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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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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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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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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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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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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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A new species of Triangocypretta Ferreira, Higuti & Martens, 2023 (Ostracoda: Cyprididae) from a Brazilian floodplain, with a key to the species of the genus
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We describe a new species of ostracods, Triangocypretta mariae spec. nov. from lakes in the Upper Paraná River floodplain, Brazil. The genus is characterized mainly by its triangular shape in lateral view, the presence of anterior marginal septa on left and right valves, the smooth, not crenulated, posterior inner list on the right valve, and the short and narrow α and β setae on the mandibular palp. Triangocypretta mariae spec. nov. is allocated to this genus, but differs from its congeners by the almost circular shape of the carapace in dorsal and ventral views, the presence of two serrated claws on the third endite of maxillula, the four sub-apical setae on the protopodite of first thoracopod and by the fact that seta d2 on the second thoracopod is twice the length of seta d1. The populations found were all asexual. We provide an identification key for the five species in Triangocypretta Ferreira, Higuti & Martens, 2023.
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Community Assembly of Cladoceran Zooplankton in Relation to Pond Age and the Establishment of Macrophytes and Fish
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1. A substantial body of research has assessed the relative importance of local and regional factors shaping ecological communities, often using lakes and ponds as model systems. However, little is known about how habitat age can help to explain current community structure. The present study investigates the effect of pond age on zooplankton community composition and diversity in farmland ponds. 2. We used a dataset of > 100 morphologically similar farmland ponds of different ages (recent: 3 years; older: 4–15 years, and old: > 15 years) to analyse the extent to which the diversity and composition of current water flea assemblages (Crustacea; Anomopoda) reflect variation in pond age. 3. Young ponds had lower local species richness than old ponds and their communities were nested within those in ecologically similar old ponds. The presence of macrophytes enhanced local richness by promoting the establishment of additional species, while the presence of fish resulted in community turnover and lower local species richness compared to old ponds without fish. 4. Our results demonstrate that pond age is an important factor determining cladoceran species richness and community composition. Newly created ponds are rapidly colonised by regionally common species, while the colonisation by regionally rare species was more restricted. In older ponds, effective species sorting occurred in response to changes in local environmental conditions associated with the establishment of macrophytes and fish. 5. These findings highlight the need for longer time perspectives in colonisation studies to understand patterns of community succession in newly created habitats.
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Monomyxum ligophori n. sp. in a ParasiteBlitz: a monopisthocotylan as a myxozoan host in South Carolina and monophyly of a cosmopolitan hyperparasitic clade
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A ParasiteBlitz event offers a brief, intense opportunity to discover diverse parasite species and to reveal life cycles of heteroxenous parasite taxa. In this study, we describe Monomyxum ligophori n. sp., a hyperparasitic myxozoan (Monomyxidae) proliferating in a dactylogyrid monopisthocotylan flatworm (Ligophorus mugilinus) infecting mugilid fishes (Mugil cephalus, Mugil curema) on the Atlantic coast of North America. Furthermore, we used DNA barcoding, to infer the parasite’s complex life cycle, matching its hyperparasitic myxospore stages with actinospore stages infecting the polychaete Streblospio benedicti found in the same locality during the ParasiteBlitz and also reported previously from the same region. Thus we provide evidence inferring the first life cycle of a myxozoan that does not require a vertebrate host. Hyperparasitic myxozoans are rare with only five species reported worldwide to infect flatworms. This study provides more evidence of the previously debated high-host specificity towards monopisthocotylan hosts of these monomyxid myxozoan hyperaparasites. Notably, Monomyxum ligophori n. sp. was detected only in L. mugilinus, and not in the other species of monopisthocotylan parasitic flatworms (Ligophorus cf. uruguayense and Metamicrocotyla macracantha) found infecting the same fish individuals during the ParasiteBlitz. Our molecular data and phylogenetic analysis support the previously suggested common origin of Monomyxum species infecting monopisthocotylan flatworms, and contribute to understanding the life cycle and host interactions of this unique hyperparasitic myxozoan lineage.
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Systematics and phylogeny of Chalcinotrematinae (Digenea: Haploporidae): Erection of a new genus and description of two new species from South America through integrated analyses
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The subfamily Chalcinotrematinae (Haploporidae) comprises an understudied group of digenean parasites infecting freshwater and brackish water fishes across the Americas, Africa, and Asia. Its systematics have rarely been investigated using molecular data, with DNA sequences available for only a few species representing two of the six recognised genera. We collected chalcinotrematine trematodes from freshwater fishes in the Jari River, Amazon Basin, Brazil, and in Misiones, Argentina. Specimens from Brazil were characterised through an integrative approach combining morphological examination with molecular data (partial 28S and ITS2 rDNA sequences), whereas those from Argentina were analysed morphologically. As a result, we describe two new species from Brazil: Chalcinotrema arleneae sp. nov. from Leporinus friderici and Laemolyta proxima, and Unicoelium gerardoi sp. nov. from Hypostomus plecostomus. This study provides the first molecular data for both Chalcinotrema and Unicoelium, expanding the phylogenetic framework of Chalcinotrematinae. Paralecithobotrys brasiliensis is recorded from Argentina in Megaleporinus obtusidens, extending its geographical range. We reassessed the generic limits of Saccocoelioides, the most species-rich genus within the subfamily. Based on combined morphological, molecular, host, and distributional evidence, we propose taxonomic revisions, establishing Neosaccocoelioides gen. nov. for several South American species formerly assigned to Saccocoelioides: N. antonioi comb. nov., N. bacilliformis comb. nov., N. elongatus comb. nov., N. magnus comb. nov., N. miguelmontesi comb. nov. (type species), and N. szidati comb. nov. Additionally, N. platense comb. nov., previously placed in Chalcinotrema, is transferred to the new genus. Saccocoelioides chilkaensis and S. lizae are considered species inquirendae; and S. guaporense is considered incertae sedis. These findings refine Chalcinotrematinae relationships and highlight the need for expanded molecular datasets to resolve systematic and biogeographical uncertainties.
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