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The introduction of freshwater mussels in France was unintentional and relatively recent. Two species were introduced in the second half of the nineteenth century, and a further eight after World War II. This note summarises the available information on introduced freshwater bivalves in France, focusing on the main pathways and vectors of dispersal, based on the data provided by the French National Database (INPN) and environmental DNA data. The introductions were either by sea (mainly for brackish water species, but also for Asiatic Clams), or by the European river system and its canals connecting the Danube to the Rhine (Dreissenidae, Sphaeriidae). A third mean of introduction was the transport of fish, for the Chinese pound mussel, which first established in southern France. Canals connect the major French basins (Rhine, Rhône, Seine, Loire and Garonne) and the route of dispersal of introduced species through natural hydrosystems and canals can be traced by looking at their progression, decade by decade. Fish transport within France is probably an important dispersal vector for the Chinese pound mussel, as occasional introductions appear to have contributed to its spread in the north-east and west of France. The use of the eDNA was an effective tool in completing the species distribution maps. [ABSTRACT FROM AUTHOR]

In this review, we synthesize the current knowledge of the biology, ecology, and impact of Sinanodonta freshwater mussels (Bivalvia, Unionidae), native to East Asia, that have successfully invaded Europe, Central America, North Africa, and several Asian regions. The main introduction pathways of Sinanodonta were reconstructed based on DNA sequence data and distribution records. We show that invasive lineages of Sinanodonta belong to three species, namely, S. woodiana s. str. ("temperate invasive" lineage), S. pacifica ("tropical invasive" lineage), and S. lauta. Their generalist fish-dispersed larvae, short life span, high fecundity, use by humans for multiple purposes, and ability to establish populations in anthropogenically disturbed conditions were identified as crucial traits driving their invasions. Information on the consequences is scarcer, but Sinanodonta can impact native species through larval parasitism, host fish/food competition, and parasite transmission. In addition, ecosystem effects through their filtration—biodeposition—excretion activity and the occurrence of massive die-offs were detected. Ecosystem services and disservices have not yet been quantified, even at local scales, and management methods in the invasive range are understudied. A better understanding of Sinanodonta ecology, impacts, and management options is urgently needed to make informed decisions and set realistic and impactful restoration goals. [ABSTRACT FROM AUTHOR]

The Asian clam Corbicula fluminea has been widely introduced into aquatic ecosystems and may impact the physiological condition and survival of native freshwater mussels. However, very few studies have evaluated this issue quantitatively. To fill this gap, manipulative field experiments were performed to assess two possible mechanisms of impact on native mussels: (i) interspecific interactions, and (ii) C. fluminea die-offs. We assessed these effects by measuring the physiological condition through the analysis of glycogen content in the foot tissue of the native freshwater mussel species Anodonta anatina, Potomida littoralis, and Unio delphinus. Although with interspecific differences, our results suggest that C. fluminea can impact the physiological condition of native freshwater mussels. Anodonta anatina showed positive significant variations on glycogen content when subjected to high densities of live C. fluminea in contrast to the other native species studied, P. littoralis and U. delphinus, where no significances were observed. On the other hand, these native species do not seem be significantly impacted by the decomposition of C. fluminea resulting from a die-off. Overall, and contrary to our expectations, both experiments showed a positive (or no) effect of C. fluminea on the physiological condition of the three freshwater mussel species. [ABSTRACT FROM AUTHOR]

Simpsonaias ambigua (Salamander Mussel) is a freshwater mussel of the Family Unionidae endemic to North America, and it is considered endangered across most of its range. This species is unique among the Unionidae, because it uses the salamander, Necturus maculosus (Mudpuppy), as its larval host rather than fish like all other unionids. The overall goal of this study was to obtain baseline data on the current distribution and life history traits of S. ambigua in Ontario, Canada. These data are critical for future recovery efforts to protect, restore, or augment populations of S. ambigua across its range. Conventional survey methods were adapted to target S. ambigua, and an additional method was employed to detect this species: trapping N. maculosus and inspecting for signs of encysted glochidia. Both methods were successful at detecting S. ambigua when they were present. Furthermore, Simpsonaias ambigua's life history traits were investigated, and more information is now available on the reproductive timing windows related to gonad and glochidia development and the host infestation period, as well as on longevity. [ABSTRACT FROM AUTHOR]

Freshwater pearl mussels (Margaritifera margaritifera) are vital bioindicators in river ecosystems, with their population health reflecting broader environmental conditions. Mussel population declines are well documented across Europe, and in Estonia, Pudisoo River supports the last remaining population. Long-term monitoring also indicates a significant decline in Pudisoo River, but the causes remain underexplored. This study aimed to assess how geology, geomorphology, and land use changes could impact pearl mussel population trends and distribution. We conducted field surveys, bioindication tests, and hydrological and morphometric analyses to evaluate physicochemical and environmental parameters in the Pudisoo River. The study revealed a declining but stabilizing population, concentrated in river sections with higher gradients and coarser riverbed substrates. Sediment transport and accumulation, influenced by both natural and human-induced factors, significantly affect habitat suitability, especially for juvenile mussels. Positive correlations were found between mussel populations and river sinuosity, suggesting that the varied microhabitats created by sinuosity, such as gradients in flow velocity and sediment deposition, play an important role in supporting the species. This finding highlights the importance of directing in-channel restoration efforts towards enhancing channel morphology to create more diverse habitats. Research on sediment dynamics and hydrological connectivity will be crucial for developing effective habitat management strategies for the species, especially considering the impacts of land use and climate change. [ABSTRACT FROM AUTHOR]

Wastewater effluents increase contaminant levels in the aquatic environment, leading to various disruptive effects. In this study, responses of Unio ravoisieri transplanted into wastewater from Wadi Guenniche were monitored using filtration rate, oxidative stress, lipo-peroxidation, neurotoxicity and histopathological markers. The filtration rate was significantly increased by exposure to diluted wastewater, rising from 35.13 mg indiv−1 h−1 in the control to 63.49 mg indiv−1 h−1 in the mussels after 96 h of exposure. In contrast, this exposure significantly reduces catalase, glutathione-S-transferase and acetylcholinesterase activities in both organs. This decrease is dependent on the effluent concentration and time exposure. The malondihaldehyde content showed an increasing profile in both organs. It is only in the gills that this increase is significant for mussels transplanted in situ for 48 h. Contamination by wastewater causes histopathological changes in both organs, marked by infiltration, vacuolisation, secretion of lipofuscins and cell necrosis. The intensity of these lesions depends on the duration of exposure and the degree of pollution. The mean incidence of lesions increases depending on effluent concentration and exposure time in both organs. Our study contributes to the database on behavioural, biochemical and histopathological effects in mussels following the discharge of wastewater effluent into a freshwater ecosystem. [ABSTRACT FROM AUTHOR]

This investigation examined the behavioral responses of freshwater mussels to neonicotinoid pesticide exposure, a widely implemented agricultural crop protection agent. The study systematically evaluated the behavioral modifications of U. tumidus under controlled laboratory conditions, with particular emphasis on shell dynamics and activity patterns during both acute (2.5 h) and prolonged (20 h) exposure to imidacloprid at 50 µg/L concentration. The experimental findings revealed consistent and statistically significant behavioral alterations. Upon initial pesticide exposure, specimens exhibited an immediate reduction in shell aperture, followed by a sustained period of enhanced opening amplitude. Activity metrics demonstrated acute elevation immediately post-exposure, indicative of stress-induced responses, subsequently achieving homeostatic equilibrium before declining in later temporal phases. These behavioral modifications demonstrated statistical significance across all four experimental iterations, indicating a robust and reproducible stress response pattern. This study demonstrated that exposure to high concentrations of the neonicotinoid pesticide imidacloprid significantly affects the freshwater mussel causing significant, repeatable changes in mussel behavior: initial shell closure followed by prolonged opening and increased activity, indicating stress and subsequent toxic effects. [ABSTRACT FROM AUTHOR]

The presence of predators influences the selection of oviposition sites, with females often choosing locations that minimize the risk of predation. Bitterlings, freshwater fish that deposit their eggs into the gills of mussels, face the threat of predation from mussel-associated leeches Hemiclepsis kasmiana, which feed on bitterling embryos. In this study, we investigated the host preferences of two species of spring-spawning bitterlings, Tanakia limbata and T. lanceolata, based on the parasitic density of mussel-associated leeches. Our methodology involved observing female bitterling spawning behavior and dissecting mussels to locate bitterling embryos. Our results revealed a preference of female T. limbata for spawning on uninfested mussels or those with lower leech infestation densities, supported by both spawning observations and mussel dissections. Female T. lanceolata exhibited a tendency to avoid mussels with higher leech infestation densities, supported by only mussel dissections, although this avoidance is not statistically significant. The difference in host preference between the two spring-spawning bitterling species may be due to their contrasting reproductive strategies aimed at minimizing the total risk of predation and host mortality. [ABSTRACT FROM AUTHOR]

The global decline of freshwater mussels and their crucial ecological services highlights the necessity and urgency of developing and guiding conservation efforts for this group. Accurately delineating species and understanding their phylogeny are crucial to the core of species conservation. Here, we integrate shell morphology, soft-body anatomy, and molecular systematics to describe a new species of freshwater mussel from the Shi River in Xinyang City, Henan Province, China, i.e., Cuneopsis celtiosimilis sp. nov. Morphologically, this new species resembles its congeneric species C. kiangsiensis and C. celtiformis in shell size, shape, and sculpture. However, this new species can be distinguished from closely related congeners by the pseudocardinal teeth. For the new species, two pseudocardinal teeth of the left valve join together to form a continuous strip; the single pseudocardinal tooth on the right valve is more squashed and lower; the papillae of the incurrent aperture are shorter, forming a pyramidal shape and arranged in two rows. Molecularly, based on the mitochondrial barcoding gene cytochrome c oxidase subunit I (COI), the minimum genetic distance between the new species and other known congeners is 4.6% (C. celtiosimilis sp. nov. vs. C. kiangsiensis). Additionally, the complete mitogenome of C. celtiosimilis sp. nov. was also assembled and annotated. Based on the mitochondrial phylogenomic analyses, the results clarify the phylogenetic position of the new species and establish the most comprehensive phylogenetic relationship of the genus Cuneopsis to date, as follows: ((((C. demangei + C. heudei) + C. szechenyii) + ((C. kiangsiensis + C. celtiosimilis sp. nov.) + C. celtiformis)) + C. rufescens). The discovery of this new taxon contributes to the existing knowledge on freshwater mussels in China, and a key to all known species of Cuneopsis is provided to aid the identification of species in this understudied genus. [ABSTRACT FROM AUTHOR]

The genus Nodularia poses a significant challenge to traditional species classification and identification due to its highly convergent and variable shells, rendering it one of the most intricate groups within the family Unionidae. Fortunately, significant progress has been made by researchers in recent years regarding the species validity and the phylogeny of this group based on molecular data. However, the inadequate exploration of regional constraints and inherent limitations in research methodologies remains a crucial factor contributing to the underestimation of species diversity. In this study, a new species of freshwater mussel from the Qingshui River in Nanning City, Guangxi Province, China, Nodularia guiensis sp. nov., is described based on shell morphology, anatomical characters, and molecular phylogenetics. Mitochondrial phylogenomic analyses reveal the following phylogenetic relationships: (((Nodularia hanensis + Nodularia micheloti) + Nodularia dorri) + (Nodularia breviconcha + (Nodularia huana + (Nodularia fusiformans + (Nodularia guiensis sp. nov. + ((Nodularia nuxpersicae + Nodularia nipponensis) + (Nodularia dualobtusus + Nodularia douglasiae))))))). The discovery of this new taxon further enhances the diversity level within the genus Nodularia in China and also highlights the necessity for comprehensive surveys of unexplored regions in order to potentially unveil additional new taxa in the future. [ABSTRACT FROM AUTHOR]

The isolated river drainages of eastern North America serve as a natural laboratory to investigate the roles of allopatry and secondary contact in the evolutionary trajectories of recently diverged lineages. Drainage divides facilitate allopatric speciation, but due to their sensitivity to climatic and geomorphological changes, neighboring rivers frequently coalesce, creating recurrent opportunities of isolation and contact throughout the history of aquatic lineages. The freshwater mussel Quadrula quadrula is widely distributed across isolated rivers of eastern North America and possesses high phenotypic and molecular variation across its range. We integrate sequence data from three genomes, including female‐ and male‐inherited mitochondrial markers and thousands of nuclear encoded SNPs with morphology and geography to illuminate the group's divergence history. Across contemporary isolated rivers, we found continuums of molecular and morphological variation, following a pattern of isolation by distance. In contact zones, hybridization was frequent with no apparent fitness consequences, as advanced hybrids were common. Accordingly, we recognize Q. quadrula as a single cohesive species with subspecific variation (Q. quadrula rumphiana). Demographic modeling and divergence dating supported a divergence history characterized by allopatric vicariance followed by secondary contact, likely driven by river rearrangements and Pleistocene glacial cycles. Despite clinal range‐wide variation and hybridization in contact zones, the process‐based species delimitation tool delimitR, which considers demographic scenarios like secondary contact, supported the delimitation of the maximum number of species tested. As such, when interpreting species delimitation results, we suggest careful consideration of spatial sampling and subsequent geographic patterns of biological variation, particularly for wide‐ranging taxa. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA) is a chemical compound extensively employed in plastic manufacturing, and this pollutant has been detected in diverse aquatic organisms, notably bivalves. In order to comprehend the ecological and toxicological consequences of BPA Bisphenol A in these organisms, it is essential to examine the physiological and biochemical effects and identify areas where our understanding is lacking. This knowledge is crucial for determining the environn ental threat posed by bisphenol A and assisting decision-makers in establishing the appropriate priorities. This investigation aimed to assess the impact of BPA on the biochemical and physiological parameters of the freshwater mussel Potomida littoralis. In a laboratory setting, mussels were subjected to two different levels of BPA (20 and 100 μg/L) for a duration of 21 days. Filtration rate was calculated from the clearance of neutral red, fed to mussels at different BPA concentrations. The mussel's filtration rate capacity declined as BPA exposure intensified, potentially due to the mussel's attempt to close its valves and minimize BPA absorption, thus preventing cellular damage. In the digestive gland tissue, key antioxidant and detoxification defenses, including catalase (CAT) activity, glutathione-S-transferase (GST) activity, and levels of H2O2 and glutathione (GSH), were activated, particularly at the 100 μg/L BPA concentration. This activation helped protect against lipid damage at higher BPA concentrations. This study underscores the significance of preventing and regulating BPA release into the environment to avert detrimental consequences for aquatic ecosystems. [ABSTRACT FROM AUTHOR]

The extensive use of nanoparticles (NPs) increases the possibility of their deposition into water ecosystems and endangering aquatic life. Thus, this study aimed to assess the acute effect of copper oxide nanoparticles (CuO NPs) on the freshwater clam, Corbicula fluminea. Biochemical, histopathological, and genotoxic biomarkers were examined to achieve this purpose. Clams were exposed to 1.8 and 6.6 mg/l of CuO NPs for 96 h. By comparison with control clams, a significant increase in both malondialdehyde (MDA) and nitric oxide (NO) levels occurred with a concomitant decrease in catalase (CAT) and acetylcholinesterase (AChE) activities and reduced glutathione (GSH) content in clam's tissues treated with both sub-lethal concentrations. Histopathological alterations were observed in the mantle, gills, digestive glands, and gonads of C. fluminea exposed to both sub-lethal concentrations and the histopathological indices for all the reaction patterns in the examined tissues were significantly higher in clams exposed to the higher concentration of CuO NPs (6.6 mg/l). DNA damage evaluated by changes in RAPD profiles. These findings revealed that CuO NPs have a toxicological impact on Corbicula fluminea even after a short period of exposure, thereby immense care should be taken regarding its use. [ABSTRACT FROM AUTHOR]

The freshwater clam Corbicula fluminea is a simultaneous hermaphrodite that reproduces through androgenesis. However, we found the coexistence of males and hermaphrodites (androdioecy) of C. fluminea in the Yasu River in Shiga Prefecture and in the Shirakawa River in Kyoto, Japan. In this study, we investigated the genetic structure of the androdioecious populations and the genetic relationship between brooding clams and brooded juveniles in their egg pouches, using genotyping by random amplicon sequencing–direct (GRAS-Di) to detect single nucleotide polymorphisms in gill tissue samples. Principal component analysis and assignment tests showed that males collected from the Yasu River were genetically distinct from males collected from the Shirakawa River and from hermaphrodites collected from both rivers. The results reveal maintenance of a male lineage in the Yasu River from 2009 to 2018, whereas in the Shirakawa River males were not distinct from hermaphrodites. In the study locations, this species exhibited two shell colour phenotypes ('yellow' and 'green'), but correspondence between shell colour and genotype was not detected. A perfect match of all 6968 single nucleotide polymorphisms was found between the brooding clams and brooded juveniles, which confirmed the clonal reproduction with androgenesis reported previously from cytological observations. [ABSTRACT FROM AUTHOR]

Zooarchaeological mollusc assemblages can show communities as they existed prior to any extensive modern impacts, representing an ecological baseline against which current populations can be evaluated. Here data are presented from the Pruitt Shelter sites (Late Woodland-Early Mississippian; ca. AD 700–1300), located on the Buffalo National River (Arkansas), where over 1000 freshwater mussels and over 20,000 gastropods (aquatic and terrestrial combined) were recovered. To date, these archaeofaunas represent the most detailed and robust mollusc assemblage from the Ozark Highlands, while also demonstrating biogeographical, paleoenvironmental, and population characteristics that should be valuable to modern conservation efforts in the region. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) are ubiquitous pollutants in freshwater environments. In this study, freshwater mussels, Unio delicatus, were exposed to both environmental MPs (e-MP) and commercial MPs (c-MP) that include green fluorescent MP (gf-MP), polyethylene (c-PE) and polystyrene (c-PS) at environmental concentrations (5 mg/L and 50 mg/L) over duration of 7 and 30 days. According to in vivo experiment results, both e-MPs and c-MPs induced significant changes in the total hemocyte counts of mussels (p < 0.05). Exposure to high concentrations of e-MPs and c-MPs for 7 days led to decreased cellular glutathione levels in the mussels, while exposure to low concentrations of e-MPs and c-PS for 7 days resulted in increased advanced oxidation protein products (AOPP). Mussels exposed to high concentrations of e-MPs for 30 days exhibited decreases in both glutathione levels and AOPP values. Although no damage was observed in tissues other than gills and digestive gland, histopathological alterations were observed in these tissues following exposure to 50 mg/L c-MPs. Additionally, MPs were observed in the intestine tissues. In vitro experiments using the MTT assay showed no significant difference in cell viability between the MP-exposed group and the control group at tested concentrations, with no observed dose-response relationship (p > 0.05). Nevertheless, certain cells exhibited signs of cell death, such as disrupted cellular structures, condensed nuclei, and loss of cellular integrity. These observations were consistent with mechanical compression, indicating that physical contact with MPs may result in cell damage or death. These findings demonstrate that environmentally relevant concentrations of MPs have toxic effects on freshwater mussels and multiple parameters provide valuable insight for the evaluation of health risks of organisms. [ABSTRACT FROM AUTHOR]

Abstract Background Amidst the escalating loss of global biodiversity, freshwater mussels (family Unionidae) have become one of the most imperiled animal groups. Acquiring more biological and phylogenetic information on understudied taxa constitutes a pivotal aspect of conservation biology. Consequently, a comprehensive examination was conducted on Koreosolenaia, Parvasolenaia, and Sinosolenaia from China encompassing morphology, anatomy, distribution, and molecular systematics to provide theoretical support for future species endangerment assessments and biodiversity conservation. Results The shell characteristics of Koreosolenaia, Parvasolenaia, and Sinosolenaia were clearly distinct, and the soft-body morphology could also be easily distinguished from each other. The papillae of the incurrent aperture of Sinosolenaia iridinea, Sinosolenaia recognita, and Sinosolenaia oleivora, which were previously described as difficult, exhibited significant variations that could be utilized for species diagnosis. Furthermore, both incurrent and excurrent apertures of the Sinosolenaia species had small cysts on their dorsal surfaces which may be unique to this particular group. Comparative analysis of six mitochondrial genomes (Parvasolenaia rivularis, Koreosolenaia sitgyensis, Sinosolenaia iridinea, Sinosolenaia recognita, Sinosolenaia carinata, and Sinosolenaia oleivora) revealed a completely consistent gene arrangement pattern. Additionally, there was a high consistency in nucleotide base content and skewness, amino acid usage, and relative synonymous codon usage among the six complete mitochondrial genomes. Mitochondrial phylogenomics of these genomes with additional taxa within Gonideinae robustly supported the generic relationships as follows: (Inversidens + ((Microcondylaea + Sinosolenaia) + (Parvasolenaia + (Koreosolenaia + (Ptychorhynchus + (Postolata + Cosmopseudodon)))))). Conclusions The present study provided significant data on the shell morphology and soft-body anatomy of Koreosolenaia, Parvasolenaia, and Sinosolenaia, thereby clarifying the diagnostic characteristics for these challenging taxa. Additionally, we established a robust phylogenetic framework at both the generic and species levels based on mitochondrial genomics.

Background: Amidst the escalating loss of global biodiversity, freshwater mussels (family Unionidae) have become one of the most imperiled animal groups. Acquiring more biological and phylogenetic information on understudied taxa constitutes a pivotal aspect of conservation biology. Consequently, a comprehensive examination was conducted on Koreosolenaia, Parvasolenaia, and Sinosolenaia from China encompassing morphology, anatomy, distribution, and molecular systematics to provide theoretical support for future species endangerment assessments and biodiversity conservation. Results: The shell characteristics of Koreosolenaia, Parvasolenaia, and Sinosolenaia were clearly distinct, and the soft-body morphology could also be easily distinguished from each other. The papillae of the incurrent aperture of Sinosolenaia iridinea, Sinosolenaia recognita, and Sinosolenaia oleivora, which were previously described as difficult, exhibited significant variations that could be utilized for species diagnosis. Furthermore, both incurrent and excurrent apertures of the Sinosolenaia species had small cysts on their dorsal surfaces which may be unique to this particular group. Comparative analysis of six mitochondrial genomes (Parvasolenaia rivularis, Koreosolenaia sitgyensis, Sinosolenaia iridinea, Sinosolenaia recognita, Sinosolenaia carinata, and Sinosolenaia oleivora) revealed a completely consistent gene arrangement pattern. Additionally, there was a high consistency in nucleotide base content and skewness, amino acid usage, and relative synonymous codon usage among the six complete mitochondrial genomes. Mitochondrial phylogenomics of these genomes with additional taxa within Gonideinae robustly supported the generic relationships as follows: (Inversidens + ((Microcondylaea + Sinosolenaia) + (Parvasolenaia + (Koreosolenaia + (Ptychorhynchus + (Postolata + Cosmopseudodon)))))). Conclusions: The present study provided significant data on the shell morphology and soft-body anatomy of Koreosolenaia, Parvasolenaia, and Sinosolenaia, thereby clarifying the diagnostic characteristics for these challenging taxa. Additionally, we established a robust phylogenetic framework at both the generic and species levels based on mitochondrial genomics. [ABSTRACT FROM AUTHOR]

Ecological theory predicts that species turnover among communities (e.g. β-diversity) and genetic turnover among populations within species (e.g. FST) should be positively correlated if similar processes influence colonization and occupancy of species and gene flow and genetic drift of populations within a metacommunity. Using recently published population genomic data from multiple populations of 15 freshwater mussel (Unionidae) species across seven rivers in the Mobile and Tennessee River basins of the south-eastern USA, we conducted novel analyses examining the relationship between taxonomic turnover (β-diversity) among communities and genetic differentiation (FST) within these species. FST and β-diversity were both hierarchically structured, and strong basin effects and isolation-by-distance were observed for β-diversity and for FST among populations within most species. Furthermore, β-diversity and FST were directly correlated for the overall community and among sites for individual species, indicating that factors shaping turnover among mussel assemblages are similar at the species and genetic levels. The widespread associations between turnover metrics at the community and population genetic levels of biological organization suggest that parallel processes govern species composition and intraspecific connectivity in freshwater mussel metacommunities. [ABSTRACT FROM AUTHOR]

ABSTRACT Hydrodynamic forces and their absence appear to exert differential selection pressure on aquatic biodiversity in lake and stream habitats, creating a tight fit between organismal phenotypes and their environments. Ecophenotypic variants may be the result of genetic differentiation or phenotypic plasticity, where a genotype can produce multiple phenotypes dependent on the environment. Freshwater mussels possess a wide degree of morphological variation that frequently covaries with the environment, making them a good system to understand the mechanisms of ecophenotypic variation across hydrological conditions. We designed a two‐year experiment where individuals from the same Pyganodon grandis maternal brood (half and full siblings) were reared at a controlled site and four natural sites involving one lake and three streams. At the end of the experiment, shell shape was quantified for recaptured (N = 70), wild (N = 206), and zoo‐reared (N = 305) mussels. The maternal individual and 46 recaptured mussels were sequenced for genomic single nucleotide polymorphisms to test for multiple paternity and its effect on offspring morphology. Analysis of covariance found significant differences in shell shape between rearing sites, particularly between stream and lake habitats, but no shape differences were detected across the three stream sites. At two of the four sites, the shell shape of recaptured individuals was not significantly different than that of wild populations. Genomic sequencing and parentage analysis identified 11–27 different fathers among recaptured individuals. Yet no genetic differences were present between stream and lake habitats, and there was no paternal effect on shell shape. Taken together, phenotypic plasticity, over genetic differentiation, is identified as the primary mechanism of ecophenotypic variation. Plasticity is likely ubiquitous across freshwater mussels and may be a key adaptation given their high variance in habitat use. Multiple paternity may also play a role in the evolution of phenotypic plasticity, allowing more males from greater distances opportunities for fertilization, thus increasing genetic connectivity. Lastly, phenotypic plasticity and multiple paternity are convenient properties for freshwater mussel conservation and propagation. Multiple fathers increase the genetic variation of propagated broods, while plasticity may provide resilience to the release of stocked individuals across environmental heterogeneity. [ABSTRACT FROM AUTHOR]

Freshwater bivalves (Bivalvia, Unionida, Unionidae) are among the most threatened groups of animals in the world. Taxonomic uncertainties pose a particular challenge due to significant intraspecific variation and apparent plasticity in shell morphology among these species, impeding efficient conservation planning and management. The species Unio szechenyii that is endemic to China has long been regarded as a synonym for Cuneopsis heudei due to the high convergence in shell morphology. The recently validated species Middendorffinaia mongolica is currently restricted to the Amur Basin and Primorye in eastern Russia. This species is classified under the tribe Middendorffinaiini of the subfamily Unioninae within the family Unionidae based on multilocus phylogeny. However, the lack of comprehensive taxonomic information and sufficient molecular phylogenetic data casts uncertainty on the validity and taxonomic status of these two species. We aim to reassess the validity of Unio szechenyii and confirm the taxonomic status of Middendorffinaia mongolica , a new record for China, by integrating taxonomy with robust mitochondrial phylogenomics. We support the validity of Unio szechenyii and propose a recombination as Cuneopsis szechenyii comb. nov. by integrating shell morphometry, soft-body anatomy and molecular evidence. By determination of the mitochondrial genome of Cuneopsis szechenyii , Cuneopsis kiangsiensis , Middendorffinaia mongolica and Pseudocuneopsis wuana , we elucidate intrageneric relationships within the genera Cuneopsis and Pseudocuneopsis. In addition, based on the updated consensus taxonomic framework including tribes and subtribes in Unioninae, mitochondrial phylogenomics strongly support the transfer of Middendorffinaia mongolica from the tribe Middendorffinaiini to the tribe Unionini and classification under the subtribe Middendorffinaiina stat. rev. ZooBank: The maternal mitochondrial genomes of Unio szechenyii , Cuneopsis kiangsiensis , Middendorffinaia mongolica and Pseudocuneopsis wuana are sequenced. The validity of Unio szechenyii , previously considered a synonym of Cuneopsis heudei , is supported by the integration of conchometry, soft-body anatomy and molecular evidence, and a recombination as Cuneopsis szechenyii comb. nov. is proposed. The intrageneric relationships within the genera Cuneopsis and Pseudocuneopsis are elucidated based on the mitochondrial phylogenomics. Middendorffinaia mongolica , a new record for China, is proposed for transfer from the tribe Middendorffinaiini to the tribe Unionini and classification under the subtribe Middendorffinaiina stat. rev. (Image credit: Ruiwen Wu.) [ABSTRACT FROM AUTHOR]

The Indian subcontinent houses a unique fauna of freshwater mussels. Tectonic and biogeographic reconstructions indicate that this fauna represents a derivative of Mesozoic Gondwanan biota and that it arrived in Asia on the Indian Plate, using this tectonic block as a 'biotic ferry'. Though a preliminary integrative revision of the Indian Unionidae was published recently, the level of endemism and taxonomic richness of regional assemblages are unsatisfactorily known. Here, we revise the taxonomy of freshwater mussels from the Brahmaputra River basin based on a large DNA-sequence and morphological dataset that was sampled in Assam, north-eastern India. We managed to collect and sequence topotypes for nearly all nominal species described from the region, except for Lamellidens friersoni and Parreysia smaragdites. Our phylogenetic and morphology-based research reveals that the regional Unionidae assemblage contains nine species, belonging to a single subfamily, the Parreysiinae. Seven species and three genera (Balwantia , Pseudoscabies Bolotov, Sonowal, Kardong, Pasupuleti and Subba Rao gen. nov. , and Assamnaia Bolotov, Sonowal, Kardong, Pasupuleti and Subba Rao gen. nov.) appear to be endemic to the region, indicating that the Brahmaputra River may represent an endemism hotspot of global significance. Our findings highlight that this region should be considered a high-priority area for freshwater conservation management. [ABSTRACT FROM AUTHOR]

Oxygen isotopes in stream water can serve as natural tracers of watershed dynamics. Freshwater pearl mussels provide δ18Owater estimates that overcome temporal and spatial limitations of instrumental records. The reliability of shell‐based δ18Owater reconstructions depends on understanding which shell layer biomineralizes closer to oxygen isotopic equilibrium with ambient water. To determine this, both the (outer) prismatic and (inner) nacreous sublayers of the outer shell layer were sampled. Over 2500 isotope values were obtained from shells collected from the Our River (Luxembourg) and from mussels cultured in tanks at constant temperature and monitored δ18Owater. Calculated δ18Owater from the prismatic portion was in excellent agreement with monitored δ18Owater, while δ18Oshell of the nacreous portion was systematically offset by +0.43‰, overestimating δ18Owater by +0.53‰. Although shell portions were formed simultaneously from the same extrapallial fluid, they underwent different fractionation mechanisms, presumably due to differences in carbonic anhydrase activity catalyzing mineralization processes. [ABSTRACT FROM AUTHOR]

The shells of freshwater mussels, commonly found at archaeological sites associated with the Kodjadermen-Gumelnița-Karanovo VI human groups (5th millennium BCE, Romania and Bulgaria), were a significant dietary component for this population. The organic matrix of these ancient shells is often well-preserved and can be analysed using stable isotopes. This study establishes the empirical relationship between the isotopic composition of the acid-insoluble shell organic matrix (AIM) and the soft tissues of modern Unio tumidus. A quality criterion for AIM (C:N ratio 3.6 (3.3–<3.8)) was defined, and isotopic offsets (Δ15NAIM-defatted body = +0.95‰, Δ13CAIM-defatted body = +0.93‰ for soft tissues; Δ15NAIM-muscle = +1.7‰, Δ13CAIM-muscle = +0.3‰ for the adductor muscle) were determined. Our data suggest that the Gumelnița mussels were omnivorous, with a similar trophic level to carp and pond turtles, sourced from diverse water bodies (rivers, lakes ...) based on δ13C values. [ABSTRACT FROM AUTHOR]

Microplastics have been found in freshwater systems, and in turn have been detected in freshwater bivalves. However, there is limited research that defines the toxicity of bicroplastics to native freshwater bivalves that have long been imperiled in North America. Our objective was to determine whether a suite of pristine microplastics has an adverse effect on two early life stages of unionid freshwater mussels. Glochidia of Lampsilis fasciola (a Canadian species at risk) and Lampsilis siliquoidea (widespread across Canada) were individually exposed to spheres of polystyrene (6 and 90 μm), polyethylene (28, 90, and 1000 μm), and cellulose acetate (1000 μm), as well as fibers of polyethylene terephthalate (60 μm). After 24 h, there was no significant decrease in glochidia viability in either species. Juvenile L. siliquoidea mussels were also exposed to spheres of polystyrene (6 and 90 μm) and polyethylene (28 μm), and fibers of polyethylene terephthalate (60 μm) in individual 28‐day subchronic tests followed by a 7‐day depuration period. Burial was assessed weekly, and ingestion of each microplastic was compared in nondepurated and depurated mussels. There was no sustained effect on juvenile burial with any microplastic tested. Ingestion of microplastics was concentration dependent, and depuration occurred for all particles and size ranges tested. The results suggest that pristine microplastics were not acutely toxic to the early life stages of these freshwater mussels, but that the energetic costs associated with particle uptake and depuration, which were not measured in our study, may have an impact on fitness that warrants further investigation. In addition, testing with other shapes and polymers of microplastics typically detected in the environment is recommended. Environ Toxicol Chem 2024;43:2557–2568. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The study extended over 60 days to assess the impact of extractive species on improving water quality and enhancing GIFT fish production performance within the FIMTA system. Prior to initiating the experiment, the extraction capacities of both organic and inorganic extractives were assessed. Subsequently, based on these evaluations, GIFT fish were co-cultured with freshwater mussels and aquatic macrophytes as organic and inorganic extractive agents, respectively, within 1000 L FRP tanks. Three treatment combinations were established: GIFT fish with Lemna minor (T1), GIFT fish with Lamellidens marginalis (T2), and GIFT fish with both L. minor and L. marginalis (T3). The control treatment (C) consisted solely of GIFT fish. GIFT fish were stocked at a density of 40 m−2, while L. marginalis at 250 g per tank and L. minor covering 25% of the tank surface. GIFT fish were fed with floating commercial pelleted feed at 4% of body weight (30% CP). The results indicated that among the water quality parameters, chlorophyll a, dissolved solids, and suspended solids showed a reduction in T3. The control group exhibited elevated levels of BOD and COD, whereas the treatment groups showed significantly lower levels. Furthermore, the control group demonstrated increased conductivity levels, while T3 exhibited the lowest levels. In T3, a significant reduction was observed in both POM and POC. Growth variables like SGR and PWG were found to be highest in T3. Regarding enzyme activity, the control group exhibited lower levels of protease, lipase, and amylase, while the highest levels were observed in T3. Physiological enzyme activities such as LDH, MDH, ALP, and ACP were significantly increased (p < 0.05) in the control system, indicating elevated water pollution levels. Meanwhile, bacterial load was found to be very low in the FIMTA system (T3). These findings suggest that the integration of GIFT with L. minor and L. marginalis in the FIMTA system has the potential to enhance water quality and physiological responses, ultimately contributing to higher yields. [ABSTRACT FROM AUTHOR]

Freshwater mussels of the tribe Gonideini (Bivalvia: Unionidae: Gonideinae) constitute one of the most taxonomically diverse groups and serve as keystone species in riverine and lacustrine ecosystems across East Asia. A new genus and species of Gonideini (Bivalvia: Unionidae) is described from Jiangxi, China, as Pseudopostolata angula gen. et sp. nov. based on an integrative analysis of shell morphology and molecular data. The validity of the new genus and species is supported by distinct conchological features: a short, rounded anterior; a long, wide posterior; a slightly downward-curved dorsal margin; and a distinctly obtuse angle at the center of the posterior margin. The multi-locus (COI + 16S rRNA + 28S rRNA) phylogeny showed that the species formed a monophyletic group in the tribe Gonideini of the subfamily Gonideinae. Pseudopostolata angula gen. et sp. nov. is identified as the sister group to a clade comprising the genera Postolata, Cosmopseudodon, Obovalis, Ptychorhynchus, Parvasolenaia, and Koreosolenaia. We emphasize the significant morphological convergence in freshwater mussels, particularly within Gonideini, highlighting the necessity of an integrated taxonomic approach for accurate generic classification of this group. [ABSTRACT FROM AUTHOR]

Two new genera and three new species of freshwater mussels in the tribe Pseudodontini (Bivalvia, Unionidae) are described from the Mekong Basin in Thailand based on an integrative taxonomic study involving morphology and multi-locus phylogenetic analyses (mitochondrial COI and 16S, and nuclear 28S genes). The monotypic genus, Lannanaia kokensis gen. et sp. nov., presents unique features of being rather compressed, sub-trigonal in outline with short and high shell, and with a distinct posterior wing. Another new genus, Isannaia gen. nov., is characterized by having a thin and moderately inflated shell, with rhomboidal to ovate outline. It includes two lineages that are genetically separated by 3.54% uncorrected COI p-distance, and are herein described as I. fortunata sp. nov. and I. occultata sp. nov. Phylogenetic analyses further revealed that these two new genera were nested within a clade of subtribe Pseudodontina, and with pairwise uncorrected COI p-distance to other genera ranging from 11.42 to 15.66%. Based on the present data, Lannanaia gen. nov. is known only from the Kok River in the north of Thailand, whereas the two species of Isannaia gen. nov. are restricted to tributaries of the Mekong River in the northeast of Thailand. The discovery of rare and probably endemic freshwater mussels in the Mekong Basin thus again highlights the importance of this region among freshwater biodiversity hotspots of the world. [ABSTRACT FROM AUTHOR]

The Pearl River Basin, China's second-largest freshwater basin, hosts a significant diversity of species and a highly endemic freshwater mussel fauna. In this study, a new species from the Liuxi River in Guangzhou, Guangdong, China, Pletholophus guangzhouensis sp. nov., is described based on morphological diagnostic features and molecular phylogenetics. The glochidia shells of the new species are subtriangular, medium-sized, and have a styliform hook on the ventral angle of each valve. Phylogenetic analyses based on the COI and 28S rRNA gene fragments indicated that Pletholophus guangzhouensis sp. nov. is the sister to Pletholophus tenuis + Pletholophus reinianus. The pairwise uncorrected COI p-distance analysis demonstrated genetic distances ranging from 5.27% (between P. guangzhouensis sp. nov. and P. tenuis) to 11.06% (between P. guangzhouensis sp. nov. and P. honglinhensis). Our findings suggest a significant underestimation of the diversity of freshwater mussel species in Guangdong. Further field collections and systematic studies are necessary to fully explore the biodiversity of this region. Furthermore, integrative classification methods and genetic research are essential for informing the development of effective conservation strategies. [ABSTRACT FROM AUTHOR]

Native freshwater mussel (Unionidae) mortality events have been occurring with increased frequency in recent decades, with few investigations into potential etiological agents. In the western United States, no surveys have been published regarding the bacteria associated with unionid mussels. Herein, we examine locations of known mussel mortality events in the Chehalis River (Washington), in the Crooked River (Oregon), and Owyhee River (Oregon). Mussel populations considered healthy were sampled in the Skookumchuck River (Washington) for comparison. A variety of bacteria were isolated from these populations, and most notably, Acinetobacter spp. were identified from 82% of moribund individuals of Gonidea angulata in the Owyhee River. Future work evaluating whether Acinetobacter spp. are pathogenic to freshwater mussels could be valuable in unraveling the factors associated with these enigmatic mortality events. [ABSTRACT FROM AUTHOR]

The rise in human population has led to the expansion of settlements and an increase in the types and amounts of wastes released into the aquatic environment. Bivalves have an important place among the invertebrate communities of freshwater environments. Mussels remove suspended substances from the water and contribute significantly to the regulation of the physical properties of water. This study was conducted to determine the microbiome load in the intestinal tissue of the freshwater mussel Unio stevenianus (Bivalvia: Unionidae) living in Karasu River. Amplification of the V3–V4 region of the bacterial 16S rRNA gene fragment was performed in tissue samples. Bacterial species were divided into operational taxonomic units using the Kraken metagenomics program. The percentage bacterial distribution with the highest reading sequence at the phylum level was determined as Bacteroidota > Bacillota > Pseudomonadota > Actinomycetota > Cyanobacteriota > Campylobacterota in Arısu samples; while in Zeve samples, it was determined as Pseudomonadota > Actinomycetota > Bacillota > Bacteroidota > Cyanobacteriota > Campylobacterota. The detection of various bacterial phylum indicates that the water environment in which the mussel samples were collected is exposed to a large number of bacterial sources, especially domestic waste. The continued existence of freshwater mussels is necessary for them to fulfill their important duties in the ecosystem. To achieve this, uncontrolled and untreated waste discharges should be abandoned. Pollutants in the water and mussel populations should also be monitored through a monitoring program. [ABSTRACT FROM AUTHOR]

The stream benthic substrate is associated with ecosystem functioning and provides important habitat for a multitude of organisms from microbes to larger macrofauna. Microbially mediated biogeochemical transformations are critical ecological processes that occur within benthic sediments. Benthic macrofauna, such as freshwater mussels (Bivalvia: Unionoida), can influence these processes by chemically and physically altering the stream substrate, consequently altering redox conditions and the sediment microbial community. However, few studies have investigated the interactions between burrowing macrofauna, benthic nutrient fluxes, and the associated microbial communities in freshwater substrata. We used a mesocosm experiment to investigate how mussels physically (via bioturbation) and chemically (via excretion and egestion) influence sediment–water nutrient fluxes and sediment bacterial community composition. Because many microbially mediated N-transforming pathways can be stimulated by mussel-derived nutrient inputs (excreted NH4+ or organic matter biodeposits) or altered by bioturbation, we predicted that mussels would enhance sediment N-removal potentials and alter the sediment microbial community structure, but that these effects would be mediated by mussel species identity and functional traits. Overall, the presence of mussels enhanced N-removal and modified sediment bacteria community composition and structure. The differences across mussel treatments in sediment N-removal potentials and alpha diversity of bacterial communities suggest that mussel species identity and assemblage composition play a critical role at the benthic–water-column interface in streams. Given the current declines in mussel species richness and abundance, a better understanding of the functional effects of mussel species and assemblage composition is critical to predicting changes in the functioning of stream ecosystems. [ABSTRACT FROM AUTHOR]

Objective: Freshwater mussels of the order Unionoida are among the most imperiled taxa in North America, and many species are undergoing enigmatic decline without fully understood causation. Disease pathology and parasitology have been identified as areas with significant knowledge gaps in relation to these declines. We investigated a shell deformity of unknown cause that is widespread in northeastern North America by adding to the clinical description from a mussel assemblage in Massachusetts with a deformity prevalence exceeding 50%. We build upon previous qualitative descriptions of this deformity with investigations of shell morphology and mussel age. Methods: We conducted a qualitative survey of the mussel community to evaluate the prevalence of deformity. Mussels were classified as deformed based on the presence of a distinct truncation of the posterior margin of the shell. For the eastern elliptio Elliptio complanata, we evaluated the shell height, shell length, and height : length ratio of animals classified as deformed versus normal and we conducted a comparison to a reference population. We also incorporated shell thin sectioning and aging to qualitatively describe the deformity in cross section and to compare age distributions between deformed and normal eastern elliptio. Result: We observed the presence of this deformity in four species, including the eastern elliptio, eastern lampmussel Lampsilis radiata, eastern pearlshell Margaritifera margaritifera, and creeper Strophitus undulatus. In cross section, the deformity appeared to be caused by repeated disturbance in growth in the posterior portion of the shell. Deformed eastern elliptio had markedly shorter shells for a given shell height when compared to normal and reference mussels, and they tended to be older at shorter shell lengths than normal mussels from the same site. Conclusion: The cause of the shell deformity in the United States remains unknown, although it appears similar in description to the deformity caused by a commensal midge, Xenochironomus canterburyensis, which infects a distantly related freshwater mussel in New Zealand. We highlight potential causes and the need for further investigation. Impact StatementFreshwater mussels in the order Unionoida are among the most imperiled taxa in North America; pathogens, parasites, and environmental contaminants are among several potential causes of endangerment. Our work adds to the description of a deformity observed in mussels from northeastern North America and outlines a potential parasitic cause evidenced from across the globe. [ABSTRACT FROM AUTHOR]

Asexual taxa are often considered as rare and vowed to long-term extinction, notably because of their reduced ability for rapid genetic changes and potential adaptation. The rate at which they derive from sexual ancestors and their developmental mode however influence genetic variation in asexual populations. Understanding the transition from sexuality to asexuality is therefore important to infer the evolutionary outcome of asexual taxa. The present work explored the transition from sexuality to androgenesis, a reproductive mode in which the males use female resources to clone themselves, in the freshwater Corbicula clams. Since androgenetic lineages are distinguishable from sexual clams by the production of unreduced sperm, this study investigated the cytological mechanisms underlying spermatogenesis in Corbicula by following the DNA content variation of male germ cells. The widespread androgenetic C. sp. form A/R lineage was compared to the sexual species C. japonica and C. sandai. While in C. japonica, the last stages of spermatogenesis are reduced through a canonical meiosis process, no reduced or duplicated stages were observed in C. sp. form A/R, suggesting a meiosis modification in this lineage. However, 45% of C. sandai spermatozoa were unreduced. The production of unreduced sperm may condition or provide the potential for the emergence of androgenesis in this sexual species. Being closely related to androgenetic lineages and found in sympatry with them in Lake Biwa (Japan), C. sandai might be an origin of androgenetic lineage emergence, or even an origin of the androgenetic reproductive mode in Corbicula. [ABSTRACT FROM AUTHOR]

Centuries of beaver extirpation, deforestation, and other anthropogenic impacts have disconnected North American rivers from their floodplains and concentrated more hydraulic energy within their channels, degrading aquatic habitat and making the streambed more prone to erosion. Rivers naturally adjust via systematic downcutting, bank erosion, channel widening, bar building, and the gradual recovery of geomorphic equilibrium with well‐connected benches that dissipate hydraulic energy and restore a more natural streambed disturbance regime. The life histories of two endangered freshwater mussels, the fanshell (Cyprogenia stegaria) and snuffbox (Epioblasma triquetra), suggest they have evolved to and depend on the natural disturbance regime. Young juveniles excyst from their host fish in early summer, burrow into the top few millimeters of the streambed, and then need ca. 3 months of streambed stability prior to growing large enough to be less vulnerable to streambed mobilization. We propose a conceptual model that suggests a potential prerequisite to supporting fanshell and snuffbox populations is a geomorphically recovering (i.e. at least one stable bank and a wide enough channel corridor for at least partially vegetated bars/benches) or recovered (i.e. stable banks and vegetated benches) channel and floodplain corridor that sufficiently dissipates its hydraulic energy to maintain seasonal streambed stability during typical (non‐hurricane) summer/autumns. To explore this conceptual model, we conducted mussel and geomorphic surveys in a reach of the Rolling Fork River that spanned a range of channel conditions from chronically failing streambanks to a geomorphically recovered channel with wide, vegetated benches. Our analyses documented increasing mussel species richness, including the presence of the endangered fanshell or snuffbox, with increasing width of seasonally stable streambed habitat. [ABSTRACT FROM AUTHOR]

The coevolutionary dynamic of host–parasite associations varies from strictly local adaptations to diffuse guild coevolution. How innate and acquired immune responses modulate host resistance to parasitism and how host specificity and geographic scaling affect the efficacy of host response have consequences for range dynamics and biological invasions.Using reciprocal transplant experiments, we tested whether local or diffuse coevolution shapes host response to parasitism in the host–parasite association between bitterling fishes and larval stages (glochidia) of freshwater mussels from Europe and East Asia.We found that glochidia initially indiscriminately attached to all study host species, but immune responses elicited significant differences in host responses within 24 h of infection, which intensified during glochidial development. European bitterlings were more resistant to European glochidia and Asian bitterlings to Asian glochidia, with the strongest geographic bias in resistance in the Asian bitterling hosts.This finding suggests a strong effect of local adaptation but also indicates the non‐negligible role of coevolutionary hotspots. Low natural glochidia load on bitterling species overall hence arise from competent immune response rather than glochidia avoidance behaviour. Bitterling immune response is primarily innate and not acquired.Overall, our data demonstrate the complex outcome of parasite pressure on the evolution of host resistance, and important role of geographically structured coevolution in shaping host response. [ABSTRACT FROM AUTHOR]

Niche partitioning promotes species coexistence. Yet, it remains unclear how phylogeny and morphology influence the trophic niches of closely related aquatic species with shared feeding modes. Freshwater mussels (Family: Unionidae) are a group of filter‐feeding bivalves that are ideal for investigating mechanisms of niche partitioning. Particle size selection and patterns of ingestion are controlled by gill latero‐frontal cirri density (CD) and the number of cilia per cirrus (CC). We investigated trophic assimilation and niche area using stable isotope signatures (훿13C and 훿15N) and gill morphology with scanning‐electron microscopy for a diverse mussel assemblage from the Sipsey River, Alabama, USA. We predicted that (1) trophic niches and gill morphology would differ within and among species across sites; (2) co‐occurring species would partition food resources; (3) greater phylogenetic distances among species would result in increased trophic dissimilarity; (4) more CC and higher CD would result in a narrower trophic niche area, or more constrained range of food items assimilated. We found that (1) species identity and site influenced gill morphology and stable isotope signatures but that the trophic niche area of a species was only affected by species identity; (2) the average proportion of niche area overlap between co‐occurring species was low across sites (0.04 to 0.18); (3) trophic dissimilarity among species increased with phylogenetic distance; (4) CD but not the number of CC negatively related to trophic niche area. Our results indicate that gill morphology and evolutionary history are likely key factors governing the trophic niches of mussels. In addition, intraspecific variation in gill morphology across sites may either reflect a phenotypic response to differences in local resource availability or suggest that other mechanisms shape particle selection. Examining the interplay among the trophic niche, phylogeny, and morphology among functionally similar species further informs our understanding of the mechanisms facilitating their coexistence. [ABSTRACT FROM AUTHOR]

The presence of sub-micron-sized plastics in the environment has been increasing, with the possible risks of these particles remaining relatively unknown. In order to assess the toxicity of these particles, 100 nm diameter green fluorescent nano-polystyrene spheres (NPS) (20–60 mg/L) were exposed to zebra mussels (Dreissena polymorpha) to investigate the mortality, clearance rate and stress-related biomarker responses. D. polymorpha were collected and analysed with standard OECD toxicological tests and biomarker analysis to detect both physical and biochemical responses after exposure to NPS. The toxicity of the NPS to D. polymorpha was low, with 60 mg/L NPS causing a mortality rate of 11.1% at 96 h which was statistically significant compared to the 4.2% control. No statistical change could be found for the condition factor (kc) of D. polymorpha after NPS exposure. Clearance rates in D. polymorpha using R. subcapitata algae showed NPS-exposed mussels had a reduction of filtering efficiency of up to 30.5%. Bioassay testing shows a mixed but undeniably negative response from the D. polymorpha to the NPS, notably a significant rise in DNA Strand Breaks (DSB) and Metallothionein (MT) responses for high NPS concentrations. Additionally, Lipid Peroxidation (LPO) and Ferric Reducing Antioxidant Power (FRAP) assay tests showed a significant increase in response from the higher (>40 mg/L) concentrations of NPS exposure. Although Glutathione S-Transferase (GST) assay showed no statistical change from the control for all NPS-exposed samples, an increase of 20% had occurred for 60 mg/L NPS. Overall, a minimal toxic response from D. polymorpha to the NPS exposure below 40 mg/L was seen. After 40 mg/L NPS, mussels presented more acute toxicity in terms of mortality, along with reduced algal clearance rates and anincrease in biomarker response. This study revealed a clear induction of oxidative stress and DSB in the digestive gland of zebra mussels following exposure to nano-polystyrene. While these findings provide valuable insights into the potential harmful effects of nanoplastics in freshwater bivalves, further studies are necessary to help understand the level of threat plastic pollution may pose to the health of freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Freshwater mussels are a globally threatened taxon, but little is known about population trajectories for species outside Europe and North America. To contribute to understanding of mussel conservation status outside these regions, we surveyed mussel and other invertebrate populations in waterbodies across Dhaka, Bangladesh, to assess population trends and the role of mussels in structuring benthic communities.We found that mussel populations in Dhanmondi Lake, our focal waterbody, have declined in density by approximately 90% between 2010 and 2023. Lamellidens marginalis declined by 90.8% from an average density of 47.9 ± SE 7.1 mussels 0.25 m−2 in 2010 to 4.4 ± SE 0.7 mussels 0.25 m−2 in 2023, while Indonaia caerulea declined by 89.4% from an average density of 6.6 ± SE 1.0 mussels 0.25 m−2 in 2010 to 0.7 ± SE 0.1 mussels 0.25 m−2 in 2023.Previously detected associations between mussels and other invertebrate taxa, and between mussels and community composition, have been lost. Non‐mussel invertebrates have also declined significantly, with an average decrease in abundance of 27%, alongside decreases in family richness and Shannon‐Wiener diversity. These declines occurred despite apparent improvements in water quality.Findings from other waterbodies across Dhaka also suggest the loss of mussel species including L. marginalis, I. caerulea and Parreysia corrugata from some locations, as well as the presence of the non‐native mussel Pilsbryoconcha exilis at river sites.Our results reflect a wider, global pattern of enigmatic declines in freshwater mussels and the possible loss of associated ecosystem functioning, which may be going unnoticed in less‐studied areas including the subtropics. [ABSTRACT FROM AUTHOR]

Sulfate is increasingly found in elevated concentrations in freshwater ecosystems due to anthropogenic activities. Chronic exposure to sulfate has been reported to cause sublethal effects on freshwater invertebrates. Previous sulfate toxicity tests have mostly been conducted in hard or moderately hard waters, and research on species inhabiting soft water is needed, given that freshwater organisms face heightened sensitivity to toxicants in water of lower hardness. In the present study, we examined sulfate sensitivity of two endangered freshwater mussel species, Unio crassus, and Margaritifera margaritifera. Glochidia and juveniles of both species were subjected to acute and/or chronic sulfate exposures in soft water to compare sulfate sensitivity across age groups, and effective concentrations (EC)/lethal concentrations (LC) values were estimated. Mussels were individually exposed to allow relatively larger numbers of replicates per treatment. Chronic sulfate exposure significantly reduced growth, foot movement, and relative water content (RWC) in juvenile mussels of M. margaritifera. Mussels at younger stages were not necessarily more sensitive to sulfate. In the acute tests, LC50 of glochidia of M. margaritifera and U. crassus was 1301 and 857 mg/L, respectively. Chronic LC10 was 843 mg/L for 3-week-old U. crassus juveniles, 1051 mg/L for 7-week-old M. margaritifera juveniles, and 683 mg/L for 2-year-old M. margaritifera juveniles. True chronic Lowest Effective Concentration for 7-week-old M. margaritifera may be within the 95% interval of EC10 based on RWC (EC10 = 446 mg/L, 95%CI = 265–626 mg/L). Our study contributed to the understanding of sulfate toxicity to endangered freshwater mussel species in soft water. [ABSTRACT FROM AUTHOR]

The Host-Habitat Continuum Concept (HHCC) predicts changes in the proportions of freshwater mussels with different life-history strategies (i.e., equilibrium, periodic, opportunistic) along stream gradients and between habitat types. We analyzed mussel assemblages from a large, diverse geographic area to test predictions of the HHCC and to assess if species richness, abundance, and host strategy patterns change predictably among different habitats (lakes, reservoirs, and streams) and stream sizes. Species richness and abundance were low in lakes, reservoirs, and small streams and increased with stream size. Mussels use various strategies to attract fish hosts and the proportion of mussels that release conglutinates (i.e., packets of glochida) increased with stream size and the proportion that use lures decreased. Our results supported predictions of the HHCC: greater proportions of opportunistic or periodic strategists in lakes, reservoirs, and small streams and a shift to equilibrium strategists in larger streams. Patterns differed slightly in lakes and reservoirs with a higher proportion of periodic strategists than expected. Not all watersheds followed predictions of the HHCC likely due to the effects of biogeography and anthropogenic impacts. These life history strategy patterns can be used to test the expected composition of mussel communities and to detect possible anthropogenic impacts. [ABSTRACT FROM AUTHOR]

(1) Mercury (Hg) is a persistent, ubiquitous contaminant that readily biomagnifies into higher trophic level species in aquatic environments across the globe. It is crucial to understand the movement of environmentally relevant concentrations of Hg in impacted freshwater streams to minimize risks to ecological and human health. (2) The bioconcentration kinetics of aqueous Hg exposure (20, 100, and 200 ng/L) in the invasive Asian Clam, Corbicula fluminea, were measured. A toxicokinetic model, the first parameterized for Hg accumulation in freshwater clams, was developed to estimate uptake and efflux parameters and compared to previous parameter values estimated for other mollusk species. (3) Results demonstrated that even at low Hg concentrations, Corbicula record signals of contamination through bioconcentration, and both direct measurement and toxicokinetic models demonstrate large Hg bioconcentration factors (as high as 1.34 × 105 mL/g dry tissue), similar to partitioning coefficients seen in engineered Hg sorbents. (4) Our study found that Corbicula accumulated Hg at aqueous concentrations relevant to impacted streams, but well below regulatory drinking water limits, demonstrating their utility as a sensitive sentinel species and potential bioremediator. [ABSTRACT FROM AUTHOR]

Understanding the age structure and growth patterns of freshwater bivalve species is crucial for their conservation, and these data are still lacking for many species and locations. The main objective of this study was to gain insight into the age structure and growth patterns of the endangered mussel Unio crassus at the unpolluted and polluted sites on the Mrežnica River (Croatia), as well as construct the first-ever chronology for this species. Bivalve sampling was carried out in July 2020. The age and growth dynamics were determined by analysing internal growth lines in acetate peel replicas of shell cross sections. The length range of shells from the unpolluted station was 4.5–5.6 cm, with an estimated age range of 10 to 29 years, whereas shell length at the polluted site was 5.2–6.1 cm, with an estimated age range of 10 to 22 years. Our results indicate that industrial pollution may influence life strategies in U. crassus populations, with mussels growing faster and living shorter at polluted site. Compared to other parts of Europe, the estimated ages obtained in our study were the most similar to those in central Europe. According to growth curves, mussels grow the fastest during their first 10 years, after which their growth significantly slows down. Growth chronologies were constructed by measuring growth increments in acetate peels of shell cross-section, and some correlations between shell growth and environmental parameters have been observed, indicating the potential for further sclerochronology research on this species. [ABSTRACT FROM AUTHOR]