Reservoir ecosystems support large pools of fish biomass.

Humans increasingly dominate Earth's natural freshwater ecosystems, but biomass production of modified ecosystems is rarely studied. We estimate potential fish total standing stock in USA reservoirs is 3.4 billion (B) kg, and approximate annual secondary production is 4.5 B kg y-1. We also observe varied and non-linear trends in reservoir fish biomass over time, thus previous assertions that reservoir fisheries decline over time are not universal. Reservoirs are globally relevant pools of freshwater fisheries, in part due to their immense limnetic footprint and spatial extent. This study further shows that reservoir ecosystems play major roles in food security and fisheries conservation. We encourage additional effort be expended to effectively manage reservoir environments for the good of humanity, biodiversity, and fish conservation.

Dearomatization drives complexity generation in freshwater organic matter.

Dissolved organic matter (DOM) is one of the most complex, dynamic and abundant sources of organic carbon, but its chemical reactivity remains uncertain1-3. Greater insights into DOM structural features could facilitate understanding its synthesis, turnover and processing in the global carbon cycle4,5. Here we use complementary multiplicity-edited 13C nuclear magnetic resonance (NMR) spectra to quantify key substructures assembling the carbon skeletons of DOM from four main Amazon rivers and two mid-size Swedish boreal lakes. We find that one type of reaction mechanism, oxidative dearomatization (ODA), widely used in organic synthetic chemistry to create natural product scaffolds6-10, is probably a key driver for generating structural diversity during processing of DOM that are rich in suitable polyphenolic precursor molecules. Our data suggest a high abundance of tetrahedral quaternary carbons bound to one oxygen and three carbon atoms (OCqC3 units). These units are rare in common biomolecules but could be readily produced by ODA of lignin-derived and tannin-derived polyphenols. Tautomerization of (poly)phenols by ODA creates non-planar cyclohexadienones, which are subject to immediate and parallel cycloadditions. This combination leads to a proliferation of structural diversity of DOM compounds from early stages of DOM processing, with an increase in oxygenated aliphatic structures. Overall, we propose that ODA is a key reaction mechanism for complexity acceleration in the processing of DOM molecules, creation of new oxygenated aliphatic molecules and that it could be prevalent in nature.

Cyanobacteria and Macroinvertebrate Relationships in Freshwater Benthic Communities beyond Cytotoxicity.

Cyanobacteria are harmful algae that are monitored worldwide to prevent the effects of the toxins that they can produce. Most research efforts have focused on direct or indirect effects on human populations, with a view to gain easy accurate detection and quantification methods, mainly in planktic communities, but with increasing interest shown in benthos. However, cyanobacteria have played a fundamental role from the very beginning in both the development of our planet's biodiversity and the construction of new habitats. These organisms have colonized almost every possible planktic or benthic environment on earth, including the most extreme ones, and display a vast number of adaptations. All this explains why they are the most important or the only phototrophs in some habitats. The negative effects of cyanotoxins on macroinvertebrates have been demonstrated, but usually under conditions that are far from natural, and on forms of exposure, toxin concentration, or composition. The cohabitation of cyanobacteria with most invertebrate groups is long-standing and has probably contributed to the development of detoxification means, which would explain the survival of some species inside cyanobacteria colonies. This review focuses on benthic cyanobacteria, their capacity to produce several types of toxins, and their relationships with benthic macroinvertebrates beyond toxicity.

THE COCCIDIA SPECIES PFEIFFERINELLA ELLIPSOIDES EXHIBITS SPATIAL AND SPECIES-SPECIFIC VARIATION IN PREVALENCE AMONG FRESHWATER SNAILS.

Freshwater snails are commonly studied within the context of their role as intermediate hosts for digenetic trematodes. However, there are fundamental data deficiencies related to our understanding of directly transmitted parasites, such as coccidia, for freshwater snails. Because variation in coccidia pathogenicity and transmission among snail species likely has major impacts on snail community structure, we aimed to investigate the spatial distribution and prevalence of coccidia in several freshwater snail species throughout the Ozark and Ouachita Mountains ecoregions in Arkansas. We opportunistically collected 220 freshwater snails from 24 Ozark sites in summer 2022 and scanned fecal slides for the presence of coccidia. In summer 2023, we surveyed an additional 146 snails from 19 Ouachita sites. To test for apparent interactions among coccidia and trematodes, we scanned feces from a subset of snails (Physa and Planorbella in the Ozarks) that did not have concurrent trematode infections and from those that did. We observed oocysts that morphologically conformed to Pfeifferinella ellipsoides in 2 of the 9 snail taxa from 7 of the 43 sites. Planorbella trivolvis was infected at 2 of 6 sites in the Ozarks and 0 of 5 sites in the Ouachitas. Physa species were infected at 6 of 14 sites in the Ozarks and 0 of 12 sites in the Ouachitas. In the Ozarks, Pl. trivolvis had an overall prevalence of 0.13 (6 of 47), whereas individuals in the genus Physa had an overall prevalence of 0.08 (8 of 97). Our chi-square and Fisher exact tests revealed no significant evidence for trematode-coccidia competition or synergism within the two snail species. There were no other species infected, and we did not observe any coccidia in the snails from the Ouachitas. Our survey of 366 snails among 9 taxa and 43 sites represents the largest survey for freshwater snail coccidia to date and indicates that both Pl. trivolvis and Physa spp. may be primary hosts and/or reservoir hosts for Pf. ellipsoides in freshwater snail communities. The highly aggregated distribution of Pf. ellipsoides in northwestern Arkansas requires further investigation. Our results led to proposal of several hypotheses for additional research, including questions regarding the variation of coccidia host specificity and virulence.

Influence of temporary emigration on wood turtle (Glyptemys insculpta) detectability, with implications for abundance estimation.

Reliable population estimates are important for making informed management decisions about wildlife species. Standardized survey protocols have been developed for monitoring population trends of the wood turtle (Glyptemys insculpta), a semi-aquatic freshwater turtle species of conservation concern throughout its distribution in east-central North America. The protocols use repeated active search surveys of defined areas, allowing for estimation of survey-specific detection probability (p) and site-specific abundance. These protocols assume population closure within the survey area during the survey period, which is unlikely to be met as wood turtles are a highly mobile species. Additionally, current protocols use a single-pass design that does not allow for separation of availability (pa) and detectability (pd). If there are systematic influences on pa or pd that are not accounted for in the survey design or data analysis, then resulting abundance estimates could be biased. The objectives of this study were to determine if pa is a random process and if pa and pd are influenced by demographic characteristics. We modified the wood turtle survey protocol used in the upper Midwest to include a double-pass design, allowing us to estimate pa and pd using a robust design capture-recapture model. The modified protocol was implemented at 14 wood turtle monitoring sites in Minnesota and Wisconsin between 2017 and 2022. Our results indicated that pa was non-random and that pd increased with turtle carapace length. Our study suggests that model assumptions for current wood turtle population models may be violated, likely resulting in an overestimation of abundance. We discuss possible protocol and modeling modifications that could result in more accurate wood turtle abundance estimates.

Some trematodes including three new species from freshwater fishes of Venezuela.

The present paper comprises a systematic survey of trematodes found in 13 species of freshwater fishes in Venezuela collected in 1992, 1996 and 2001. The following 15 trematode species were recorded: Adults: Genarchella venezuelaensis sp. n., Thometrema dissimilis sp. n., Megacoelium spinicavum Thatcher et Varella, 1981, Doradamphistoma bacuense Thatcher, 1999, Crassicutis cichlasomae Manter, 1936, Parspina carapo Ostrowski de Núñez, Arredonto et Gil de Pertierra, 2011, Phyllodistomoides hoplerythrini sp. n. Larvae (metacercariae): Clinostomatopsis sorbens (Braun, 1899), Clinostomum marginatum (Rudolphi, 1819), C. detruncatum Braun, 1899, Ithyoclinostomum dimorphum (Diesing, 1850), Odhneriotrema microcephala (Travassos, 1922), Tylodelphys sp., Posthodiplostomum sp., Sphincterodiplostomum sp. All these parasites are reported from Venezuela for the first time and many of these findings represent new host records. The new species G. venezuelaensis sp. n., T. dissimilis sp. n. and P. hoplerythrini sp. n. were collected from the accessory respiratory organ of Loricariichthys brunneus (Hancock) (Loricariidae), from the stomach of Hoplerythrinus unitaeniatus (Spix et Agassiz) (Erythrinidae) and from the intestine of H. unitaeniatus, respectively. All parasites are briefly described and illustrated and problems concerning their morphology, taxonomy, hosts and geographical distribution are discussed. Megacoelium spinispecum Thatcher et Varella, 1981 is considered a junior synonym of M. spinicavum Thatcher et Varella, 1981, and Crassicutis opisthoseminis Bravo-Hollis et Arroyo, 1962 as a junior synonym of C. cichlasomae Manter, 1936.

Spatial versus spatio-temporal approaches for studying metacommunities: a multi-taxon analysis in Mediterranean and tropical temporary ponds.

Prior research on metacommunities has largely focused on snapshot surveys, often overlooking temporal dynamics. In this study, our aim was to compare the insights obtained from metacommunity analyses based on a spatial approach repeated over time, with a spatio-temporal approach that consolidates all data into a single model. We empirically assessed the influence of temporal variation in the environment and spatial connectivity on the structure of metacommunities in tropical and Mediterranean temporary ponds. Employing a standardized methodology across both regions, we surveyed multiple freshwater taxa in three time periods within the same hydrological year from multiple temporary ponds in each region. To evaluate how environmental, spatial and temporal influences vary between the two approaches, we used nonlinear variation partitioning analyses based on generalized additive models. Overall, this study underscores the importance of adopting spatio-temporal analytics to better understand the processes shaping metacommunities. While the spatial approach suggested that environmental factors had a greater influence, our spatio-temporal analysis revealed that spatial connectivity was the primary driver influencing metacommunity structure in both regions. Temporal effects were equally important as environmental effects, suggesting a significant role of ecological succession in metacommunity structure.

Global introductions and environmental impacts of freshwater megafish.

Freshwater megafish species, such as sturgeons, salmonids, carps, and catfishes, have a maximum reported weight ≥30 kg. Due to their charisma and economic value, they have been widely introduced outside of their native ranges. Here, we provide a comprehensive overview of the introduction of freshwater megafish and an assessment of their environmental impacts. Of the 134 extant freshwater megafish species, 46% have been introduced to new environments, and of these, 69% have established self-sustaining alien populations. These introductions affect 59% of the world's main basins, with the USA and western Europe being particular hotspots of megafish introductions. The common carp (Cyprinus carpio) is the most widely introduced species. Using the Environmental Impact Classification for Alien Taxa (EICAT and EICAT+) frameworks, we assessed the severity and type of negative and positive impacts posed by alien megafish on native species. Alien megafish caused negative impacts through nine different mechanisms, with predation being the most frequently reported mechanism, followed by herbivory and competition. Moreover, 58% of the alien megafish species with sufficient data to evaluate the severity of their impacts caused declining populations of native species, or worse, extirpations of native species populations. The positive environmental impacts of alien megafish were far less frequently documented. They include biotic interactions that benefit native species, and the provision of trophic resources or habitats. Widely introduced or extensively studied species are more likely to have documented severe impacts on native species. There is a clear trade-off between the economic benefits associated with megafish introductions and the severe adverse impacts they have on native biodiversity. Our study highlights the need for comprehensive risk assessments to evaluate the potential environmental impacts of megafish. More research and long-term monitoring schemes are required to inform management actions to protect biodiversity, particularly in the Global South.

Sphingobium cyanobacteriorum sp. nov., isolated from fresh water.

A novel Gram-stain-negative, yellow-pigmented, short rod-shaped bacterial strain, HBC34T, was isolated from a freshwater sample collected from Daechung Reservoir, Republic of Korea. The results of 16S rRNA gene sequence analysis indicated that HBC34T was affiliated with the genus Sphingobium and shared the highest sequence similarity to the type strains of Sphingobium vermicomposti (98.01 %), Sphingobium psychrophilum (97.87 %) and Sphingobium rhizovicinum (97.59 %). The average nucleotide identity (ANI) and digital DNA-DNA hybridisation (dDDH) values between HBC34T and species of the genus Sphingobium with validly published names were below 84.01 and 28.1 %, respectively. These values were lower than the accepted species-delineation thresholds, supporting its recognition as representing a novel species of the genus Sphingobium. The major fatty acids (>10 % of the total fatty acids) were identified as summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and summed feature 3 (C16 : 1ω7c and/or C16 : 1ω6c). The main polar lipids were phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, two phospholipids and two unidentified polar lipids. The respiratory quinone was Q-10. The genomic DNA G+C content of HBC34T was 64.04 %. The polyphasic evidence supports the classification of HBC34T as the type strain of a novel species of the genus Sphingobium, for which the name Sphingobium cyanobacteriorum sp. nov is proposed. The type strain is HBC34T (= KCTC 8002T= LMG 33140T).

Building adjustment capacity to cope with running water in cultured grass carp through flow stimulation conditions.

The adaptability of cultured fish to complex flow conditions is crucial for their survival after being released into the wild. Running water in natural environments poses significant challenges for the proliferation and release of cultured fish. This study aimed to investigate the effects of flow stimulation on the adjustment capacity of cultured fish to cope with running water. The target fish were cultured grass carp. An annular flume was used to conduct tests on training and control groups. The results demonstrated an enhancement in the adjustment capacity of cultured fish following appropriate flow stimulation training. (1) The trained fish exhibited a heightened preference for low-velocity areas. (2) The trained fish displayed the ability to select a route characterized by low energy consumption, predominantly following the periphery of the low-velocity area. This suggested that an appropriate flow velocity could improve the sensitivity of training fish to water flow information, and their adjustment capacity to cope with running water improved to a certain extent. A higher adjustment capacity allowed them to process flow rate information rapidly and identify a migration strategy with lower energy consumption. This study provides a useful reference for enhancing the survival rate of grass carp through stock enhancement initiatives and contributes to the sustainability of freshwater ecosystems.

Assessment of toxic effects of imidacloprid on freshwater zooplankton: An experimental test for 27 species.

The neonicotinoid pesticide imidacloprid has been used worldwide since 1992. As one of the most important chemicals used in pest control, there have been concerns that its run-off into rivers and lakes could adversely affect aquatic ecosystems, where zooplankton play a central role in the energy flow from primary to higher trophic levels. However, studies assessing the effects of pesticides at the species level have relied on a Daphnia-centric approach, and no studies have been conducted using species-level assessments on a broad range of zooplankton taxa. In the present study, we therefore investigated the acute toxicity of imidacloprid on 27 freshwater crustacean zooplankton (18 cladocerans, 3 calanoid copepods and 6 cyclopoid copepods). The experiment showed that a majority of calanoid copepods and cladocerans were not affected at all by imidacloprid, with the exception of one species each of Ceriodaphnia and Diaphasoma, while all six cyclopoid copepods showed high mortality rates, even at concentrations of imidacloprid typically found in nature. In addition, we found a remarkable intra-taxonomic variation in susceptibility to this chemical. As many cyclopoid copepods are omnivorous, they act as predators as well as competitors with other zooplankton. Accordingly, their susceptibility to imidacloprid is likely to cause different responses at the community level through changes in predation pressure as well as changes in competitive interactions. The present results demonstrate the need for species-level assessments of various zooplankton taxa to understand the complex responses of aquatic communities to pesticide disturbance.

The transcriptome assembly of the European freshwater mussel Unio elongatulus C. Pfeiffer, 1825.

Freshwater mussels of the order Unionida are a global conservation concern. Species of this group are strictly freshwater, sessile, slow-growing animals and, extremely sensitive to environmental changes. Human-mediated changes in freshwater habitats are imposing enormous pressure on the survival of freshwater mussels. Although a few flagship species are protected in Europe, other highly imperilled species receive much less attention. Moreover, knowledge about biology, ecology, and evolution and proper conservation assessments of many European species are still sparse. This knowledge gap is further aggravated by the lack of genomic resources available, which are key tools for conservation. Here we present the transcriptome assembly of Unio elongatulus C. Pfeiffer, 1825, one of the least studied European freshwater mussels. Using the individual sequencing outputs from eight physiologically representative mussel tissues, we provide an annotated panel of tissue-specific Relative Gene Expression profiles. These resources are pivotal to studying the species' biological and ecological features, as well as helping to understand its vulnerability to current and future threats.

A comparative study on eDNA-based detection of Siamese bat catfish (Oreoglanis siamensis) in wet and dry conditions.

The use of environmental DNA (eDNA) analysis has demonstrated notable efficacy in detecting the existence of freshwater species, including those that are endangered or uncommon. This application holds significant potential for enhancing environmental monitoring and management efforts. However, the efficacy of eDNA-based detection relies on several factors. In this study, we assessed the impact of rainfall on the detection of eDNA for the Siamese bat catfish (Oreoglanis siamensis). Quantitative polymerase chain reaction (qPCR) analysis indicated that samples from days with average rainfall exceeding 35 mm (classified as heavy and very heavy rain) yielded negative results. While eDNA detection remains feasible on light or moderate rainy days, a noteworthy reduction in eDNA concentration and qPCR-positive likelihood was observed. Analysis across 12 sampling sites established a statistically significant negative relationship (p < 0.001) between eDNA detection and rainfall. Specifically, for each 1 mm increase in rainfall, there was an observed drop in eDNA concentration of 0.19 copies/mL (±0.14). The findings of this study provide definitive evidence that precipitation has a significant impact on the detection of eDNA in Siamese bat catfish. However, in the case of adverse weather conditions occurring on the day of sampling, our research indicates that it is acceptable to continue with the task, as long as the rainfall is not heavy or very heavy. To enhance the effectiveness of an eDNA survey, it is crucial to consider many factors related to climatic conditions. The aforementioned factor holds significant importance not only for the specific species under scrutiny but also for the broader dynamics of the climate.

Impact of ultrastructural and molecular identified Babesiosoma spp. in both Egyptian freshwater fishes (common carp and African catfish): Hematological, biochemical, and histopathological findings.

Background: Babesiosomes are apicomplexan parasites of both marine and freshwater fish species. Aim: In this study, we recorded the prevalence of Babesiosoma spp in two Egyptian freshwater fish species; the common carp and the African catfish with full pathological evaluation of the diseased condition, hematological and biochemical analysis of some parameters with exact recognition of the parasite with different methods. Methods: Two hundred and forty fish blood samples from Al-Sharqiya and Al-Ismailia governorates from August 2022 to January 2023 followed by blood film examinations, performing electron microscopy and molecular detection of the parasite via polymerase chain reaction. Results: The total infection prevalence was 63.75% with a higher prevalence observed among African catfish (42.5%) than Common carp (21.25%). Regarding hematologic parameters, the obtained results showed a significant decrease in the hematocrit values and a significant increase in the total leukocyte and lymphocyte values in both infected fish species. The serum ferritin, superoxide dismutase, and glutathione peroxidase were also significantly increased. However, the total iron binding capacity was significantly decreased. There was also a significant increase in the total serum bilirubin in the examined fish, all at (p < 0.001). Histopathologically, the lesions were more intense in the African catfish than the common carp but generally, the infected fish showed many changes with the gills being severely affected with pronounced hyperplasia of secondary lamellae with fusion and telangiectasis. The spleen, heart, and kidney are also affected. Conclusion: Serious adverse effects on the health status of previously examined fishes infected with Babesia spp. were observed and detected by several diagnostic and descriptive tools. Histopathological, hematological, and biochemical studies give an idea of the extent of these changes which are largely fatal affecting the economic system depending on the fish industry.

Radioactivity from oil and gas produced water accumulated in freshwater mussels.

Legacy disposal of oil and gas produced water (OGPW) to surface water has led to radium contamination in streambed sediment creating a long-term radium source. Increased radium activities pose a potential health hazard to benthic organisms, such as freshwater mussels, as radium is capable of bioaccumulation. This project quantifies the impact of OGPW disposal on adult freshwater mussels, Eurynia dilatata, which were examined along the Allegheny River adjacent to a centralized waste treatment facility (CWT) that historically treated and then discharged OGPW. Radium isotopes (226Ra and 228Ra) were measured in streambed sediment, mussel soft tissue, and mussel hard shell collected upstream, at the outfall, 0.5 km downstream, and 5 km downstream of the CWT. Total radium activity was significantly higher (p < 0.05) in mussel tissue (mean = 3.44 ± 0.95 pCi/g), sediment (mean = 1.45 ± 0.19 pCi/g), and hard shell (mean = 0.34 ± 0.11 pCi/g) samples 0.5 km downstream than background samples collected upstream (mean = 1.27 ± 0.24; 0.91 ± 0.09; 0.10 ± 0.02 pCi/g respectively). Mussel shells displayed increased 226Ra activities up to 5 km downstream of the original discharge. Downstream soft tissue and hard shell 87Sr/86Sr ratios, as well as hard shell metal/calcium (e.g., Na/Ca; K/Ca; Mg/Ca) and 228Ra/226Ra ratios demonstrated trends towards values characteristic of Marcellus OGPW. Combined, this study demonstrates multiple lines of evidence for radium retention and bioaccumulation in freshwater mussels resulting from exposure to Marcellus OGPW.

Relating target fish DNA concentration to community composition analysis in freshwater fish via metabarcoding.

Metabarcoding has been widely accepted as a useful tool for biodiversity assessment based on eDNA. The method allows for the detection of entire groups of organisms in a single sample, making it particularly applicable in aquatic habitats. The high sensitivity of the molecular approaches is especially beneficial in detecting elusive and rare fish species, improving biodiversity assessments. Numerous biotic and abiotic factors that affect the persistence and availability of fish DNA in surface waters and therefore affecting species detectability, have been identified. However, little is known about the relationship between the total fish DNA concentration and the detectability of differential abundant species. In this study three controlled mock-community DNA samples (56 individual samples) were analyzed by (i) metabarcoding (MiSeq) of 12S rDNA (175 bp) and by (ii) total freshwater fish DNA quantification (via qPCR of 12S rDNA). We show that the fish DNA quantity affects the relative abundance of species-specific sequences and the detectability of rare species. In particular we found that samples with a concentration between 1000 pg/µL down to 10 pg/µL of total fish DNA revealed a stable relative frequency of DNA sequences obtained for a specific fish species, as well as a low variability between replicates. Additionally, we observed that even in complex mock-community DNA samples, a total fish DNA concentration of 23 pg/µL was sufficient to reliably detect all species in every replicate, including three rare species with proportions of ≤0.5 %. We also found that the DNA barcode similarity between species can affect detectability, if evenness is low. Our data suggest that the total DNA concentration of fish is an important factor to consider when analyzing and interpreting relative sequence abundance data. Therefore, the workflow proposed here will contribute to an ecologically and economically efficient application of metabarcoding in fish biodiversity assessment.

The masking phenomenon of microplastics additives on oxidative stress responses in freshwater food chains.

The variability and intrinsic mechanisms of oxidative stress induced by microplastics at different trophic levels in freshwater food chains are not well understood. To comprehensively assess the oxidative stress induced by polystyrene microplastics (PS-MPs) in freshwater food chains, the present study first quantified the oxidative stress induced by PS-MPs in organisms at different trophic levels using factorial experimental design and molecular dynamics methods. Then focuses on analyzing the variability of these responses across different trophic levels using mathematical statistical analysis. Notably, higher trophic level organisms exhibit diminished responses under PS-MPs exposure. Furthermore, the coexistence of multiple additives was found to mask these responses, with antioxidant plastic additives significantly influencing oxidative stress responses. Mechanism analysis using computational chemistry simulation determines that protein structure and amino acid characteristics are key factors driving PS-MPs induced oxidative stress variation in freshwater organisms at different nutrient levels. Increased hydrophobic additives induce protein helicalization and amino acid residue aggregation. This study systematically reveals the variability of biological oxidative stress response under different nutrient levels, emphasizing the pivotal role of chemical additives. Overall, this study offers crucial insights into PS-MPs' impact on oxidative stress responses in freshwater ecosystems, informing future environmental risk assessment.

Parallel evolution despite low genetic diversity in three-spined sticklebacks.

When populations repeatedly adapt to similar environments they can evolve similar phenotypes based on shared genetic mechanisms (parallel evolution). The likelihood of parallel evolution is affected by demographic history, as it depends on the standing genetic variation of the source population. The three-spined stickleback (Gasterosteus aculeatus) repeatedly colonized and adapted to brackish and freshwater. Most parallel evolution studies in G. aculeatus were conducted at high latitudes, where freshwater populations maintain connectivity to the source marine populations. Here, we analysed southern and northern European marine and freshwater populations to test two hypotheses. First, that southern European freshwater populations (which currently lack connection to marine populations) lost genetic diversity due to bottlenecks and inbreeding compared to their northern counterparts. Second, that the degree of genetic parallelism is higher among northern than southern European freshwater populations, as the latter have been subjected to strong drift due to isolation. The results show that southern populations exhibit lower genetic diversity but a higher degree of genetic parallelism than northern populations. Hence, they confirm the hypothesis that southern populations have lost genetic diversity, but this loss probably happened after they had already adapted to freshwater conditions, explaining the high degree of genetic parallelism in the south.

Environmental DNA unveils deep phylogeographic structure of a freshwater fish.

Phylogeography bears an important part in ecology and evolution. However, current phylogeographic studies are largely constrained by limited numbers of individual samples. Using an environmental DNA (eDNA) assay for phylogeographic analyses, this study provides detailed information regarding the history of Siberian stone loach Barbatula toni, a primary freshwater fish across the whole range of Hokkaido, Japan. Based on an eDNA metabarcoding on 293 river water samples, we detected eDNA from B. toni in 189 rivers. A total of 51 samples, representing the entire island, were then selected from the B. toni eDNA-positive sample set for the subsequent analyses. To elucidate the phylogeographic structure of B. toni, newly developed eDNA metabarcoding primers (Barba-cytb-F/R) were applied to these samples, specifically targeting their haplotypic variation in cytochrome b. After a bioinformatic processing to mitigate haplotypic false positives, a total of 50 eDNA haplotypes were identified. Two regionally restricted, genetically distinct lineages of the species were revealed as a result of phylogeographic analyses on the haplotypes and tissue-derived DNA from B. toni. According to a molecular clock analysis, they have been genetically isolated for at least 1.5 million years, suggesting their ancient origin and colonisation of Hokkaido, presumably in the glacial periods. These results demonstrate how freshwater fishes can alter their distributions over evolutionary timescales and how eDNA assay can deepen our understanding of phylogeography.

Closing the knowledge gap: Helminth parasites of freshwater turtles from the Chaco-Pampa Plain, Southern South America.

Six species of freshwater turtles dominate the Chaco-Pampa Plain in southern South America and their parasites have been relatively understudied, with most records concentrated in Brazil. Particularly in Argentina, there are only scattered records of parasites for most of the turtles that inhabit the region, leaving a large knowledge gap. The purpose of the present contribution is to increase the knowledge of the internal parasites of six species of freshwater turtles from Argentina, after 15 years of fieldwork, by providing new hosts and additional geographic records for many host-parasite relationships. Some molecular sequences of the studied parasites were provided as a tool for better species identification. We processed 433 stomach and fecal samples from live individuals and visceral and soft tissue samples from 54 dissected turtles collected from a wide range and different ecoregions. We found 6230 helminths belonging to 18 taxa (one cestode, 11 digeneans and six nematodes). Fourteen new parasite-host associations are reported here, and for the first time parasites are recorded for Phrynops williamsi. This work contributes significantly to the knowledge of the parasitofauna in freshwater turtles in Argentina, providing a detailed list of parasites present in each turtle species and reporting molecular characters for future studies.