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In freshwater habitats, aerobic animals and microorganisms can react to oxygen deprivation by a series of behavioural and physiological changes, either as a direct consequence of hindered performance or as adaptive responses towards hypoxic conditions. Since oxygen availability can vary throughout the water column, different strategies exist to avoid hypoxia, including that of active 'flight' from low‐oxygen sites. Alternatively, some organisms may invest in slower movement, saving energy until conditions return to more favourable levels, which may be described as a 'sit‐and‐wait' strategy. Here, we aimed to determine which, if any, of these strategies could be used by the freshwater ciliate Tetrahymena thermophila when faced with decreasing levels of oxygen availability in the culture medium. We manipulated oxygen flux into clonal cultures of six strains (i.e. genotypes) and followed their growth kinetics for several weeks using automated image analysis, allowing to precisely quantify changes in density, morphology and movement patterns. Oxygen effects on demography and morphology were comparable across strains: reducing oxygen flux decreased the growth rate and maximal density of experimental cultures, while greatly expanding the duration of their stationary phase. Cells sampled during their exponential growth phase were larger and had a more elongated shape under hypoxic conditions, likely mirroring a shift in resource investment towards individual development rather than frequent divisions. In addition to these general patterns, we found evidence for intraspecific variability in movement responses to oxygen limitation. Some strains showed a reduction in swimming speed, potentially associated with a 'sit‐and‐wait' strategy; however, the frequent alteration of movement paths towards more linear trajectories also suggests the existence of an inducible 'flight response' in this species. Considering the inherent costs of turns associated with non‐linear movement, such a strategy may allow ciliates to escape suboptimal environments at a low energetic cost. [ABSTRACT FROM AUTHOR]

Water crickets of the subfamily Haloveliinae are semi‐aquatic bugs occurring in freshwater and marine habitats throughout the Indo‐Australian region, presently including six genera with more than 80 extant species. Whether lineage diversification in Haloveliinae is associated with the utilization of new ecological niches caused by transition events between freshwater and marine habitats remains poorly understood. We investigate the evolutionary history of Haloveliinae using large‐scale phylogenomic datasets and a set of novel redefined morphological characters based on 24 ingroup taxa representing all recognized genera. Our phylogenetic results based on the novel datasets definitively indicate that the freshwater genus Strongylovelia Esaki as currently defined is paraphyletic and supports the establishment of a new genus: Metavelia gen. nov., including three congeneric species: Metavelia patiooni comb. nov. (type species), Metavelia priori comb. nov. and Metavelia albicolli comb. nov. Reconstruction of ancestral habitats suggests a freshwater origin for the Haloveliinae. Divergence time estimations reveal that the origin of the monophyletic marine clade occurred at around 83 Ma (95% highest posterior density: 71–98 Ma) in the Late Cretaceous, involving a single transition event from freshwater to marine habitats. This time coincides with the period of high global sea levels in the Late Cretaceous. During this period, the marine incursions caused by the massive sea level rise flooded the continental margins, especially in Southeast Asia, where ancestral Haloveliinae were probably distributed. The appearance of new marine habitats after the marine incursions (e.g., intertidal, mangroves and estuarine) probably led to a subsequent establishment and diversification of the marine lineages. [ABSTRACT FROM AUTHOR]

The continued loss of freshwater habitats poses a significant threat to global biodiversity. We reviewed the extinction risk of 166 freshwater aquatic and semiaquatic mammals—a group rarely documented as a collective. We used the International Union for the Conservation of Nature Red List of Threatened Species categories as of December 2021 to determine extinction risk. Extinction risk was then compared among taxonomic groups, geographic areas, and biological traits. Thirty percent of all freshwater mammals were listed as threatened. Decreasing population trends were common (44.0%), including a greater rate of decline (3.6% in 20 years) than for mammals or freshwater species as a whole. Aquatic freshwater mammals were at a greater risk of extinction than semiaquatic freshwater mammals (95% CI –7.20 to –1.11). Twenty‐nine species were data deficient or not evaluated. Large species (95% CI 0.01 to 0.03) with large dispersal distances (95% CI 0.03 to 0.15) had a higher risk of extinction than small species with small dispersal distances. The number of threatening processes associated with a species compounded their risk of extinction (95% CI 0.28 to 0.77). Hunting, land clearing for logging and agriculture, pollution, residential development, and habitat modification or destruction from dams and water management posed the greatest threats to these species. The basic life‐history traits of many species were poorly known, highlighting the need for more research. Conservation of freshwater mammals requires a host of management actions centered around increased protection of riparian areas and more conscientious water management to aid the recovery of threatened species. [ABSTRACT FROM AUTHOR]

The impacts of climate change are widespread and threaten natural systems globally. Yet, within regions, heterogeneous physical landscapes can differentially filter climate, leading to local response diversity. For example, it is possible that while freshwater lakes are sensitive to climate change, they may exhibit a diversity of thermal responses owing to their unique morphology, which in turn can differentially affect the growth and survival of vulnerable biota such as fishes. In particular, salmonids are cold‐water fishes with complex life histories shaped by diverse freshwater habitats that are sensitive to warming temperatures. Here we examine the influence of habitat on the growth of sockeye salmon (Oncorhynchus nerka) in nursery lakes of Canada's Skeena River watershed over a century of change in regional temperature and intraspecific competition. We found that freshwater growth has generally increased over the last century. While growth tended to be higher in years with relatively higher summer air temperatures (a proxy for lake temperature), long‐term increases in growth appear largely influenced by reduced competition. However, habitat played an important role in modulating the effect of high temperature. Specifically, growth was positively associated with rising temperatures in relatively deep (>50 m) nursery lakes, whereas warmer temperatures were not associated with a change in growth for fish among shallow lakes. The influence of temperature on growth also was modulated by glacier extent whereby the growth of fish from lakes situated in watersheds with little (i.e., <5%) glacier cover increased with rising temperatures, but decreased with rising temperatures for fish in lakes within more glaciated watersheds. Maintaining the integrity of an array of freshwater habitats—and the processes that generate and maintain them—will help foster a diverse climate‐response portfolio for important fish species, which in turn can ensure that salmon watersheds are resilient to future environmental change. [ABSTRACT FROM AUTHOR]

The East American mudminnow Umbra pygmaea was introduced to Europe a century ago and is now established in at least six European countries. Although considered harmless and with low spread potential, this fish species shows potential to colonise a broad range of habitats due to its wide environmental tolerance. Stomach content analyses were conducted over 3 years to obtain a first insight into this species' diet, which could indicate the potential to alter the biotic composition of recipient ecosystems. The results showed that this fish can potentially have a high impact on insects, fish, and even amphibians through predation. Species distribution models further indicated that environmental conditions of Central European ecoregions are currently a limiting factor for the spread of this species which seems, at least for now, to be driven by anthropogenically driven introductions. Considering the species' potential to be invasive and impact native biota, monitoring of potential spread is recommended. [ABSTRACT FROM AUTHOR]

Dispersal is a main determinant of community assembly. Landscape configurations of rivers, lakes, or ponds are often independently considered in this framework. However, these systems share species conforming to a waterscape with different environments coupled by dispersal. While empirical results support a main role of this coupling on biodiversity organization, it is difficult to assess its importance at large geographic scales. Using a theoretical approach, we quantified the potential role of dispersal through different freshwater ecosystems of the United Kingdom and Ireland on biogeographic diversity patterns. We implemented a coalescent model considering 11,131 communities connected by distance-dependent dispersal and with species that have different performances for recruitment in three different aquatic habitats. Biogeographic diversity patterns were estimated for each habitat alone or for the whole waterscape combining ephemeral, temporal, and permanent waters. The results indicated that the coupling between different types of environments fostered local diversity, in a magnitude that increased from the ephemeral to permanent waters and from poorer to richer communities. Furthermore, a strong spatial structure in the potential effect of dispersal among different freshwater environments was observed, indicating that freshwater biogeography was likely determined by the connection among freshwater ecosystems to a larger extent than previously thought. [ABSTRACT FROM AUTHOR]

Hypotrichs are among the most complex and highly differentiated ciliate lineages, which are distributed in diverse habitats. Members of the family Deviatidae Foissner, 2016 are commonly found in freshwater or low-salinity habitats, as well as soils. During a study of freshwater wetland diversity in China, a novel deviatid ciliate Heterodeviata sinica gen. nov. et sp. nov. and a distinct population of Deviata multilineae Zhang et al. 2022 were investigated based on morphology, morphogenesis, and 18S rRNA gene sequences. The new genus Heterodeviata gen. nov. can be characterized by having two or more left and right marginal rows each, one frontoventral cirral row, the presence of caudal cirri, and two dorsal kineties, one of them being a dorsomarginal kinety. Phylogenetic analyses reveal that Heterodeviata is nested in a well-supported clade with Deviata Eigner, 1995, Perisincirra Jankowski, 1978 and Pseudosincirra Gao et al. 2021, which suggests that the family Deviatidae is monophyletic. The close relationship among the Deviatidae genera were supported after extensive morphological and morphogenetic investigations, as well as molecular phylogeny presented here. [ABSTRACT FROM AUTHOR]

Research in freshwater ecosystems has always had a strong focus on ecological interactions. The vast majority of studies, however, have investigated trophic interactions and food webs, overlooking a wider suite of non‐trophic interactions (e.g. facilitation, competition, symbiosis and parasitism) and the ecological networks they form.Without a complete understanding of all potential interactions, ranging from mutualistic through to antagonistic, we may be missing important ecological processes with consequences for ecosystem assembly, structure and function. Ecological networks can be constructed at different scales, from genes to ecosystems, but also local to global, and as such there is significant opportunity to put them to work in freshwater research.To expand beyond food webs, we need to leverage technological and methodological advances and look to recent research in marine and terrestrial systems—which are far more advanced in terms of detecting, measuring and contextualising ecological interactions.Future studies should look to emerging technologies to aid in merging the wide range of ecological interactions in freshwater ecosystems into networks to advance our understanding and ultimately increase the efficacy of conservation, management, restoration and other applications. [ABSTRACT FROM AUTHOR]

Populations experiencing negligible predation pressure are expected to evolve higher behavioral activity. However, when sexes have different expected benefits from high activity, the adaptive shift is expected to be sex-specific. Here, we compared movement activity of one cave (lack of predation) and three adjacent surface (high and diverse predation) populations of Asellus aquaticus , a freshwater isopod known for its independent colonization of several caves across Europe. We predicted 1) higher activity in cave than in surface populations, with 2) the difference being more pronounced in males as they are known for active mate searching behavior, while females are not. Activity was assessed both in the presence and absence of light. Our results supported both predictions: movement activity was higher in the cave than in the surface populations, particularly in males. Relaxed predation pressure in the cave-adapted population is most likely the main selective factor behind increased behavioral activity, but we also showed that the extent of increase is sex-specific. [ABSTRACT FROM AUTHOR]

The freshwater isopod Asellus aquaticus is an important decomposer of leaf detritus, and its diverse gut microbiome has been depicted as key contributors in lignocellulose degradation as of terrestrial isopods. However, it is not clear whether the individual‐level microbiome profiles in the isopod digestive system across different habitats match the implied robust digestion function of the microbiome. Here, we described the bacterial diversity and abundance in the digestive system (hindgut and caeca) of multiple A. aquaticus individuals from two contrasting freshwater habitats. Individuals from a lake and a stream harboured distinct microbiomes, indicating a strong link between the host‐associated microbiome and microbes inhabiting the environments. While faeces likely reflected the variations in environmental microbial communities included in the diet, the microbial communities also substantially differed in the hindgut and caeca. Microbes closely related to lignocellulose degradation are found consistently more enriched in the hindgut in each individual. Caeca often associated with taxa implicated in endosymbiotic/parasitic roles (Mycoplasmatales and Rickettsiales), highlighting a complex host–parasite–microbiome interaction. The results highlight the lability of the A. aquaticus microbiome supporting the different functions of the two digestive organs, which may confer particular advantages in freshwater environments characterized by seasonally fluctuating and spatially disparate resource availability. [ABSTRACT FROM AUTHOR]

The salinity gradient separating marine and freshwater environments is a major ecological divide, and the mechanisms by which most organisms adapt to new salinity environments are poorly understood. Diatoms are a lineage of ancestrally marine microalgae that have repeatedly colonized and diversified in freshwaters. Cyclotella cryptica is a euryhaline diatom found in salinities ranging from fully freshwater to fully marine, thus providing a powerful system for understanding the genomic mechanisms for mitigating and acclimating to low salinity. To understand how diatoms mitigate acute hypo‐osmotic stress, we abruptly shifted C. cryptica from seawater to freshwater and performed transcriptional profiling during the first 10 h. Freshwater shock dramatically remodelled the transcriptome, with ~50% of the genome differentially expressed in at least one time point. The peak response occurred within 1 h, with strong repression of genes involved in cell growth and osmolyte production, and strong induction of specific stress defence genes. Transcripts largely returned to baseline levels within 4–10 h, with growth resuming shortly thereafter, suggesting that gene expression dynamics may be useful for predicting acclimation. Moreover, comparison to a transcriptomics study of C. cryptica following months‐long acclimation to freshwater revealed little overlap between the genes and processes differentially expressed in cells exposed to acute stress versus fully acclimated conditions. Altogether, this study highlights the power of time‐resolved transcriptomics to reveal fundamental insights into how cells dynamically respond to an acute environmental shift and provides new insights into how diatoms mitigate natural salinity fluctuations and have successfully diversified across freshwater habitats worldwide. see also the Perspective by Gust Bilcke and Shiho Kamakura [ABSTRACT FROM AUTHOR]

As the global climate is changing, average water temperatures and the supply of CO2 to water bodies are increasing. To determine how the effects of these changes on freshwater communities interact, we ran a month‐long factorial mesocosm experiment, in which we manipulated water temperature (heated, ambient) and pCO2 (preindustrial, ambient, future). We found that the total phytoplankton biomass responded positively to the pCO2 and temperature treatments but no interactive effects were detected. Green algae were positively affected by temperature and, over the course of the experiment, responded to pCO2 first positively, then negatively. Heterokonts, on the other hand, were unaffected by temperature but responded positively to pCO2. pCO2 enrichment also led to increases in seston C : N stoichiometry, although the experiment ended before we could observe any effects of pCO2 on the zooplankton community composition. Warming caused shifts in zooplankton community composition, primarily through higher abundances of the cladoceran Bosmina longirostris and the rotifer Conochilus unicornis, and lower abundances of the rotifer Polyarthra vulgaris. We found that, in contrast to the effects of temperature, which can be explained by temperature‐dependent plankton growth curves, the responses of algal groups to pCO2 enrichment were difficult to anticipate, despite the availability of priors from previous pCO2 enrichment experiments in the same lake mesocosms. We conclude that climate change‐induced increases in aquatic pCO2 and temperatures are likely to affect pelagic ecosystems, though further research in freshwater systems is needed before generalized claims regarding the simple and interactive effects of pCO2 can be made. [ABSTRACT FROM AUTHOR]

Freshwater science has grown and evolved extensively since its inception in the late 1800s. Many of the models and conceptual frameworks developed for and used in freshwater research were originally proposed by researchers in the Global North to explain patterns and processes in temperate streams. This view of freshwater ecosystems has extended to research in Latin America, potentially limiting our ability to understand unique ecological and socioeconomic attributes of the watersheds found in our region. Recently, there has been an increase in freshwater research being conducted by Latin American scientists, who may be able to apply and validate more suitable models and conceptual frameworks given their personal experiences and insights about local realities. In this BRIDGES cluster, we feature the work of early career Latin American researchers who are addressing environmental concerns pertinent to the region through research that challenges some of the ideas developed for river networks in the Global North. [ABSTRACT FROM AUTHOR]

Invasive non‐native species and climate change are two of the greatest pressures facing freshwater communities; however, how they interact to impact ecosystem function remains poorly understood despite the potential for impacts on key functional behaviours, such as detritivory, which could have wide‐reaching impacts. We quantified the rates of detrital processing and survival of one U.K. native (Gammarus pulex) and two invasive non‐native (Dikerogammarus villosus and Dikerogammarus haemobaphes) freshwater amphipod species, across three temperatures (8°C, 14°C, and 20°C), and three leaf diets of varying resource quality (oak, sycamore, and alder) in laboratory microcosms. We also compared amphipod survival across the different temperature and diet treatments. Rates of detrital processing varied between the native and invasive non‐native amphipod species, with native G. pulex having a faster processing rate than both invasive non‐native species at the lower temperatures. However, as the temperature treatments increased, between‐species differences decreased, while the effects of leaf diets became more apparent. Although the survival probability did not vary with amphipod species, amphipod survival was higher at lower temperatures and in treatments containing higher quality leaf diets. We propose that the invasive non‐native Dikerogammarus species will affect native communities through lower rates of detrital processing; however, this impact may change under predicted climatic warming and be increasingly similar to native amphipod species. [ABSTRACT FROM AUTHOR]

During the investigation of lignicolous freshwater fungi in the Tibetan Plateau habitat, fifteen collections were isolated from submerged decaying wood. Fungal characteristics are commonly found as punctiform or powdery colonies with dark pigmented and muriform conidia. Multigene phylogenetic analyses of combined ITS, LSU, SSU and TEF DNA sequences showed that they belong to three families in Pleosporales. Among them, Paramonodictys dispersa, Pleopunctum megalosporum, Pl. multicellularum and Pl. rotundatum are established as new species. Paradictyoarthrinium hydei, Pleopunctum ellipsoideum and Pl. pseudoellipsoideum are reported as new records on the freshwater habitats in Tibetan Plateau, China. The morphological descriptions and illustrations of the new collections are provided. [ABSTRACT FROM AUTHOR]

Canadian coastal waters of the Pacific Ocean and the Atlantic Ocean as well as inland freshwater habitats in Ontario were sampled for centrohelid heliozoans (free-living heterotrophic single-celled organisms) over a period of nearly five decades. More than 60 species and subspecies were revealed, including 1 Triangulopteris, 1 Raphidocystis, 2 Pseudoraphidocystis, 3 Raineriophrys, 4 Pseudoraphidiophrys, 12 Choanocystis, 15 Pterocystis, and 25 Acanthocystis taxa. Of these, 22 were officially named and described as new to science based primarily on the morphology of the siliceous scales that cover the cell. New species were compared with images and/or descriptions of close "relatives" to validate their new species assignments. New data on five species of Acanthocystis and one species of Choanocystis required revisions of their descriptive taxonomy that in some cases resulted in the splitting off of separate species or subspecies. Very little can be concluded about global distribution of centrohelid heliozoans, owing to the paucity of records. For many of the taxa reported here, previous records consist of just one or two findings from other parts of the world. One example is Choanocystis antarctica Tikhonenkov and Mylnikov, 2011 that was previously known only from Antarctic seawater, but is reported here from an Ontario softwater lake. [ABSTRACT FROM AUTHOR]

Microsporidia are a large group of obligate intracellular eukaryotic parasites related to fungi primarily known as parasites of vertebrates and invertebrates. They are well described as parasites of organisms of interest (e.g., edible fish and crustaceans, honeybees, bioindicators such as daphnia, humans) on which they can have an important impact (e.g., reduced survival or fecundity and sex ratio distortion). However, their diversity in aquatic environments, especially in marine ecosystems, has been greatly understudied since they are not targeted by classical eukaryotic primers used in metabarcoding studies. Moreover, little is known about their hosts among protists or microzooplankton and therefore about their impact on the trophic food web functioning. In this work, we sampled 15 different sites across marine and freshwater environments, size‐fractioned the samples, and used microsporidian specific primers associated with metabarcoding to study the microsporidian diversity (and the associated spatial variation). Co‐occurrence networks as well as tyramide signal amplification‐fluorescent in situ hybridization were used to link potential hosts (planktonic eukaryotes < 150 μm) and Microsporidia diversity. Our analysis unraveled a large microsporidian diversity which was widely divergent between the two environments studied. In both of them, an important part of this diversity was not affiliated to a genus, suggesting an important reservoir of new microsporidian species and thus new hosts among planktonic eukaryotes. Co‐occurrence networks and fluorescence microscopy showed for the first‐time associations between Microsporidia and dinoflagellates in freshwater and marine environments. [ABSTRACT FROM AUTHOR]

The ecological significance of freshwater ecosystems for conservation in the temperate zone has been determined by aquatic biologists using a variety of ecological techniques. One such tool is the Community Conservation Index (CCI), which was primarily developed in Britain but is also recommended for international use. The current study intends to further test the CCI's applicability and its sensitivity in identifying freshwater systems of high conservation importance. The pristine condition of three natural monument (Arinta, Ekor, and Oowu waterfalls) streams was evaluated in this study using the macroinvertebrate metric indicators, and the results were compared with their CCIs. The relative compositions of stress-sensitive species, facultative species, functional feeding guilds (FFGs), and modes of locomotion or microhabitat preference (ML/MP) were selected as the macroinvertebrate metrics. The fauna was dominated by the taxonomic group EPT (Ephemeroptera, Plecoptera, Trichoptera), with the highest EPT-related metrics found at Oowu Waterfalls. Ironically, because a vulnerable species (i.e. Pentaphlebia stahli) is present there, the Ekor Waterfalls, which had the lowest values for the EPT-related metrics, had the highest CCI. Although both the CCI (>20) and macroinvertebrate metrics suggest that the three sites had high conservation value, the CCI proved to be more goal-oriented in determining the conservation value of pristine freshwater ecosystems. In light of the findings of this study, it is recommended that the CCI be utilized in conjunction with macroinvertebrate metric indicators for studies of a similar nature, particularly in Afrotropics' protected and pristine sites that are a potential refuge for rare and threatened species. [ABSTRACT FROM AUTHOR]

Resource quantity (i.e. organic matter; OM) is a main driver of the prevailing energy pathway in freshwater food webs. The OM pool is mainly composed of allochthonous material, a primary resource for freshwater consumers. Contrastingly, small amounts of autochthonous OM (i.e. algae) can subsidize aquatic communities due to its higher nutritional quality. To date, there is no consensus about the relative importance of allochthonous and autochthonous OM for freshwater food webs or the environmental factors driving their relative importance. We fill this gap by evaluating the relative importance of allochthonous and autochthonous OM sources for freshwater food webs on a global scale through a meta‐analytical approach. We gathered the outcome of stable isotope mixing models of 2789 cases from 58 published studies and calculated a response ratio between the mean contributions of allochthonous and autochthonous OM for freshwater consumers. Using mixed‐effect models and a multimodel inference approach, we tested the influence of latitude, habitat type, ecosystem size, climate and terrestrial productivity over the response ratio. The relative contribution of autochthonous OM was higher in lotic systems. In lentic systems, increasing terrestrial productivity increased the relative contribution of autochthonous OM, while increasing precipitation and temperature seasonality reduced this relative contribution. We suggested that factors increasing terrestrial productivity might also boost autochthonous OM in these systems, while precipitation increases the transport of allochthonous OM to freshwater habitats. We did not find any relationship between environmental factors and the relative contribution of autochthonous OM for lotic systems. We concluded that the relative contribution of allochthonous and autochthonous energy sources to freshwater food webs differs between lotic and lentic ecosystems and it is dependent on multiple environmental factors. [ABSTRACT FROM AUTHOR]

The presence of submerged macrophytes is a desired environmental target for coastal freshwater ecosystems. Maintaining a rich community of these species can be challenging as salinisation by sea‐level rise poses an increasing threat to ecosystem integrity.We tested the effect of salinisation on the growth and germination of freshwater macrophytes experimentally using field sediment. In a 56‐day experiment, a macrophyte community was exposed to salinity treatments representing seasonal water management scenarios (a decreasing salinity from 1,500 to 300 mg NaCl/L, a stable salinity of 300 mg NaCl/L, an increasing salinity from 300 to 1,500 mg NaCl/L and a stable salinity of 1,500 mg NaCl/L), crossed with treatments simulating periodic turbidity pulses.All species except Elodea nuttallii grew poorly on the saline and eutrophic sediment, reflecting the challenges of growth in eutrophic coastal systems. Surprisingly, the highest community biomass was achieved in the salinity scenario of 1,500 mg NaCl/L.In a second experiment, field‐collected sediments were incubated at 300 and 1,500 mg NaCl/L salinity (representing summer and winter scenarios), and the germination capacity of the existing seedbank was quantified.Most germinated seedlings did not reach maturity irrespective of salinity treatment. This indicated that sediment salinity, rather than water column salinity, determined seedling establishment success. Interestingly, the established species were characteristic of freshwater habitats, thus indicating maladaptation of the seedbank.Our results show that a mismatch between the high salinity level of eutrophic sediment and the overlaying freshwater may hamper macrophyte growth. Furthermore, target species in coastal eutrophic freshwaters should be evaluated carefully. Elodea nuttalli, which has a wide tolerance range for nutrients and salinity, outperformed other macrophyte species in our study. Thus, species with similar traits may be most successful in establishing macrophyte stands in coastal eutropic wetlands. [ABSTRACT FROM AUTHOR]

Environmental DNA (eDNA) has seen a massive increase in application in freshwater systems with a concurrent growth in protocol developments and a drive to gain a better understanding of the 'ecology' of eDNA. This raises the question of whether we are currently still in an early, developmental phase of eDNA-based assessments or already transitioning into a more applied stage for biomonitoring. I conducted a systematic literature review on 381 eDNA-focused studies in freshwater systems targeting macro-organisms over the last 5 years, assessing study goals, methods, target systems and taxa and study design aspects. The results show an increase of biomonitoring-focused studies throughout the years, while the fraction of studies investigating the 'ecology' of eDNA decreased. The application of metabarcoding significantly increased while studies applying qPCRs tentatively declined. A geographic inequality was observed concerning study numbers and study goals biased towards the global North. Descriptive studies increased, but the fraction of in-field studies and studies applying eDNA and conventional methods combined revealed no trend. These results show a shift towards application-focused work for eDNA-based assessments but also reveal this field to still be developing. In this transitional phase, practitioners need to ensure consistency and data comparability for long-term monitoring programmes. [ABSTRACT FROM AUTHOR]

Globally, many freshwater species are depleting and require population-level assessments. Many species distribution modelling frameworks are available for such assessments, but comparisons are needed to understand their predictive performance under different settings. K-fold cross-validation techniques were employed to compare the performance of three commonly used frameworks: machine learning, spatiotemporal modelling, and Gaussian process (GP) modelling. Through application to New Zealand populations of longfin eel (Anguilla dieffenbachii) and shortfin eel (Anguilla australis), area under the receiver operating characteristic curve (AUC) and true skill statistic (TSS) model performance metrics were estimated. All modelling frameworks produced approximately consistent distribution maps but differed in predictive performance. AUC and TSS results indicated that model predictions from the spatiotemporal modelling framework were the most accurate, followed by GP modelling. However, all modelling frameworks performed similarly when training and test data were spatially independent. In addition to having the best predictive performance, the spatiotemporal modelling framework showed the greatest promise for advancement in population-level assessment and is therefore recommended. The results are useful for freshwater ecologists and resource managers to make informed decisions on the appropriateness of a modelling framework for their research objective. [ABSTRACT FROM AUTHOR]

Having parts of three freshwater ecoregions, i.e., Oman Mountains, Southwestern Arabian Coast, and Arabian Interior, Oman is considered to have the greatest freshwater biodiversity among the Arabian Peninsula countries. Freshwater habitats and biodiversity of Oman are unique and greatly valued for the crucial role they play in people's survival, as well as that of its native/endemic biota. An obvious starting point and fundamental step to conserve biodiversity and implementing planning management strategies is correct identification and delineating of the taxonomic and conservation units, and their distribution ranges especially endemic and native faunal elements including small, colorful, and mosquito-eating fish species of the genus Aphaniops. Five species of Aphaniops are present in the northern marginal basins of the Indian Ocean, however, there is still a lack of distributional and taxonomic data in many parts, and the species have not been studied yet for their phylogeographic and population structures, which are essential in designing habitat management and conservation plans. This study analyses mitochondrial COI data of Aphaniops samples collected from numerous widespread localities in Oman, a rarely studied area for this group, using a phylogenetic and phylogeographic framework. Our results confirm the presence of two species in Oman, A. kruppi and A. stoliczkanus, revise and suggest wider distributional ranges for both species, and suggest that A. kruppi is represented by two northern and one southern management units, while A. stoliczkanus is divided into two evolutionary units worthy of additional taxonomic evaluation. [ABSTRACT FROM AUTHOR]

Neotropical freshwater stingrays (subfamily Potamotrygoninae) are carnivorous bottom feeder batoids widely distributed in most river basins of South America. They represent the unique extant group of elasmobranchs that evolved to live exclusively in freshwater environments. These species are exploited either by commercial fisheries (e.g., for food or ornamental industry) or by indigenous communities allocated along with their natural range. Restrictive life history characteristics coupled with habitat degradation make Potamotrygoninae species highly vulnerable to human impacts and highlight the necessity of studies to inform basic biological aspects, from ecology to genetics, to guide their conservation and clarify the molecular basis of adaptation to the freshwater environment. We used available and newly assembled Potamotrygon spp. mitogenomes to perform a comparative investigation of their molecular evolution. A phylogenetic estimation using the mitogenome of Potamotrygon falkneri and other Elasmobranchii supports monophyly for Potamotrygonidae and indicates a close relationship to Dasyatidae. A synteny analysis comprising 3 Potamotrygon and other 51 batoids revealed a highly conserved mitogenomic context. We detected various amino acid sites under positive selection exclusively in Potamotrygon spp., within the sequences of ND4, ND5, ND6, and COXII genes. Positively selected mutational events in key genes of energetic metabolism may be related to the physiological adaptation of Potamotrygon spp. during the ancient incursion into freshwater. This broad comparative mitogenomic study provides novel insights into the evolutionary history of neotropical freshwater stingrays and their relatives and stands out as a valuable resource to aid in current and future research on elasmobranch molecular evolution. [ABSTRACT FROM AUTHOR]

Many anguillid eel species display facultative catadromy. Some eel spend their entire life cycle in marine coastal areas, but the geographical extent of this, especially at the extremes of their distributional ranges, is unknown. We analysed otolith Sr:Ca and Ba:Ca from yellow-stage European eel (Anguilla anguilla) sampled along the coast of Norway and in several freshwater lakes (58°N–63°N), to infer their initial settlement and later life movement patterns with regards to habitat salinity. Most eel (80%) sampled in marine habitats (n = 371) had settled and remained in marine water, but 20% had moved between marine and freshwater habitats and were hence classified as inter-habitat shifters. Among freshwater sampled eel (n = 99), 80% had settled and remained in fresh water, but 20% were classified as inter-habitat shifters. The average growth rates for marine water residents, inter-habitat shifters, and freshwater residents were 35, 27, and 17 mm·year–1, respectively. Northern European shallow marine habitats may serve as important yellow eel growth habitats and may be critical to buffer the European eel population against the general decrease in continental recruitment. [ABSTRACT FROM AUTHOR]

†Protosyngnathus sumatrensis is known from six specimens from Eocene lacustrine deposits of the Sangkarawang Formation of Sumatra, Indonesia. The fish was named almost 150 years ago, but has never been well described or figured. Probably because of this, it has not been included in phylogenies of extant pipefishes and seahorses (Syngnathiformes). A detailed description is provided, along with a new phylogenetic analysis of morphological characters that allows the Eocene fish to be confidently placed with the extant families Syngnathidae (pipefishes and seahorses) and Solenostomidae (ghost seahorses) along with the Paleocene marine fossil †Eekaulostomus cuevasae from Mexico. The vast majority of these fishes are marine inhabitants, with a few syngnathids entering brackish or freshwater habitats. †Protosyngnathus documents the occurrence of syngnathiform fishes in a lacustrine environment, indicating that this lineage invaded and became adapted to the freshwater environment early in the evolution of this group. [ABSTRACT FROM AUTHOR]

N2‐fixing heterocytous cyanobacteria are considered to play a minor role in sustaining coastal microbial mat communities developing under normal marine to hypersaline conditions. Here, we investigated microbial mats growing under different salinities from freshwater mats of Giblin River (Tasmania) to metahaline and hypersaline mats of Shark Bay (Western Australia). Analyses of genetic (rRNA and mRNA) and biological markers (heterocyte glycolipids) revealed an unexpectedly large diversity of heterocytous cyanobacteria in all the studied microbial mat communities. It was observed that the taxonomic distribution as well as abundance of cyanobacteria is strongly affected by salinity. Low salinity favoured the presence of heterocytous cyanobacteria in freshwater mats, while mats thriving in higher salinities mainly supported the growth unicellular and filamentous non‐heterocytous genera. However, even though mRNA transcripts derived from heterocytous cyanobacteria were lower in Shark Bay (<6%) microbial mats, functional analyses revealed that these diazotrophs were transcribing a substantial proportion of the genes involved in biofilm formation and nitrogen fixation. Overall, our data reveal an unexpectedly high diversity of heterocytous cyanobacteria (e.g. Calothrix, Scytonema, Nodularia, Gloeotrichia, Stigonema, Fischerella and Chlorogloeopsis) that had yet to be described in metahaline and hypersaline microbial mats from Shark Bay and that they play a vital role in sustaining the ecosystem functioning of coastal‐marine microbial mat systems. [ABSTRACT FROM AUTHOR]

The Konya Closed Basin (KCB) in Türkiye plays a key role in agricultural production and freshwater supply. However, the basin is impacted by humanly derived nitrogenous compounds and toxic metals. Keeping the water quality at a potable level in the basin is compulsory. This study was part of a project yielding monitoring of water quality in KCB in accordance with the Water Framework Directive (2000/60/EC). Eleven stations, except Beyşehir Lake and Mamasın Dam, were sampled for the first time for freshwater molluscs. Community structure indexes and multivariate statistical analyses were applied to determine the microhabitats of gastropods and their responses to environmental changes. The structure and distribution of gastropod assemblages differed depending on total phosphate, total nitrogen, dissolved oxygen, and pH. This study revealed that most of the gastropods in KCB are relatively tolerant to biodegradable pollution. However, there is a strong observed decline in population size requiring intensive future monitoring; measures have to be taken to preserve the remaining populations. Two endemic species need an urgent action plan to protect their habitats: Theodoxus anatolicus of Çeltik Canal and Bithynia pseudemmericia of Beyşehir Lake; a re-assessment of their extinction risk according to the IUCN rules is needed (2022). The results of this study will be useful for comparison with future studies to document potential improvements or continued ecological regression in the quality of aquatic ecosystems in the watershed. [ABSTRACT FROM AUTHOR]

Aim: Biological invasions are a major threat to biodiversity in aquatic and terrestrial habitats. Insects represent an important group of species in freshwater and terrestrial habitats, and they constitute a large proportion of non‐native species. However, while many non‐native insects are known from terrestrial ecosystems, they appear to be less represented in freshwater habitats. Comparisons between freshwater and terrestrial habitats of invader richness relative to native species richness are scarce, which hinders syntheses of invasion processes. Here, we used data from three regions on different continents to determine whether non‐native insects are indeed under‐represented in freshwater compared with terrestrial assemblages. Location: Europe, North America, New Zealand. Methods: We compiled a comprehensive inventory of native and non‐native insect species established in freshwater and terrestrial habitats of the three study regions. We then contrasted the richness of non‐native and native species among freshwater and terrestrial insects for all insect orders in each region. Using binomial regression, we analysed the proportions of non‐native species in freshwater and terrestrial habitats. Marine insect species were excluded from our analysis, and insects in low‐salinity brackish water were considered as freshwater insects. Results: In most insect orders living in freshwater, non‐native species were under‐represented, while they were over‐represented in a number of terrestrial orders. This pattern occurred in purely aquatic orders and in orders with both freshwater and terrestrial species. Overall, the proportion of non‐native species was significantly lower in freshwater than in terrestrial species. Main conclusions: Despite the numerical and ecological importance of insects among all non‐native species, non‐native insect species are surprisingly rare in freshwater habitats. This is consistent across the three investigated regions. We review hypotheses concerning species traits and invasion pathways that are most likely to explain these patterns. Our findings contribute to a growing appreciation of drivers and impacts of biological invasions. [ABSTRACT FROM AUTHOR]

Many studies examining plant and terrestrial invertebrate communities have revealed the high conservation potential of spoil heaps. On the other hand, the freshwater communities inhabiting post‐mining ponds within these human‐made habitats are almost unexplored. We focused on aquatic macroinvertebrate, zooplankton, and phytoplankton communities in the littoral zones of 24 ponds situated on spoil heaps created after lignite mining in the Czech Republic. We compared environmental factors, taxa richness, and conservation value (number of threatened aquatic macroinvertebrate species) in the ponds, based on the type of restoration approach applied, that is, technical reclamation, spontaneous succession, and their combination (semi‐spontaneous succession). While macroinvertebrate and zooplankton taxa richness did not differ significantly between the three types of pond, the phytoplankton community did, with the highest taxa richness recorded in technically established ponds. From a nature conservation point of view, the spontaneously developed ponds hosted almost twice as many threatened macroinvertebrates as the other ponds; nevertheless, even the technically constructed ponds hosted considerable populations of rare species, e.g. the regionally extinct beetle Limnebius nitidus (Marsham, 1802), and contributed to the overall conservation value of the spoil heaps. The most significant driver structuring post‐mining pond freshwater communities was the percentage of vegetation in the littoral zone. [ABSTRACT FROM AUTHOR]

Twelve new specimens of sporidesmium-like taxa were collected from freshwater habitats in China and Thailand. Phylogenetic analysis of nuc 28S rDNA (LSU), internal transcribed spacer (ITS), translation elongation factor 1-alpha (TEF1-α) and second-largest subunit of RNA polymerase II (RPB2) sequence data, combined with morphological data, revealed that they are Distoseptispora species. Among them, six new species, including D. aqualignicola, D. aquamyces, D. crassispora, D. curvularia, D. nonrostrata and D. pachyconidia, are introduced. Two new combinations, D. adscendens and D. leonensis, are transferred from Ellisembia. A new habitat and geographical record are reported for D. clematidis, collected from a freshwater habitat in China. New RPB2 sequence data for D. dehongensis are provided. [ABSTRACT FROM AUTHOR]

Freshwater recreational angling is growing in popularity internationally. Due to the potential negative environmental impacts, various regulatory systems exist. In South Africa, freshwater recreational angling is regulated through a complex legal framework, consisting of national and provincial legislation dating back to the 1960s. The legislation also relates to historical and current provincial boundaries, adding to the regulatory complexity. Due to this complexity, the question arises whether freshwater recreational bank anglers in South Africa are aware of the regulatory requirements applicable to them. Low levels of awareness could lead to non-compliance, which would suggest an ineffective regulatory system. The aim of this research was thus to determine the environmental regulatory awareness of freshwater recreational bank anglers in South Africa. This was achieved through a literature review of national and provincial legislation, as well as the rules applicable to organised freshwater recreational bank angling. An online survey was completed by 100 members of the South African Freshwater Bank Angling Federation (SAFBAF). The results of the survey indicate that the regulatory awareness of the sample of SAFBAF freshwater recreational anglers is low in certain key areas, such as bag and size limits for specific fish species, catch and release requirements, as well as legal definitions for alien and invasive and TOPS species listings. However, the low level of awareness can be ascribed to the complex regulatory system and not unwillingness of anglers to comply per se. It is recommended that (i) a single consolidated and simplified regulatory system for freshwater recreational bank angling be developed, and (ii) that angling organisational and competition rules be aligned with relevant regulatory requirements, to improve overall awareness and promote higher levels of regulatory compliance. [ABSTRACT FROM AUTHOR]

Surfactants are used to control microbial biofilms in industrial and medical settings. Their known toxicity on aquatic biota, and their longevity in the environment, has encouraged research on biodegradable alternatives such as rhamnolipids. While previous research has investigated the effects of biological surfactants on single species biofilms, there remains a lack of information regarding the effects of synthetic and biological surfactants in freshwater ecosystems. We conducted a mesocosm experiment to test how the surfactant sodium dodecyl sulfate (SDS) and the biological surfactant rhamnolipid altered community composition and metabolic activity of freshwater biofilms. Biofilms were cultured in the flumes using lake water from Lake Lunz in Austria, under high (300 ppm) and low (150 ppm) concentrations of either surfactant over a four-week period. Our results show that both surfactants significantly affected microbial diversity. Up to 36% of microbial operational taxonomic units were lost after surfactant exposure. Rhamnolipid exposure also increased the production of the extracellular enzymes, leucine aminopeptidase, and glucosidase, while SDS exposure reduced leucine aminopeptidase and glucosidase. This study demonstrates that exposure of freshwater biofilms to chemical and biological surfactants caused a reduction of microbial diversity and changes in biofilm metabolism, exemplified by shifts in extracellular enzyme activities. Key points: • Microbial biofilm diversity decreased significantly after surfactant exposure. • Exposure to either surfactant altered extracellular enzyme activity. • Overall metabolic activity was not altered, suggesting functional redundancy. [ABSTRACT FROM AUTHOR]

The fungal-like family Saprolegniaceae (Oomycota), also called "water mold," includes mostly aquatic saprophytes as well as notorious aquatic animal pathogens. Most studies on Saprolegniaceae have been biased toward pathogenic species that are important to aquaculture rather than saprotrophic species, despite the latter's crucial roles in carbon cycling of freshwater ecosystems. Few attempts have been made to study the diversity and ecology of Saprolegniaceae; thus, their ecological role is not well-known. During a survey of oomycetes between 2016 and 2021, we investigated the diversity and distribution of culturable Saprolegniaceae species in freshwater ecosystems of Korea. In the present study, members of Saprolegniaceae were isolated and identified at species level based on their cultural, morphological, and molecular phylogenetic analyses. Furthermore, substrate preference and seasonal dynamics for each were examined. Most of the species were previously reported as animal pathogens; however, in the present study, they were often isolated from other freshwater substrates, such as plant debris, algae, water, and soil sediment. The relative abundance of Saprolegniaceae was higher in the cold to cool season than that in the warm to hot season of Korea. This study enhances our understanding of the diversity and ecological attributes of Saprolegniaceae in freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Freshwater ascomycetes are a group of fungi of great ecological importance because they are involved in decomposition processes and the recycling of organic matter in aquatic ecosystems. The taxonomy of these fungi is complex, with representatives in several orders of the phylum Ascomycota. In the present study, we collected ninety-two samples of plant debris submerged in freshwater in different locations in Spain. The plant specimens were placed in wet chambers and developed several fungi that were later isolated in pure culture. A main phylogenetic tree using the nucleotide sequences of D1–D2 domains of the 28S nrRNA gene (LSU) was built to show the taxonomic placement of all our fungal strains, and, later, individual phylogenies for the different families were built using single or concatenated nucleotide sequences of the most suitable molecular markers. As a result, we found a new species of Amniculicola that produces a coelomycetous asexual state, a new species of Elongatopedicellata that produces an asexual state, a new species of Neovaginatispora that forms both sexual and asexual states in vitro, and the sexual states of two species of Pyrenochaetopsis, none of which have been reported before for these genera. In addition, we describe a new species of Pilidium characterized by the production of copper-colored globose conidiomata, and of Pseudosigmoidea, which produces well-developed conidiophores. [ABSTRACT FROM AUTHOR]

This series of papers highlights research into how biological exchanges between salty and freshwater habitats have transformed the biosphere. Life in the ocean and in freshwaters have long been intertwined; multiple major branches of the tree of life originated in the oceans and then adapted to and diversified in freshwaters. Similar exchanges continue to this day, including some species that continually migrate between marine and fresh waters. The series addresses key themes of transitions, transformations, and current threats with a series of questions: When did major colonizations of fresh waters happen? What physiographic changes facilitated transitions? What organismal characteristics facilitate colonization? Once a lineage has colonized freshwater, how frequently is there a return to the sea? Have transitions impelled diversification? How do organisms adapt physiologically to changes in halohabitat, and are such adaptive changes predictable? How do marine and freshwater taxa differ in morphology? How are present-day global changes in the environment influencing halohabitat and how are organisms contending with them? The purpose of the symposium and the papers in this volume is to integrate findings at multiple levels of biological organization and from disparate fields, across biological and geoscience disciplines. [ABSTRACT FROM AUTHOR]

The Threespine Stickleback is ancestrally a marine fish, but many marine populations breed in fresh water (i.e. are anadromous), facilitating their colonization of isolated freshwater habitats a few years after they form. Repeated adaptation to fresh water during at least 10 My and continuing today has led to Threespine Stickleback becoming a premier system to study rapid adaptation. Anadromous and freshwater stickleback breed in sympatry and may hybridize, resulting in introgression of freshwater-adaptive alleles into anadromous populations, where they are maintained at low frequencies as ancient standing genetic variation. Anadromous stickleback have accumulated hundreds of freshwater-adaptive alleles that are disbursed as few loci per marine individual and provide the basis for adaptation when they colonize fresh water. Recent whole-lake experiments in lakes around Cook Inlet, Alaska have revealed how astonishingly rapid and repeatable this process is, with the frequency of 40% of the identified freshwater-adaptive alleles increasing from negligible (∼1%) in the marine founder to ≥50% within ten generations in fresh water, and freshwater phenotypes evolving accordingly. These high rates of genomic and phenotypic evolution imply very intense directional selection on phenotypes of heterozygotes. Sexual recombination rapidly assembles freshwater-adaptive alleles that originated in different founders into multilocus freshwater haplotypes, and regions important for adaptation to freshwater have suppressed recombination that keeps advantageous alleles linked within large haploblocks. These large haploblocks are also older and appear to have accumulated linked advantageous mutations. The contemporary evolution of Threespine Stickleback has provided broadly applicable insights into the mechanisms that facilitate rapid adaptation. [ABSTRACT FROM AUTHOR]

During the study of lignicolous freshwater fungi from Thailand, three pleurotheciaceous species were collected from freshwater habitats in Thailand. Two were identified as Pleurothecium aquaticum and Rhexoacrodictys fimicola, and the third is a new species Dematipyriforma muriformis sp. nov.. Rhexoacrodictys is accepted in Pleurotheciaceae based on phylogenetic analysis. Rhexoacrodictys nigrospora is transferred to Dematipyriforma based on phylogenetic analysis and morphological characters. Pleurothecium aquaticum and Rhexoacrodictys fimicola are reported from Thailand for the first time. [ABSTRACT FROM AUTHOR]

Although Corbicula fluminea has been one of the more prolific freshwater invasive species in the world, previous studies have suggested a low probability for overwinter survival in northern latitudes without an artificially created thermal refuge. The discovery of live C. fluminea in a central Minnesota lake absent any known thermal refuge in 2020 presented an opportunity to further evaluate the overwinter survival and population structure of C. fluminea at the presumed edge of their potential range. The population was monitored from December 2020 through September 2021 alongside water temperature to better understand at which temperatures C. fluminea survived and if the population structure suggested reproduction occurring in the lake. We documented live C. fluminea in temperatures as low as 0.3°C. Shell size of recovered individuals suggested multiple cohorts, and the appearance of a new cohort at the end of the study, indicating active reproduction in the lake and suggesting the population had likely been present in the lake for at least two winters by the conclusion of the study period. Our findings provide evidence of the survival below historically documented lower lethal temperature limits and suggests adaptations to modeling predicting suitable habitat, both present and in a changing climate, are necessary to better assess risk of invasion by this species. [ABSTRACT FROM AUTHOR]

Arthrobotrys is the most complex genus of Orbiliaceae nematode-trapping fungi. Its members are widely distributed in various habitats worldwide due to their unique nematode-trapping survival strategies. During a survey of nematophagous fungi in Yunnan Province, China, twelve taxa were isolated from terrestrial soil and freshwater sediment habitats and were identified as six new species in Arthrobotrys based on evidence from morphological and multigene (ITS, TEF, and RPB2) phylogenetic analyses. These new species i.e., Arthrobotrys eryuanensis, A. jinpingensis, A. lanpingensis, A. luquanensis, A. shuifuensis, and A. zhaoyangensis are named in recognition of their places of origin. Morphological descriptions, illustrations, taxonomic notes, and a multilocus phylogenetic analysis are provided for all new taxa. In addition, a key to known species in Arthrobotrys is provided, and the inadequacies in the taxonomic study of nematode-trapping fungi are also discussed. [ABSTRACT FROM AUTHOR]

The risk of a newly discovered non-native fish species in Florida (USA): Cichlasoma dimerus ([Heckel, 1840]; Family: Cichlidae) is assessed. Its tolerance to cold temperatures was experimentally evaluated and information on its biology and ecology was synthesized. In the cold-temperature tolerance experiment, temperature was lowered from 24 °C by increments of 1 °C per hour, mimicking a typical cold weather front. Fish lost equilibrium at a mean temperature of 7.8 °C and died at 4.7 °C. Those values are lower than most other non-native fishes from the state that have been experimentally evaluated, and it appears C. dimerus is the most cold-tolerant cichlid established in Florida. The combination of cold-temperature tolerance and other biological/ecological factors (e.g., adult size, reproduction and parental care, diet, habitat, and other behaviors) along with the geographic range and habitat diversity of specimens vouchered in museums, indicate C. dimerus may be able to invade many freshwater ecosystems in the state, including environmentally sensitive freshwater springs. [ABSTRACT FROM AUTHOR]

Many biodiversity studies focus on explaining high tropical species richness, but an equally dramatic yet understudied pattern involves the divergent richness of land, sea and freshwater. Here, we reveal the origins of these richness differences among habitats across animals and plants. Most plant and animal species are terrestrial, although these habitats cover only ~28% of Earth's surface. Marine habitats have fewer species over a larger area (~70%). Freshwater habitats have relatively high richness and exceptional phylogenetic diversity given their tiny area (2%). The relative richness of habitats is related to variation in diversification rates. Based on ancestral reconstructions of habitat, we find that most marine species are descended from marine ancestors and most terrestrial species from freshwater ancestors. Yet, most extant animal richness in freshwater is derived from terrestrial ancestors. Overall, our results reveal the origins of fundamental but neglected biodiversity patterns, and highlight the conservation importance of freshwater habitats. [ABSTRACT FROM AUTHOR]

Climate change and pollution are affecting remote mountain ecosystems that have traditionally been described as pristine. Due to the environmental stress factors present in mountain freshwater systems, their organisms may be more sensitive to change. The damage caused to them will also have repercussions downstream. Michael Gross reports. Climate change and pollution are affecting remote mountain ecosystems that have traditionally been described as pristine. Due to the environmental stress factors present in mountain freshwater systems, their organisms may be more sensitive to change. The damage caused to them will also have repercussions downstream. [ABSTRACT FROM AUTHOR]

The widespread salinisation of freshwater ecosystems poses a major threat to the biodiversity, functioning, and services that they provide. Human activities promote freshwater salinisation through multiple drivers (e.g., agriculture, resource extraction, urbanisation) that are amplified by climate change. Due to its complexity, we are still far from fully understanding the ecological and evolutionary consequences of freshwater salinisation. Here, we assess current research gaps and present a research agenda to guide future studies. We identified different gaps in taxonomic groups, levels of biological organisation, and geographic regions. We suggest focusing on global- and landscape-scale processes, functional approaches, genetic and molecular levels, and eco-evolutionary dynamics as key future avenues to predict the consequences of freshwater salinisation for ecosystems and human societies. The global acceleration of freshwater salinisation due to human activities such as agriculture, resource extraction, and urbanisation and its amplification by climate change is unequivocal. Although research in this field is growing, there are key aspects at the ecological and evolutionary levels that remain unaddressed. Increasing salinisation is a problem as it can increase the stress or mortality of freshwater organisms, leading to a loss of diversity and/or functionality of freshwater ecosystems but also the services and benefits to human societies that they provide. We identify the main gaps of recent research and suggest a research agenda to facilitate future research efforts in order to achieve a more comprehensive understanding on freshwater salinisation. [ABSTRACT FROM AUTHOR]

Since 2011, we have collected fungi that form synnema-like structures (SSs) bearing many acanthophyses at the apex on water-splashed wood in streams in various regions of Japan. A provisional phylogenetic analysis of strains isolated from SSs based on their nrDNA sequences implied affinity with Physisporinus (Polyporales, Basidiomycota). However, it has not been reported that this genus forms SSs in freshwater habitats. We found a fungus forming not only SSs on the water-boundary part of wood but also resupinate basidiocarps with poroid hymenophores on nonsubmerged parts, and the morphological characteristics of the basidiocarps matched those of Physisporinus. Therefore, we investigated the relationship between SS-forming fungi and their sexual states by taxonomic approaches. Phylogenetic analyses based on nrDNA internal transcribed spacer (ITS) and large subunit (LSU) sequences indicated that SS-forming fungi diverged into five clades in Physisporinus. Each clade was discriminated by the color of SSs, morphology of acanthophyses, and cultural characteristics. Of the five clades, Clade 1, which consisted only of sequences of strains isolated from SSs and basidiocarps produced on rhizomorphs, was closely related to P. eminens and P. undatus, but the morphology of basidiocarps and the manner of basidiocarp development differed. Clade 5 was closely related to P. castanopsidis, P. crocatus, P. pouzarii, P. sanguinolentus, P. subcrocatus, P. tibeticus, and P. vitreus, but the basidiocarp morphology differed. Therefore, Clades 1 and 5 were described as two new species. Regarding Clades 2, 3, and 4, further taxonomic studies with additional specimens are required. SS and acanthophysis formation in wet habitats in streams and in culture could be recognized as new taxonomic and ecological characters of Physisporinus. [ABSTRACT FROM AUTHOR]

Aim: To assess spatio‐temporal and taxonomic patterns of available information on the costs of invasive freshwater bivalves, as well as to identify knowledge gaps. Location: Global. Time period: 1980–2020. Taxon studied: Bivalvia. Methods: We synthesize published global economic costs of impacts from freshwater bivalves using the InvaCost database and associated R package, explicitly considering the reliability of estimation methodologies, cost types, economic sectors and impacted regions. Results: Cumulative total global costs of invasive macrofouling bivalves were $ 63.7 billion (2017 US$) across all regions and socio‐economic sectors between 1980 and 2020. Costs were heavily biased taxonomically and spatially, dominated by two families, Dreissenidae and Cyrenidae (Corbiculidae), and largely reported in North America. The greatest share of reported costs ($ 31.5 billion) did not make the distinction between damage and management. However, of those that did, damages and resource losses were one order of magnitude higher ($ 30.5 billion) than control or preventative measures ($ 1.7 billion). Moreover, although many impacted socio‐economic sectors lacked specification, the largest shares of costs were incurred by authorities and stakeholders ($ 27.7 billion, e.g., public and private sector interventions) and through impacts on public and social welfare ($ 10.1 billion, e.g., via power/drinking water plant and irrigation system damage) in North America. Average cost estimates over the entire period amounted to approximately $ 1.6 billion per year, most of which was incurred in North America. Main conclusions: Our results highlight the burgeoning economic threat caused by invasive freshwater bivalves, offering a strong economic incentive to invest in preventative management such as biosecurity and rapid response eradications. Even if the damages and resource losses are severely understated because economic impacts are lacking for most invaded countries and invasive bivalve species, these impacts are substantial and likely growing. [ABSTRACT FROM AUTHOR]

Aggressive encounters between invasive and native species are considered a key threat associated with the spread of invasive species. Extrinsic factors such as habitat complexity can profoundly influence the outcome of aggressive interactions between conspecifics, and this may also be the case in invasive‐native species interactions. This study used invasive and native freshwater crayfish species in Australia as a model system to investigate the influence of habitat complexity on aggression in both intraspecific and interspecific contests. Paired contests between the native Euastacus spinifer and the invasive Cherax destructor were conducted in the laboratory under high and low habitat complexity conditions. Furthermore, the influence of prior residency was examined, with one individual assigned the resident and the other as the intruder. In intraspecific contests, the number of interactions and aggression score were significantly reduced under high complexity conditions; however, complexity had no effect on the time spent interacting and contest outcome. Instead, the two crayfish species differed in terms of time spent interacting. In interspecific contests, complexity had no effect on any of the aggression metrics. Alarmingly, however, we demonstrate that when C. destructor was a resident the likelihood that E. spinifer won a contest fell to a mere 8% compared to 31% when E. spinifer was resident. This study suggests that while habitat complexity plays a role in shaping aggressive behaviour in intraspecific interactions, invasive species are competitively dominant if they are already established i.e. resident in a location and even as intruders. Therefore, preserving habitat complexity in freshwater systems may not be sufficient to sustain populations of native species, and other measures that mitigate the potential for range overlap between the species would also be needed to prevent the further spread of invasive species such as C. destructor within freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Background: Odonata (dragonfly and damselfly) are particularly good indicators of freshwater ecosystem health. The constant disturbance of freshwater habitats can result in the reduction of Odonata species diversity. Changes in Odonata biodiversity are influenced by several human activities, such as agriculture, urbanization, input of pollutants in water and construction. This study was carried out to assess the abundance and diversity of Odonata, evaluate the physicochemical characteristics of water, and compare the community structure of Odonata at three selected sites along River Aponmu in Ipogun. Adult odonates were sampled and identified for 11 months using a sweep net, water samples were collected and some parameters were determined during the study period. Results: A total of 906 specimens representing sixty-four (64) species and sixteen (16) genera in seven (7) families (Coenagrionidae, Lestidae, Platycnemididae, Chlorocyphidae, Calopterygidae, Libellulidae, and Gomphidae) were collected and identified. Of the 906 specimens, Libellulidae had the highest percentage composition (44%) with 395 individuals out of which Trithemis arteriosa (a pollution tolerant species) had the highest number of individuals (225) and Gomphidae had the lowest percentage composition (0.03%) with 1 individual. Most of the species collected are known for their tolerance to disturbed environments. They include Pseudagrion melanicterum, Paragomphus genei, and Orthetrum Julia. Aponmu area had the highest species diversity (H′ = 2.312) while Idi area had the least species diversity (H′ = 2.021). Alaasin area had the highest Simpson_d value (0.8557) and the best taxa distribution (Evenness = 0.524; Equitability_J = 0.7764) which makes the area more pristine than other sites while Aponmu area had the least distribution (Evenness = 0.3365; Equitability_J = 0.6798). Analysis of variance (ANOVA) result of physicochemical parameters revealed that temperature (°C), pH, Dissolved Oxygen (mg/L), turbidity (NTU), Biochemical Oxygen Demand (mg/L), NO3 (mg/L), and PO4 (mg/L) did not show significant difference at the three sites while EC (µS/cm) and TDS (mg/L) which have moderately high mean values indicated significant difference at Aponmu area (p < 0.05). T. arteriosa exhibited a weak negative correlation to both temperature and DO. Conclusions: This study has provided information on Odonata assemblage at River Aponmu and infers based on the assemblage that the river may be somewhat polluted at the period the research was carried out. It is therefore recommended that efforts should therefore be taken to discourage water pollution in order to preserve the diversity of these insects and the water quality. [ABSTRACT FROM AUTHOR]

Worldwide, scientists are increasingly collaborating with the general public. Citizen science methods are readily applicable to freshwater research, monitoring, and education. In addition to providing cost‐effective data on spatial and temporal scales that are otherwise unattainable, citizen science provides unique opportunities for engagement with local communities and stakeholders in resource management and decision‐making. However, these methods are not infallible. Citizen science projects require deliberate planning in order to collect high data quality and sustain meaningful community partnerships. Citizen science practitioners also have an ethical responsibility to ensure that projects are not putting the safety of participants at stake. We discuss here how citizen science is being applied in freshwater research, emerging challenges in project planning and implementation, as well as how citizen science is shaping public understanding, policy, and management of freshwaters. This article is categorized under:Science of Water > Water QualityWater and Life > Conservation, Management, and AwarenessHuman Water > Water GovernanceWater and Life > Methods [ABSTRACT FROM AUTHOR]

Freshwater habitats are under stress from agricultural land use, most notably the influx of neonicotinoid pesticides and increased nutrient pressure from fertilizer. Traditional studies investigating the effects of stressors on freshwater systems are often limited to a narrow range of taxa, depending heavily on morphological expertise. Additionally, disentanglement of multiple simultaneous stressors can be difficult in field studies, whereas controlled laboratory conditions do not accurately reflect natural conditions and food webs. To overcome these drawbacks, we investigated the impacts of two agricultural stressors (the neonicotinoid insecticide thiacloprid and fertilizer) in full‐factorial design in a semi‐natural research site, using environmental DNA sampling to study three different taxonomic groups representing three trophic levels: bacteria (decomposers), phytoplankton (primary producers), and chironomids (consumers). The results show considerable impact of both stressors across trophic levels, with an additive effect of fertilizer and thiacloprid on community composition at all levels. These findings suggest that agricultural stressors affect the entire food web, either directly or through cascade reactions. They are also consistent with morphological assessments that were performed in the same study site, even at a lower number of replicates. The study presented shows that the use of multimarker environmental DNA provides a more comprehensive assessment of stressor impacts across multiple trophic levels, at a higher taxonomic resolution than traditional surveys. Additionally, many putative novel bioindicators for both agricultural stressors were discovered. We encourage further investigations into stressors impacts at different trophic levels, which will lead to more effective monitoring and management of freshwater systems. [ABSTRACT FROM AUTHOR]