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We identified 14 emerging and poorly understood threats and opportunities for addressing the global conservation of freshwater mussels over the next decade. A panel of 17 researchers and stakeholders from six continents submitted a total of 56 topics that were ranked and prioritized using a consensus‐building Delphi technique. Our 14 priority topics fell into five broad themes (autecology, population dynamics, global stressors, global diversity, and ecosystem services) and included understanding diets throughout mussel life history; identifying the drivers of population declines; defining metrics for quantifying mussel health; assessing the role of predators, parasites, and disease; informed guidance on the risks and opportunities for captive breeding and translocations; the loss of mussel–fish co‐evolutionary relationships; assessing the effects of increasing surface water changes; understanding the effects of sand and aggregate mining; understanding the effects of drug pollution and other emerging contaminants such as nanomaterials; appreciating the threats and opportunities arising from river restoration; conserving understudied hotspots by building local capacity through the principles of decolonization; identifying appropriate taxonomic units for conservation; improved quantification of the ecosystem services provided by mussels; and understanding how many mussels are enough to provide these services. Solutions for addressing the topics ranged from ecological studies to technological advances and socio‐political engagement. Prioritization of our topics can help to drive a proactive approach to the conservation of this declining group which provides a multitude of important ecosystem services. [ABSTRACT FROM AUTHOR]

Contaminants of emerging concern pose a serious hazard to aquatic wildlife, especially freshwater mussels. The growing number of contaminants in aquatic systems requires scientists and managers to prioritize contaminants that are most likely to elicit a biological response for further monitoring and toxicological testing. The objectives of this study were to identify a sub-category of contaminants most likely to affect Pyganodon grandis and to describe alterations in metabolites and gene expression between various sites. Mussels were deployed in cages for two weeks at four sites along the Maumee River Basin, Ohio, USA. Water samples were analyzed for the presence of 220 contaminants. Hemolymph samples were collected for metabolomics and analyzed using mass spectrometry. Contaminants that significantly covaried with metabolites were identified using partial least-squares (PLS) regression. Tissue samples were collected for transcriptomics, RNA was sequenced using an Illumina HiSeq 2500, and differential expression analysis was performed on assembled transcripts. Of the 220 targeted contaminants, 69 were detected in at least one water sample. Of the 186 metabolites detected in mussel hemolymph, 43 showed significant differences between the four sites. The PLS model identified 44 contaminants that significantly covaried with changes in metabolites. A total of 296 transcripts were differentially expressed between two or more sites, 107 received BLAST hits, and 52 were annotated and assigned to one or more Gene Ontology domains. Our analyses reveal the contaminants that significantly covaried with changes in metabolites and are most likely to negatively impact freshwater mussel health and contribute to ongoing population declines in this group of highly endangered animals. Our integration of "omics" technologies provides a broad and in-depth assessment of the short-term effects of contaminants on organismal physiology. Our findings highlight which contaminants are most likely to be causing these changes and should be prioritized for more extensive toxicological testing. [ABSTRACT FROM AUTHOR]

Freshwater mussels are typically considered to be primarily filter-feeders with an ability to pedal feed, however there is limited information regarding interspecific differences in food resources and feeding modes. The objective of this study was to investigate interspecific variation in food resource usage among mussels in a lentic system associated with a reservoir drawdown. We quantified carbon-13 and nitrogen-15 isotopic signatures for three mussel species, including a Federally Threatened species, and their potential food resources in Gantt Lake, Alabama, USA. For all species, carbon-13 derived from limnetic, benthic fine particulate organic matter (FPOM) contributed on average 99% to the mussel diet. Paradoxically, mussels collected from the littoral zone relied primarily on food resources from the limnetic zone, although this spatial disconnect may have been an artifact of the sampling regime. Carbon-13 associated with littoral FPOM, limnetic and littoral suspended particulate organic matter (SPOM) and coarse particulate organic matter (CPOM) contributed < 1%. Elliptio pullata (Lea, Proceedings of the Academy of Natural Science 8: 262, 1856) collected live but emersed for 8 weeks were enriched in nitrogen-15, providing evidence of catabolism during emersion. Results suggest that benthic sources can be a dominant food resource for unionids and that stranded unionids rely on internal energy stores to survive emersion. [ABSTRACT FROM AUTHOR]

Fipronil is widely used against insects in agriculture and ectoparasites in domestic areas and veterinary medicine. However, fipronil may influence non-target species as a result of the contamination of aquatic ecosystems. The present study aimed to investigate the acute and sublethal effects of fipronil in freshwater mussels (Unio delicatus), a non-target species, with physiological, antioxidant action mechanisms and histopathological observations. The 96-h LC50 value of fipronil was found to be 2.64 (1.45–4.56) mg/L. Sublethal concentrations were applied at 1/10 and 1/5 of 96-h LC50 as 0.264 mg/L and 0.528 mg/L for 48-h and 7-d. Haemolymph samples, digestive gland and gill tissues of mussels were taken after exposure times. While the Total Haemocyte Counts decreased in 48-h of exposure, it was only high at 0.264 mg/L fipronil-exposed for 7-d (p < 0.05). While glutathione values in digestive glands and gills were higher in the fipronil applied groups (p < 0.05), the AOPP values were only higher in the digestive glands at 7-d of exposure (p < 0.05). Moreover, fipronil caused histopathological alterations on gills and digestive glands. These things considered, the principal component analysis revealed that the most pronounced changes in the antioxidant action mechanisms were caused by the fipronil exposure. These results show that sublethal concentrations of fipronil are toxic to freshwater mussels. [ABSTRACT FROM AUTHOR]

Limnoperna fortunei, a problematic freshwater invasive mussel in South America, was first detected in 1991 at Bagliardi Beach, Río de la Plata (Argentina). Since then, there has been a high increase in population density, reaching up to 150,000 ind. m−2. The distribution, density, individual sizes, and associated mollusk assemblages of L. fortunei were evaluated 30 years after its first detection. Seven sites along Río de la Plata River were sampled between 2018 and 2020. The highest density was recorded in the La Balandra Beach (above the stabilization value) and the lowest density in the Martín García Island (IMG—by its acronym in Spanish—, below the stabilization value). Two reproductive events were observed: late spring and late summer. Our results showed different sets of species associated with Limnoperna fortunei, with protected areas such as the IMG standing out, showing greater species richness, including first records, versus other coastal environments. We recommend increasing conservation efforts given the constant advance of urbanization in the coastal sites of the province of Buenos Aires, with environmental impact studies prior to coastal reforms, and implementation of density control strategies for Limnoperna fortunei in protected areas. [ABSTRACT FROM AUTHOR]

Southern Thailand represents a region of unique freshwater biodiversity with many endemic taxa, including a number of freshwater mussel species (Bivalvia: Unionidae). In this study, we recognize 13 taxa in the tribes Contradentini, Rectidentini, Pseudodontini (subfamily Gonideinae), and Indochinellini (subfamily Parreysiinae) that inhabit different localities in the Songkhla Lake, Tapi River, and Tha Taphao River basins. Based on the results of morphological and phylogenetic analyses, we discovered among these mussels six taxa new to science, including one genus, three species, and two subspecies. New taxonomic names are introduced here as follows: Songkhlanaiagen. nov.; S. tamodienicagen. & sp. nov.; Sundadontina plugpomenicasp. nov.; Monodontina vondembuschiana tapienicassp. nov.; M. vondembuschiana thasaenicassp. nov. (Pseudodontini); and Trapezoideus thachiadensissp. nov. (Contradentini). These new taxa confirm the high conservation priority of the Southern Thai freshwater mussel fauna. [ABSTRACT FROM AUTHOR]

A pioneering, quantitative study published in Journal of Animal Ecology in 1966 on freshwater mussel populations in the River Thames, UK, continues to be cited extensively as evidence of the major contribution that mussels make to benthic biomass and ecosystem functioning in global river ecosystems.Ecological alteration, as well as declines in freshwater mussel populations elsewhere, suggest that changes to mussel populations in the River Thames are likely to have occurred over the half century since this study.We resurveyed the site reported in Negus (1966) and quantified the changes in mussel population density, species composition, growth patterns and productivity.We found large declines in population density for all unionid species. The duck mussel Anodonta anatina decreased to 1.1% of 1964 density. The painter's mussel Unio pictorum fell to 3.2% of 1964 density. The swollen river mussel Unio tumidus showed statistically nonsignificant declines. In contrast to 1964, in 2020 we found no living specimens of the depressed river mussel Pseudanodonta complanata (classified as Vulnerable by the IUCN Red List) but found new records of the invasive, nonnative zebra mussel Dreissena polymorpha and Asian clam Corbicula fluminea. Additionally, we found strong decreases in size‐at‐age for all species, which now grow to 65–90% of maximum lengths in 1964. As a result of reduced density and size, estimated annual biomass production fell to 7.5% of 1964 levels.Since mussels can be important to ecosystem functioning, providing key regulating and provisioning services, the declines we found imply substantial degradation of freshwater ecosystem services in the River Thames, one of the UK's largest rivers. Our study also highlights the importance to conservationists and ecologists of updating and validating assumptions and data about wild populations, which in the present era of anthropogenic ecosystem alteration are undergoing significant and rapid changes. Regular population surveys of key species are essential to maintain an accurate picture of ecosystem health and to guide management. [ABSTRACT FROM AUTHOR]

Copper is a water and sediment pollutant that can be biomagnified by phytoplankton, and it often co‐occurs with fecal bacteria. We addressed the combined effects of copper and Escherichia coli on the immune response and gill oxidative balance of the freshwater mussel Diplodon chilensis. Bivalves were sorted into four groups fed with 1) control algae, 2) bacteria (E. coli), 3) copper‐enriched algae (Cu2+) algae, and 4) copper‐enriched algae followed by bacteria (Cu2+ + E. coli). Cellular and humoral immune and cytotoxic variables were analyzed in hemolymph, and detoxifying/antioxidant enzyme activities (glutathione S‐transferase [GST] and catalase [CAT]) and lipid peroxidation (thiobarbituric acid reactive substances [TBARS]) were studied in gill tissue. The total hemocyte number increased after Cu2+ exposure, independently of the E. coli challenge. The proportion of hyalinocytes significantly diminished in the E. coli and Cu2+ groups but not in Cu2+ + E. coli groups; granulocytes significantly increased with E. coli but not with Cu2+ + E. coli treatments. Phagocytic activity was higher in all treatments than in control mussels. Acid phosphatase activity was increased by E. coli and inhibited by Cu2+ and Cu2+ + E. coli. Both E. coli and Cu2+ but not Cu2+ + E. coli augmented alkaline phosphatase activity. The Cu2+ and Cu2+ + E. coli treatments reduced the lysosomal membrane stability and cell viability. Humoral bacteriolytic and phenol oxidase activities were not affected by any treatment. The Cu2+ treatment induced gill CAT and GST activities and increased TBARS levels. The Cu2+ + E. coli treatment reversed this CAT and GST stimulation and increased the Cu2+ effect on TBARS. Dietary Cu2+ affects bivalves' immunological and oxidative status and impairs defensive responses against bacteria. In turn, E. coli potentiates the gill oxidative effects of Cu2+. Environ Toxicol Chem 2023;42:154–165. © 2022 SETAC [ABSTRACT FROM AUTHOR]

Freshwater mussels belonging to the genus Cristaria Schumacher, 1817 (Bivalvia: Unionidae) are widespread from Mongolia to Indochina while the range of one species, C. plicata (Leach, 1814), covers two biogeographic subregions, i.e., East Asian (Amur River to Vietnam) and Sundaland (Mekong River basin). We present here a taxonomic revision of the nominal taxon Anodonta bellua Morelet, 1866 which was described from the Mekong (Lake Tonle-Sap, Cambodia) but is currently considered a synonym of C. plicata. We obtained molecular data for newly collected Cristaria representatives from the Mekong's tributaries in Laos, which were found as a divergent species-level phylogenetic clade within the genus that is distant from C. plicata. Nevertheless, comparative morphological and morphometric studies did not reveal any significant differences between these two congeners. Our time-calibrated biogeographic modeling reveals that the split between Cristaria bellua (Mekong) and C. clessini (East Asia) probably occurred in the mid-Miocene (15.8 Ma) and may reflect an ancient stream capture between the Mekong Basin and East Asian rivers. [ABSTRACT FROM AUTHOR]

The Purple Wartyback (Cyclonaias tuberculata) is a long-lived species of freshwater mussel currently found in three watersheds in Canada from lower Lake Huron through Lake St. Clair. The species was assessed by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) in May 2021 as Threatened, owing to a small number of extant locations and a continuing decline of habitat quality throughout its range. The species is considered extirpated from two historical locations. The Recovery Potential Assessment provides background information and scientific advice needed to fulfill various requirements of the Species at Risk Act (SARA). This research document provides the current state of knowledge on the species including its biology, distribution, population trends, habitat requirements, and threats. Purple Wartyback is a short-term brooder that is thought to use North American catfishes (Ictaluridae) as hosts for completing its life cycle. It is found in relatively deep, medium to large rivers with moderate to swift currents and occasionally lentic areas over sand, gravel, and cobble substrates. Long-term standardized sampling data suggest that at least two of the three populations in Canada may be growing; however, more years of data are required to span a full generation of this long-lived species. A threat assessment identified the greatest threats to Purple Wartyback in Canada as pollution from agricultural and urban sources, climate change (notably droughts), aquatic invasive species (including dreissenid mussels and Round Goby (Neogobius melanostomus)), and dredging. Limited information exists evaluating the impacts of these threats on Purple Wartyback specifically. Mitigation measures and alternative activities regarding habitat-related threats are presented. Important knowledge gaps remain surrounding the full extent of its distribution within known watersheds, habitat preferences by life stage, mussel-host interactions, and physiological tolerances to environmental conditions and pollutants. [ABSTRACT FROM AUTHOR]

The Green River in Kentucky in the eastern United States is a freshwater mussel biodiversity hotspot, with 71 known species. Among them, the endangered Pleurobema plenum coexists with other morphologically similar species in the genera Fusconaia and Pleurobema, known colloquially as "pigtoes." Identification of species in these genera is challenging even for mussel experts familiar with them. In our study, the correct identification of these species by experts ranged from 57% to 83%. We delineated taxonomic boundaries among seven species and tested for cryptic biodiversity among these look‐alike mussels utilizing mitochondrial and nuclear DNA sequence variation. Phylogenetic analysis of combined (1215 bp) mitochondrial DNA cytochrome oxidase I (COI) and NADH dehydrogenase 1 (ND1) genes showed five well‐diverged groups that included F. flava, F. subrotunda, P. cordatum, and P. plenum as distinct clades, with P. sintoxia and P. rubrum grouped into a single clade. While our mitochondrial DNA analyses did not distinguish P. sintoxia and P. rubrum as phylogenetically distinct species, the typical shell forms of these two nominal taxa are very distinct. Further phylogenetic analysis using nuclear ribosomal transcribed spacer region subunit I (ITS1) DNA sequences also showed that P. sintoxia and P. rubrum were not distinct lineages. No cryptic species were detected in the Fusconaia and Pleurobema samples analyzed from the Green River. The highest haplotype diversity (h), average number of nucleotide differences (k), and nucleotide diversity (π) were observed for F. subrotunda at both the COI (h = 0.896, k = 3.805, π = 0.00808) and ND1 (h = 0.984, k = 6.595, π = 0.00886) markers, with similarly high genetic diversity in the other taxa. Our results give managers confidence that cryptic taxa do not occur within or among these morphologically similar species in the Green River, and populations appear genetically diverse, indicative of large and healthy populations. [ABSTRACT FROM AUTHOR]

Despite potentially playing a pivotal role in freshwater ecosystems, the Margaritiferidae are one of the most threatened mollusc taxa on the planet. Margaritiferid species are the focus of numerous conservation projects, including ex situ captive breeding programmes that involve exposing host salmonids to glochidial infestation and encystment. Glochidia of margaritiferids parasitise salmonid hosts for long periods of time, and whilst hyper-encystment is known to negatively affect fish, glochidial infection intensities that more closely reflect natural infections are assumed to not have a negative influence on host fitness, as this would ultimately impact the fitness of glochidia. However, experimental investigations of the effect of glochidia on host fitness often produce mixed results, leaving glochidia-fish relationships poorly understood. This study aims to broaden understanding of salmonid behaviour and physiology in response to glochidiosis by conducting a systematic review and meta-analyses of published evidence from glochidia-infected salmonids. The systematic review indicates glochidia infestation can affect salmonid physiology and behaviour, whilst meta-anal- yses indicate glochidia infestation causes increased blood haematocrit but has no relation to fork length, wet mass, Fulton's condition factor, or drift-foraging rate. However, the reliability and predictive value of the meta-analyses are limited by small sample sizes and high heterogeneity, especially in the types of behaviours investigated by different authors. Finally, we recommend key areas and aspects of host behaviour and physiology that need further empirical investigation in order to improve the robustness of our meta-analysis and provide a standardised suite of methodologies to that end. Future investigations can use this approach to "fill in the gaps" and increase the predictive accuracy of the meta-analyses and provide further detail that will hopefully definitively answer the question of the impacts of glochidiosis on salmonid fish. [ABSTRACT FROM AUTHOR]

Bivalves are important components of freshwater ecosystems; however, they are also one of the most threatened animal groups, especially members of the order Unionida. The main threats to freshwater bivalves are habitat modification and invasive species. Protected areas are a common way to minimize impacts and preserve native species, but they are rarely designated with a focus on freshwater invertebrates.The main goal of this article was to describe the distribution of freshwater bivalves in the state of Rio de Janeiro, and the relationship between these species and bioclimatic areas, land use and protected areas.Five native and two invasive bivalve species have been reported in Rio de Janeiro. They occur mainly in bioclimatic areas related to the Paraíba do Sul River and Campista Lowlands. The few records of bivalves inside protected areas are in areas of sustainable use that offer a lower level of protection, and frequently in sympatry with invasive bivalves.Thus, the established protected areas in Rio de Janeiro are not adequately effective for freshwater bivalve conservation, and some species remain under threat even within them. Freshwater bivalves thus remain largely unprotected in the state.The development of new protected areas and management plans should consider other faunal groups that are usually ignored, such as freshwater bivalves, to achieve more inclusive and effective protection. [ABSTRACT FROM AUTHOR]

The quagga mussel Dreissena rostriformis bugensis is an invasive species that has recently spread to western Europe, causing major impacts on aquatic ecosystems and human activities. We considered lakes Lugano and Maggiore (Ticino River basin, Italy and Switzerland) to be at high risk of colonization due to leisure boat traffic from already-colonized lakes. We performed an environmental DNA based survey to detect any quagga mussel invasions in these lakes as early as possible. The results of the survey confirmed the presence of this species in the lakes and support the use of molecular approaches for the early detection of invasive mussels. [ABSTRACT FROM AUTHOR]

To complete their life cycle, freshwater mussels of the order Unionida depend on fishes as hosts for their obligatory parasitic larval phase, the glochidium. Here we report the first documentation of gobioid fishes as hosts of glochidia of unionid mussels in the wild in Italy and in southern Europe (outside of the Danube drainage area). We also examined the pattern of the attached glochidia. A recent review reported 326 fish species as suitable hosts for unionids, but only eight (2.5%) of these were Gobioidei. Host identification and the documentation of their benefits or threats for the interaction of the mussels with their hosts is important for conservation of freshwater mussels. But the co-existence of mussels with non-native fish species is only poorly understood, including the compatibility of these two groups. Knipowitschia panizzae and Pomatoschistuscanestrinii, two translocated sand gobies, were sampled in 2022 at the east shore of Lake Trasimeno (Italy). Two species of anodontine mussels were present at this locality, the native Anodonta anatina and the translocated Sinanodonta woodiana. Genetic data revealed that both sand gobies hosted glochidia only of A. anatina but not of S. woodiana, possibly because of seasonal bias. About 50% of the specimens of both fish species were infested. The paired fins were the most prominent targets. The examined individuals of both sand gobies carried only few glochidia (max. 5). Nevertheless, the two species showed a divergent pattern of glochidia attachment. [ABSTRACT FROM AUTHOR]

Contemporary pharmacological studies have reported that freshwater clam (Corbicula fluminea) can provide a broad spectrum of bioactivities, including antioxidant, anticancer, antihypertensive, hepatoprotective, and hypocholesterolemic effects. The aim of this study was to evaluate the gastroprotective effects of water extract of freshwater clam (WEC) on indomethacin (IND)-induced gastric mucosal cell damage in vitro and gastric ulcer in vivo. The cell viability of rat gastric mucosa RGM-1 cells was markedly decreased by 0.8 mM of IND treatment, and pre-treated with various concentration of WEC significantly restored IND-induced cell damage in a dose-dependent manner. WEC also significantly attenuated the elevated reactive oxygen species (ROS) levels, inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expression, and nuclear factor-κB (NF-κB) p65 nuclear translocation induced by IND. In the in vivo study, IND caused severe gastric ulcer in Wistar rats, while WEC pretreatment effectively reduced the ulcer area and edema in the submucosa. We found that WEC significantly restored glutathione (GSH) content in gastric mucosa in a dose-dependent manner (p < 0.05). The reduction of prostaglandin E2 (PGE2) caused by IND was also improved with higher doses of WEC administration. Moreover, the overexpression of COX-2, iNOS, and tumor necrosis factor-α (TNF-α) proteins in gastric mucosa was downregulated by administration of WEC. Consequently, WEC can be used as a potential nutritional supplement to improve NSAIDs-caused gastric mucosal lesions. [ABSTRACT FROM AUTHOR]

Mainland Southeast Asia, also known as Indochina, is recognized as a global biodiversity hotspot for freshwater mussels, hosting a significant number of species and exhibiting high levels of endemism. Recently, the monotypic genus Songkhlanaia was described from the Songkhla Lake Basin in southern Thailand. In this study, two additional lineages are revealed, S.moreleti comb. nov. and S.songkhramensis sp. nov. , from the Mekong Basin through an integrative taxonomic approach combining morphological characters and molecular phylogenetic analyses. The multi-locus phylogenetic inference supported the monophyly of the genus and further elucidated the sister relationship between S.moreleti and the new species, and with S.tamodienica positioned as a basal lineage. Pairwise uncorrected COI p-distances among these three species also supported the species validity and ranged from 4.2% to 8.24%. Notably, S.songkhramensis sp. nov. and S.moreleti exhibit similarities in shell morphology; however, the new species can be differentiated by more robust pseudocardinal teeth. Both species are distinguishable from S.tamodienica by their approximately twice larger size, more inflated shells, and more prominent, roughened, irregular growth lines on the shell surface. Furthermore, based on the current data, these three species are recognized as endemic and are restricted to disjunct biogeographic areas in Indochina: S.tamodienica in the Songkhla Lake Basin in southern Thailand, S.moreleti in the Tonle Sap and Lower Mekong basins, and S.songkhramensis sp. nov. in the Songkhram Basin and its nearby tributaries of the Middle Mekong Basin., Competing Interests: The authors have declared that no competing interests exist., (Ekgachai Jeratthitikul, Chirasak Sutcharit, Pongpun Prasankok.)

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 H 2 O 2 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.

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., (© 2024 The Author(s). Molecular Ecology published by John Wiley & Sons Ltd. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.)

Freshwater mussels are important indicators of the overall health of their environment but have suffered declines that have been attributed to factors such as habitat degradation, a loss of fish hosts, climate change, and excessive nutrient inputs. The loss of mussel biodiversity can negatively impact freshwater ecosystems such that understanding the mussel’s gut microbiome has been identified as a priority topic for developing conservation strategies. In this study, we determine whether ethanol-stored specimens of freshwater mussels can yield representative information about their gut microbiomes such that changes in the microbiome through time could potentially be determined from museum mussel collections. A short-term preservation experiment using the invasive clam Corbicula fluminea was used to validate the use of ethanol as a method for storing the bivalve microbiome, and the gut microbiomes of nine native mussel species that had been preserved in ethanol for between 2 and 9 years were assessed. We show that ethanol preservation is a valid storage method for bivalve specimens in terms of maintaining an effective sequencing depth and the richness of their gut bacterial assemblages and provide further insight into the gut microbiomes of the invasive clam C. fluminea and nine species of native mussels. From this, we identify a “core” genus of bacteria (Romboutsia) that is potentially common to all freshwater bivalve species studied. These findings support the potential use of ethanol-preserved museum specimens to examine patterns in the gut microbiomes of freshwater mussels over long periods.

The quality of pearls is related closely to the position where the nucleus is inserted. The visceral mass of freshwater pearl mussels has the physiological condition for the culture of pearls, but the appropriate position for inserting the nucleus has not been determined. In this study, the physiological responses and cultured pearl biology were used to explore the most suitable of five positions in the visceral mass for inserting the nuclei (I: the front end axe foot visceral mass, II: the central axe foot visceral group, III: near the gonad department, IV: near the stomach and V: near the kidney). Overall, kidney damage (urea nitrogen/BUN, urine creatinine/Cr, uric acid/UA) and calcium metabolism indicators were in decline, whereas liver damage indicators (aspartate aminotransferase/AST, alanine aminotransferase/ALT) rose. Enzyme activity index was determined by enzyme‐linked immunosorbent assay. These results indicated that the insertion caused metabolic disorders and immune inflammation. The axe foot visceral group was not significant that compared with the control group, so it was suitable for nucleation. The peak of granulocytes and hyalinocytes in the blood cells appeared on day 10 (thd) and exerted an early immune defence function. Furthermore, the granulosa synthesized by the epidermal cells of the pearl capsule was in the mature stage of normal nacre secretion, thus forming a thicker deposit of pearls. This study filled the gaps in knowledge of visceral mass cultivating pearls and provided a theoretical basis for artificial pearl breeding. [ABSTRACT FROM AUTHOR]

Effects of wildfire and subsequent hydric erosion on freshwater communities are of increasing interest. While freshwater biodiversity is in a global state of decline, examples of climate-driven wildfire impacts to freshwater mussel populations are especially limited. We discovered a population of native floater mussels (Anodonta californiensis/ nuttalliana), documented fish species, and recorded data on river substrate characteristics before and after an influx of wildfire runoff in Monterey County, California, USA. Pre-wildfire runoff surveys documented robust and naturally reproducing populations of mussels and 3 species of native fishes (Monterey sucker, Catostomus occidentalis mnioltiltus; Monterey roach, Lavinia symmetricus subditus; and Sacramento pikeminnow, Ptychocheilus grandis). Post-wildfire, we did not detect live mussels using visual, tactile, and environmental DNA; and live fish observations included only Monterey roach and speckled dace (Rhinichthys osculus). River substrates shifted to sand, and thalweg depth decreased from 1.77 m to only 0.2 m. The potential for future extreme wildfire runoff to impact aquatic systems, and freshwater mussels specifically, should be more broadly evaluated. Increasing duration and severity of wildfire seasons in particular appear to be major future and additional challenges to freshwater mussels and ecosystems worldwide. [ABSTRACT FROM AUTHOR]

Shell shape variation of the freshwater mussel Castalia ambigua in relation to environmental and genetic drivers remains unresolved in South America. Along an increasing upstream to downstream hydrological gradient in the Caeté River, eastern Amazon, Brazil, we evaluated two co-occurring morphotypes of C. ambigua: the first is elongated and compressed; the second is rounded and inflated. We performed multivariate shape analysis on the lateral view of the right valve and the umbonal view, to identify potential ecophenotypic trends. We also investigated whether the degree of shell inflation was associated with sexual dimorphism. Castalia ambigua shell shape differed along the hydrological gradient and between sexes. However, in high hydraulic energy habitats the two morphotypes tend to a similar shape. Inflated shells of C. ambigua corresponded to female specimens, implying that shell shape variation in low hydraulic energy habitats was associated with sexual dimorphism. We found strong evidence of shell variation in the freshwater mussel C. ambigua associated with the environment and sexual dimorphism. Hydrological conditions appears to override sex-associated shell shape determination in high-energy habitats. Differences in shell shape and the identification of ecomorphotypes are important for management efforts, such as protecting the specific habitats associated with both morphotypes. [ABSTRACT FROM AUTHOR]

Aims: We examined the effects of a mixture of contaminants found in agricultural watersheds on the gut microbiota and physiology of both the freshwater mussel Lampsilis cardium, and L. cardium host fish Micropterus salmoides. Methods and results: Lampsilis cardium and M. salmoides were exposed to three concentrations of agricultural contaminants for 60 days (observing behaviour daily) before being sampled for gut microbiota analyses. DNA was extracted from the gut samples, amplified via PCR, and sequenced using the Illumina Mi‐Seq platform. Only L. cardium guts had differing microbiota across treatments, with an increase in potentially pathogenic Aeromonas. We also provide novel evidence of a core microbiota within L. cardium and M. salmoides. In terms of physiology, female L. cardium exhibited a decrease in movement and marsupial gill display in contaminant exposures. Conclusions: Exposure to contaminants from agricultural watersheds may affect population recruitment within freshwater mussel communities over time. Specifically, increased pathogenic micro‐organisms and altered behaviour can reduce the likelihood of glochidia dispersal. Significance and impact of the study: This study supports emerging research that contaminants found in agricultural watersheds may be a factor in freshwater mussel population declines. It also provides novel evidence that unionids have a core gut microbiota. [ABSTRACT FROM AUTHOR]

Parasite conservation is important for the maintenance of ecosystem diversity and function. Conserving parasites relies first on understanding parasite biodiversity and second on estimating the extinction risk to that biodiversity. Although steps have been taken independently in both these areas, previous studies have overwhelmingly focused on helminths in vertebrate hosts over broad scales, providing low resolution and excluding a large proportion of possible host and parasite diversity. We estimated both total obligate parasite richness and parasite extinction risk in freshwater mussels (Unionidae and Margaritiferidae) from Europe and the United States to provide a case study for considering parasite conservation in a severely understudied system. We used currently reported host–parasite relationships to extrapolate parasite diversity to all possible mussel hosts and then used the threat levels of those hosts to estimate the extinction risk for both described and undescribed parasites. An estimated 67% of parasite richness in freshwater mussels is undescribed and over 80% of the most host‐specific groups (digenean trematodes and ciliates) are undescribed. We estimated that 21% of this total parasite fauna is at immediate risk of extinction, corresponding to 60 unique species, many of which will likely go extinct before being described. Given the important roles parasites play in community structure and function and the strong ecosystem engineering capacities of freshwater mussels, such extinctions are likely to severely affect freshwater ecosystems. Our detailed study of mussel parasites provides compelling evidence for the hidden conservation threat to parasites through extinction cascades and shows parasites are deserving of immediate attention. Article Impact Statement: Two‐thirds of freshwater mussel parasites are undescribed and over one‐fifth are at immediate risk of extinction. [ABSTRACT FROM AUTHOR]

The continued global loss of biodiversity highlights the importance of understanding how species loss may impact ecosystem function. Shifting temperatures will accelerate species loss, but will affect species differently.We investigated effects of temperature (10°C, 20°C, or 30°C) on resource acquisition and assimilation (clearance rate, respiration rate, N and P excretion) for 11 freshwater mussel species from a species‐rich assemblage in the Sipsey River, Alabama, U.S.A., to evaluate how temperatures impact co‐occurring species and the ecosystem processes they facilitate. Mussels are assigned to the same guild (i.e., filter‐feeding bivalves), but span a breadth of evolutionary lineages and have a diversity of life history strategies from short‐lived, quickly maturing species to long‐lived, slow‐growing species.Our results indicated that four species (Cyclonaias asperata, Elliptio arca, Lampsilis ornata, and Obovaria unicolor) were thermally sensitive at 30°C, using more energy than they were acquiring. These species spanned three phylogenetic tribes and two different life‐history strategies suggesting thermal tolerance may not necessarily be linked to life history strategy or phylogenetic constraints.When laboratory clearance and excretion rates were scaled to a natural mussel community over a year, we found that relative contributions by the proportion of thermally tolerant and sensitive species to total ecosystem function varied temporally across temperature and flow regimes. Thermal stress enhanced contributions by sensitive species' during summer, as individuals attempted to meet metabolic demands by increasing clearance rates and use of energy stores that increased ammonia excretion. River discharge and background nutrient concentrations also modulated the impact of ecosystem functioning facilitated by mussels. High river discharge in winter and high background nutrient concentrations in the summer decreased the relative contribution of the mussel community.Although mussel species are commonly grouped in a single guild, species‐specific thermal traits modulate their role in the community. As biodiversity decreases, even biomass replacement by surviving mussel species is unlikely to support comparable ecosystem function due to the loss of unique species traits. [ABSTRACT FROM AUTHOR]

Bitterling embryos compete with the host mussel for oxygen, and bitterling can be considered as parasites of mussels (Reichard et al., [12]). Mussels that co-occur with bitterlings have evolved a response of ejecting bitterling eggs and also show morphological and behavioral responses that can limit bitterling spawning success (Kitamura et al., [7]). Bitterling egg shape, therefore, appears to rapidly evolve in response to selection pressure from adaptations of host mussels against bitterling parasitism, generating conspicuous variation in egg shape and size. [Extracted from the article]

With an average of around 1.1 million waterbirds present in January 2016-2018, spread across 71 native waterbird species, the international Rhine Valley from the Bodensee (Lake Constance) to the North Sea is a region of major conservation importance within Europe. In these three years, 25 species were recorded in internationally relevant numbers, holding > 1% of their flyway populations. Of the 28 species for which long-term trends could be calculated, more have increased (17) than decreased (6 species) since 1981, whereas 5 species showed relatively stable numbers. In addition, 14 non-native waterbird species were recorded in the Rhine Valley in 2016-2018, which as a group have increased over 20-fold since 1981. About half of the total numbers of waterbirds was concentrated at the lake systems of Bodensee, IJsselmeer, Markermeer and Randmeren. In these sites, long-term trends were most favourable, together with trends in the Dutch part of the Niederrhein. Due to improved water quality, the cover of submerged waterplant vegetations has strongly increased in the Rhine's lake systems in the past three decades. The plants have provided a food resource for increasing numbers of herbivorous waterbirds. At the same time, stocks of filter-feeding freshwater mussels have decreased in the northern part of the Rhine Valley as a result of, e.g., lower eutrophication levels, leading to declines in numbers of benthivorous waterbirds. Fish-eating waterbirds have generally increased, but the mechanisms are not well understood. An increase in protected areas along the Rhine Valley has facilitated the general increase in waterbird numbers. In addition, particularly in the Dutch parts of the Rhine floodplains, former agricultural land has increasingly been converted into more dynamic wetlands, in the context of flood prevention and ecological restoration. Creation of such rehabilitated areas had positive effects on most waterbird species, which may have benefited through improved feeding opportunities and increased food availability, except for grass-eating specialists. Finally, it was suggested that for some species warmer winters have initiated large-scale shifts in their winter distribution in north-eastern directions, and it is likely that this shift contributed to a decline of their wintering numbers along the Rhine. [ABSTRACT FROM AUTHOR]

A surplus of unused parts of vegetables (e.g., white cabbage [cabbage] cores and outer leaves) is generated daily by factories of fresh‐cut vegetables. These parts are difficult to effectively utilize and are often discarded as biodegradable industrial waste. This study aimed to develop an efficient method for producing l‐ornithine from cabbage residues. First, we added protease (Sumizyme FP) to the cores and outer leaves of sterile cabbages. After 8 days, the amount of l‐arginine released was approximately fivefold the amount in the initial content. As l‐arginine is a precursor of l‐ornithine, the addition of protease combined with Pediococcus pentosaceus produced l‐ornithine. However, the rapid lactic acid fermentation suppressed the metabolism of l‐arginine to l‐ornithine, which we overcame by adjusting the pH by adding eggshell. The anaerobic fermentation of the cores and outer leaves of sterile cabbages with 5% eggshell for 8 days produced 184 ± 2 μmol of l‐ornithine/100 g cabbage. Practical applications: This level of l‐ornithine production is higher than that observed in freshwater clams (81–116 μmol/100 g), which are considered to be high in l‐ornithine. This method can be applied to the production of inexpensive and safe l‐ornithine‐containing food materials derived from vegetables. Furthermore, ingestions of vegetables fermented by this method would provide a variety of health benefits of l‐ornithine. The widespread adoption of this method will not only reduce the amount of waste generated daily from fresh‐cut vegetable factories, but will also enable upcycling as a higher value‐added food material. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Unionida) are among the world's most imperiled taxa, but the relationship between freshwater mussel mortality events and infectious disease is largely unstudied. We surveyed viromes of a widespread and abundant species (mucket, Actinonaias ligamentina; syn: Ortmanniana ligamentina) experiencing a mortality event of unknown etiology in the Huron River, Michigan, in 2019–2020 and compared them to viromes from mucket in a healthy population in the St. Croix River, Wisconsin and a population from the Clinch River, Virginia and Tennessee, where a mortality event was affecting the congeneric pheasantshell (Actinonaias pectorosa; syn: Ortmanniana pectorosa) population. We identified 38 viruses, most of which were associated with mussels collected during the Huron River mortality event. Viral richness and cumulative viral read depths were significantly higher in moribund mussels from the Huron River than in healthy controls from each of the three populations. Our results demonstrate significant increases in the number and intensity of viral infections for freshwater mussels experiencing mortality events, whereas individuals from healthy populations have a substantially reduced virome comprising a limited number of species at low viral read depths. [ABSTRACT FROM AUTHOR]

Freshwater mussels in the order Unionida are highly adapted to parasitize fish for the primary purpose of dispersal. The parasitic larval stage affixes itself to the gills or fins of the host where it becomes encysted in the tissue, eventually excysting to develop into a free-living adult. Research on the parasitic interactions between unionids and their host fishes has garnered attention recently due to the increase in worldwide preservation efforts surrounding this highly endangered and ecologically significant order. With the exception of heavy infestation events, these mussels cause minor effects to their hosts, typically only observable effect in combination with other stressors. Moreover, the range of effect intensities on the host varies greatly with the species involved in the interaction, an effect that may arise from different evolutionary strategies between long- and short-infesting mussels; a distinction not typically made in conservation practices. Lower growth and reduced osmotic potential in infested hosts are commonly observed and correlated with infestation load. These effects are typically also associated with increases in metabolic rate and behaviour indicative of stress. Host fish seem to compensate for this through a combination of rapid wound healing in the parasitized areas and higher ventilation rates. The findings are heavily biased towards Margaritifera margaritifera , a unique mussel not well suited for cross-species generalizations. Furthermore, the small body of molecular and genetic studies should be expanded as many conclusions are drawn from studies on the ultimate effects of glochidiosis rather than proximate studies on the underlying mechanisms. [ABSTRACT FROM AUTHOR]

The body of knowledge regarding the classification and evolution of freshwater mussels in the family Unionidae (Bivalvia) in Indochina has recently increased. However, the taxonomic revision of all extant taxa in the region is still ongoing. In this study, the genus Pilsbryoconcha was revised based on an integrative analysis of shell morphology, biogeography, and molecular data. Multi-locus phylogeny indicated the availability of eight species within the genus. Four previously recognized species are P. exilis (Lea, 1838), P. schomburgki (Martens, 1860) stat. rev., P. linguaeformis (Morelet, 1875), and P. carinifera (Conrad, 1837), while four other species are described herein as P. acuta sp. nov., P. mekongiana sp. nov., P. kittitati sp. nov., and P. hoikaab sp. nov. In addition, the neotype of P. carinifera is also designated to clarify its long taxonomic ambiguity. Divergent time estimation and historical biogeography analysis revealed that Pilsbryoconcha originated in the area now called the Khorat Plateau around the middle of the Eocene (mean age = 43.12 Mya), before its range was expanded across Indochina through a series of complex geomorphological changes of river systems, which also led to diversification of the genus. [ABSTRACT FROM AUTHOR]

The freshwater mussel Westralunio carteri (Iredale, 1934) has long been considered the sole Westralunio species in Australia, limited to the Southwest and listed as vulnerable on the IUCN Red List and under Australian legislation. Here, we used species delimitation models based on COI mtDNA sequences to confirm existence of three evolutionarily significant units (ESUs) within this taxon and conducted morphometric analyses to investigate whether shell shape differed significantly among these ESUs. "W. carteri" I was found to be significantly larger and more elongated than "W. carteri" II and "W. carteri" II + III combined, but not different from "W. carteri" III alone. We recognise and redescribe "W. carteri" I as Westralunio carteri (Iredale, 1934) from western coastal drainages and describe "W. carteri" II and "W. carteri" III as Westralunio inbisi sp. nov. from southern and lower southwestern drainages. Two subspecies are further delineated: "W. carteri" II is formally described as Westralunio inbisi inbisi subsp. nov. from southern coastal drainages, and "W. carteri" III as Westralunio inbisi meridiemus subsp. nov. from the southwestern corner. Because this study profoundly compresses the range of Westralunio carteri northward and introduces additional southern and southwestern taxa with restricted distributions, new threatened species nominations are necessary. [ABSTRACT FROM AUTHOR]

Some corbiculids (bivalve clams in the genus Corbicula) are invasive, having spread nearly worldwide and are thought to impact native unionid mussels. To determine the density and distributional associations of invasive corbiculids co‐occurring with native unionids, corbiculid clam and unionid mussel surveys were conducted at 122 sites in the Kalamazoo River catchment, Michigan, U.S.A.Unionid densities ranged from 0 to 97 (x̅ = 7.45 ± 15.38 SD) live unionids found per person hour while corbiculid densities varied from 0 to 0.24 (0.012 ± 0.037) g/cm3. Corbiculid distributions were clumped (Moran's I test: Index = 0.281, Z = 2.228, p = 0.026) and highest along the main branch of the river. Unionid distributions, both individual species and at family level, were found to be randomly distributed throughout the catchment (Moran's I test: Index = 0.343 to −0.022, Z = 1.913 to −0.118, p value = 0.056 to 0.970).Overall, unionid species richness, as well as the distribution of 13 unionid species, were negatively associated with corbiculid density. Although corbiculids can inhabit the same river reaches with unionids, unionid species richness and densities may be negatively influenced by the presence of corbiculids.Although many species of unionids were negatively associated with corbiculid density, our research showed that they can co‐exist in the same river reaches. Overall, unionids were positively correlated with corbiculids throughout the catchment, probably because the two groups have similar habitat requirements. It is therefore important to consider unionids and corbiculids concurrently in conservation planning and the management of invasive corbiculids. [ABSTRACT FROM AUTHOR]

The Trinity Pigtoe, Fusconaia chunii (Lea, 1862), is a freshwater mussel endemic to the Trinity River drainage in Texas. Here, we report the first population of F. chunii in the San Jacinto River drainage in Texas. We identified three specimens of F. chunii using DNA barcoding, which were morphologically indistinguishable from syntopic Fusconaia flava (Rafinesque, 1820). A similar issue occurs in the Trinity River drainage. Fusconaia chunii is listed as state threatened, and future research is necessary to assess its status within the San Jacinto River drainage. [ABSTRACT FROM AUTHOR]

Population declines in freshwater mussels (Unionida) resulting from failed recruitment, together with episodic water pollution potentially leading to juvenile mussel mortality, are often suspected (but rarely well documented), even in the most strictly protected aquatic areas.The aim of this study was to test a robust design for an in situ investigation of the water pollution effects on juvenile freshwater pearl mussel (FPM, Margaritifera margaritifera) in the protected Malše River (Czech Republic), which acts as a model system. A 30‐km river reach was delineated to include a section with previously recorded episodic multiple point‐source pollution events, as well as downstream and upstream control sections. Juvenile FPMs in open water mesh cages were exposed to river water at 15 sites in 42 exposure units (342 juveniles in individual chambers), and their survival and shell growth were assessed after a 33‐day period of low‐flow and high‐temperature conditions. The main physicochemical indicators related to municipal water pollution were measured weekly.The study results confirmed significantly impaired water quality indicated by episodic changes in total ammonia nitrogen (up to 1.037 mg L−1), total phosphorus (up to 0.516 mg L−1) and oxygen saturation (down to 75.0%) in the impaired section. While the growth of FPM (corrected for temperature effects) was significantly increased (shell length increment: 32.7 ± 9.7% – impaired, 26.4 ± 10.0% – control sections; mean ± SD), the survival (mean ± SD) of juveniles was significantly decreased in the impaired section (86.4 ± 12.5%) compared with the control sections (97.4 ± 5.7%).This study has demonstrated the capacity of applying a caged bivalve model at a fine spatial scale within a longitudinal river profile to document the impacts of water pollution. The methodology applied here may provide a useful tool for assessing and improving the level of water quality management and is applicable in FPM action plans and stream biotope conservation in general. [ABSTRACT FROM AUTHOR]

Although rivers support significant unionid mussel (Unionida: Unionidae) diversity, Gulf of Mexico tributary rivers have been subject to changes in water quality and habitat due to altered watershed land use. We quantified mussel species richness and relative abundance and environmental factors in small tributary streams of the Pearl River, Mississippi-Louisiana. Freshwater mussel and habitat surveys were conducted at 27 stream sampling sites over two summers (9 sites revisited), and coverage of seven land use categories and seven geological categories above each reach were calculated. Mussels were patchily distributed (53% of sites sampled yielded mussels) and typically not abundant (only 26% of sites yielded >10 mussels). Surveys revealed nine species, with total abundance ranging from 0–66 mussels and richness ranging from 0–5 species per site. Assemblages were driven by an upper to lower watershed gradient of decreasing CPUE and richness, with microhabitat and water quality, land cover, and geology locally modifying this gradient. Environmental variables did not seem of sufficient magnitude to account for the patchy distributions and low abundances of mussels at most study sites, and we hypothesize that high discharge events related to tropical storm passage may have exerted an overriding influence on mussel assemblages in these streams through direct mortality and/or altered availability of suitable glochidial hosts. [ABSTRACT FROM AUTHOR]

Effective conservation actions to counteract the current decline of populations and species require a deep knowledge on their genetic structure. We used Single Nucleotide Polymorphisms (SNPs) to infer the population structure of the highly threatened freshwater pearl mussel Margaritifera margaritifera in the Iberian Peninsula. A total of 130 individuals were collected from 26 locations belonging to 16 basins. We obtained 31,692 SNPs through Genotyping by Sequencing (GBS) and used this dataset to infer population structure. Genetic diversity given as observed heterozygosity was low. Pairwise FST comparisons revealed low levels of genetic differentiation among geographically close populations. Up to 3 major genetic lineages were determined: Atlantic, Cantabrian and Douro. This structure suggests a close co-evolutionary process with brown trout (Salmo trutta), the primordial fish host of this mussel in the studied area. Some sub-basins showed some genetic structuring, whereas in others no intrapopulation differentiation was found. Our results confirm that genetic conservation units do not match individual basins, and that knowledge about the genetic structure is necessary before planning recovery plans that may involve relocation or restocking. The same reasoning should be applied to strictly freshwater species that are sessile or have restricted dispersal abilities and are currently imperiled worldwide. [ABSTRACT FROM AUTHOR]

Here we describe a new subgenus and three new species of parasitic water mites in the genus Unionicola (Acari: Hydrachnidia) from Myanmar: Myanmaratax subgen. nov., Unionicola (Myanmaratax) savadiensis subgen. and sp. nov. (hosts: Lamellidens savadiensis and L. generosus), U. (My.) generosa sp. nov. (the same hosts), and U. (My.) trapezidenssp. nov. (hosts: Trapezidens dolichorhynchus and T. angustior). These taxa were identified based on a two-gene phylogenetic analysis (COI + 28S), which also confirms the division of the genus Unionicola into numerous subgenera. The new species are cryptic species, which are morphologically indistinguishable but strongly resemble U. (Prasadatax) brandti Vidrine, 1985 described from Thailand (hosts: Lens spp. and Ensidens spp.). We also transfer the latter taxon from Prasadatax to Myanmaratax based on a set of morphological evidence and propose U. (My.) brandti comb. nov. The new subgenus contains a total of five species, one of which needs future sampling efforts and will be described elsewhere. Additionally, 56 valid subgenera, which were placed in the synonymy of the genus and in one case raised to the genus level, are restored here until robust phylogenetic evidence on their taxonomic status is available. Our results also confirm that Unionicola mites are narrow host specialists that are associated with either one or a few closely related freshwater mussel species belonging to one or two sister genera. [ABSTRACT FROM AUTHOR]

Aim: Ecological marginality is the existence of species/populations in the margins of their ecological niche, where conditions are harsher, and the risk of extinction is more pronounced. In threatened long‐lived species, the disparity between distribution and population demography may provide understanding of how environmental heterogeneity shapes ecological marginality, potential extinction patterns and range shifts. We set out to evaluate this by combining a species distribution model (SDM) with population‐specific demography data. Location: Sweden, 450,000 km2. Major Taxa Studied: Freshwater pearl mussel (FPM, Margaritifera margaritifera) and two salmonid fish species. Methods: A SDM for the mussel was constructed with MaxEnt using salmonid host fish (Salmo trutta plus S. salar) density, extreme low and high temperatures, precipitation, altitude, and clay content as explanatory variables. The output was used to test the ecological marginality hypothesis by evaluating whether lowly predicted populations had higher loss of recruitment. Logistic regression was used to explicitly test the factors involved in recruitment loss. Results: Host fish density contributed the most (50.3%) to the mussel distribution, followed by lowest temperature the coldest month (34.3%) and altitude (10.3%), while the remaining explanatory variables contributed minimally (<3.3%). Populations with lower SDM scores lacked recruitment to a significantly higher degree. Populations inhabiting areas at low altitude, with lower densities of host fish, and warmer winter temperatures have lost recruitment to a higher degree. Main Conclusions: We found support for the ecological marginality hypothesis. The patterns indicate that FPM habitat niche may shift northwards over time. Salmonid host fish density seems to be a driving factor for both historical distribution and recent demographic performance. Finally, we emphasize the value of combining SDMs with independent data on population demography as it both lends rigidity to model validation and understanding of how ecological marginality affects species distribution and viability. [ABSTRACT FROM AUTHOR]

Unio crassus and Unio tumidus mussels were collected at four sampling sites in the Tisza River (Hungary) to investigate their applicability as sentinel species for the biomonitoring of microplastic contamination. Since mussels, as filter feeders, are able to ingest particles only below a physically defined size, it was expected that their sentinel role in rivers is restricted to small particles, including fibers or microfibers. This assumption was confirmed by our results, as fibers were detected as the dominant particles in all the 80 mussel samples investigated. The length and diameter of the fibers changed in the size range of 20–1000 μm and 10–75 μm, respectively. The number of fibers in the individuals originating from the same sampling site was nearly two times higher in Unio tumidus than in Unio crassus and amounted to 2.7–4.9 and 5.2–8.3 items/individual. The fiber/g soft tissue ratio between these species could be characterized by a factor of three. After applying Raman spectrometry, mostly indigo-dyed polyethylene terephthalate and cellulose-based fibers, as well as a few larger (200 um) polyamide fragments, were identified. The microplastic particles stored temporarily by mussels provide only restricted qualitative information on the microplastic load of the Tisza River, and as our observations confirmed, the sampling efficiency of these 'living sampling devices' is highly species-specific. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Bivalvia: Unionoida) are globally imperilled and are the subjects of wide‐ranging conservation initiatives. This study combined traditional species‐monitoring surveys with a novel functional trait classification scheme and publicly available environmental data to assess potential environmental drivers of declining mussel abundance and species richness.Surveys to document mussel abundance and assemblage composition in south‐east Oklahoma, United States were conducted on the Glover, Mountain Fork and upper Little rivers. Present day survey results (2015–2021) were compared with those from previous studies (1993–1999, 2010) to document long‐term changes in the species and functional composition of mussel assemblages and concurrent changes in climate and land use.Mussel catch per unit effort declined by 71.5% between historical and present day surveys. Species richness declined by 44.4% over this same period. Using a novel classification of mussel drought sensitivity, it was found that the declines were associated with a disproportionate loss of drought‐sensitive taxa (67.0% decline) – those classified as drought‐tolerant did not decline in abundance. Mussel declines coincided with the loss of open surface waters (such as streams, ponds and lakes) and riparian wetlands, increased local air temperatures and longer and more intense hydrological drought.These findings indicate that for a complete understanding of the causes and consequences of mussel declines, conservation biologists must not only monitor the species composition and abundance of threatened organisms, but also consider functional traits. The results further underscore the importance of long‐term monitoring for long‐lived organisms owing to the decadal time scales over which climate and land use change occur. [ABSTRACT FROM AUTHOR]

The global decline of freshwater mussels emphasizes the need to establish genetic resources to better understand their biology, including a unique mitochondrial biology known as doubly uniparental inheritance. In this study, we present the complete male-type (M-type) mitochondrial genome of the freshwater mussel, Potamilus streckersoni Smith, Johnson, Inoue, Doyle, & Randklev, 2019. The M-type mtDNA is approximately 16 kilobases and contains 22 tRNAs, two rRNAs, and 14 protein-coding genes, including a male-specific open reading frame. Read coverage revealed that M-type mtDNA was more abundant than female-type mtDNA in male gonadal tissue, with respect to a non-spawning male individual. Novel mitogenomes were resolved within previously described sex-specific monophyletic clades across the subfamily Ambleminae. The availability of high-quality nuclear and mitochondrial genomic data for P. streckersoni makes it a model for future research into the potential role of mtDNA in sex determination or sexual development in freshwater mussels. [ABSTRACT FROM AUTHOR]

The polymorphism of the inner shell color of mussel is instrumental in identifying subgroups and guiding breed selection. To tackle the challenges of slow and inaccurate visual sorting of inner shell color of Hyriopsis schlegelii during selective breeding, we proposed a rapid and precise classification approach by integrating machine learning algorithms and image processing technologies. High-resolution nacre images were processed to extract and analyze color features, and the K-means clustering algorithm was employed to segment the nacre color clusters based on features extracted from the L*a*b* color space. The results revealed that nacre images from the posterior region of two-year-old H. schlegelii exhibited optimal clustering characteristics, successfully categorizing the pearl mussels into four groups: gray, white, purple, and gold. Further analysis of the classified groups revealed significant variations in their spectral and microstructural attributes. Raman spectra showed the presence of stretching peaks around 1126 cm−1 for C C single bonds (ν 2) and around 1509 cm−1 for C C double bonds (ν 1) in colored nacre, predominantly due to polyene organic pigments. Notably, darker inner shells, predominantly purple, exhibited a shift to lower wavenumbers in the stretching vibrations of these bonds compared to the lighter, yellow-toned shells. The relative content of organic pigments (R value, I 1124–1134 /I 1085) increased with the deepening of inner shell color. Microstructural analysis showed differences in the surface of the nacreous layers in three different inner shell color groups. The distance of groove spacing between the aragonitic layer was quantified, with purple nacres showing the smallest groove spacing (20.02 ± 5.6 μm), followed by white nacres (26.51 ± 6.64 μm), and yellow nacres exhibiting the largest spacing (30.97 ± 8.31 μm). Through validation using Raman spectroscopy and surface microstructure analysis, we found that the inner shell color sorting method based on the K-means algorithm can effectively distinguish color types and establish systematic color sorting criteria. Utilizing image processing technology and machine learning algorithms, the speed and stability of color sorting for H. schlegelii with various inner shell colors are markedly improved, offering a reference for the subsequent selection and breeding of pearl mussel families with diverse colors. • A novel method for rapid and accurate distinction of nacre color. • The inner shell colors of Hyriopsis schlegelii can be categorized into four groups. • Each nacre color group exhibits unique Raman spectral features associated with organic pigments. • Each nacre color group displays distinct microstructural features on the shell surface. [ABSTRACT FROM AUTHOR]

The conservation of at-risk species is rooted in the ability of natural resource agencies to recognize when a species is imperiled and in need of regulatory action, which can be a difficult task due to incomplete information. Freshwater mussels (Bivalvia: Unionidae), are a highly imperiled group of aquatic organisms and conservation tools such as the NatureServe Conservation Methodology provide a framework to determine whether a species is in decline and in need of potential management. For data deficient species like mussels this method relies heavily on expert opinion, which can lead to biased estimates of conservation status that may not reflect the true nature of their conservation need. To address these concerns, we developed a standardized and repeatable conservation ranking framework that builds upon the established NatureServe methodology. We compiled a data set of 12,018 species occurrence records of 48 freshwater mussel species, 17 geospatial layers representing environmental threats, and life history information to estimate their response to those threats. Estimated ranks were compared to previous status ranking metrics from IUCN, NatureServe, USFWS and Texas Parks and Wildlife Department. Of the 48 species we evaluated, three were classified as critically imperiled, 16 were imperiled, 15 were vulnerable, 13 were apparently secure, and one was secure. We found 48% of species assessed were less imperiled than NatureServe estimates and found 10% of species assessed to have a higher conservation status than previous evaluations. Our approach can be applied to other species in other regions and should be useful for managers and scientists interested in reducing uncertainty and improving reproducibility in assignment of conservation ranks, particularly for those with limited information. • Recognizing imperiled species is critical for conservation but often hindered by incomplete data. • Incorporating geospatial data into species status assessments reduces biases and allows for repeatability. • Organizational differences in conservation rankings underscores the need for more standardization. • Data-driven frameworks offer better transferability for evaluating at-risk species and guiding future efforts. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms are increasingly common in aquatic environments, raising concerns about the health impacts associated with the toxins they produce. One of these toxins is β-methylamino-L-alanine (BMAA), a neurotoxin linked to neurodegenerative diseases. Monitoring BMAA levels in the environment is challenging due to trace concentrations and complex matrices, and new approaches are needed for assessing exposure risk. In this laboratory study, Australian freshwater mussels, Velesunio ambiguus , were exposed to a BMAA-producing cyanobacterium, Microcystis aeruginosa , to assess its accumulation of the toxin over time. A sample preparation and analysis method was developed to allow accurate quantification of BMAA in the mussels at concentrations as low as 0.4 ng/g. Mussels exposed to M. aeruginosa accumulated BMAA, with concentrations increasing over the exposure period. Rapid depuration occurred after exposure to the cyanobacterium ended, with concentrations of BMAA quickly returning to pre-exposure levels. These results demonstrate the potential for mussels to be used as bioindicators in the field for monitoring BMAA levels over time, where rapid depuration is unlikely. [Display omitted] • V. ambiguus mussels have potential as bioindicators of BMAA. • Mussels showed BMAA uptake when exposed to Microcystis aeruginosa. • Rapid depuration following exposure demands careful sampling plans in situ. • A sensitive method was developed to detect BMAA in mussels at 0.4 ng/g. [ABSTRACT FROM AUTHOR]