintaining favourable habitat conditions and connectivity for host fish. [ABSTRACT FROM AUTHOR]

The family Margaritiferidae encompasses 12 valid species, which are distributed widely but disjunctively in the Northern Hemisphere. A lack of a well resolved and temporally calibrated phylogenetic framework of Margaritiferidae has made it difficult to discuss the evolutionary pattern and process. Phylogenetic relationships between five major clades, which were revealed in earlier studies, remain elusive and unresolved. Lamprotula rochechouartii has long been classified within the family Unionidae based on shell morphology, but our preliminary molecular study on this species made us hypothesize that it has an affinity with margaritiferids. Hence, five loci (COI, 16S, 18S, 28S and histone H3) were used to investigate the phylogenetic position of L. rochechouartii and intra-familial relationships within Margaritiferidae using various partitioning strategies. Moreover, two mitochondrial genomes were newly obtained to further resolve and validate the five-clade relationships within Margaritiferidae in a broad view of Unionoida evolution. Both five-gene and mitogenome datasets strongly advocated treating Lamprotula rochechouartii as Margaritifera rochechouartii comb . nov . Maximum likelihood and Bayesian inference analyses using partitioned five-gene dataset resulted in various topologies, but five well-supported clades were obtained. The most probable cladistic relationships generated by five-gene dataset analyses were identical to subsequent whole mitogenome analyses except the position of M. monodonta . M. rochechouartii and M. laosensis had a well-supported sister relationship and formed a basal clade splitting from the rest of the family. Based on six reliable fossils, crown age of the extant Margaritiferidae was estimated during the Late Cretaceous at 88.3 Ma (95% HPD = 66.2–117.4). But we hypothesized a much earlier origin of this family due to the Permian stem age (mean = 257 Ma, 95% HPD = 230.0–296.0) and a high extinction rate in the whole order. Biogeographic scenarios supported a Laurasian origin of extant Margaritiferidae during the Late Cretaceous, and suggested that Asian margaritiferids may have had two origins, having either Asia ( M. rochechouartii, M. laosensis ) or North America ( M. dahurica, M. laevis, and M. middendorffi ) as ancestral. The newly added Margaritiferidae species M. rochechouartii expands our recognized distribution range of modern margaritiferids. Our results indicate that whole mitogenome sequences can be used to reconstruct robust phylogenetic relationships for freshwater mussels, especially with the help of adding M-type mitogenomes. [ABSTRACT FROM AUTHOR]

SinceMargaritifera marocana(Pallary, 1918) andM. laosensis(Lea, 1863) were rediscovered,M. homsensis(Lea, 1865) remains the only pearl mussel species known solely based on old shell samples from natural history museums. This is also the last pearl mussel species, which is absent in a phylogeny of the family. Here, we aimed to provide an integrative revision of the taxonomic status ofM. homsensisfrom the Orontes Basin. Using a newly collected specimen from the River Karasu, Hatay Province, southern Turkey, five gene partitions were sequenced, the cytochrome c oxidase subunit I (COI), large ribosomal subunit rRNA (16S), large ribosomal subunit rDNA (28S) and its D3 expansion segment (D3), and small ribosomal subunit rDNA (18S). The multi-gene phylogeny indicates thatM. homsensisis a sister taxon ofM. auricularia, but both these species are closely related toM. marocanaby nuclear genes. The main conchological features, i.e., the shell shape, teeth morphology, and mantle attachment scars, as well as Fourier shell shape analysis have not shown principal differences betweenM. homsensisandM. auricularia. Based on these data, we concluded thatM. homsensisis a valid species that is most closely related toM. auricularia. Special conservation efforts for a population ofM. homsensisdiscovered in Turkey, including the formation of a nature reserve, might contribute to the conservation of the species. Finally, an extensive search for surviving populations in Orontes drainage (southern Turkey, Lebanon, and Syria) and the Nahr-el-Kabir River (Lebanon and Syria) remains necessary to develop a transboundary conservation strategy for this unique taxon. [ABSTRACT FROM AUTHOR]

Age-related declines in survival and function (senescence) were thought not to exist in wild populations, as organisms, and particularly in invertebrates, do not live long enough. While recent evidence has demonstrated that senescence is both common and measurable even in wild populations under field conditions, there are still organisms that are thought to exhibit 'negligible senescence'. We explore variation in rates and patterns of senescence in the biogerontological model organism, the freshwater pearl mussel Margaritifera margaritifera, across five populations, which differ in their age profile. In particular, we tested the theory of negligible senescence using time-at-death records for 1091 specimens of M. margaritifera. There is clear evidence of senescence in all populations, as indicated by an increase in mortality with age, but the nature of the relationship varies subtly between populations. We find strong evidence of a mortality plateau at later ages in some populations, but this is unequivocally absent from others. We then demonstrate that the temporal scaling of the rates of senescence between five populations of M. margaritifera can be explained by the variation in the thermal environment of the population. Hence, climate change may pose a threat to the demography of this long-lived, endangered species, and a greater understanding of the relationship between river temperature and population structure will be essential to secure the species against global temperature increases. Our findings demonstrate that useful insights can be drawn from a non-invasive monitoring method to derive demographic data, and we suggest a wide-scale application of this method to monitor populations across the whole latitudinal (and, hence, thermal) range of the species. [ABSTRACT FROM AUTHOR]

Information on the southern populations of the freshwater pearl mussel in Russia (Novgorodskaya and Leningradskaya oblast) is very scarce and has never been mentioned in the international scientific literature. Pearl fishing used to be common in this area in the fifteenth to eighteenth centuries but collapsed afterwards. Long-term field survey undertaken in 2006-2012 revealed that eight populations survived and at least 22 became extinct. The total number of mussels found was about 50,000, with the largest population in one small river consisting of approximately 40,000 individuals. Juveniles were found in six populations. The data obtained are of interest for assessing the resilience and stability of pearl mussel populations in response to potentially negative environmental and particularly anthropogenic impacts. The results are expected to inform future management strategies for conservation of suitable habitats for successful pearl mussel reproduction. The decline in host fish populations in the rivers appears to be the most significant threat to the survival of the existing pearl mussel populations. [ABSTRACT FROM AUTHOR]

The critically endangered freshwater pearl mussel ( Margaritifera margaritifera Linnaeus 1758) is the target species of an Austrian conservation project that involves captive breeding. In order to optimize the operational procedure, controls were conducted at several decisive stages, including infection of host fish (for which a time- and work-saving enclosure approach was tested), larval growth during the parasitic stage, growth of juvenile mussels in climate chambers at different temperatures, and growth and survival of re-introduced juveniles in field cages. High infection rates could be attained under near natural conditions. Distinctive patterns in the way the gill arches of the host fish were infected could be detected. Encysted glochidia showed significantly different successive growth stages, related to water temperature. In all, five distinctive growth stages could be detected in the course of the first 562 days of observation. The stages are described and the respective daily increments given. Very high survival rates were achieved during hibernation in the field as well as at the laboratory. The study suggests a way for saving time in the infection procedure that can more effectively be invested in an intensive maintenance of juveniles at the laboratory and during hibernation in the field. [ABSTRACT FROM AUTHOR]

The endangered freshwater pearl mussel ( Margaritifera margaritifera) requires brown trout or Atlantic salmon as a host to complete its life cycle. In Norway, populations have been identified using almost exclusively either salmon or trout as hosts, even when both hosts are present. In this study we tested the hypothesis that the genetic variation in freshwater pearl mussel is host-dependent. A total of 587 specimens from 25 different localities were assayed for genetic variation at eight microsatellite loci. Within populations, the trout-mussel populations had significantly lower allelic richness and expected heterozygosity than the salmon-mussel populations. The genetic differentiation among trout-mussel populations was very large ( F = 0.332), and significantly larger than among salmon-mussel populations ( F = 0.023). Host affiliation explained more of the genetic differentiation among freshwater pearl mussel populations ( F = 0.150) than geographical location ( F = 0.013). Collectively these results suggest that there is strong reproductive isolation between freshwater pearl mussel populations. More importantly, our results indicate that trout- and salmon-mussel populations are differently genetically structured. Because of the mandatory parasitic larval stage on trout and salmon, the host-dependent genetic variation has implications for restoration and management plans for this species. [ABSTRACT FROM AUTHOR]

This paper summarises data on the occurrence of freshwater pearl mussel Margaritifera margaritifera in the western part of Northern European Russia adjacent to White Sea, Barents Sea, Onega Lake and Ladoga Lake basins. Also, this article provides an overview of the literature-based data and archive materials on the history of pearl harvesting. We include a list of rivers of Northwestern Russia, where pearls were harvested during the period of the sixteenth to twentieth centuries. The pearl mussel populations at the present time exist in at least 24 water streams in Northwestern Russia. Many of these populations are in high abundance and are able to reproduce normally. Data on the status of populations are given in this paper. Data indicate that the pearl mussel population in Russia contains >143.5 million individuals, but this estimation is certainly undervalued. Timber floating (timber floating is the transport of timber on waterways), hydro-engineering construction, pollution of rivers by industrial wastes and introduction of alien species, as well as a reduction in host fish species numbers can all be cited as the main factors that transformed the ecosystems inhabited by pearl mussel of Northern Russia. In addition, methods used in the Russian Federation for decreasing the anthropogenic load on pearl mussel populations were considered. [ABSTRACT FROM AUTHOR]

Quantitative real-time polymerase chain reaction is a sensitive technique for quantifying gene expression levels. One or more appropriate reference genes must be selected to accurately compare mRNA transcript levels across different samples and tissues. The freshwater pearl, Hyriopsis cumingii (Lea), is an important economic species cultured in China. To date, no reference genes for gene expression analysis in this species have been validated. This study aimed to compare the relative expression of seven housekeeping genes across different tissue types and in the mantle or pearl sac during three biomineralization processes: seasonal shell growth, shell healing and pearl-sac formation in H. cumingii. Three programs evaluated the expression stabilities of the seven genes: BestKeeper, geNorm and NormFinder. The beta actin gene ( ACTB), commonly used as a housekeeping gene in many studies, was the least stable. The expressions of Ubiquitin ( Ubi) and Ribosomal protein L18 ( Rpl18) and Elongation factor 1-alpha ( EF1α) were more stable than the remaining four genes. Therefore, we suggest that Ubi, Rpl18 and EF1α are suitable reference genes. The three selected reference genes are expected to facilitate analysis of gene expressions during shell or pearl formation in H. cumingii. [ABSTRACT FROM AUTHOR]

Nondestructive tissue sampling is desirable for genetic or physiological studies of endangered freshwater mussels. We used the freshwater pearl mussel (Margaritifera margaritifera) to evaluate 4 sampling methods (haemolymph extraction, foot scraping, mantle biopsy, and viscera swabbing) with regard to their effectiveness for deoxyribonucleic acid (DNA) analyses and their effects on sampled mussels. One hundred twenty-eight days subsequent to tissue sampling (1 June-7 October), all sampled individuals were alive, and average growth of sampled individuals was not significantly different from unsampled, control individuals, except that the viscera-swabbing group had lower growth. The magnitude of decreased growth in viscera-swabbed individuals was small (~0.5 mm less than controls), and the biological significance of this result is unclear. DNA yields from haemolymph extraction and foot scraping were significantly lower and more variable than yields from the other methods. Genotyping success was lowest for haemolymph extraction and mantle biopsy, but was high for the other methods. Viscera-swab samples stored in lysis buffer at room temperature prior to DNA extraction had higher DNA yield than samples stored in buffer at 4°C or samples stored dry, but genotyping success was equivalent among storage methods. On the basis of these results, we recommend use of the noninvasive viscera-swabbing method. [ABSTRACT FROM AUTHOR]

Abstract: After excision of mantle tissue from Hyriopsis cumingii Lea, survival rates, specific growth rate, healing and regeneration were observed and quantified for three months. High survival rates (94.7%, 92%, 95.3% and 94.7%, respectively) of mussels with small (8–12mm×8–12mm) (S-group)excision taken from the front, middle and back of the ventral mantle margin, and control mussels were observed, and no significant difference was observed among the four groups. The specific growth rates, SGR (length), SGR (thickness) and SGR (weight) of H. cumingii with different excision locations did not differ significantly but the SGR (height) of the group with the front excision was significantly lower than that of the other excised groups and controls. Mussels were excised with small, medium (8–12mm×28–32mm) (M-group) or large (8–12mm×48–52mm) (L-group) from the middle ventral mantle margin. The survival rates of mussels with S-, M- and L-group and controls were, respectively, 92%, 90%, 90.7% and 94.7%. The survival rate of the L-group was significantly lower than that of the other three groups. The trends in SGR (length), SGR (height), SGR (thickness) and SGR (weight) among the four groups were similar: controls>S-group>M-group>L-group. Macroscopic observation of mantle tissue showed that the wound area became reduced since 12th d after the excision. To grow to the same level as the surrounding normal tissue, the regenerated tissue needed 40d, 75d and 90d, respectively, in the S-, M-, and L-group. Histological observation of wound tissues showed that haemocytes aggregated at the wound site soon after excision and completely sealed the wound after 12h. Epithelialization sealed the wound completely after 72h. The three mantle lobes began to form at 15d. The regenerated lobes were morphologically different from normal tissues after 25d but were identical to the normal mantle lobes, in both morphological structure and function, by 90d. This is the first report on the survival rate, growth rate, wound healing, and regeneration in the freshwater pearl mussel after excision of its mantle tissue. The study demonstrates that donor mussels, without being killed, may donate mantle pieces (saibos) for evaluating the effect of donor mussel on pearl quality. Donor mussels contributing to pearl quality, this provides support for selective breeding of donor mussels in the future. [Copyright &y& Elsevier]

Abstract: The River Moriston in NW Scotland is a cobble–gravel bedded river that has been dammed and regulated for hydroelectric power (HEP) since 1956. The river supports a functional population of the critically endangered freshwater pearl mussel (Margaritifera margaritifera) in the lower part. In contrast the population in the upper reach is sparse and shows no signs of juvenile recruitment, leading to speculation that hydrological and geomorphic changes associated with HEP have degraded the habitat they depend on. A combination of historical analysis, field mapping and geomorphic survey of channel and active bar sites was used to assess habitat changes and current quality. During the post-dam period, the naturally stability of much of the channel has increased, active bars have been stabilised through vegetation colonisation, riparian tree cover has increased and the active channel width has significantly reduced locally (>50%); adjustments that are indicative of a reduction in the incidence of competent flows caused by flow regulation. However area and stability of habitat for freshwater pearl mussels have not been reduced greatly. The channel sites examined are characterised by mixed cobble–gravel substrates (D 50 range=46–188mm), predicted to be highly stable, that provide suitable habitat for adult freshwater pearl mussels. However a degree of bed compaction at one site was observed that could be limiting the recruitment of juvenile mussels. It is hypothesised that the sparse, non-functional status of the freshwater pearl mussel population reflects significant historical pearl fishing and the limitation of recovery due to HEP related pressures of fish migration obstruction and bed compaction. The implications of these factors for conservation of the species are discussed. [Copyright &y& Elsevier]

Data are presented on the distribution and state of populations of a rare species, the European freshwater pearl mussel, in the rivers of Karelia. Populations of Atlantic salmon in the rivers surveyed, and pearl mussel glochidial infection in salmon juveniles were analyzed. It is demonstrated that timber floating, hydropower engineering, pearl harvesting and deforestation have resulted in extinction of the pearl mussel in several rivers. Decline in juvenile salmon abundance has negative influence on the pearl mussel recruitment. However, our data prove that Karelia, both the White Sea and the Baltic Sea catchments, still possesses viable populations of the pearl mussel. [ABSTRACT FROM AUTHOR]

The identification and prioritization of sites for conservation actions to protect biodiversity in lotic systems is crucial when economic resources or available areas are limited. Challenges include the incorporation of multi-scale interactions, and the application of species distribution models (SDMs) to rare organism with multiple life stages. To support the planning of conservation actions for the highly endangered Freshwater Pearl Mussel Margaritifera margaritifera (FPM), this paper aims at developing an ecohydrological modeling cascade including a hydrological model (SWAT) and a hydraulic model (HEC-RAS). Building on hydrology and hydraulics, Random Forest models for potential risk to juveniles due to sand accumulation, SDMs for adults habitat niche, and a landscape connectivity assessment of dispersal potential were developed. The feasibility of such models integration was tested in the Aist catchment (630 km2) in Austria. The potential FPM habitat and the sand accumulation risk for the whole catchment were predicted with good accuracy. Results show that while the potentially suitable habitats for adults FPM cover 34% of the river network, only few habitat patches can maximize the dispersal potential (4% of the river network) and even less are showing limited impact of accumulations (3.5% of river network). No habitat patch that meets all the three criteria is available, suggesting approaches that target the patch-specific critical life stage-factors are promising for conservation. Unlabelled Image • Ecohydrological modeling cascades support multi-scaled conservation planning. • A tool for modeling the life stages of the Freshwater Pearl Mussels is developed. • Hydrological, hydraulic, sand accumulation, species distribution models are linked. • Sites for life-stage-specific conservation actions are identified and prioritized. • Critical life stages drive choice of conservation action. [ABSTRACT FROM AUTHOR]

• We evaluate the importance of anthropogenic habitats for an endangered species. • Water mill canals seem to provide stable conditions for freshwater pearl mussels. • During droughts these canals may function as an ecological trap. • Actions to protect freshwater pearl mussels should take in account these canals. Anthropogenic habitats may serve as a refuge for aquatic species, including freshwater mussels (Bivalvia, Unionida). Evaluating the role of anthropogenic habitats is a fundamental, but still ignored, conservation issue given the pace that humans have been converting natural ecosystems. In this study, possible differences in abundance, size and condition index of the freshwater pearl mussel Margaritifera margaritifera colonizing anthropogenic (water mill canals) and natural (Tuela River) habitats were assessed. No differences were found in the abundance of freshwater pearl mussels colonizing both habitats, but individuals present in the water mill canals have a significantly higher condition index and size. Water mill canals seem to provide stable conditions for the settlement, growth and survival of freshwater pearl mussels. However, the occurrence of an exceptional drought during the late summer of 2017 was responsible for an almost 100% mortality in one of the two water mill canals surveyed in this study. Therefore, and during extreme climatic events, these anthropogenic structures may function as an ecological trap for freshwater pearl mussels. This study can be used by managers to promote future actions that enhance freshwater pearl mussel protection and guarantee their survival, including on anthropogenic habitats. [ABSTRACT FROM AUTHOR]