Simona Georgieva

The Antarctic Peninsula, particularly its northern part, is one of the regions that has experienced significant warming over the past 50 years, at a rate higher than the global average (Kim et al. 2014; Carrasco et al. 2021). The rise in atmospheric temperature and sea surface temperature affects cryospheric processes and the ecosystems in this region (Convey and Peck 2019). Amphipod crustaceans are one of the most speciose and dominant groups in the sublittoral zone of the Southern Ocean, with a high diversity in life styles, trophic types and habitats (Broyer et al. 2008). They constitute a significant trophic resource for a number of Southern Ocean fishes, invertebrates, seabirds and mammals and play a key role in coastal Antarctic ecosystems in terms of carbon flow, nutrient storage, and nutrient cycling (Jażdżewska 2011; Jażdżewska and Siciński 2017; Revanales et al. 2024). The integrative approach to studying benthic Antarctic amphipods is a multi-component strategy that combines morphological analysis, molecular and genetic methods, ecological and biogeographical data, and behavioral and functional traits to obtain a more complete and reliable picture of their taxonomy, ecology, and evolution. The taxonomic composition of benthic amphipods from Maritime Antarctica was studied during the austral summers of 2019/20 and 2022/23, within the frameworks of the XXVIII and XXXI Bulgarian Antarctic Expeditions and the IV Turkish Antarctic Expedition. A total of 27 localities were surveyed: 15 along the coastline of the South Bay (Livingston Island) and 12 along the coastline of the Marguerite Bay (Horseshoe and Dismal Islands). For the purpose of this research, two mitochondrial ( cox 1 and 16S rDNA) and two nuclear (Histone 3 and 28S rDNA) regions were sequenced for representative specimens. Within the integrative taxonomy we applied, a total of 38 amphipod species, belonging to 23 families were revealed (Fig. 1). Species relationships were assessed on individual gene-based phylogenetic hypotheses. Biogeographic and phylogenetic relationships were explored based on the multilocus phylogeny ( cox 1+16S+28S+H3). Our analyses revealed higher than previously thought diversity with evidence of several species-complexes. Despite the increasing research efforts in recent years, only 10% of known Antarctic amphipod species are represented by barcodes (Grant and Linse 2009; Jażdżewska et al. 2021). This study highlights the importance of integrating multiple lines of evidence to address the significant knowledge gap in Antarctic amphipod diversity. Expanding morphological and genetic datasets across different regions is crucial for advancing our understanding of the evolutionary history and ecological roles of benthic amphipods in Southern Ocean ecosystems.

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.

A BioBlitz is a rapid and intensive survey of a specific geographic area that brings together experts and often lay participants to assess biodiversity, typically of macrobiota that are easily observed and identifiable on-site. This concept has become popular across taxonomic fields, attracting interest globally to increase knowledge of local biodiversity. Inspired by the success of the approach, we undertook a ‘ParasiteBlitz’ at an unexplored locality (Stono Preserve, Charleston, South Carolina, USA) to determine its feasibility for parasites, whose assessment of diversity is largely neglected worldwide. We assembled a team of parasitologists with complementary expertise. Over 12 days (3 days in each habitat) in April 2023, we intensively screened fishes and aquatic invertebrates for parasites, and sampled sediment and water for environmental DNA (eDNA) metabarcoding from four aquatic habitats: wetland, freshwater pond, brackish impoundment, and tidal creek. We incorporated assistance from non-parasitologists and students. Details on methodologies and results are provided in individual papers in this Special Collection. Traditional methods revealed the presence of ca. 100 species of seven major metazoan parasite taxa, and the eDNA survey yielded over 1,000 amplicon sequence variants identified as parasites, most with sequences unmatched in GenBank, and resulting in only a few species identified as named species in the one-year post-Blitz timeframe we imposed upon ourselves for identification. Limitations and challenges of the ParasiteBlitz are discussed, and our results support that this approach can be effective for rapid discovery of the dimensions of parasite assemblages in an understudied environment and contribute to parasitology knowledge.

The East Asian finless porpoise, Neophocaena asiaeorientalis sunameri, ranks among the most endangered species with rapidly decreasing population in the Northwest Pacific. Trematode parasites of the genus Nasitrema that inhabit the air sinuses, inner ear, and the central nervous system of cetaceans frequently cause equilibrium dysfunction, disorientation, interference with echolocation, incoordination, and nervous system degeneration. Due to their specific location and associated pathologies, they have been recognized as one of the causes of cetacean strandings. Stranding data provides crucial information on the species’ biology, population health, and on the status of entire marine ecosystem. However, published data on parasite-induced standings that include information on the causative parasite pathogens are scarce. As part of a wider survey on the causes of East Asian finless porpoise strandings along the west coast of Korea, herein, we provide novel morphological and molecular data on two sympatric species of Nasitrema, namely, Nasitrema spathulatum and Nasitrema sunameri based on newly collected specimens from a stranded alive East Asian finless porpoise at the West coast of Korea. Our study adds a new distribution record for important parasite pathogens in cetaceans and provides the first molecular data for the parasite species recovered, which enabled us to re-evaluate the species relationships within the family Brachycladiidae, a group of important parasite pathogens of marine mammals.

Background: Lake Tanganyika is considered a biodiversity hotspot with exceptional species richness and level of endemism. Given the global importance of the lake in the field of evolutionary biology, the understudied status of its parasite fauna is surprising with a single digenean species reported to date. Although the most famous group within the lake’s fish fauna are cichlids, the pelagic zone is occupied mainly by endemic species of clupeids (Actinopterygii: Clupeidae) and lates perches (Actinopterygii: Latidae,LatesCuvier), which are an important commercial source for local fisheries. In this study, we focused on the lake’s four lates perches and targeted their thus far unexplored endoparasitic digenean fauna.Methods: A total of 85 lates perches from four localities in Lake Tanganyika were examined. Cryptogonimid digeneans were studied by means of morphological and molecular characterisation. Partial sequences of the nuclear28SrRNA gene and the mitochondrial cytochromecoxidase subunit 1 (cox1) gene were sequenced for a representative subset of the specimens recovered. Phylogenetic analyses were conducted at the family level under Bayesian inference.Results: Our integrative approach revealed the presence of six species within the family Cryptogonimidae Ward, 1917. Three out of the four species ofLateswere found to be infected with at least one cryptogonimid species. Two out of the three reported genera are new to science. Low interspecific but high intraspecific phenotypic and genetic diversity was found amongNeocladocystisspp. Phylogenetic inference based on partial28SrDNA sequences revealed a sister group relationship for two of the newly erected genera and their close relatedness to the widely distributed genus AcanthostomumLooss, 1899.Conclusions: The present study provides the first comprehensive characterisation of the digenean diversity in a fish family from Lake Tanganyika which will serve as a baseline for future explorations of the lake’s digenean fauna. Our study highlights the importance of employing an integrative approach for revealing the diversity in this unique host-parasite system.

Background: Microcotyle erythrinivan Beneden & Hesse, 1863 (Platyhelminthes: Monogenea) and other closely related species of the genus are often considered as cryptic. Records in hosts other than the type-host with no species confirmation by molecular analyses have contributed to this situation.Methods: Gill parasites of five sparid fishes,Boops boops(L.),Pagellus erythrinus(L.),P. acarne(Risso), Dentex dentex(L.) andPagrus pagrus(L.), from the Western Mediterranean off Spain were collected. Specimens ofMicrocotylespp. were characterised both molecularly and morphologically. Partial fragments (domains D1-D3) of the28SrRNA gene and the cytochromecoxidase subunit 1 (cox1) gene were amplified and used for molecular identification and phylogenetic reconstruction. Principal components analysis was used to look for patterns of morphological separation.Results: Molecular analyses confirmed the identity of three species:M. erythriniexP. erythrinusandPa. pagrus;M. isyebiBouguerche, Gey, Justine & Tazerouti, 2019 exB. boops; and a species new to science described herein,M. whittingtonin. sp. exD. dentex.The specific morphological traits and confirmed hosts (P. erythrinusandPa. pagrus) are delimited here in order to avoid misidentifications ofM. erythrini(sensu stricto).Microcotyle erythrini(s.s.) is mostly differentiated by the shape of its haptor, which is also longer than in the other congeners. New morphological and molecular data are provided forM. isyebifrom the Spanish Mediterranean enlarging the data on its geographical range.Microcotyle whittingtonin. sp. is described fromD. dentexand distinguished from the remaining currently recognised species of the genus by the number and robustness of the clamps.Conclusions: New diagnostic morphological traits useful to differentiateMicrocotylespp. are suggested: (i) haptor dimensions including lobes; (ii) the thickness of the clamps; (iii) the size and shape of spines of the genital atrium; (iv) the extension of the posterior extremities of vitelline fields; and (v) the shape of egg filaments. The use of new morphological approaches may allow considering these species ofMicrocotyleas being pseudocryptic. The use of representative undamaged specimens that have been genetically confirmed as conspecific is considered crucial to avoid abnormally wide morphological ranges that prevent species differentiation.