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Vertical transmission of Cardinium bacteria in parthenogenetic non-marine ostracods (Crustacea)
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Bacterial endosymbionts are common in terrestrial arthropods, where they can manipulate host biology and reproduction, with Wolbachia and Cardinium as the best-known examples. Vertical transmission is a hallmark of such endosymbiosis. The high incidence of parthenogenesis makes non-marine ostracods (small, bivalved crustaceans) excellent models for exploring the potential effects of endosymbiosis on host reproduction in fully aquatic arthropods. Here, we complement DNA sequencing-based detection of Cardinium in non-marine ostracods with an imaging approach based on microdissection and fluorescence in situ hybridization (FISH). We use confocal microscopy to illustrate the location and spatial organization of Cardinium cells within female ovaries and eggs in natural, parthenogenetic populations of three species of ostracods with mixed reproduction. Our results provide evidence that these bacteria are stable endosymbionts and confirm vertical transmission of Cardinium in non-marine ostracods. The location of Cardinium in reproductive tissues of parthenogenetic females further indicates that these intracellular bacteria are potential reproductive manipulators in at least some non-marine ostracod species. Given that our knowledge on endosymbionts is still largely biased towards terrestrial arthropods with haplodiploidy, our results open the way to novel comparative studies of reproductive manipulation by endosymbionts in a much wider range of taxa.
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Reduced-representation sequencing detects trans-Arctic connectivity and local adaptation in polar cod (Boreogadus saida)
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Information on connectivity and genetic structure of marine organisms remains sparse in frontier ecosystems such as the Arctic Ocean. Filling these knowledge gaps becomes increasingly urgent, as the Arctic is undergoing rapid physical, ecological, and socio-economic changes. The abundant and widely distributed polar cod (Boreogadus saida) is highly adapted to Arctic waters, and its larvae and juveniles live in close association with sea ice. Through a reduced-representation sequencing approach, this study explored the spatial genetic structure of polar cod at a circum-Arctic scale. Genomic variation was partitioned into neutral and adaptive components to respectively investigate genetic connectivity and local adaptation. Based on 922 high-quality single nucleotide polymorphism (SNP) markers genotyped in 611 polar cod, broad-scale differentiation was detected among three groups: (i) Beaufort-Chukchi seas, (ii) all regions connected by the Transpolar Drift, ranging from the Laptev Sea to Iceland, including the European Arctic, and (iii) West Greenland. Patterns of neutral genetic structure suggested broadscale oceanographic and sea ice drift features (i.e. Beaufort Gyre and Transpolar Drift) as important drivers of connectivity. Genomic variation at 35 outlier loci indicated adaptive divergence of the West Greenland, and the Beaufort-Chukchi Seas populations, possibly driven by environmental conditions. Sea ice decline and changing ocean currents can alter or disrupt connectivity between polar cod from the three genetic groups, potentially undermining their resilience to climate change, even in putative refugia, such as the Central Arctic Ocean and the Arctic Archipelago.
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Exploring hidden parasite diversity with environmental DNA metabarcoding during a ParasiteBlitz across a coastal habitat gradient
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Environmental DNA (eDNA) metabarcoding has lagged in parasite biodiversity assessments. We implemented this method to examine parasite diversity in sediment and water from 4 physically connected aquatic habitats in coastal South Carolina, USA, as part of a ParasiteBlitz in April 2023. Sediment was collected using a syringe corer, and water was sampled using active filtration and passive collection. Five amplicon libraries, using primers targeting portions of the mitochondrial COI of platyhelminths and 18S ribosomal RNA genes of nematodes, myxozoans, microsporidians, and protists, successfully yielded parasite sequences. Out of >5.8 million sequences, we identified >1,000 parasite amplicon sequence variants (ASVs) corresponding to ~600 parasite operational taxonomic units, from 6 parasite groups. Most diversity was observed among the microsporidians, whose assay demonstrated the highest fidelity. Actively-filtered water samples captured ASVs of all 6 groups, whereas sediment captured only 4, despite yielding 3× as many ASVs. Low DNA yields from passive water samples resulted in fewer, but some unique, ASVs representing 3 parasite groups. The most efficient sampling method varied with respect to parasite group across habitats, and the parasite communities from each habitat were distinct regardless of sampling method. We detected ASVs of 9 named species, 4 of which may represent introductions to the US. The abundance of our results demonstrates the effectiveness and efficiency of eDNA metabarcoding for assessing parasite diversity during short, intensive surveys, and highlights the critical need for more comprehensive sequence databases and the development of primers for those parasite taxa that elude detection using eDNA methods.
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Stygobitic Candonidae (Crustacea, Ostracoda) as potential environmental indicators of groundwater quality in tropical West Afric
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1. Ostracods are important components of groundwater communities that are influenced by abiotic environmental conditions and biotic interactions. We aimed to identify the factors associated with ostracod assemblages inhabiting groundwaters accessed through dug wells in several regions of Benin in West Africa, exposed to chronic influences of anthropogenic disturbances such as nutrient enrichment from infiltration of sewage or fertilisers from the surface. 2. Ostracods were collected from 219 wells in seven catchment areas using two complementary methods: active sampling with a phreatobiological net and passive trapping with a baited trap. Associations with 31 statistical predictor variables (a range of abiotic descriptors of water, hydrology, protection, usage and the type of well) and ostracod occurrence was evaluated using distance-based linear models and redundancy analysis. 3. We identified 60 ostracod species representing two ecological groups: 36 species of stygobites of the family Candonidae, an endemic species flock of a vast evolutionary radiation, and 24 species of non-stygobites, mostly of the family Cyprididae. This is the first large groundwater ostracod species flock reported from the entire African continent. 4. A number of variables associated with the structure of ostracod assemblages were identified. Except for the descriptors of wells, these included well-known chemical and physical properties (electrical conductivity, pH, temperature or bicarbonate concentration), but also the concentration of NO2−. Although NO2− has not yet been demonstrated to be important for ostracod assemblages, stygobites occurred significantly less frequently in higher concentrations of NO2− than most non-stygobites. 5. We determined that stygobitic (candonid) ostracod species and genera may be a good potential environmental indicator of groundwater quality especially nitrite pollution of groundwater in tropical West Africa. 6. In tropical West Africa, many human populations rely on groundwater for domestic use and agricultural irrigation, while these aquatic resources are also often affected by anthropogenic disturbances. The use of stygobitic ostracods as potential indicators of groundwater quality offers a valuable tool for environmental monitoring and protection in tropical regions in West Africa, and may be also globally.
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On Cytheridella whitmani sp. nov. (Crustacea, Ostracoda) from Cape Cod (Ma, USA), with a reappraisal of the taxonomy of the genus
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Cytheridella whitmani Martens, sp. nov. is described from lakes on Cape Cod (MA, USA). The species differs from its congeners mainly by the shape of the female carapace and by the morphology of the hemipenis, especially of the distal lobe and the copulatory process. The literature on the genus is reviewed and the synonymy of the fossil Cytheridellaboldii Purper, 1974 with the type species C. ilosvayi Daday, 1905, both described from South America, is confirmed. The status of Cytheridella americana (Furtos, 1936) is reverted to that of “uncertain species”. Beside the type species and the new species, the genus currently includes only three further species from Africa: C. monodi Klie, 1936, C. damasi Klie, 1944 (with synonym C. chariessa Rome, 1977), and C. tepida Victor, 1987. The morphology of the new species is discussed in comparison with the congeneric species, especially regarding the valve ornamentation, the structure and function of the third thoracopod, the hemipenis and the caudal ramus. It is suggested that C. whitmani is a recent invasive species in the lakes of the Cape Cod peninsula. Its occurrence at northern latitudes is unexpected, as its congeneric species are consistently (sub-) tropical.
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Divergent feeding habits of sister species of the Antarctic amphipod genus Charcotia
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Climate change and resource exploitation in the Southern Ocean are important anthropogenic pressures on Antarctic food webs. Understanding the eco-functional roles of Antarctic communities is essential for ecosystem management and conservation. Amphipods are among the most dominant and ecologically important benthic taxa in the Southern Ocean. The amphipod genus Charcotia is part of the scavenger guild playing a dominant role in nutrient recycling. To study the trophic habits of two sister species C. amundseni and C. obesa, stable isotope ratios of carbon and nitrogen were measured along geographical and bathymetrical gradients. Charcotia obesa belongs to the fourth and C. amundseni to the fifth trophic level, based on significant differences in δ15N values. Both benthic and pelagic primary producers dominate the diet in both species as derived from their low δ13C values. Charcotia obesa, the species with the narrowest depth range of the two studied species, did not show a depth-related pattern in isotopic ratios. An increasing geographic gradient of both δ15N and δ13C values was observed for C. obesa, ranging from the northern most tip of the Western Antarctic Peninsula to the southwestern most part in the Bellingshausen Sea. This might be linked to nutrient rich glacial meltwater in the latter part of the Southern Ocean. Nitrogen stable isotope ratios of C. amundseni showed a significant difference between Crown Bay and the other locations; this might be explained by the close location of the Filchner Area to nutrient rich upwelling in the Weddell Sea Gyre. Our study provides evidence for niche differentiation between two closely related amphipod species. Incorporation of additional samples from other locations and depth ranges in combination with isotope analysis and DNA-based prey identification might clarify the trophic position of benthic amphipods.
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Unveiling hidden species diversity within Southern Ocean Iphimediidae (Crustacea, Amphipoda) through DNA and 3D-geometric morphometrics, with the description of 10 new species
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The Antarctic shelf benthos is threatened by climate-related environmental changes and anthropogenic stressors. A baseline knowledge of biodiversity and species distribution ranges is essential for effective monitoring and conservation. Here, we integrate DNA-based species delimitation methods with morphological analyses to explore species diversity within Antarctic Iphimediidae. Our results reveal that ten nominal species are complexes of multiple species, most of which can be distinguished by small but consistent morphological differences. We formally describe ten of these new species: Stegopanoploea brevidentata sp. nov., Maxilliphimedia acutilobata sp. nov., Maxilliphimedia oliveri sp. nov., Echiniphimedia spinosior sp. nov., Echiniphimedia maxima sp. nov., Iphimediella longidentata sp. nov., Iphimediella brachyodonta sp. nov., Iphimediella longilobata sp. nov., Labriphimedia adeliae sp. nov., and Labriphimedia anneninae sp. nov. Most previously recorded circum-Antarctic iphimediid species are found to consist of regionally distributed species. Furthermore, we apply 3D-geometric morphometrics on the Gnathiphimedia sexdentata complex to investigate whether ‘cryptic’ species can be differentiated by variation in continuous morphological traits. This method provides additional diagnostic characters for the morphological identification of two G. sexdentata clades. This integrative taxonomy study increases the number of nominal Antarctic iphimediid species from 39 to 49, with 14 additional putative species requiring further study for formal description.
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Going Dutch: Invasion pathways and current European distribution of non-native land flatworm species belonging to Geoplaninae and Bipaliinae with focus on the Netherlands
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Non-native land flatworms can have a negative impact on local ecosystems, due to their voracious appetites for earthworms or snails. Accurate knowledge on the distribution of non-native populations of land flatworms is necessary to design effective policy to control their spread across Europe. The aim of this study is to address the spatiotemporal distribution of selected species of non-native land flatworms (Geoplaninae and Bipaliinae) in the Netherlands, and provide their current distribution and introduction pathways in a pan-European perspective. Specimens of Obama spp., Bipalium kewense and Diversibipalium multilineatum were reported across selected Dutch gardens, greenhouses, plant nurseries or garden centers. European distribution of these planarians species was reconstructed using previously published datasets and from records available on GBIF. Morphological species identification was supported by DNA barcoding using a portion of the 28S rDNA marker. Introduction pathways were addressed via haplotype networks based on COI mtDNA. In total, 27 specimens of non-native land flatworms were collected in the Netherlands. Their different spatiotemporal distribution pattern indicates differences in tolerance to environmental conditions in Northern Europe between B. kewense restricted to greenhouses and D. multilineatum found in gardens. Generally, an increasing trend in the number of records of Obama nungara is observed in the Netherlands and in Europe, with the highest number of records per country reported in France (1.428) followed by the Netherlands (149) and Italy (64). The high numbers of France are, however, artificial and originate from communication towards the public, which has not been as pronounced in other European countries. Genetic analyses suggest multiple introductions of O. nungara in Europe. The combination of morphological and molecular species identification revealed the presence of Obama anthropophila being the first record of this species outside its native range in Brazil. Our results further support the established status of these species in Europe and highlight the importance of citizen scientists in non-native species research.
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Scanning Electron Microscopy Reveals New Ultrastructural Features in Metacercariae of Clinostomum cutaneum (Digenea: Clinostomidae) Infecting Oreochromis niloticus (Actinopterygii: Cichlidae) in Kenya
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Clinostomum is a genus of parasitic trematodes found worldwide, infecting a wide range of hosts, including freshwater fishes, snails, birds and occasionally humans. In this study, clinostomid metacercariae were collected from Nile tilapia raised in fish farms in the Upper Tana River region, Kenya. The prevalence of infection was 17.2%, with metacercariae infecting the skin, gills and buccal cavity of the fish. Using light microscopy, scanning electron microscopy (SEM) and molecular methods targeting both nuclear ribosomal (ITS1, 5.8S, ITS2) and mitochondrial (COI) regions, the metacercariae were identified as C. cutaneum, C. phalacrocoracis, C. tilapiae and Euclinostomum heterostomum. The three species of Clinostomum have previously been reported to infect fish or piscivorous birds in Kenya, while this is the first report of E. heterostomum in this country. SEM analysis revealed new ultrastructural features of C. cutaneum, including an excretory pore surrounded by minute spiny papillae, an everted cirrus and dome-shaped papillae on the tegumental area around the genital pore. The cirrus lacked basal papillae, showing morphological variation between the adult and metacercarial stages. Our study, therefore, provides new insights into the phenotypic identification of flukes that may be pathogenic to fishes and humans and, therefore, of scientific and practical importance.
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A Scanning Electron Microscopy method to visualise the copulatory organ morphology of microturbellarian flatworms: Trigonostomum Schmidt, 1852 as a case study
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Traditional methods for studying the morphology of microturbellarian flatworms rely on light microscopy, which often lacks the resolution necessary to capture fine structural details. Therefore, we present a protocol to improve the visualisation of structural morphological details in microturbellarians by means of scanning electron microscopy (SEM). We demonstrate this method by imaging the sclerotised copulatory organs of three species of Trigonostomum (Rhabdocoela, Trigonostomidae): T. venenosum, T. setigerum, and T. penicillatum. Additionally, we successfully visualise the bursal appendage of T. penicillatum. SEM imaging offered new morphological insights for the genus, and corrected earlier interpretations made with light microscopy. The method requires precision and careful handling, especially during the isolation of the hard parts. However, it is cost-effective and straightforward to carry out in any standard laboratory setting. Hence, our SEM protocol complements traditional light microscopy and opens new avenues for taxonomical research in microturbellarian taxa with hard parts.
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