Search

Co-infections are common in host-parasite interactions, but studies about their impact on the virulence of parasites/diseases are still scarce. The present study compared mortality induced by a fatal bacterial pathogen, Flavobacterium columnare between brown trout infected with glochidia from the endangered freshwater pearl mussel, Margaritifera margaritifera, and uninfected control fish during the parasitic period and after the parasitic period (i.e. glochidia detached) in a laboratory experiment. We hypothesised that glochidial infection would increase host susceptibility to and/or pathogenicity of the bacterial infection. We found that the highly virulent strain of F. columnare caused an intense disease outbreak, with mortality reaching 100% within 29 h. Opposite to the study hypothesis, both fresh ongoing and past infection (14 months post-infection) with glochidia prolonged the fish host’s survival statistically significantly by 1 h compared to the control fish (two-way ANOVA: fresh-infection, F1, 82 = 7.144, p = 0.009 and post-infection, F1, 51 = 4.227, p = 0.044). Furthermore, fish survival time increased with glochidia abundance (MLR: post-infection, t = 2.103, p = 0.045). The mechanism could be connected to an enhanced non-specific immunity or changed gill structure of the fish, as F. columnare enters the fish body mainly via the gills, which is also the glochidia’s attachment site. The results increase current knowledge about the interactions between freshwater mussels and their (commercially important) fish hosts and fish pathogens and also emphasise the importance of (unknown) ecosystem services (e.g., protection against pathogens) potentially associated with imperilled freshwater mussels.

The freshwater pearl mussel (Margaritifera margaritifera) is a highly host-specific parasite, with an obligate parasitic stage on salmonid fish. Atlantic salmon (Salmo salar) and brown trout (Salmo trutta f. truttaandSalmo trutta f. fario) are the only hosts in their European distribution. SomeM. margaritiferapopulations exclusively infest either Atlantic salmon or brown trout, while others infest both hosts with one salmonid species typically being the principal host and the other a less suitable host. Glochidial abundance, prevalence and growth are often used as parameters to measure host suitability, with the most suitable host species displaying the highest parameters. However, it is not known if the degree of host specialisation will negatively influence host fitness (virulence) among different host species. In this study we examined the hypothesis that glochidial infestation would result in differential virulence in two salmonid host species and that lower virulence would be observed on the most suitable host. Atlantic salmon and brown trout were infested with glochidia from twoM. margaritiferapopulations that use Atlantic salmon as their principal host, and the difference in host mortality among infested and control (sham infested) fish was examined. Higher mortality was observed in infested brown trout (the less suitable host) groups, compared to the other test groups. Genetic assignment was used to identify offspring from individual mother mussels. We found that glochidia from individual mothers can infest both the salmonid hosts; however, some mothers displayed a bias towards either salmon or trout. We believe that the differences in host-dependent virulence and the host bias displayed by individual mothers were a result of genotype × genotype interactions between the glochidia and their hosts, indicating that there is an underlying genetic component for this parasite-host interaction.

The conditions for cohabitation of juvenile Salmo salar and Margaritifera margaritifera in the River Kamennaya (River Kem catchment, White Sea drainage basin, Russia) were studied. The M. margaritifera population in the River Kamennaya contains about 1000 specimens. The only intermediate host capable of sustaining the existence of this rare North European mussel is the juvenile S. salar. In this study, we investigated a set of parameters and processes to get a more comprehensive insight into the ecology of the M. margaritifera. One of such parameters is the individual linear growth, which was investigated in freshwater mussels from the River Kamennaya. Growth deceleration coefficients varied widely and differed significantly among specimens. The population-averaged coefficient of growth deceleration was 0.076. The growth of mussels in the River Kamennaya involves three regular biorhythms with the following periods: 11.5, 6.4 and 4.0 years. The biorhythm periods were roughly constant both through an individual's ontogeny and among different individuals. A comparison of our results with data on other M. margaritifera populations in the Republic of Karelia and the Murmansk Region reveals a reliable (p < 0.01) negative correlation between growth deceleration coefficients and mean annual temperature in the M. margaritifera habitat. The abundance, spatial distribution and age structure of juvenile S. salar and M. margaritifera are presented. The rates of glochidial infection in S. salar juveniles at different ages were estimated. The developmental stages and the status of glochidia encysted on juvenile S. salar gills were observed and described using histological methods. The results of this study will be used to suggest activities and measures aimed to preserve populations of M. margaritifera and S. salar in the River Kamennaya, primarily to promote juvenile S. salar numbers and M. margaritifera settlement in rapids with a high density of young individuals.

Margaritifera monodonta, or the Spectaclecase Mussel, is a federally endangered freshwater mussel species that has experienced a 55% reduction in range and is currently concentrated in 3 ri...

Three freshwater bivalve taxa are described from the Villar del Arzobispo Formation (Late Jurassic-Early Cretaceous) of Riodeva, Teruel, Spain. The stratigraphic range of the large and geographically widely distributed bivalve Margaritifera, previously recorded from the Early Cretaceous of Spain and southern England, is recognised to extend back probably into the Late Jurassic. This new record extends the palaeogeographic and temporal distribution of the family Margaritiferidae in Europe

Sediment depth preference was tested on 1-year-old freshwater pearl mussel juveniles. Mesh tubes allowing vertical migration with a possibility to leave hyporheic space, filled with 1–2-mm granulometry size substrate and populated with groups of juveniles, were placed in the natural river bed of the Tepla Vltava River, Czech Republic. The depth position of the juveniles was recorded after 1- and 2-month exposure during the summer and after 8 months including wintering. The juveniles showed a tendency not to stay on the sediment surface, but to penetrate into a very shallow depth, and to accumulate and stay 2–3 cm deep in the substrate in the summer period. No juvenile was found below 8 cm sediment depth, neither in the summer nor after wintering. In the experimental tubes, various survival rates (0–100%) were recorded in close relation to substrate oxygenation development at the tested sites. Oxygen decrease was accompanied by juveniles trying to escape the hyporheal.

The stable isotope composition of lacustrine sediments is routinely used to infer Late Holocene changes in precipitation over Scandinavia and, ultimately, atmospheric circulation dynamics in the North Atlantic realm. However, such archives only provide a low temporal resolution (ca. 15 years), precluding the ability to identify changes on inter-annual and quasi-decadal timescales. Here, we present a new, high-resolution reconstruction using shells of freshwater pearl mussels, Margaritifera margaritifera, from three streams in northern Sweden. We present seasonally to annually resolved, calendar-aligned stable oxygen and carbon isotope data from 10 specimens, covering the time interval from 1819 to 1998. The bivalves studied formed their shells near equilibrium with the oxygen isotope signature of ambient water and, thus, reflect hydrological processes in the catchment as well as changes, albeit damped, in the isotope signature of local atmospheric precipitation. The shell oxygen isotopes were significantly correlated with the North Atlantic Oscillation index (up to 56 % explained variability), suggesting that the moisture that winter precipitation formed from originated predominantly in the North Atlantic during NAO+ years but in the Arctic during NAO− years. The isotope signature of winter precipitation was attenuated in the stream water, and this damping effect was eventually recorded by the shells. Shell stable carbon isotope values did not show consistent ontogenetic trends, but rather oscillated around an average that ranged from ca. −12.00 to −13.00 ‰ among the streams studied. Results of this study contribute to an improved understanding of climate dynamics in Scandinavia and the North Atlantic sector and can help to constrain eco-hydrological changes in riverine ecosystems. Moreover, long isotope records of precipitation and streamflow are pivotal to improve our understanding and modeling of hydrological, ecological, biogeochemical and atmospheric processes. Our new approach offers a much higher temporal resolution and superior dating control than data from existing archives.

Environmental DNA (eDNA) from water samples is increasingly used to detect the presence and distribution of species in aquatic ecosystems. However, before implementing eDNA in monitoring programmes, various species-specific sampling or analytical issues remain to be resolved in order to minimize frequencies of false-positive and -negative results. For example, empty shells from freshwater pearl mussels (Margaritifera margaritifera) contain extractable DNA (chemical extraction from ground-up shells) suggesting a risk of false-positive samples at stream sites with extinct populations but with empty shell material remaining. The aim of this study was to investigate whether empty and naturally degrading shells from M. margaritifera can cause false-positive eDNA signals in water samples. Water samples were collected from outdoor stream channels (in Lemming, Denmark) with living freshwater pearl mussels or empty shell material (density ~10 individuals m −2) during a 3-week experimental period. Living freshwater pearl mussels were collected from Hemgravs stream in Sweden and transported to Denmark according to permissions granted by the Swedish and Danish authorities. All water samples from stream channels containing empty shells were negative for eDNA indicating that eDNA traces in stream water are most likely to originate from living individuals located upstream of the sampling site. Water samples collected from stream channels containing living individuals of M. margaritifera were consistently positive for eDNA except for one sample (interpreted as a false negative). The study shows that positive eDNA signals for freshwater pearl mussels most likely reflect the presence of living individuals. Consequently, we suggest that eDNA should be used to locate remaining population fragments of M. margaritifera in deep and turbulent streams, providing a platform for faster and more efficient decision making when launching investigative and mitigation initiatives.

This is the peer reviewed version of the following article: Castrillo PA, Varela‐Dopico C, Ondina P, Quiroga MI, Bermúdez R. (2020). Early stages of Margaritifera margaritifera glochidiosis in Atlantic salmon: Morphopathological characterization. J Fish Dis., which has been published in final form at https://doi.org/10.1111/jfd.13100. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. 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 critical 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 postexposure 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. European Project Life Margal Ulla, Grant/Award Number: 09NAT/ES/00514; Strategic Researcher Cluster BioReDes of Xunta de Galicia, Grant/Award Number: ED431D 2017/22; Fundación Biodiversidad (MarMaCul Project), Grant/Award Number: CAQ2016; Spanish Ministry of Education, Culture and Sport, Grant/Award Number: FPU17/02004 SI

Calothyrza margaritifera (Westwood) is briefly described and illustrated. This is probably the first authentic record of the species from India.

A characteristic feature shared by all Margaritiferidae mussels consists in the presence of scars on the internal surface of their shells. These scars mark places of mantle attachment by specific epithelial cells. According to some authors, such parameters of mantle attachment scars as the density and degree of their manifestation can be used for the purposes of species identification. To this end, quality indicators (numerous or few, pronounced or poorly visible scars) are typically used; however, the use of quantitative criteria is preferable. This work was aimed at developing quantitative indicators of mantle attachment scars in the Margaritifera margaritifera freshwater pearl mussels for the populations of the Syuskyuyanyoki and Livoyoki rivers (Karelia). It is shown that the density and size of mantle attachment scars are approximately the same for all the investigated shell samples. These parameters display the absence of dependence on the age and size of molluscs. The regression coefficients for the linear dependence of the density or size of mantle attachment scars on the age or length of the shell show no significant difference from 0. For all the investigated molluscs, the density and size of mantle attachment scars are established to vary within the range of 0.37–1.16 scars/cm2 (0.71 ± 0.03 scars/cm2 on average) and 215–690 µm (417 ± 2 µm on average), respectively. According to a two-factor analysis of variance, the distribution of mantle attachment scars appears to be irregular across the shell surface. At the same time, a significant (p < 0.001) increase in their density is observed in the posterior and ventral directions, as well as diagonally in the posterior ventral direction. Issues associated with the application of the investigated parameters for the purposes of mollusc species identification are discussed.

The freshwater pearl mussel Margaritifera margaritifera (L., 1758) is considered to be a critically endangered species. It is important to obtain information on the distribution and status of the surviving populations of the species, but in Russia this work is still problematic due to the size of the country’s territory, combined with the insufficient number of available specialists. “Searching rules” have been proposed to remotely identify potential pearl mussel habitats in rivers. The most important criteria are relating to the lakes found at the rivers’ sources, as well as to the extent of the deforestation along river basins. About 200 watercourses of the Russian section of the Baltic Sea basin were evaluated using these “rules”. As a result, two previously unknown, viable populations were discovered (comprising about 53,000 specimens), while the absence of pearl mussels was made evident among some rivers which were traditionally believed to be their habitats. The obtained data provides an update on the status of pearl mussels in Russian territories located south of the 61 st degree of latitude. There are 10 populations of this species; 4 of them are almost extinct, 6 are relatively numerous but declining. The total number of pearl mussels hardly exceeds 90,000 individuals.

Environmental DNA (eDNA) can be used to detect the presence and abundance of aquatic organisms from water samples. Before implementing this methodology as a tool for monitoring, more knowledge is needed on variation in eDNA concentrations in relation to species abundance and potential confounding factors. Shedding and decay of eDNA may vary extensively over the season and are dependent on environmental factors such as water temperature and on biological processes such as Activity level and reproduction. In lotic systems, eDNA concentrations are also affected by downstream transport of eDNA. Sessile freshwater mussels provide an ideal study system for investigating the relationship between species spatial distribution and eDNA concentrations in lotic systems. We quantified freshwater pearl mussel (Margaritifera margaritifera) eDNA concentrations at four localities in a natural river with detailed knowledge of mussel spatial distribution: (a) upstream of the known species distribution, just downstream (b) a small and (c) a large aggregation and (d) 1,700 m downstream of the large aggregation. To study seasonal variation, we quantified eDNA concentrations during three periods: (a) in late spring, with cold water and relatively inactive mussels; (b) in mid‐summer, with higher water temperature and active mussel filtration; and (c) in late summer, during the release of larvae. Species detection was highly reliable, with no detection of eDNA upstream of the species distribution and complete detection downstream of the large aggregation. Detection success of the small aggregation was low, with 13% of the samples testing positive. Downstream transport was efficient, with no significant decrease in eDNA concentrations over 1,700 m river distance. Seasonal variation was strong, with a 20‐fold increase in eDNA concentrations from late spring to late summer, during reproduction. Our results highlight both the potential and challenges of eDNA monitoring in lotic systems.

Margaritiferidae is an ancient freshwater bivalve family originated in the Jurassic in East Asia. Here, we revise several nominal taxa of fossil freshwater pearl mussels that were recovered from the Upper Pliocene and Pleistocene deposits of the Dniester and Prut river valleys. Based on morphological and stratigraphic data, we found that these nominal taxa belong to the genus Pseudunio and are junior synonyms of P. flabellatiformis (Grigorowitch-Beresowski, 1915). The new synonymy is proposed as follows: Margaritifera (Pseudunio) moldavica Chepalyga, 1964 syn. nov. , Margaritifera (Pseudunio) robusta robusta Chepalyga, 1964 syn. nov. , Margaritifera (Pseudunio) robusta speensis Chepalyga, 1964 syn. nov. , and Margaritifera (Pseudunio) robusta tirassica Chepalyga, 1964 syn. nov. All these fossil nominal taxa were described based on minor differences in the shell shape and size, hinge structure, and stratigraphic position. Finally, we suggest an updated phylogenetic scheme of the genus Pseudunio , which contains five valid species: P. marocanus (Pallary, 1918) [Eocene – Recent, Morocco], P. auricularius (Spengler, 1793) [Pliocene – Recent, Southern and Western Europe], P. homsensis (Lea, 1865) [Pliocene – Recent, Orontes and Nahr al-Kabir basins], P. flabellatiformis (Grigorowitch-Beresowski, 1915) comb. rev. [Pliocene – Late Pleistocene, paleo-Dniester and paleo-Danube basins, an extinct lineage related to P. auricularius and P. homsensis ], and P. flabellatus (Goldfuss, 1837) comb. rev. [Miocene, paleo-Danube Basin, a stem lineage, MRCA of P. auricularius - P. homsensis clade].

The freshwater pearl mussel (Margaritifera margaritifera) is an endangered bivalve with an obligate parasitic stage on salmonids. Host suitability studies have shown that glochidial growth and load vary significantly between host strains as well as among individuals of a suitable strain. Variation in host suitability has been linked to environmental conditions, host age and/or size, genetic composition of the host and parasite, or a combination of these factors. In our study, we wanted to investigate if brown trout (Salmo trutta) displayed an age-dependent response to glochidial infestation. We hypothesised that 1+ naive brown trout hosts tolerate glochidial infestation better than 0+ hosts. In order to test our hypothesis, we infested 0+ and 1+ hatchery reared brown trout with glochidia from closely related mothers and kept them under common garden conditions. This allowed us to observe a pure age dependent host response to infestation, as we eliminated the confounding effect of genotype-specific host interactions. We analysed the interaction between glochidial load and host condition, weight and length, and observed a significant age-dependent relationship. Glochidial load was negatively correlated to host condition in 0+ fish hosts and positively correlated in 1+ hosts. These contradictory findings can be explained by a change in host response strategy, from resistance in young to a higher tolerance in older fish. In addition, we also examined the relationship between glochidial load and haematocrit values in the 1+ hosts and observed that haematocrit values were significantly higher in heavily infested hosts. Our results have important conservation implications for the management of wild pearl mussel populations, as well as for captive breeding programmes.

International audience; Aquaculture of nacreous gems, such as cultured pearls, mabé or keshi, is done mostly using different mollusc species grown in countries of the Indo-Pacific region. To date, no single species has been exploited for the simultaneous generation of more than one of these bioproducts, but all require animals with colourful shells. Historically, Pinctada species have mainly been used for nucleated pearl production, selecting the rarer colourful individuals to be used as graft donors. By contrast, colourful Pteria species have mostly been used for mabé production, as the grafting operation for pearl production is associated with low yield. In this study, we report the potential for cumulating cultured pearl and mabé (MP), or keshi and mabé (MK) production, using a colourful hatchery-produced G2 family of P. margaritifera. For these trials, MP and MK combinations were compared with the operations to produce pearls (P), mabé (M) or keshi (K) alone in an experimental design using groups of small and large recipients from the G2 family. Results showed no significant impact of combining operation types on subsequent pearl weight, keshi weight, or mabé thickness within recipient oyster size group. By contrast, significant differences were observed between the large and small recipients. The small group produced the thickest mabé, while the large group produced the heaviest pearls and keshi. These contrasting results revealed: 1) the relative independence between the two tissues capable of biomineralisation activities, the mantle (shell and mabé growth) and the pearl sac (pearl or keshi growth); 2) the potential compensatory growth of the small recipient oyster group, which had the highest shell growth performance; and 3) the regulation capacity of the larger oyster group of pearl sac activity. With the same growing area and number of cultured oysters, it would be possible for the P. margaritifera pearl industry to benefit from hatchery propagation of selected colourful shell and produce valuable keshi and mabé together with cultured pearls.

International audience; In French Polynesia black pearl farming represents one of the dominant business sectors. However, it still entirely relies on unpredictable Pinctada margaritifera spat collection success, which is itself conditioned by larval development completion. To assess the relationship between larval development and recruitment success, we studied under controlled conditions the effect of food concentration on development, growth, ingestion rate, survival and metabolic rate at the larval stage. Larvae were exposed to four different phytoplankton densities (2,5; 7,5; 15 and 30 cell.mu L-1). Larvae survived equally all over the range of phytoplankton concentration with an average survival rate of 16% at the end of experiments. Food concentration significantly affected the larval physiology throughout its development from birth to metamorphosis. Growth and feeding were close to those reported by previous laboratory observations with young spat of 210 mu m long obtained in 18 days of rearing at 28 degrees C for the highest food concentration. Differences in length at metamorphosis and cumulated energy ingested until settlement occurred according to trophic levels with a saturation threshold close to 0.0086 J.ind(-1). This level was reached at the food concentration of 15 cell.mu L-1. Larval development stages could be divided on the basis of the energy balance between feeding and respiration rates. An initial mixotrophic period with a lower and constant ingestion/respiration ratio over the first three days (from birth to D-veliger larva) was followed by an exotrophic phase characterized by a sharp increase in energy balance highly dependent of food concentration. Finally two sharp decreases of feeding rates were recorded during metamorphosis before umbonate and eyed stages. This study provided numerous new clues to establish a quasi-deterministic relationship between food condition and larval development. It highlights the major effect of food concentration and how energy intake through feeding as well as behavioral and physiological transitions can optimize larval development duration and minimize "the risky phase" of their life cycle. By taking into account the observed metabolic switches, the results provide a strong foundation for Dynamic Energy Budget model development and better description of the complex interactions between P. margaritifera physiology and environmental conditions.

The black-lip pearl oyster, Pinctada margaritifera, used for round pearl production in Polynesia, is generally cultured using “ear-hanging” where they are attached to a rope to form “chaplets.” In other countries, pearl oysters are cultured using panel (pocket) nets that are more expensive than chaplets but afford more protection to cultured oysters. Prior research has shown panel nets produce pearls of higher quality and value, potentially generating higher profits. This study used cost–benefit analysis to compare pearl production using chaplet-based and panel net-based culture methods. Whole farm data, including gross revenues and annual production costs, fixed and variable, were analyzed. Average production cost per pearl using panel net-based culture was USD 22.47 and for chaplet-based culture was USD 21.55. However, use of panel nets saved around 3,430 hr (USD 6,860) of labor a year, offsetting the greater capital investment. A chaplet-based pearl farm generated USD 65,738 in annual profits compared to USD 88,774 for a panel net-based farm. Positive cash flow was achieved 1 year earlier (Year 7) for the panel net-based farm. This is the first economic analysis of different pearl culture methods for P. margaritifera and evidence of profitability will support further development of the black-lip pearl industry in the Indo-Pacific region.

Since historical times, the inherent human fascination with pearls turned the freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758) into a highly valuable cultural and economic resource. Although pearl harvesting in M. margaritifera is nowadays residual, other human threats have aggravated the species conservation status, especially in Europe. This mussel presents a myriad of rare biological features, e.g. high longevity coupled with low senescence and Doubly Uniparental Inheritance of mitochondrial DNA, for which the underlying molecular mechanisms are poorly known. Here, the first draft genome assembly of M. margaritifera was produced using a combination of Illumina Paired-end and Mate-pair approaches. The genome assembly was 2.4 Gb long, possessing 105,185 scaffolds and a scaffold N50 length of 288,726 bp. The ab initio gene prediction allowed the identification of 35,119 protein-coding genes. This genome represents an essential resource for studying this species' unique biological and evolutionary features and ultimately will help to develop new tools to promote its conservation. A.G.-d.-S. was funded by the Portuguese Foundation for Science and Technology (FCT) under the grants SFRH/BD/137935/2018, EF (CEECIND/00627/2017) and MLL (2020.03608.CEECIND). This research was developed under ConBiomics: the missing approach for the Conservation of freshwater Bivalves Project No. NORTE-01-0145-FEDER- 030286, co-financed by COMPETE 2020, Portugal 2020 and the European Union through the ERDF, and by FCT through national funds. Additional strategic funding was provided by FCT UIDB/04423/2020 and UIDP/04423/2020. Authors’ interaction and writing of the article was promoted and facilitated by the COST Action CA18239: CONFREMU—Conservation of freshwater mussels: a pan- European approach. info:eu-repo/semantics/publishedVersion

Ocean warming is a particularly challenging threat for tropical marine bivalves’ species because many live already near their upper thermal limits. The thermal sensitivity of organisms is a strong contributor to the biogeographic boundaries of populations and species. The potential of thermal plastic response (range of thermal breadth) is typically reduced for marine populations living in stable thermal environments, e.g., in extreme latitudes organisms as traduced in the climatic variability hypothesis. However, regional-scale heterogeneity among tropical environments, such as archipelagos in French Polynesia, might also serve in modulating this plastic potential. The questions remain now, how tropical organisms are able to cope with abnormally elevated temperature on long-term (several weeks) and how environmental-variability might drive the potential of resilience? To answer these questions, we benefit from two ecologically divergent populations of a marine tropical mollusc species,Pinctada margaritifera, that usually experience either large diurnal variations (tide-pools, Marquesas archipelago) or lower temperature with stable to moderate variations (Gambier archipelago). Individuals were maintained in common garden experiment at several controlled temperature conditions (23°C, 28°C, 32°C and 34°C) over a 48 days period. We explored genetic divergence as well as thermal plastic responses by combining lipidomic and transcriptomic approaches. We show thatP. margaritiferahave capacities to adjust to long-term elevated temperatures that was thus far largely underestimated. Furthermore, we identified genetic variation between populations that overlapped with genes expression variations, including genes involved in the respiration machinery, a central process delimiting critical temperatures in marine invertebrates. This study is the first of a series looking at the global adaptation and acclimation mechanisms in response to climate change inPinctadaspecies.

Freshwater mussels are among the most endangered groups of fauna anywhere in world. The indiscriminate use of antibiotics has led to the emergence of resistant strains. These antibiotic-resistant bacteria play a key role in increasing the risk allied with the use of surface water and in spread of resistance genes. Two endangered freshwater mussel species, Margaritifera margaritifera and Potomida littoralis, were sampled at 4 sampling sites along a 50 km stretch of River Tua. Water samples were taken at same sites. Of the total of 135 isolates, 64.44% (39.26% from water and 25.19% from mussels) were coliform bacteria. Site T1, with the lowest concentration of coliform bacteria, and site T2 were the only ones where M. margaritifera was found. No E. coli isolates were found in this species and the pattern between water and mussels was similar. P. littoralis, which was present at T3/T4 sites, is the one that faces the highest concentration of bacterial toxins, which are found in treated wastewater effluents and around population centers. Sites T3/T4 have the isolates (water and mussels) with the highest resistance pattern, mainly to β-lactams. Water and P. littoralis isolates (T3/T4) showed resistance to penicillins and their combination with clavulanic acid, and to cephalosporins, precisely to a fourth generation of cephalosporin antibiotics. The analysis provides important information on the risk to water systems, as well as the need to investigate possible management measures. It is suggested that future studies on the health status of freshwater bivalves should incorporate measures to indicate bacteriological water quality. This work was supported by the Portuguese Foundation for Science and Technology (FCT) and the Operational Competitiveness Programme (COMPETE), under projects UIDB/04033/2020 and UIDP/04033/2020 (CITAB-Inov4Agro-UTAD). This research was also funded by the Conselleira de Educación, Universidade e Formación Profesional, Xunta de Galicia, Spain, under project R815 131H 64502 (Xana Álvarez). Funding for open access charge was from the Universidade de Vigo/CISUG. info:eu-repo/semantics/publishedVersion

Effect of freshwater mussels’ (Unionoida) glochidia on the growth of fish host has remained poorly studied. We compared the specific growth rate of the juvenile, PIT-marked brown trout (Salmo trutta) between uninfected controls to those experimentally infected (average initial intensity of infection 8000 fish−1) with Margaritifera margaritifera glochidia, kept in high and low feeding. Growth and mortality of fish were monitored for 10 months. Our hypothesis was that glochidiosis would impair the growth of fish. According to our hypothesis, infected fish gained statistically significantly less weight than the control fish throughout the experiment. A proportional increase in weight of control individuals was 11% higher than that of the infected fish. However, neither the feeding regime (high, low) nor the period (September–November, November–March, March–May), had a significant effect on the growth difference between control and infected fish. As the effect of infection on the growth of fish was subtle and no effect on host mortality was detected either, this may turn public opinion favorable for M. margaritifera conservation even if the salmonid host population is important for commercial or recreational fishing.

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.

International audience; The shell color of the Mollusca has attracted naturalists and collectors for hundreds of years, while the molecular pathways regulating pigment production and the pigments themselves remain poorly described. In this study, our aim was to identify the main pigments and their molecular pathways in the pearl oyster Pinctada margaritifera—the species displaying the broadest range of colors. Three inner shell colors were investigated—red, yellow, and green. To maximize phenotypic homogeneity, a controlled population approach combined with common garden conditioning was used. Comparative analysis of transcriptomes (RNA-seq) of P. margaritifera with different shell colors revealed the central role of the heme pathway, which is involved in the production of red (uroporphyrin and derivates), yellow (bilirubin), and green (biliverdin and cobalamin forms) pigments. In addition, the Raper–Mason, and purine metabolism pathways were shown to produce yellow pigments (pheomelanin and xanthine) and the black pigment eumelanin. The presence of these pigments in pigmented shell was validated by Raman spectroscopy. This method also highlighted that all the identified pathways and pigments are expressed ubiquitously and that the dominant color of the shell is due to the preferential expression of one pathway compared with another. These pathways could likely be extrapolated to many other organisms presenting broad chromatic variation

Juveniles of the endangered freshwater pearl mussel (FPM,Margaritifera margaritifera) live burrowed in stream substrate for the first years of their life. Fine sediments block water exchange within substrate and may cause juvenile mortality and recruitment failure. To better understand the connection between success of juvenile FPM and substrate particle size, it would be important to understand behavioural responses of FPM to varying substrate sizes at this critical life stage. We placed newly detached FPM juveniles in a 7-mm layer of sieved sand sorted into five sizes (

We describe through integrative taxonomy a new Amazonian species of leaf-litter toad of the Rhinella margaritifera species group. The new species inhabits open lowland forest in southwest Amazonia in Brazil, Peru, and Bolivia. It is closely related to a Bolivian species tentatively identified as Rhinella cf. paraguayensis. Both the new species and R. paraguayensis share an uncommon breeding strategy among their Amazonian congeners: each breeds in moderate to large rivers instead of small streams or ponds formed by rainwater. The new species is easily differentiated from other members of the R. margaritifera species group by having a strongly developed bony protrusion at the angle of the jaw, a snout–vent length of 63.4–84.7 mm in females and 56.3–72.3 mm in males, well-developed supratympanic crests with the proximal portion shorter than the parotoid gland in lateral view, a divided distal subarticular tubercle on finger III, and multinoted calls composed of groups of 7–9 pulsed notes and a dominant frequency of 1,012–1,163 Hz. Recent studies have shown that the upper Madeira Basin harbors a megadiverse fauna of anurans, including several candidate species. This is the first member of the R. margaritifera species group to be described from this region in recent years, and at least two additional unnamed species await formal description.

Since historical times, the inherent human fascination with pearls turned the freshwater pearl mussel Margaritifera margaritifera (Linnaeus, 1758) into a highly valuable cultural and economic resource. Although pearl harvesting in M. margaritifera is nowadays residual, other human threats have aggravated the species conservation status, especially in Europe. This mussel presents a myriad of rare biological features, e.g. high longevity coupled with low senescence and Doubly Uniparental Inheritance of mitochondrial DNA, for which the underlying molecular mechanisms are poorly known. Here, the first draft genome assembly of M. margaritifera was produced using a combination of Illumina Paired-end and Mate-pair approaches. The genome assembly was 2,4 Gb long, possessing 105,185 scaffolds and a scaffold N50 length of 288,726 bp. The ab initio gene prediction allowed the identification of 35,119 protein-coding genes. This genome represents an essential resource for studying this species’ unique biological and evolutionary features and ultimately will help to develop new tools to promote its conservation.

WOS:000571443200012; International audience; A combined approach integrating bioenergetics and major biological activities is essential to properly understand the impact of microplastics (MP) on marine organisms. Following experimental exposure of polystyrene microbeads (micro-PS of 6 and 10 mu m) at 0.25, 2.5, and 25 mu g L-1, which demonstrated a dose-dependent decrease of energy balance in the pearl oyster Pinctada margaritifera, a transcriptomic study was conducted on mantle tissue. Transcriptomic data helped us to decipher the molecular mechanisms involved in P. margaritifera responses to micro-PS and search more broadly for effects on energetically expensive maintenance functions. Genes related to the detoxification process were impacted by long-term micro-PS exposure through a decrease in antioxidant response functioning, most likely leading to oxidative stress and damage, especially at higher micro-PS doses. The immune response was also found to be dose-specific, with a stress-related activity stimulated by the lowest dose present after a 2-month exposure period. This stress response was not observed following exposure to higher doses, reflecting an energy-limited capacity of pearl oysters to cope with prolonged stress and a dramatic shift to adjust to pessimum conditions, mostly limited and hampered by a lowered energetic budget. This preliminary experiment lays the foundation for exploring pathways and gene expression in P. margaritifera, and marine mollusks in general, under MP exposure. We also propose a conceptual framework to properly assess realistic MP effects on organisms and population resilience in future investigations. (C) 2020 The Authors. Published by Elsevier Ltd.

Many landscape and biotic processes shape the genetic structure of populations. The genetic structure of species with parasitic stages may also depend on the life history and ecology of their host. We investigated population genetic structure of the mussel Margaritifera margaritifera in Southern Sweden, and in relation to the population size and life history of its hosts, Salmo trutta and S. salar. Mussel populations were genetically differentiated into two clusters, further subdivided into four clusters and distinct conservation units. Regardless of host species, the genetic differentiation was lower among mussel populations sustained by sea-migrating than by resident hosts, while the genetic diversity was higher in mussel populations sustained by sea-migrating than by resident hosts. Genetic diversity of mussel populations was positively related to host abundance. Mussel population size was positively related to high genetic diversity of mussels sustained by resident hosts, while low mussel population size sustained by sea-migrating hosts had a high genetic diversity. The results of our study suggest a combined influence of mussels and host fish on genetic structure of unionoid mussels. We suggest to conserve not only mussel population sizes and host fish species, but also consider host migratory/resident behaviour and abundance when designing conservation programs.

A total of 312 specimens of freshwater pearl mussel (Margaritifera margaritifera) were sampled from 11 populations, located in four different river systems in Southeast Norway, and analyzed for 11 simple sequence repeat (SSR) (microsatellite) markers. All study populations have landlocked brown trout (Salmo trutta) as the only possible host. Several populations had experienced recruitment failure, probably due to low pH (about 6.0) and calcium concentration. STRUCTURE clustering analysis revealed two genetic clusters, of which one cluster occurred mainly in the western river systems, and totally dominated in one population (Fallselva (A-FAL)) that had higher genetic diversity than the others. Cluster 2 completely dominated in the populations of the eastern river systems, and all of them had low genetic diversity. Bottleneck events were indicated in all populations and the inbreeding coefficient FIS was significant in all populations, except for the southernmost population (S&oslash, rkedalselva (B-S&Oslash, R)), which was the only population with genotypes in Hardy&ndash, Weinberg equilibrium. FIS were especially high in the populations of the eastern river systems, and maximum shell length was negatively correlated to FIS. If artificially breeding and stocking should become necessary for future preservation, it should be based on single populations, alternatively, the eastern populations should be based on cross-breeding of populations within the cluster to increase their genetic diversity.

Background Albino mutations are commonly observed in the animal kingdom, including in bivalves. In the black-lipped pearl oyster Pinctada margaritifera, albino specimens are characterized by total or partial absence of colouration resulting in typical white shell phenotype expression. The relationship of shell colour with resulting cultured pearl colour is of great economic interest in P. margaritifera, on which a pearl industry is based. Hence, the albino phenotype provides a useful way to examine the molecular mechanisms underlying pigmentation. Results Whole transcriptome RNA-sequencing analysis comparing albino and black wild-type phenotypes at three stages over the culture cycle of P. margaritifera revealed a total of 1606, 798 and 187 differentially expressed genes in whole juvenile, adult mantle and pearl sac tissue, respectively. These genes were found to be involved in five main molecular pathways, tightly linked to known pigmentation pathways: melanogenesis, calcium signalling pathway, Notch signalling pathway, pigment transport and biomineralization. Additionally, significant phenotype-associated SNPs were selected (N = 159), including two located in the Pif biomineralization gene, which codes for nacre formation. Interestingly, significantly different transcript splicing was detected between juvenile (N = 1366) and adult mantle tissue (N = 313) in, e.g., the tyrosinase Tyr-1 gene, which showed more complex regulation in mantle, and the Notch1 encoding gene, which was upregulated in albino juveniles. Conclusion This multiple RNA-seq approach provided new knowledge about genes associated with the P. margaritifera albino phenotype, highlighting: 1) new molecular pathways, such as the Notch signalling pathway in pigmentation, 2) associated SNP markers with biomineraliszation gene of interest like Pif for marker-assisted selection and prevention of inbreeding, and 3) alternative gene splicing for melanin biosynthesis implicating tyrosinase.

The freshwater pearl mussel (FWPM) Margaritifera margaritifera (L.1758) is critically endangered in Europe and ecotoxicological studies on the species are scares. Here, 96 h acute toxicity tests were conducted at 16 &deg, C with sodium chloride (NaCl), nitrates (NO3&minus, ), ortho-phosphates (PO43&minus, ), cadmium (Cd), aluminum (Al) and arsenic (As) on 13- to 28-month-old post-parasitic juveniles. The experimental protocol was developed according to conditions described in a standard guide and was modified in order to assess toxicity thresholds for the Dronne River. Results showed that juveniles were tolerant to concentrations of Al, Cd, As, PO43&minus, NO3&minus, and NaCl, largely higher than those found in the Dronne river, since 96 h EC50s (effective concentrations) were &gt, 954 &micro, g/L for Al, &gt, 110 &micro, g/L for Cd, 127 &micro, g/L for As, 5.01 mg/L for PO43&minus, between 1000 and 1500 mg/L for NO3&minus, and were 1.19 and 1.33 g/L for NaCl. Moreover, the use of a substrate in experiments was found not to affect juvenile responses and younger juveniles seemed more sensitive than older individuals. This study thus provides new data about the tolerance of FWPM to environmental pollution and suggests that pollutant concentrations in the river are significantly lower than levels affecting them.

European freshwater pearl mussel (Margaritifera margaritifera) populations are declining despite a growing effort to conserve them. Here we used a combination of local ecological knowledge (LEK) and field sampling to assess past and current distribution and conservation status of this endangered species in Cávado and Neiva Rivers (Portugal). We performed face-to-face interviews in both rivers and sampled the entire area where the respondents confirmed the historical presence of this species. Abiotic characterization, water quality and fish diversity were also assessed in both rivers. We found that freshwater pearl mussels are now possibly extinct in Cávado River but almost 50% of the respondents confirm its presence in the past, especially elders that lived in villages near its historical distribution. To the contrary, and although the species is still present in Neiva River, only 3.8% of the respondents remembered its presence in the past. In both rivers, respondents suggested pollution as the most important explanation for the freshwater pearl mussels decline. However, nowadays both rivers present excellent water quality and trout Salmo trutta (the freshwater pearl mussel fish host) is still abundant. Since we identified the areas where the species was present in a recent past, this information is vital for possible management actions with the aim of re-introduce or increase the abundance of M. margaritifera populations and/or for the rehabilitation of habitats in both rivers. We also highlight the vital importance of getting LEK, mainly from elders, in order to avoid shifting baseline syndromes and to get qualitative accurate information of past references and/or experience with historical conditions. Results reported here reinforce concern about the conservation status of freshwater pearl mussel populations in Portugal and can be used to guide future research and management initiatives to better conserve this species., This work was supported by POSEUR-03-2215-FC-000096 and ICNF funds under project CP01-MARG-QUERCUS/2018. We acknowledge André Vinhas Fernandes, Bruna Gonçalves, Maria Inês Carvalho and José Vasco for the help in doing the interviews and field work. We thank Ivan Bolotov and two anonymous referees for the valuable suggestions made, which increased the clarity of our manuscript.

The shells of marine mollusks represent promising metagenomic archives of the past, adding to bones, teeth, hairs, and environmental samples most commonly examined in ancient DNA research. Seminal work has established that DNA recovery from marine mollusk shells depends on their microstructure, preservation and disease state, and that authentic ancient DNA could be retrieved from specimens as old as 7,000 years. Here, we significantly push the temporal limit for shell DNA recovery to >= 100,000 years with the successful genetic characterization of one Portlandia arctica and one Mytilus mussel sample collected within a dated permafrost layer from the Taimyr Peninsula, Russia. We expand the analysis of ancient DNA in carbonate shells to a larger number of genera (Arctica, Cernuella, Crassostrea, Dreissena, Haliotis, Lymnaea, Margaritifera, Pecten, Ruditapes, Venerupis) from marine, freshwater and terrestrial environments. We demonstrate that DNA from ancient shells can provide sufficient resolution for taxonomic, phylogenetic and/or population assignment. Our results confirm mollusk shells as long-term DNA reservoirs, opening new avenues for the investigation of environmental changes, commercial species management, biological invasion, and extinction. This is especially timely in light of modern threats to biodiversity and ecosystems.

High quality of sperm is essential to a high fertilization rate, especially post- cryopreservation. Assessment of sperm integrity, motility and energy reserves before cryopreservation is necessary for selection of milt with optimal fertilizing potential. We describe the effect of cryopreservation on the quality of black-lip pearl oyster, Pinctada margaritifera var. cumingii sperm. Evaluated quality indices of fresh and frozen/thawed P. margaritifera spermatozoa, included morphology, ultrastructure and motility characteristics relative to the energy content (ATP) and its capacity to be sustained by mitochondrial respiration. Morphology and ultrastructure were quantitatively evaluated using images obtained by optical microscopy assisted by the Image J software and TEM, respectively. Sperm motility was assessed using Image J software combined with a computer assisted sperm analysis plugin adapted for assessing P. margaritifera spermatozoa. Other sperm quality parameters evaluated included O2 consumption, ATP content, and creatine kinase activity. Frozen/thawed spermatozoa exhibited damage to the head but retained a compact spherical shape. Sperm motility indicators showed a significant decrease in quality resulting from the freeze/thaw process. The percent of motile cells was 54% compared to 84% in fresh sperm, O2 consumption was 4.8 compared to 44 nanomol min−1, ATP content was 0.72 nmol/109 spermatozoa in the activating medium compared to 4.54 nmol/109 spermatozoa, and creatine kinase activity was 9.06 × 10−5 IU mg−1 protein compared to 12.5 × 10−5 IU mg−1 protein. The cryopreservation protocol allowed obtaining an acceptable motility rate after thawing, confirming the predictive value of sperm motility measurements before cryopreservation in terms of their ability to withstand freezing process.

Foundation for Science and Technology (FCT), Grant/Award Numbers: PTDC/AGR-FOR/1627/2014, 3599 and SFRH/BD/115728/2016