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Freshwater mussel declines range from dramatic to subtle, but there are few methods for quantifying the extent of decline and overall assemblage health. Available assessment tools are specific to particular streams or regions and depend on untested assumptions or subjective assessments of species' tolerance to various factors. We developed a broadly applicable, objective mussel assemblage health index (MAHI). We compiled a dataset of mussel survey data from 50 streams across eastern North America and evaluated the ability of 19 candidate metrics to discriminate healthy and degraded assemblages. MAHI includes 4 metrics representing fundamental aspects of assemblage or population health (species loss, recruitment, abundance, and population growth). Metrics are scaled from 0 to 10 (representing increasing health), and the composite score is the unweighted mean of the 4 metrics. MAHI effectively discriminated healthy (median score = 8.3) and degraded (3.2) assemblages. The composite score is robust to missing values—omitting any single metric resulted in a median score change of ≤0.7. Composite scores were similar to independent scores provided by experts, but MAHI eliminates variation due to differences in individual perception or experience. MAHI can be applied to streams across eastern North America using commonly collected mussel survey data, and it may be adapted to other regions. MAHI is free of untested assumptions or subjective assessments, and it accounts for expected differences in mussel assemblages due to stream size, biogeographic region, and other intrinsic factors. MAHI will be a valuable tool for early detection of mussel declines, better understanding the causes of declines, and evaluating the effectiveness of conservation strategies and management actions. We developed a Microsoft Excel application that calculates MAHI scores, and we provide a link to that resource. [ABSTRACT FROM AUTHOR]

Unknown causes behind the loss of freshwater mussel populations have prompted population restoration as a tool to recover these imperiled species. However, water quality conditions that support mussel species within natural environments and potential causes of water quality impairment in systems with declining populations are typically unknown and may be critical knowledge needed before reintroducing mussels. Our objective was to relate the growth and survival of declining freshwater mussel populations of the Brook Floater Alasmidonta varicosa (Lamarck, 1819) to water quality parameters within 4 Massachusetts, USA, rivers containing extant populations. We deployed propagated age-1 and age-2 Brook Floater in contained systems (silos) for 1 growing season (June–October). Through biweekly sampling, we tracked the growth and survival of mussels then modeled their relationships with water quality variables. Mussels had a higher growth rate at a higher chlorophyll a (Chl a) value (2.82 µg/L) over the temperature range measured (biweekly mean = 16–26°C) when compared with lower Chl a values (0.61 and 1.17 µg/L). Age-1 mussel growth rate was negatively affected by low Chl a concentration (0.61 µg/L) across the temperature range, but age-2 mussel growth rate was not negatively affected until temperatures were above ~22°C. Na+ limited the growth rate of mussels, with the rate of change in growth rate for age-1 mussels greater than for age-2 mussels. Other cations (Mg2+, K+, and Ca2+)—potentially linked to road deicers—also negatively affected growth rate in all 4 rivers but may have had a greater impact on mussels in rivers with reduced growth rates from lower temperatures and Chl a. However, survival was uniformly high across all rivers, indicating water quality parameters may have sublethal but not lethal effects. Additional assessments for chronic water quality stressors along with changing land cover, land management, and climates are important considerations for restoration potential and the long-term persistence of populations. [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]

Freshwater bivalves play key ecological roles in lakes and rivers, largely contributing to healthy ecosystems. The freshwater pearl mussel, Margaritifera margaritifera, is found in Europe and on the East coast of North America. Once common in oxygenated streams, M. margaritifera is rapidly declining and consequently assessed as a threatened species worldwide. Deterioration of water quality has been considered the main factor for the mass mortality events affecting this species. Yet, the role of parasitic infections has not been investigated. Here, we report the discovery of three novel protist lineages found in Swedish populations of M. margaritifera belonging to one of the terrestrial groups of gregarines (Eugregarinorida, Apicomplexa). These lineages are closely related–but clearly separated–from the tadpole parasite Nematopsis temporariae. In one lineage, which is specifically associated with mortality events of M. margaritifera, we found cysts containing single vermiform zoites in the gills and other organs of diseased individuals using microscopy and in situ hybridization. This represents the first report of a parasitic infection in M. margaritifera that may be linked to the decline of this mussel species. We propose a tentative life cycle with the distribution of different developmental stages and potential exit from the host into the environment. [ABSTRACT FROM AUTHOR]

Freshwater mussels provide invaluable ecological services but are threatened by habitat alteration, poor water quality, invasive species, climate change, and contaminants, including contaminants of emerging concern (CECs). Contaminants of emerging concerns are well documented in aquatic environments, including the Great Lakes Basin, but limited information is available on how environmentally relevant mixtures affect freshwater mussel biology throughout their varied life stages. Our main goal was to assess mussels' reproductive output in response to exposure to agricultural and urban CEC mixtures during glochidial development through juvenile transformation and excystment focusing on how exposure duration and treatment affect: (1) the number of glochidia prematurely released by brooding females, (2) glochidial transformation through host‐fish excystment, and (3) the number of fully metamorphosed juveniles able to continue the lifecycle. Mussels and host fish were exposed to either a control water (CW), control ethanol (CE), agriculture CEC mixture (AM), or urban CEC mixture (UM) for 40 and 100 days. We found no effect from treatment or exposure duration on the number of glochidia prematurely released. Fewer partially and fully metamorphosed AM juveniles were observed during the 100‐day exposure, compared with the 40‐day. During the 40‐day exposure, CW produced more fully metamorphosed individuals compared with CE and UM, but during the 100‐day exposure AM produced more fully metamorphosed individuals compared with the CW. There was reduction in fully metamorphosed juveniles compared with partially metamorphosed for CE and UM during the 40‐day exposure, as well as in the CW during the 100‐day exposure. These results will be important for understanding how mussel populations are affected by CEC exposure. The experiments also yielded many insights for laboratory toxicology exposure studies. Environ Toxicol Chem 2024;43:1112–1125. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

The ASTM International standard test method for freshwater mussels (E2455‐13) recommends 4‐week toxicity testing with juveniles to evaluate chronic effects on survival and growth. However, concerns remain that the method may not adequately address the sensitivity of mussels to longer term exposures (>4 weeks), particularly in relation to potential reproductive impairments. No standard method directly evaluates toxicant effects on mussel reproduction. The objectives of the present study were to (1) evaluate toxicity endpoints related to reproduction in fatmucket (Lampsilis siliquoidea) using two common reference toxicants, potassium chloride (KCl) and nickel (Ni); (2) evaluate the survival and growth of juvenile fatmucket in standard 4‐week and longer term (12‐week) KCl and Ni tests following a method refined from the standard method; and (3) compare the sensitivity of the reproductive endpoints with the endpoints obtained from the juvenile mussel tests. Reproductive toxicity tests were conducted by first exposing female fatmucket brooding mature larvae (glochidia) to five test concentrations of KCl and Ni for 6 weeks. Subsamples of the glochidia were then removed from the adults to determine three reproductive endpoints: (1) the viability of brooded glochidia; (2) the viability of free glochidia in a 24‐h exposure to the same toxicant concentrations as their mother; and (3) the success of glochidia parasitism on host fish. Mean viability of brooded glochidia was significantly reduced in the high KCl concentration (26 mg K/L) relative to the control, with a 20% effect concentration (EC20) of 14 mg K/L, but there were no significant differences between the control and any Ni treatment (EC20 > 95 µg Ni/L). The EC20s for viability of free glochidia after the additional 24‐h exposure and parasitism success were similar to the EC20s of brooded glochidia. The EC20s based on the most sensitive biomass endpoint in the 4‐week juvenile tests were 15 mg K/L and 91 µg Ni/L, similar to or greater than the EC20s from the reproductive KCl and Ni tests, respectively. When exposure duration in the juvenile tests was extended from 4 to 12 weeks, the EC20s decreased by more than 50% in the KCl test but by only 8% in the Ni test. Overall, these results indicate that a standard 4‐week test with juvenile mussels can prove effective for estimating effects in chronic exposures with different life stages although a longer term 12‐week exposure with juvenile mussels may reveal higher sensitivity of mussels to some toxicants, such as KCl. Environ Toxicol Chem 2024;43:1097–1111. © 2024 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Species diversity can be underestimated due to a lack of regional studies and limitations in research methods. China is widely recognized as one of the primary hotspots for the biodiversity of freshwater mussels as it harbours a wealth of endemic species. Pseudocuneopsis was recently established to belong to the Unioninae subfamily within Unionidae and is endemic to China. Recent research has expanded the diversity and range of distribution of this genus. However, sufficient data is required to precisely determine the phylogenetic relationships within Pseudocuneopsis. This study conducted an integrative taxonomy using morphological, COI barcode, and complete maternal mitogenome data to clarify the taxonomy of Pseudocuneopsis. Both morphological and COI barcode data supported the validity of all Pseudocuneopsis species. Furthermore, a new species, Pseudocuneopsis yemaoi sp. n. was described from a tributary of the Man River in Hubei, China. Mitochondrial phylogenomic analyses showed that P. yemaoi was closely related to P. sichuanensis and resolved phylogenetic relationship as (P. capitata + (P. yangshuoensis + (P. sichuanensis + P. yemaoi))). Our results highlight the significance of utilizing integrative classification methods. Moreover, we propose enhancing the research and preservation measures of minor streams in China, as these streams may house distinctive species. [ABSTRACT FROM AUTHOR]

The razor clam genus Novaculina is a secondary marine-derived freshwater taxa within the otherwise exclusively marine family Pharidae. Novaculina currently comprises four valid species that are distributed allopatrically across several drainages in Asia. We employed an integrated approach, combining morphology and molecular phylogenetic analyses to elucidate the taxonomic placement of members within this genus. The multi-locus phylogenetic trees based on cytochrome c oxidase subunit I (COI), 16S rRNA and 28S rRNA gene sequences demonstrate that Novaculina is polyphyletic. Specimens identified as N. siamensis form a distinct clade that is not sister group to other currently recognised congeners. Furthermore, morphological examination reveals distinct characteristics in 'N. siamensis', namely a fused, fringed siphon, in contrast to the separated, smooth siphons observed in other species. Based on these findings, we propose the establishment of a new genus, Cenonovaculina gen. nov., to accommodate 'N. siamensis'. The new genus is distinguished from other genera in having a short shell, deep pallial sinus, elongate, oval to bean-shaped anterior adductor scar and long fused siphons surrounded by conical tentacles. [ABSTRACT FROM AUTHOR]

Climate change and associated shifts in temperature and precipitation patterns have become an increasing concern as drivers of ongoing biodiversity loss. The Mediterranean region is particularly vulnerable, being both a biodiversity hotspot and a region very prone to desertification. Freshwater mussels are amongst the most threatened invertebrate taxa worldwide. Unio tumidiformis is an endemic and endangered species restricted to the southern Iberian Peninsula, living in temporary Mediterranean-type streams. Freshwater mussels need a fish host for successful larval transformation, meaning U. tumidiformis must belong to the genus Squalius. The main objective of this study was to evaluate the vulnerability of U. tumidiformis to climate change, by studying its population genetics and evolutionary history, its current and future habitat suitability, and that of its hosts. Genetic population structure and diversity were assessed using Single-Nucleotide Polymorphisms through Genotyping by Sequencing and used to infer species evolutionary history. The species potential distribution was modeled using an ensemble forecasting approach, and future shifts in habitat suitability were assessed with the projected climate data layers from Worldclim. Most populations showed extreme genetic differentiation (Fst up to 0.745), even from close neighboring ones. Upper Guadiana populations were more diverse and less differentiated. We hypothesize that U. tumidiformis originated in Upper Guadiana and followed the same colonization routes as their hosts with numerous founder effects and bottlenecks. Our results also predicted a reduction of 99% of climatically suitable areas for U. tumidiformis in the Iberian Peninsula until 2040. For the fish hosts, a maximum 42% reduction in suitable areas was estimated throughout the century, with remaining adequate habitats in the north. Our results suggest that difficult conservation options are necessary, prioritizing the preservation of populations, translocations to the northern area of its historical range and stream engineering to increase resilience to droughts. [ABSTRACT FROM AUTHOR]

Freshwater mussels preserve valuable information about hydrology, climate, and population dynamics, but developing seasonal chronologies can be problematic. Using clumped isotope thermometry, we produced high-resolution reconstructions of modern and historic (~ 1900) temperatures and δ18Owater from mussel shells collected from an impounded river, the Brazos in Texas, before and after damming. We also performed high-resolution growth band analyses to investigate relationships between mussel growth rate, rainfall, and seasonal temperature. Reconstructed δ18Owater and temperature vary little between the modern (3R5) and historic shell (H3R). However, a positive relationship between reconstructed δ18Owater and growth rate in H3R indicates that aside from diminished growth in winter, precipitation and flow rate are the strongest controls on mussel growth in both modern and pre-dam times. Overall, our results demonstrate (1) the impact, both positive and negative, of environmental factors such as flow alteration and temperature on mussel growth and (2) the potential for clumped isotopes in freshwater mussels as a paleohydrology and paleoclimate proxies in terrestrial environments. [ABSTRACT FROM AUTHOR]

Anodonta anatina, a widely distributed Eurasian freshwater mussel, has dramatically declined and listed as endangered species in IUCN Red List in some parts of the Europe. To better understand its basic biology and possible sex-dependent effects of parasitism on reproduction, we investigated the reproductive traits, trematode parasitism and growth between November 2020 and October 2021. Our data from a Finnish population indicates male-biased sex ratio and the gonadal development lasting throughout the year with a bradytictic brooding pattern. Gonadosomatic index of both sexes peaked in May and declined in June. Mature oocytes were smaller sized than those of previously studied unionids, fecundity was fairly low, and the maximum predicted lifespan was 14 years. Gonads were infected with digenean trematode parasites, Rhipidocotyle campanula being the dominant species. Interestingly, trematode infection rate was higher in females than in males. In July, when the water temperature reached its annual maximum, the trematode prevalence also peaked, which was accompanied with 16% of mussels being sterile. The trematode parasitism was thus negatively associated with reproduction, that might become even more affected if parasitism increases along with the predicted climate warming, which should be considered in possible future conservation and aquaculture efforts of this species. [ABSTRACT FROM AUTHOR]

China leads the world in freshwater pearl production, an industry in which the triangle sail mussel (Sinohyriopsis cumingii) plays a pivotal role. In this paper, we report a high-quality chromosome-level genome assembly of S. cumingii with a size of 2.90 Gb—the largest yet reported among bivalves—and 89.92% anchorage onto 19 linkage groups. The assembled genome has 37,696 protein-coding genes and 50.86% repeat elements. A comparative genomic analysis revealed expansions of 752 gene families, mostly associated with biomineralization, and 237 genes under strong positive selection. Notably, the fibrillin gene family exhibited gene family expansion and positive selection simultaneously, and it also exhibited multiple high expressions after mantle implantation by transcriptome analysis. Furthermore, RNA silencing and an in vitro calcium carbonate crystallization assay highlighted the pivotal role played by one fibrillin gene in calcium carbonate deposition and aragonite transformation. This study provides a valuable genomic resource and offers new insights into the mechanism of pearl biomineralization. [ABSTRACT FROM AUTHOR]

Abstract This study was carried out with the freshwater mussel Unio tigridis exposed to lead nitrate. The samples of water and mussels were collected from Qandil water resources situated in Qandil village at 36° 37' 39.55" north latitude and 44° 10' 51.80" east longitude, and it is 322 meters above sea level. In January 2022, rivers and aquariums water were tested for temperature, pH, EC, TDS, DO, total alkalinity, total hardness, and calcium and magnesium ions. Studied organisms were exposed to variable concentrations of lead nitrate ranging from 0 to 900 ppm. The 96-h median lethal concentration (LC50) was measured and a comparison was made between the behavioural responses of the control and treatment groups. Also, the concentrations of lead in the experimental media, shell, and soft tissue of mussels were measured. A sample of mussels collected from aquarium was tested for biochemical markers, including acetylcholinesterase (AChE), Glutathione S-Transferase (GST), Catalase (CAT) and malondialdehyde (MDA). After 96 hours, the LC50 was estimated to be 782.7 ppm. The findings on behaviours revealed that lead slows down species' activities. Lead concentratiom increased within the mussel body as the water lead level decreased. The value of AChE was inversely related to lead concentration. However, GST, CAT and MDA increased with lead exposure. [ABSTRACT FROM AUTHOR]

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

Bitterling fishes evolve an idiosyncratic symbiosis with freshwater mussels, in which they are obligated to spawn in the gills of mussels for reproduction. In recent years, freshwater mussel populations have been drastically diminishing, due to accelerating anthropogenic impacts, which can be large threats to the risk of bitterling's extinction cascade (i.e. 'coextinction'). The host mussel size may be an important factor driving the adaptation and evolution of bitterling's reproductive phenotypes. Here we examined the host size preference and morphological adaptation of female bitterling to the host size from 17 localities at the Han River in Korea. Using our developed molecular‐based species identification for bitterling's eggs/larvae inside the mussels, we further determined the spawning patterns of seven bitterling species. Mean length of spawned mussels (N = 453) was significantly larger than that of unspawned mussels (N = 1814), suggesting that bitterling prefers to use larger hosts as a spawning ground. Spawning probability was clearly greater as mussel size increases. Results of our reciprocal transplant experiments do provide some evidence supporting the 'bitterling's larger host preference' hypothesis. Interspecific competition appeared to be intense as two fish species often spawned eggs in the same mussel individuals simultaneously. Longer ovipositor and more elongated egg may evolve in females of Tanakia signifer in response to larger host environments. The observed bitterling's spawning preference for large‐sized mussels may evolve perhaps because of the fitness advantage in relation to the offspring survival. Our findings further inform on the development of effective conservation and management strategy for the endangered bitterling fishes. [ABSTRACT FROM AUTHOR]

The loose‐equilibrium concept (LEC) predicts that ecological assemblages change transiently but return towards an earlier or average structure. The LEC framework can help determine whether assemblages vary within expected ranges or are permanently altered following environmental change.Long‐lived, slow‐growing animals typically respond slowly to environmental change, and their assemblage dynamics may respond over decades, which transcends most ecological studies. Unionid mussels are valuable for studying dynamics of long‐lived animals because they can live >50 years and occur in dense, species‐rich assemblages (mussel beds). Mussel beds can persist for decades, but disturbance can affect species differently, resulting in variable trajectories according to differences in species composition within and among rivers.We used long‐term data sets (10–40 years) from seven rivers in the eastern United States to evaluate the magnitude, pace and directionality of mussel assemblage change within the context of the LEC.Site trajectories varied within and among streams and showed patterns consistent with either the LEC or directional change. In streams that conformed to the LEC, rank abundance of dominant species remained stable over time, but directional change in other streams was driven by changes in the rank abundance and composition of dominant species.Characteristics of mussel assemblage change varied widely, ranging from those conforming to the LEC to those showing strong directional change. Conservation approaches that attempt to maintain or create a desired assemblage condition should acknowledge this wide range of possible assemblage trajectories and that the environmental factors that influence those changes remain poorly understood. [ABSTRACT FROM AUTHOR]

Progressive floodplain terrestrialization leads to the deterioration of floodplain ecosystems. Although the importance of hydrological connectivity between floodplain habitats and river channels for floodplain‐dependent organisms has been emphasized, less attention has been paid to the temporal relationship between habitat degradation and aquatic organisms. In this study, we examined temporal changes in mussel population structures and the hydrological connectivity of pond‐like floodplain water bodies (FWBs) in the terrestrialized floodplains of a lowland river in Japan. We tested the hypothesis that FWB habitats for mussels degrade over time, while newly formed FWBs contribute to providing recruitment sites for mussels. The habitat age for 53 FWBs was determined as of 2018, using historical aerial photographs. Inundation frequency, mussel abundance, and size structures (shell length) were also investigated in the FWBs in 2007 and 2018. Mussel abundance decreased with FWB aging (6–36 years), which coincided with a decrease in inundation frequency. In most existing FWBs, mussel abundance in all size classes decreased over the decade (2007–2018). In contrast, small individuals occurred in the newly formed FWBs at age 6, and in the existing FWBs where inundation frequency slightly increased over the decade (2007–2018), such FWBs were rare. In conclusion, the "young" and "rejuvenated" FWBs were found to be critically important for the recruitment and persistence of mussel populations. This suggests that the floodplain management strategy of "cyclic floodplain rejuvenation" could be applicable for mussel conservation in terrestrialized floodplains of lowland rivers. [ABSTRACT FROM AUTHOR]

Understanding the drivers of distribution and assemblage composition of aquatic organisms is an important aspect of management and conservation, especially in freshwater systems that are inordinately facing increasing anthropogenic pressures and decreasing biodiversity. For stream organisms, habitat conditions during high flows may be impossible to measure in the field, but can be an important factor for their distribution, especially for less mobile organisms like freshwater mussels. Hence, the objective of this study was to use a two dimensional HEC-RAS model to simulate hydraulic conditions during high and baseline flows (flows approx. 10–600 x and 0.7 x median daily flows respectively) in a 20 km segment in the San Saba River, Texas in combination with existing mussel survey data from 200 sites (collected every 100m) to 1) examine whether hydraulic conditions differed between areas of increased mussel richness and diversity (referred to as hotspots) and other sites, and 2) understand how well site occupancy and species abundance could be explained by hydraulic conditions occurring under different flow conditions. The results showed that richness and diversity hotspots occurred in deeper areas with lower shear stress, stream power, and Froude number during both high and low flows. Occupancy could be predicted with 67–79% accuracy at the site scale and 60–70% accuracy at the mesohabitat scale (∼20 to 1200 m long). In addition, hydraulic conditions across flow scenarios explained up to 55% of variation in species abundances, but predictions were less successful for species often observed to occupy micro-scale flow refuges such as bedrock crevices. The results indicate that pools may serve as important refuge for all species during both high and low flow events, which may be relatively unique to bedrock-dominated systems. Understanding hydraulic conditions that occur at extreme flows such as these is important given that the frequency and magnitude of such events are increasing due to climate change. [ABSTRACT FROM AUTHOR]

Unicellular ciliates like Tetrahymena are best known as free-living bacteriovores, but many species are facultative or obligate parasites. These "histophages" feed on the tissues of hosts ranging from planarian flatworms to commercially important fish and the larvae of imperiled freshwater mussels. Here, we developed a novel bioinformatics pipeline incorporating the nonstandard ciliate genetic code and used it to search for Ciliophora sequences in 34 publicly available Platyhelminthes EST libraries. From 2,615,036 screened ESTs, we identified nearly 6,000 high-confidence ciliate transcripts, supporting parasitism of seven additional flatworm species. We also cultured and identified Tetrahymena from nine terrestrial and freshwater planarians, including invasive earthworm predators from the genus Bipalium and the widely studied regeneration models Dugesia japonica and Schmidtea mediterranea. A co-phylogenetic reconstruction provides strong evidence for the coevolution of histophagous Ciliophora with their Platyhelminthes hosts. We further report the antiprotozoal aminoglycoside paromomycin expels Tetrahymena from S. mediterranea , providing new opportunities to investigate the effects of this relationship on planarian biology. Together, our findings raise the possibility that invasive flatworms constitute a novel dispersal mechanism for Tetrahymena parasites and position the Platyhelminthes as an ideal model phylum for studying the ecology and evolution of histophagous ciliates. [ABSTRACT FROM AUTHOR]

Climate change may lead to range shifts, and barriers to such displacements may result in extirpations from previously suitable habitats. This may be particularly important in freshwater ecosystems that are highly fragmented by anthropogenic obstacles, such as dams and other smaller in‐stream barriers. Conservation planning in freshwaters should consider the dynamic effects of climate change and the ability of species to cope with it. In this study, we developed a framework for incorporating climate‐driven dispersal barriers into conservation planning taking into account the medium and long‐term impacts of climate change and species with obligatory interactions. Given that freshwater mussels (Bivalvia: Unionida) are a group of highly threatened organisms dependent on fish hosts to complete their larval development and dispersal, we used Marxan to prioritize areas for their joint conservation in the Iberian Peninsula as a case study. We tested two connectivity scenarios between current and future habitats, (i) unlimited dispersal capacity and (ii) dispersal constrained by artificial barriers, and also identified priority translocation areas for species that were unable to disperse. Accounting for the effects of climate change on species distributions allowed the identification of long‐term conservation areas, but disregarding artificial barriers to dispersal may lead to unrealistic solutions. Integrating the location of barriers allowed the identification of priority areas that are more likely to be colonized in the future following climatic shifts, although this resulted in an additional loss of six to eight features (~5%–7%) compared to solutions without dispersal constraints. Between 173 and 357 artificial barriers (~1.6%–3.3%) will potentially block species dispersal to irreplaceable planning units. Where removal of artificial barriers is unfeasible, conservation translocations may additionally cover up to eight additional features that do not meet conservation targets due to dispersal constraints. This study highlights the challenge of identifying protected areas to safeguard biodiversity under climate change. [ABSTRACT FROM AUTHOR]

A significant part of freshwater mussel populations has strongly declined and many species are severely threatened nowadays. Captive breeding programs often form a central part of conservation strategies. As the life cycles of many mussel species include an obligate parasitic phase, host fish health is a crucial component of successful mussel breeding efforts. However, information about the safe application of fish therapeutants in mussel captive breeding is scarce. This article summarizes information about practical experiences in Europe. In total, eight different therapeutants were used to treat infestations of eight pathogens. Treatment success varied depending on pathogen and prevalence when treatments were initiated. Mussels did not seem to be affected by treatments, especially as long as they remained encysted. In a second step, Virkon S was applied to treat a fungal infection in tanks with brown trout (Salmo trutta) carrying encysted freshwater pearl mussel (Margaritifera margaritifera) glochidia and to disinfect juvenile mussel rearing containers. In both cases, mussels were not harmed and treated fish fully recovered. Results indicate that certain therapeutants can be used safely and successfully at different stages of breeding cycles. Nevertheless, there is still a lack of standard protocols, which would improve efficiency and the safety of treatments. [ABSTRACT FROM AUTHOR]

The artificial propagation of the endangered Solenaia oleivora, with unknown fish hosts, was performed via in vitro culture with bighead carp, grass carp, common carp, bovine, and rabbit sera. The effects of glochidium density on transformation rates were evaluated, and the development of juveniles that metamorphosed successfully was documented. The control group had a transformation rate of 0 and a contamination rate of 0. No significant differences were found in the transformation and contamination rates of the bighead carp, grass carp, and common carp serum groups, and their transformation rates were significantly higher, and contamination rates were significantly lower than those of the bovine and rabbit serum groups. Moreover, no significant differences were observed in the transformation rates of glochidia (culture density, 2000–5000 glochidia/dish) in contamination-free conditions. Specimen shell length/height increased from 1.08 ± 0.01 on the first day to 3.08 ± 0.29 during the 13th week. On the basis of anterior and posterior growth differences, juvenile growth was divided into the following three phases: the rapid anterior growth period, distinct anterior and posterior idiophase, and rapid posterior growth period. This study not only provides technological support for the artificial propagation of S. oleivora but also lays a foundation for resource recovery. [ABSTRACT FROM AUTHOR]

Alternative raw materials unsuitable for human consumption might represent a great interest in animal nutrition. Freshwater bivalves represent an unexploited potential feed resource. The effects of freshwater mussel Sinanodonta woodiana meal on growth performance, histomorphology, and morphometric characteristics of the digestive system of rainbow trout (Oncorhynchus mykiss) were evaluated. A total of 540 rainbow trout juveniles were fed with three experimental diets consisting of fish meal (FM), fish by-product meal (FPM), and freshwater mussel meal (MM). After 90 days, the fish tripled their initial weight, despite fish fed with MM showed lower weight gain, specific growth rates, and higher feed conversion ratio than those fed with control diets. It has been estimated that the total production period of fish fed with the MM diet was 12–14 days longer than fish fed with FPM and FM, respectively, due to lower growth rates. Histological and morphometrical analyses did not reveal any diet influence on the severity of the observed lesions both in the gut and liver. No negative effects were observed with the inclusion of the MM; therefore, the use of this ingredient could be considered for rainbow trout feeding. [ABSTRACT FROM AUTHOR]

As the intensity and frequency of drought and drying events are predicted to increase globally with climate warming and increasing human water usage, there is an urgent need to understand what kind of habitats may serve as refuges for organisms to withstand adverse effects. When flows decrease in rivers, disconnected pools may provide critical habitat for survival of aquatic organisms such as freshwater mussels, a highly imperilled group for which drought and dewatering pose a major threat.The objective of this study was to (1) examine whether pools serve as ecological refuges for freshwater mussels (Bivalvia: Unionidae) in drought‐stricken streams by surveying mussel distribution in an intermittent section (i.e., a section that regularly goes dry) of the San Saba River, Texas, and (2) examine the habitat characteristics that influence whether a pool functions as a refuge.We found that pool dimensions, thermal conditions, past dryness (number of years a pool was dry between 2004 and 2020), underlying geology, and aquatic and riparian vegetation influence the abundance and species richness of freshwater mussels in pools that may serve as important refuges for mussels to avoid desiccation and lethal high temperatures. Despite this, abundances and richness of mussels were low at all sites.Our results suggest that pools that retain water during drought conditions (i.e., perennial pools) may serve as ecological refuges for globally imperilled organisms such as freshwater mussels on shorter timescales (e.g., days to years). Protection and prioritisation of maintaining suitable conditions in refuge pools may help mussels persist as drought and drying issues become more pervasive in aquatic ecosystems. However, if there is a limited number of isolated pools that only allow the survival of a small number of mussels, then these pools cannot prevent overall declines of mussels in drying rivers. Better management of surface water and groundwater in anthropogenically impacted systems could ensure the flowing conditions that are needed to protect mussels in the face of climate change. [ABSTRACT FROM AUTHOR]

The Wolastoq | Saint John River (W|SJR) in New Brunswick, Canada, is regulated by hydroelectric dams with the largest and furthest downstream being the Mactaquac Generating Station (MQGS). River regulation can disrupt ecosystem connectivity by restricting access to upstream habitat for fishes and parasitic mussel larvae dependent on fishes for dispersal. Following installation of the MQGS, the number of Gaspereau (Alewife, Alosa pseudoharengus [Wilson, 1811]) and Blueback herring, Alosa aestivalis [Mitchill, 1814]) that spawn in that region of theW|SJR has increased dramatically. We assessed ectoparasitic freshwater mussel glochidia on Gaspereau captured at the MQGS and found 100% infested with an average of 43.2 glochidia per fish. Glochidia infested gill rakers, with increasing intensities from the first to fourth gill arch (P < 0.001). At least one million Gaspereau are passed above the MQGS annually, suggesting that millions of glochidia are simultaneously passed upstream each year with their hosts. We sequenced mitochondrial markers (ND1, COI) to ascertain mussel species and confirm both Alewife and Blueback herring as hosts for Alewife Floater (Utterbackiana implicata [Say, 1829]). This study provides critical baseline data on symbiotic interactions tightly interwoven in this river ecosystem and demonstrate that river regulation and fish passage considerations are more complex than most management plans account for currently. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Order Unionoida) can provide crucial ecological functions and services. However, many of them are endangered worldwide due to local extirpation and reproductive failure, which emphasizes the importance of mussel life cycle monitoring, including reproduction. Buldowskia iwakawai (Suzuki, 1939) is one such species native to the Ishikari floodplain oxbow lakes where its reproductive failure was recently reported. In this study, a species-specific environmental DNA (eDNA) assay was developed to monitor B. iwakawai abundance and winter reproduction in the laboratory and natural environment simultaneously even at times when natural lakes are covered by ice. A positive CPUE-eDNA correlation was observed across all the 14 lakes sampled prior to ice cover formation. The eDNA concentration significantly differed between gravid and non-gravid mussels in relation to their metabolic-rate differences in laboratory experiments, but the eDNA concentration increase was not detected in the intensively monitored lakes during the glochidia release period. PCR inhibition in natural water has been suggested, and reducing its effects combined with appropriate seasonal contexts has the potential to improve the applicability of this method. This research sheds new light on the applicability of the eDNA assay for monitoring mussel reproductive activities throughout their life cycle including the winter season. [ABSTRACT FROM AUTHOR]

Accurate phylogenetic reconstructions are crucial for comprehending the evolutionary histories, reproductive traits, and ecological habits of organisms. The subfamily Gonideinae of freshwater mussels is currently thought to include eight tribes. However, due to inadequate taxon sampling and molecular data, the assignment of the freshwater mussel genus Inversidens at the tribe level has been unstable. Additionally, the lack of phylogenetic data has hindered efforts to understand the basic biology and implementation of conservation efforts of Inversidens rentianensis, an endemic species to China. Here, we first present the complete mitochondrial genome of Inversidens rentianensis and offer a detailed description of its anatomical morphology. Based on DNA sequence data from five genes (COI, ND1, 16S rRNA, 18S rRNA, and 28S rRNA) and complete mitochondrial genomes, we investigated the phylogenetic position of Inversidens using various analytical methods. Both the concatenated five-gene and mitogenome datasets strongly supported that Inversidens classified to the tribe Gonideini in Gonideinae and formed a basal clade within the tribe Gonideini. Molecular dating analysis suggested that Inversidens originated during the mid-Cretaceous era (102.73 Mya, 95% highest posterior density HPD = 72.22 ‐ 137.03 Mya) and underwent diversification in the Late Paleogene era (37.92 Mya, 95% HPD = 20.39 ‐ 60.59 Mya). Moreover, based on the Quantitative Assessment of Species for Conservation (QASCP), Inversidens rentianensis is ranked as second priority, providing valuable insights for its management and conservation efforts. Taken together, this study provides a comprehensive understanding of the systematic position and evolutionary history of Inversidens within the currently accepted subfamily Gonideinae classification framework. These findings establish a solid foundation for future investigations on the ecology, reproductive behavior patterns, and conservation biology of this taxonomic group. [ABSTRACT FROM AUTHOR]

Many freshwater mussel species require fish hosts for successful reproduction; these relationships can be highly specialized and variable across mussel species. Most mussel host-identification studies have occurred in a laboratory setting and may miss important behavioral and spatial aspects of the mussel-host relationship. As such, conducting in situ evaluations of fish host use by mussel glochidia can provide additional information regarding fish-mussel relationships in the wild. However, in situ mussel-host examinations are rare, and few have been completed along the southern Atlantic slope of the United States. The goal of our study was to examine potential host use and glochidial-release timing in a small stream in South Carolina. Our objectives were to identify fish species used as mussel hosts, examine differences in the prevalence and intensity of infestations among host species, and quantify the effects of water temperature and stream flow on the probability of fish infestation. We examined wild-caught fishes for the presence of glochidial infestations in Sleepy Creek, a small tributary to Stevens Creek in the Savannah River basin of south-central South Carolina. We inspected a total of 822 individual fishes of 14 species and detected glochidia on 92 individuals of 5 fish species. Mean intensity of infestations varied from 7 to 45 glochidia per fish, but intensities did not differ significantly among fish species. Water temperatures and fish total length had significant positive effects on the probability of glochidial infestation. Highest glochidia prevalence occurred toward the end of our study at warmer temperatures and on mid-length fishes. Our study highlights the potential of in situ studies and DNA metabarcoding for identifying host use of wild glochidia. [ABSTRACT FROM AUTHOR]

Characterizing the mechanisms influencing the distribution of genetic variation in aquatic species can be difficult due to the dynamic nature of hydrological landscapes. In North America's Central Highlands, a complex history of glacial dynamics, long-term isolation, and secondary contact have shaped genetic variation in aquatic species. Although the effects of glacial history have been demonstrated in many taxa, responses are often lineage- or species-specific and driven by organismal ecology. In this study, we reconstruct the evolutionary history of a freshwater mussel species complex using a suite of mitochondrial and nuclear loci to resolve taxonomic and demographic uncertainties. Our findings do not support Pleurobema rubrum as a valid species, which is proposed for listing as threatened under the U.S. Endangered Species Act. We synonymize P. rubrum under Pleurobema sintoxia —a common and widespread species found throughout the Mississippi River Basin. Further investigation of patterns of genetic variation in P. sintoxia identified a complex demographic history, including ancestral vicariance and secondary contact, within the Eastern Highlands. We hypothesize these patterns were shaped by ancestral vicariance driven by the formation of Lake Green and subsequent secondary contact after the last glacial maximum. Our inference aligns with demographic histories observed in other aquatic taxa in the region and mirrors patterns of genetic variation of a freshwater fish species (Erimystax dissimilis) confirmed to serve as a parasitic larval host for P. sintoxia. Our findings directly link species ecology to observed patterns of genetic variation and may have significant implications for future conservation and recovery actions of freshwater mussels. [ABSTRACT FROM AUTHOR]

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

Freshwater mussels fulfill an important ecological role in aquatic ecosystems, but they currently face many threats, including thermal regime alteration. Thermal transformation of the aquatic environment is associated with climate change, land use alteration, and other pervasive anthropogenic global changes. To enhance our understanding of ecological thermal impacts, we combined extensive field measurements of temperature in the stream water column and substrate depths (5 and 15 cm) at sites where mussels occur, measures of abundance and species richness for mussels and fish, and thermal tolerance knowledge for mussels and fish to generate a comprehensive assessment of the potential threats mussels face as temperatures continue to rise as a result of global change. Mean summer (June–August 2010–2012) temperatures at mussel-occupied sites in the upper Tar River basin of North Carolina, USA, ranged from 16.2 to 34.7 °C. The mean temperature from the hottest 96 h at each site ranged from 23.5 to 31.5 °C. At 80% of sites, a period of moderate drought coincided with the hottest 96 h period. Temperature threshold exceedance durations indicated that chronic, combined chronic/acute, and acute freshwater mussel thermal tolerance thresholds (i.e., 28 °C, 30 °C, and 33 °C, respectively) based on laboratory exposures of glochidia (larvae) and juveniles were commonly exceeded. Water temperatures exceeded 28 °C for at least 24 h at 55% of sites and for at least 96 h at 35% of sites, and they exceeded 30 °C for at least 24 h at 15% of sites. We quantified a thermal buffering effect of the substrate that may be protective of mussels. There was a mean difference of 0.5 °C between the water column and the upper substrate (5 cm) and a mean difference of 0.9 °C between the water column and the lower substrate (15 cm). Maximum differences of up to 5.5 °C between the water column and the upper substrate and 11.5 °C between the water column and the lower substrate were observed. Our models estimating the relation between the water column and substrate temperatures more realistically characterize ambient temperature exposures and have widespread implications for mussel conservation and climate change risk assessment in similar streams. Freshwater mussels currently exist on the edge of their thermal limits, but their abundance and species richness cannot be explained by temperature patterns alone. Fish species richness was related to the thermal regime, indicating that species interactions may be an important driver of freshwater mussel responses to global change. [ABSTRACT FROM AUTHOR]

Frequent and strong morphological convergence suggests that determinism tends to supersede historical contingencies in evolutionary radiations. For many lineages living within the water column of rivers and streams, hydrodynamic forces drive widespread morphological convergence. Living below the sediment-water interface may release organisms from these hydrodynamic pressures, permitting a broad array of morphologies, and thus less convergence. However, we show here that the semi-infaunal freshwater mussels have environmentally determined convergence in shell morphology. Using 3D morphometric data from 715 individuals among 164 Nearctic species, we find that species occurring in rivers with high flow rates have evolved traits that resist dislodgement from their burrowed position in the streambed: thicker shells for their body size, with the thickest sector of the shell being the most deeply buried. Species occurring in low flow environments have evolved thinner and more uniformly thickened shells, corresponding to an alternative adaptation to dislodgement: increased burrowing efficiency. Within species, individuals also show increased shell thickness for their body size at higher flow rates, suggesting that ecophenotypy may, in part, be an important mechanism for establishing populations in new environments and thus evolutionary divergence in this highly imperiledinvertebrate group. [ABSTRACT FROM AUTHOR]

Plastic-based contamination has become a major cause of concern as it pervades many environments such as air, water, sediments, and soils. This study sought to examine the presence of microplastics (MPs) and nanoplastics (NPs) in freshwater mussels placed at rainfall/street runoff overflows, downstream (15 km) of the city centre of Montréal, and 8 km downstream of a municipal effluent dispersion plume. MPs and NPs were determined using flow cytometry and size exclusion chromatography using fluorescence detection. Following 3 months of exposure during the summer season, mussels contained elevated amounts of both MPs and NPs. The rainfall overflow and downstream of the city centre were the most contaminated sites. Lipid peroxidation, metallothioneins, and protein aggregates (amyloids) were significantly increased at the most contaminated sites and were significantly correlated with NPs in tissues. Based on the levels of MPs and NPs in mussels exposed to municipal effluent, wastewater treatment plants appear to mitigate plastic contamination albeit not completely. In conclusion, the data support the hypothesis that mussels placed in urbanized areas are more contaminated by plastics, which are associated with oxidative damage. The highest responses observed at the overflow site suggest that tire wear and/or asphalt (road) erosion MPs/NPs represent important sources of contamination for the aquatic biota. [ABSTRACT FROM AUTHOR]

Freshwater mussels are both critically important in their ecosystems and rapidly declining around the world. Damming is a key reason for this decline in many locations because it affects the flow and turbidity of river systems, leading to numerous detrimental effects on benthic communities. Although the ecological effects of impoundment have been well studied on timescales ranging from years to decades, the ecological effects of impoundment on longer (50–100 years) timescales are less well understood, with a key question being: how long after the building of dams and impoundments do we expect community structure to continue changing? In this study, we explore historical changes in the freshwater mussel assemblages in Kentucky Lake (dammed in 1944) using decades-long collections housed at Murray State University in combination with other historical records. After digitizing these collections and applying a robust rarefaction protocol to account for uneven sampling, we quantify changes in unionid assemblage structure alongside coeval water quality data collected through the Kentucky Lake Long-Term Monitoring Program. We find that subsampled richness exhibited declines after dam construction with losses among opportunistic taxa, channelization-tolerant taxa, and impoundment-intolerant taxa. We also find increases in the proportions of equilibrium taxa throughout the dataset. Overall, the assemblage composition reached an equilibrium by the year 2000 (50 years after impoundment). In concert, river water quality data show a decline in turbidity and increase in light penetration in the period 1988–2020. Although the geohistorical records treated in this study are patchy in time, we argue that they are nonetheless valuable and illustrate that freshwater ecosystems may serve as potential sites of restoration decades after anthropogenic disturbance. In turn, this emphasizes the importance of geohistorical collections to studying long-term changes in community structure and developing strategies for conservation and environmental remediation. [ABSTRACT FROM AUTHOR]

Background: Leeches are an integral component of aquatic biocenosis and can be found in a wide range of ecosystems such as freshwater, saltwater, flowing, and still-water ecosystems. It especially plays an important role in the freshwater benthic community and is an important part of the food web. In this study, a leech species was found in the mantle cavity of wild freshwater mussels in Zigong City, Sichuan Province, China, and its identity was determined through morphological analysis and molecular biological analysis. Results: The leech is Hemiclepsis khankiana, a new species of Hemiclepsis that has been discovered in Russia in recent years. Through morphological analysis, the current survey observed that the morphological characteristics of Hemiclepsis khankiana eyespots were significantly different from the first reported description. The first pair of eyespots on the leech were separated and clear, while it had been reduced to unclear shadows in the previous report. The phylogenetic tree based on the COI gene showed that the COI gene sequence obtained in this study was in the same evolutionary branch as Hemiclepsis khankiana (MN295420, MN295421). Genetically, it was most closely related to Hemiclepsis kasmiana (mean COI p-distance = 3.98%). Conclusions: The current study reported on the new distribution range of Hemiclepsis khankiana, which was initially discovered in China. This study indicates that the distribution range of the leech species has expanded, laying a foundation for further studies in China. [ABSTRACT FROM AUTHOR]

The increasing attention that carbon-based nanomaterials have attracted due to their distinctive properties makes them one of the most widely used nanomaterials for industrial purposes. However, their toxicity and environmental effects must be carefully studied, particularly regarding aquatic biota. The implications of these carbon-based nanomaterials on aquatic ecosystems, due to their potential entry or accidental release during manufacturing and treatment processes, need to be studied because their impacts upon living organisms are not fully understood. In this research work, the toxicity of oxidized multi-walled carbon nanotubes (Ox-MWCNTs) was measured using the freshwater bivalve (Corbicula fluminea) after exposure to different concentrations (0, 0.1, 0.2, and 0.5 mg·L−1 Ox-MWCNTs) for 14 days. The oxidized multi-walled carbon nanotubes were analyzed (pH, Raman microscopy, high-resolution electron microscopy, and dynamic light scattering), showing their properties and behavior (size, aggregation state, and structure) in water media. The antioxidant defenses in the organism's digestive gland and gills were evaluated through measuring oxidative stress enzymes (glutathione-S-transferase, catalase, and superoxide dismutase), lipid peroxidation, and total ubiquitin. The results showed a concentration-dependent response of antioxidant enzymes (CAT and GST) in both tissues (gills and digestive glands) for all exposure periods in bivalves exposed to the different concentrations of oxidized multi-walled carbon nanotubes. Lipid peroxidation (MDA content) showed a variable response with the increase in oxidized multi-walled carbon nanotubes in the gills after 7 and 14 exposure days. Overall, after 14 days, there was an increase in total Ub compared to controls. Overall, the oxidative stress observed after the exposure of Corbicula fluminea to oxidized multi-walled carbon nanotubes indicates that the discharge of these nanomaterials into aquatic ecosystems can affect the biota as well as potentially accumulate in the trophic chain, and may even put human health at risk if they ingest contaminated animals. [ABSTRACT FROM AUTHOR]

Freshwater mussels of the genus Buldowskia (Bivalvia, Unionidae) are distributed from the Amur River basin in Russia and China southward to the Korean Peninsula and some Japanese islands. This work is an integrative morphological study of Buldowskia suifunica glochidia from locations in the Primorsky Territory, the Russian Far East. Glochidia of B. suifunica, taken from the same gill have asynchronous development. The external and internal morphology of its shell has been characterized. The morphology of its sensory system, within three stages of larval development (immature, intermediate and mature glochidia), consists of hair cells as well as nonhair cells. Their muscle system is composed of massive adductor and minor muscle bundles. The FMRFamid-ergic nervous system turned out to be a complex system includes basal cells (neurons), their neurites and anterior neurons. FMRFamide and tubulin was found in all neurons. Glochidia of B. suifunica have only four 5-HT-lir neurons. We concluded that B. suifunica glochidial nervous system differs from those of the larval systems of planktotrophic marine mollusks. [ABSTRACT FROM AUTHOR]

Understanding patterns of diversity across macro (e.g. species‐level) and micro (e.g. molecular‐level) scales can shed light on community function and stability by elucidating the abiotic and biotic drivers of diversity within ecological communities. We examined the relationships among taxonomic and genetic metrics of diversity in freshwater mussels (Bivalvia: Unionidae), an ecologically important and species‐rich group in the southeastern United States. Using quantitative community surveys and reduced‐representation genome sequencing across 22 sites in seven rivers and two river basins, we surveyed 68 mussel species and sequenced 23 of these species to characterize intrapopulation genetic variation. We tested for the presence of species diversity–abundance correlations (i.e. the more‐individuals hypothesis, MIH), species‐genetic diversity correlations (SGDCs) and abundance‐genetic diversity correlations (AGDCs) across all sites to evaluate relationships between different metrics of diversity. Sites with greater cumulative multispecies density (a standardized metric of abundance) had a greater number of species, consistent with the MIH hypothesis. Intrapopulation genetic diversity was strongly associated with the density of most species, indicating the presence of AGDCs. However, there was no consistent evidence for SGDCs. Although sites with greater overall densities of mussels had greater species richness, sites with higher genetic diversity did not always exhibit positive correlations with species richness, suggesting that there are spatial and evolutionary scales at which the processes influencing community‐level diversity and intraspecific diversity differ. Our work reveals the importance of local abundance as indicator (and possibly a driver) of intrapopulation genetic diversity. see also the Perspective by see also the Perspective by K. N. Petersen and J. P. Wares [ABSTRACT FROM AUTHOR]

Freshwater mussels are highly impacted by many human activities. As a result, it is considered one of the most threatened ecosystems worldwide. Studying genetic diversity is crucial for any further research on conservation efforts. In the present study, inter simple sequence repeat (ISSR) marker analysis was employed to study genetic diversity between 8 randomly selected specimens of bivalve. A total of 53 bands were produced from the 10 primers. Of these 37 bands were polymorphic, resulting in 69.8% polymorphism. Some primers showed more polymorphic bands than others. For example, primer ISSR M17 produced no polymorphic bands. While primer ISSR M1 produced 3 polymorphic bands (100% polymorphism). Cluster analysis, based on a similarity matrix, obtained showed that the 8 bivalve specimens can be clustered into two groups, one group containing specimens 2 and 6, and the other group representing specimens 4, 5, 1, 3, 7, and 8. These data may suggest that the bivalves in Abohomos, Behera Governorate, Egypt, may have more than one species. The implication of these data on the conservation of the bivalve is explained. The conclusion is that the bivalve population has enough genetic diversity. These populations are adapted to the environment they live in and to the climatic changes. [ABSTRACT FROM AUTHOR]

Freshwater mussels are one of the most diverse and critically endangered organismal groups in the world. In North America, many of the ∼300 species are imperiled to some degree, and numerous states, including Illinois, have instituted surveys and safeguards to protect their remaining mussel resources. In Illinois, the status of many mussel species is unknown, and additional efforts are needed to determine the health of rare and endangered mussels. The Rock River system was historically a stronghold for mussels in Illinois; however, studies over the last decade are lacking. To obtain current data on the health and status of mussels within a portion of the Rock River, we conducted survey efforts throughout the upper Rock River. We sampled mussels semi-quantitatively at 30 sites using bank-to-bank transects in July of 2021 to determine whether rare and endangered species were still extant. We also examined the abundances of species currently considered common and assessed shell-length data to determine the overall viability of the mussel fauna. We surveyed a total of 4360 m of the river and obtained 2506 live mussels of 19 species. The assemblage consisted primarily of Potamilus ohiensis (Pink Papershell) and Cyclonaias pustulosa (Pimpleback), and approximately half the assemblage consisted of recent recruits (juveniles). We collected live Cyclonaias nodulata (Wartyback), Cyclonaias tuberculata (Purple Wartyback), and Truncilla donaciformis (Fawnsfoot), all Illinois or Wisconsin state-listed species. The Purple Wartyback consisted of 2 cohorts and are the first live individuals recorded from the Rock River since the late 1980s. Furthermore, the presence of numerous juveniles indicates successful reproduction and recruitment for multiple species. Continued work on managing stream habitats is vital to protecting and reinforcing their remaining diversity, and the upper Rock River warrants further protections. [ABSTRACT FROM AUTHOR]

Animal excretion provides nutrients for primary productivity and can be a crucial component of ecosystem nutrient cycling. The concentrations of carbon (C), nitrogen (N), and phosphorus (P) in an animal's excretion are strongly influenced by the C:N:P stoichiometry (molar ratios) of its body and of the food it eats. We measured the C:N:P ratios of quagga mussel (Dreissena rostriformis bugensis) tissues and excreta and of seston across wide environmental and spatial gradients in the upper Laurentian Great Lakes. We then investigated how mussel excretion rates were impacted by stoichiometric mismatch—the difference between the C:P ratios of mussel tissues and the C:P ratios their food. Quagga mussel internal C:N:P stoichiometry varied significantly across sites and seasons, driven primarily by changes in tissue P concentrations. When mussel tissues had substantially lower C:P ratios than seston (that is, strong stoichiometric mismatch), mussels excreted significantly less N and P relative to C. Excretion C:N ratios varied by nearly threefold, while C:P ratios varied by tenfold. The effect of the stoichiometric mismatch on excretion stoichiometry was more dramatic in the spring, when mussels had higher tissue P concentrations, than in the summer. This suggests seasonality in mussel P demand. Our results challenge the assumption of strict internal homeostasis in consumers and demonstrate that food and tissue stoichiometry need to be considered to predict consumer excretion stoichiometry. These findings help to better understand the impact of consumer-driven nutrient cycling in aquatic environments and quagga mussel contributions to the nutrient budgets of invaded ecosystems. [ABSTRACT FROM AUTHOR]

We investigated an interaction between bitterlings and a parasitic leech Hemiclepsis kasmiana in freshwater mussel hosts. We found that leeches fed on bitterling eggs and embryos; this may exert a considerable negative effect on bitterling fitness. Host choices by females of three bitterling species may be differently affected by the presence of leeches within mussels; Tanakia limbata apparently avoided laying eggs in infested mussels while T. lanceolata and Acheilognathus rhombeus did not. Our novel findings suggest that relationships between the parasitic leech and the host mussel may be context dependent. [ABSTRACT FROM AUTHOR]

Animals are a critical component of biogeochemical cycles. While animal mediated fluxes of nutrients and energy have received considerable attention, the impacts of these fluxes on microbial community structure and function are comparatively understudied. Here, we investigated if freshwater mussel influences on biogeochemical cycling in stream sediment are accompanied by changes in sediment microbial community composition and ecoenzymatic activity, and if these relationships change under different nutrient regimes.We predicted that mussel effects on ecosystem function are reflected by modified sediment microbial communities. We hypothesized that if changes in either sediment ecoenzymatic function or microbial community composition are driven by mussel‐derived nutrient amendments, we should see muted changes in microbial community assemblages or function when a given nutrient is abundant. However, if microbial communities and function are influenced by other mussel functions, then we should see uniform changes regardless of nutrient availability.We transplanted freshwater mussels and natural river sediment to flow‐through mesocosms and monitored changes in microbial community composition over 1 week. Our results indicate that mussels always changed sediment microbial community composition, but the way communities changed was dependent on ambient nutrient concentrations.On the final day we measured the activity of ecoenzymes known to correlate to microbial function and nutrient availability. Mussels homogenized the stoichiometric ratios of ecoenzyme activities, indicating a consistent function of sediment microbes associated with freshwater mussels. Our results suggest that mussels may promote functional redundancy in sediment microbial communities and highlight the importance of animals in controlling biogeochemical transformations under changing nutrient conditions. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]

Sea levels across the planet are rising, particularly along the eastern coast of the United States. Climate‐induced sea level rise can result in the inundation and intrusion of seawater into freshwater drainages. This would alter salinity regimes and lead to the salinization of coastal freshwater ecosystems. Increased salinity levels in freshwater can negatively affect freshwater‐dependent species, including native mussels belonging to the order Unionida, which are highly sensitive to changes in water quality. Sea salt is largely made up of sodium and chloride ions, forming sodium chloride, a known toxicant to freshwater mussels. However, sea salt is a mixture that also contains other major ions, including potassium, sulfate, calcium, strontium, and magnesium, among others. Freshwater mussels exposed to sea salt would be exposed to each of the sea salt ions at the same time, resulting in a mixture toxicity effect. The mixture toxicity of these ions on early life stages of freshwater mussels is largely unknown because most research to date has evaluated individual salt ions in relative isolation. Therefore, we conducted acute toxicity tests on early life stages (glochidia and juvenile) of three freshwater mussel species that inhabit Atlantic Slope drainages (nonsalinity‐adapted Atlanticoncha ochracea, salinity‐adapted A. ochracea, Sagittunio nasutus, and Utterbackiana implicata). Glochidia and juveniles of each species were exposed to a control and six concentrations of Instant Ocean® Sea Salt (IOSS), a synthetic sea salt that closely resembles the ionic composition of natural sea salt. Exposure concentrations were 1 part(s) per thousand (ppt), 2 ppt, 8.5 ppt, 12.5 ppt, 17 ppt, and 34 ppt. We calculated the median effect concentration (EC50) for each of the eight acute toxicity tests and found that glochidia were more sensitive than juveniles to IOSS. At hour 24 EC50s for the glochidia ranged from 0.38 to 3.6 ppt, with the most sensitive freshwater mussel being the nonsalinity‐adapted A. ochracea, exhibiting an EC50 of 0.38 ppt (95% confidence interval [CI] 0.33–0.44). Juvenile freshwater mussels exhibited EC50s at hour 96 ranging from 5.0 to 10.4 ppt, with the least sensitive freshwater mussel being the nonsalinity‐adapted A. ochracea, exhibiting an EC50 of 10.4 ppt (95% CI 9.1–12.0). Our results show that acute exposure to sea salt adversely affects freshwater mussel viability, particularly glochidia. This information can be used to enhance freshwater mussel conservation strategies in regions that are or will be impacted by climate‐induced sea level rise and associated freshwater salinization. Environ Toxicol Chem 2023;42:2478–2489. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Positive biodiversity–ecosystem functioning (BEF) relationships observed in experiments can be challenging to identify in natural communities. Freshwater animal communities are disproportionately harmed by global change that results in accelerated species loss. Understanding how animal‐mediated ecosystems functions may change as a result of global change can help determine whether biodiversity or species‐specific conservation will be effective at maintaining function. Unionid mussels represent half of imperiled species in freshwater ecosystems globally and perform important ecological functions such as water filtration and nutrient recycling. We explored BEF relationships for 22 naturally assembled mussel aggregations spanning three river basins. We used the Price equation to partition the contributions of species richness, composition, and context dependent interactions to two functions of interests: spatially‐explicit standing‐stock biomass (indirect proxy for function) and species‐specific nitrogen (N) excretion rates (direct measure of N recycling). Random and non‐random species loss each reduced biomass and N recycling. Many rare species with low contributions to biomass contributed to standing‐stock biomass in all basins. Widespread species had variable function across sites, such that context dependent effects (CDEs) outweighed richness effects on standing‐stock biomass in two basins, and were similar to richness effects in the third. Richness effects outweighed CDEs for N recycling. Thus, many species contributed a low proportion to overall N‐recycling; a product we attribute to the high evenness and functional effect trait diversity associated with these communities. The loss of low‐functioning species reduced the function of persisting species. This novel result using observational data adds evidence that positive species interactions, such as interspecific facilitation, may be a mechanism by which biodiversity enhances ecosystem functions. Our work stresses the importance of evaluating species‐specific contributions to functions in diverse systems, such as nutrient cycling when maintaining specific animal‐mediated functions is a management goal because indirect proxies may not completely characterize BEF relationships. [ABSTRACT FROM AUTHOR]

Unionid mussels are imperiled worldwide. Understanding the impacts of thermal and hypoxia stress on larval (glochidia) and adult physiology is critical for understanding the potential impacts of climate change. We tested whether brood viability (proportion of glochidia competent to attach to a host) was correlated with oxygen demand (MO2), ability to regulate oxygen consumption (regulation index (RI)), and/or critical dissolved oxygen concentration (DOcrit). We then examined the effects of temperature on MO2, RI, and DOcrit. The results were coupled with a previous study to estimate the fraction of brooding female oxygen demand comprised of glochidial respiration. We found little evidence that respiratory patterns of glochidia changed with declining brood viability, but strong evidence for decreasing glochidial RI and increasing DOcrit with increasing temperatures. Glochidial respiration temperature coefficient (Q10) values were approximately 2–3× those estimated for brooding females, indicating greater temperature sensitivity. The proportion of gravid female respiration comprised of glochidial respiration reached its maximum at temperatures (23–28 °C) coinciding with brood expulsion. These patterns suggest high temperatures may have deleterious effects on unionids by decreasing the hypoxia tolerance of glochidia, increasing the rate at which glochidia deplete energy reserves, and increasing the proportion of oxygen consumption by gravid females that is comprised of glochidial oxygen demand. [ABSTRACT FROM AUTHOR]

Freshwater mussels (Bivalvia: Unionidae) are often described as ecosystem engineers, with the capacity to alter abiotic habitats; this can facilitate certain macroinvertebrate taxa, increasing biodiversity and potentially altering community composition. Mussel species are often implicitly considered to be broad ecological equivalents, with similar impacts on abiotic environments and benthic communities. This assumption of redundancy is important in conservation approaches that aim to preserve ecosystem functioning, rather than species identity. We tested this assumption of equivalence in two species of subtropical freshwater mussels, Lamellidens marginalis and Parreysia caerulea, studying the associations between these mussel species and macroinvertebrate communities.We measured mussel density and abundance of macroinvertebrates, identified to family level, at 50 sites within Dhanmondi Lake, a heavily polluted sub‐tropical urban lake in Dhaka, Bangladesh. We investigated the associations of mussel density on different macroinvertebrate families, which we further classified into functional feeding groups (predators, scrapers, collectors and shredders).We found that densities of the two mussel species were negatively correlated in the 1–3‐m nearshore zone; average density of Lamellidens was 46.4 ± SE 3.6 individuals/0.25 m2, and average density of Parreysia was 6.4 ± SE 1.4 individuals/0.25 m2. In total, 2319 Lamellidens and 320 Parreysia specimens were recorded. Sites containing higher densities of Lamellidens had greater similarity in macroinvertebrate community composition, while there was no effect for Parreysia. Particular macroinvertebrate families and functional feeding groups were also associated with mussels; the majority of significant associations were with Lamellidens but not Parreysia. The clearest associations were with predators and scrapers, which increased in abundance with Lamellidens density.This provides support for a possible role for mussels in structuring freshwater invertebrate communities and emphasises the importance of species identity in these effects, with one possible keystone species (Lamellidens) largely accounting for mussel–invertebrate associations. While microhabitat variables (shading and sediment type) were poor predictors of abundance in any invertebrate taxa (including mussels), manipulative studies are needed to disentangle the direct effects of mussels from the role of overlapping habitat preference between mussels and other invertebrates.Our results highlight the importance of species identity in patterns of community composition, particularly for ecosystem engineer species. We also reinforce the need to test the assumption of ecological redundancy within communities. [ABSTRACT FROM AUTHOR]

A new species of freshwater mussel belonging to the genus Pseudocuneopsis, namely Pseudocuneopsis wuana sp. nov., is diagnosed and described from Guangxi Province, China. This paper provides a detailed shell morphological description, soft-body anatomical characteristics, and partial sequences of mitochondrial COI as DNA barcode data for the novel species. The new species can be distinguished from its congeners (Pseudocuneopsis sichuanensis, P. yangshuoensis, and P. capitata) by shell shape, beak position, and surface sculpture. Phylogenetic analyses based on the mitochondrial COI gene reveal that Pseudocuneopsis wuana sp. nov. forms a sister group with P. yangshuoensis and exhibits an interspecific genetic distance of 5.1%. Therefore, we provide robust morphological and molecular evidence to support the validity of this new species. [ABSTRACT FROM AUTHOR]

The shell of a freshwater mussel (Mollusca: Bivalvia) is a composite biological material that plays an active role in maintaining ecosystem services. Mussel shells have variable structures both within and between species. In this study, the structural and biological characteristics of the shells of Potomida semirugata and Leguminaia wheatleyi were investigated in order to use freshwater mussel shells as a biological material. Close observation of the microstructure of the shells of the two common freshwater bivalves revealed a variation in construction from the outer periostracum to the inner nacreous layer. In P. semirugata, a polygonal arrangement with columnar prisms of different sizes was observed more significantly. In L. wheatleyi the prismatic columns are oval and irregularly polygonal. The nacreous layers of P. semirugata, in which the individual aragonite layers are horizontally overlapped, are more uniformly distributed. The overlapping of the aragonite sheets in L. wheatleyi is more irregular. The presence of calcium carbonate (CaCO3) in the shells was confirmed by the identification of the characteristic carbonate bands at 701.9, 713.5, and 865.8 cm-1. This information was used to classify and distinguish the different layers of the shells, allowing interspecific comparisons and variations in the different layers. The results clearly showed that shell samples were highly biocompatible and nontoxic compared to the control group. This finding suggests that these materials have promising potential for use in various biomedical applications where biocompatibility is a critical factor. The results indicated that the shells of the freshwater bivalves P. semirugata and L. wheatleyi are biological materials with potential multiple applications for human well-being and environmental quality. [ABSTRACT FROM AUTHOR]