Parasite Communities Research Articles

Development and validation of a long-read metabarcoding platform for the detection of filarial worm pathogens of animals and humans

BackgroundFilarial worms are important vector-borne pathogens of a large range of animal hosts, including humans, and are responsible for numerous debilitating neglected tropical diseases such as, lymphatic filariasis caused by Wuchereria bancrofti and Brugia spp., as well as loiasis caused by Loa loa. Moreover, some emerging or difficult-to-eliminate filarioid pathogens are zoonotic using animals like canines as reservoir hosts, for example Dirofilaria sp. ‘hongkongensis’. Diagnosis of filariasis through commonly available methods, like microscopy, can be challenging as microfilaremia may wane below the limit of detection. In contrast, conventional PCR methods are more sensitive and specific but may show limited ability to detect coinfections as well as emerging and/or novel pathogens. Use of deep-sequencing technologies obviate these challenges, providing sensitive detection of entire parasite communities, whilst also being better suited for the characterisation of rare or novel pathogens. Therefore, we developed a novel long-read metabarcoding assay for deep-sequencing the filarial nematode cytochrome c oxidase subunit I gene on Oxford Nanopore Technologies’ (ONT) MinION™ sequencer. We assessed the overall performance of our assay using kappa statistics to compare it to commonly used diagnostic methods for filarial worm detection, such as conventional PCR (cPCR) with Sanger sequencing and the microscopy-based modified Knott’s test (MKT).ResultsWe confirmed our metabarcoding assay can characterise filarial parasites from a diverse range of genera, including, Breinlia, Brugia, Cercopithifilaria, Dipetalonema, Dirofilaria, Onchocerca, Setaria, Stephanofilaria and Wuchereria. We demonstrated proof-of-concept for this assay by using blood samples from Sri Lankan dogs, whereby we identified infections with the filarioids Acanthocheilonema reconditum, Brugia sp. Sri Lanka genotype and zoonotic Dirofilaria sp. ‘hongkongensis’. When compared to traditionally used diagnostics, such as the MKT and cPCR with Sanger sequencing, we identified an additional filarioid species and over 15% more mono- and coinfections.ConclusionsOur developed metabarcoding assay may show broad applicability for the metabarcoding and diagnosis of the full spectrum of filarioids from a wide range of animal hosts, including mammals and vectors, whilst the utilisation of ONT’ small and portable MinION™ means that such methods could be deployed for field use.

Parasite assemblages of lanternfishes (Myctophidae) in deep subantarctic waters: Potential indicators for ecosystem monitoring

The Agujero Azul (Blue Hole) is an oceanic region located on the edge of the Southwestern Atlantic continental shelf that is especially impacted by intense fishing activity. It harbours a high biodiversity, including the mesopelagic lanternfishes of the numerically abundant family Myctophidae. Due to their high abundance and relevance in food webs, monitoring changes in the population and community structure of mesopelagic fishes is a valuable tool to trace changes in a warming world, especially in a highly exploited ecosystem where the effects of global change have been documented. Parasite communities of the lanternfishes Gymnoscopelus nicholsi and Electrona subaspera, caught at the Agujero Azul are analyzed. The aims of this work were to assess their value as indicators of host population structure and to establish a baseline for monitoring ecosystem variations under future scenarios of global change. The connectivity with the population of G. nicholsi from around South Georgia was also evaluated by comparing their parasite faunas. A parasitological study of 170 G. nicholsi and 31 of E. subaspera showed low parasite abundance and species richness, with significantly higher levels of parasitism in larger fishes. The paucity of parasitism in G. nicholsi from South Georgia compared to Agujero Azul suggests the existence of two discrete stocks. On the other hand, comparison with literature data supports a connection between fish from the Patagonian shelf and South Shetland Islands (Antarctica). Comparison across samples from Agujero Azul showed homogeneity in parasite assemblages, regardless of the distance separating them, ensuring that parasites are reliable representatives of such physical conditions. Thus, this representability suggests that parasites can be suitable indicators to estimate the amplitude of future changes due to global warming and other anthropogenic stressors in this region. This work provides a baseline for using the parasites of G. nicholsi as indicators to trace these ongoing and predicted changes.

Specific features of parasite communities of Siberian cisco Coregonus sardinella in polytypic water bodies of the polar regions: species richness.

The article dwells upon characteristics of the species richness of parasite communities in least cisco Coregonus sardinella Valenciennes in Polar water bodies: Kureyskoye Reservoir, Lake Kutaramakan, Khatanga River. The communities consist of parasite species common in coregonids. The main species in all the parasite communities in least cisco are Dibothriocephalus ditremus and D. dendriticus. Triaenophorus crassus plerocercoids dominate in the regulated water body (Kureyskoye Reservoir). To analyze the species richness of the component communities (s), coefficients of the power-law equation s = a × nb were applied, where a is the expected species richness in the first host individual examined, and b is the rate of species accumulation in parasite component communities (s). The resulting curves of species accumulation give statistical rigor to the assessment of differences and similarities of the species richness of the component communities of parasites in least cisco of various ages and habitats. The species richness of infra- and component parasite communities in least cisco was found to be significantly lower in the lake and the storage reservoir than in riverine habitats (Khatanga River). At the same time, the species accumulation rate for parasite communities in least cisco from Lake Kutaramakan was higher than in the reservoir due to a higher diversity of parasite infracommunities.

Host and parasite identity interact in scale-dependent fashion to determine parasite community structure.

Understanding the ecological assembly of parasite communities is critical to characterise how changing host and environmental landscapes will alter infection dynamics and outcomes. However, studies frequently assume that (a) closely related parasite species or those with identical life-history strategies are functionally equivalent, and (b) the same factors will drive infection dynamics for a single parasite across multiple host species, oversimplifying community assembly patterns. Here, we challenge these two assumptions using a naturally occurring host-parasite system, with the mussel Anodonta anatina infected by the digenean trematode Echinoparyphium recurvatum, and the snail Viviparus viviparus infected by both E. recurvatum and Echinostoma sp. By analysing the impact of temporal parasite dispersal, host species and size, and the impact of coinfection (moving from broader environmental factors to within-host dynamics), we show that neither assumption holds true, but at different ecological scales. The assumption that closely related parasites can be functionally grouped is challenged when considering dispersal to the host (i.e. larger scales), while the assumption that the same factors will drive infection dynamics for a single parasite across multiple host species is challenged when considering within-host interspecific competition (i.e. smaller scales). Our results demonstrate that host identity, parasite identity and ecological scale require simultaneous consideration in studies of parasite community composition and transmission.

Nestedness of flea assemblages harboured by small mammalian hosts revisited: phylogenetic and functional nestedness do not follow compositional nestedness.

We studied compositional, phylogenetic, and functional nestedness in the flea assemblages of 14 host species across regions. Our main questions were (a) are a host's flea assemblages compositionally, phylogenetically, or functionally nested? (b) Do similar processes drive these nestedness facets? (d) Are a host's biological traits associated with nestedness of its flea assemblages? Rows of host matrices were ordered by decreasing species richness/the sum of the branch lengths of a phylogenetic tree/functional dendrogram or by decreasing region area or by increasing distance from the centre of a host's geographic range. None of the matrices sorted by species richness/sum of branch lengths were nested from a compositionalperspective, but they were significantly nested from phylogenetic and functionalperspectives. Compositional, phylogenetic, and functional nestedness of matrices sorted by region area or by distance from the host's geographic range centre varied between hosts. In some hosts, flea assemblages were nested from all three perspectives independently of how matrix rows were sorted, whereas in other hosts, the occurrence of significant nestedness depended on the order of the matrix rows. The degree of phylogenetic and functional nestedness for matrices sorted by the sum of branch lengths was associated with a host species' morphoecological traits and the latitude of its geographic range. We conclude that consideration of nestedness based solely on species composition does not allow a comprehensive understanding of the patterns of parasite community structure. Nestedness should also be considered from phylogenetic and functional perspectives.

Parasites of Astyanax lacustris (Pisces, Characiformes) from Brazilian streams.

Astyanax lacustris is a small characid fish widely distributed in Brazil, with fast-growing and omnivorous feeding habits. Although the species presents economic and ecological importance, little is known about its parasitological fauna in stream environments. This study aimed to characterize the parasitic fauna of A. lacustris in two streams in the state of Paraná, Brazil. Fifty-two specimens of A. lacustris were collected, 22 from the Carolina stream (Lower Iguaçu River) and 30 from the Carreira stream (Upper Paraná River), in July and September 2018. In both streams, there was a low richness of parasites, and the structure of the parasitic community was predominantly composed of monogeneans. These findings may be associated with the gregarious behavior of the host species. Moreover, the low occurrence of endohelminths, may be associated with the fact that in streams, the energy flow is low, and depends directly on the input of allochthonous matter, which favors the formation of shelters for the establishment of macroinvertebrates, which represent important sources of food for the ichthyofauna, and may act as intermediate and paratenic hosts of parasites. These environments require further studies to support conservation measures aimed at maintaining the balance of ecological relationships in these preserved ecosystems.

Ecological and phylogenetic components of flatfish ectoparasites (Pleuronectiformes: Paralichthyidae) from the Southern Gulf of Mexico.

For many years, parasite ecologists have debated the relative importance of phylogeny and ecology as drivers of parasite community structure. Here, we address this issue using data on the metazoan ectoparasite communities of different flatfish species. Twenty species of flatfish were collected along the continental shelf of the Southern Gulf of Mexico and examined for ectoparasites. Eight flatfish species were parasitized by at least one ectoparasite species. In total, 326 ectoparasites, representing 11 species (4 monogeneans, 4 copepods, 1 isopod, 1 branchiurid, and 1 leech) were removed from 1622 hosts examined. The highest prevalence (37.5%) occurred in Bomolochus sp1 from Trinectes maculatus, while the lower (0.1%) for Argulus sp., Gnathia sp. and Trachellobdella lubrica from Cyclopsetta chittendeni. Changes in the ectoparasite community structure per host species and region were evaluated using a Permutational Multivariate Analysis of Variance and represented by a multidimensional scaling analysis. Significant differences in the parasite species composition among regions and hosts were detected, but no significant interaction between regions and hosts occurred. A multivariate pairwise t-test detected significant differences in the parasite infracommunities between the Yucatan Shelf and the other two regions; in addition, significant differences were detected between C. chittendeni and the Syacium species as well as between Ancylopsetta dilecta and Syacium papillosum. In this case, there is no relationship between the patterns of ectoparasitic community structure and the inherent phylogenetic affinity of the hosts; instead, the variations in ectoparasitic communities are determined by a regional ecological component.

Structure of ectoparasite communities of Nyctalus species (Chiroptera: Vespertilionidae) in the Zhiguli State Nature Reserve and Samarskaya Luka National Park (European Russia)

The ectoparasites of the bats (Chiroptera) often act as carriers of infectious agents dangerous to animals and humans. This determines the relevance of studying ectoparasite communities. In this regard, the composition of communities and interspecific relations of ectoparasites of migratory bats are of particular interest, since they can be a source of arthropods with vector potential that are atypical in a studied area. This research was aimed to study the species composition, community structure and parasite-host specificity of ectoparasites in syntopic populations of bats of the genus Nyctalus. The study has been carried out in the Zhiguli State Biosphere Reserve and Samarskaya Luka National Park (Russia). A total of 78 individuals of Nyctalus were examined, namely Nyctalus noctula (47 individuals), N. leisleri (21 individuals) and N. lasiopterus (ten individuals). They were captured by ornithological nets in the summer period in 2017–2019. The collected ectoparasites were fixed in alcohol, and permanent preparations were made using Fora-Berlese liquid. In total, we found 19 ectoparasite species, namely one Hemiptera species (Cimex lectularius), four Ischnopsyllidae species, and 14 species of Spinturnicidae and Macronyssidae families. Of these, eight ectoparasite species have been found for the first time in Russia on Nyctalus species. Nine ectoparasites species were found on Nyctalus leisleri, 15 species on N. noctula, and 11 species on N. lasiopterus. The most massive and widespread parasite on Nyctalus is Macronyssus flavus. In addition, we demonstrated a high infestation of Nyctalus noctula by Spinturnix acuminatus and Steatonyssus noctulus, of Nyctalus lasiopterus by Spinturnix acuminatus and of Nyctalus leisleri by Steatonyssus spinosus. Among casual parasites of Nyctalus, there are Spinturnix helvetiae, S. myoti, S. plecotinus, Ischnopsyllus octactenus, I. variabilis, Macronyssus ellipticus, and Steatonyssus periblepharus. The correspondence analysis of certain ectoparasite communities, differing in qualitative and quantitative composition, with the host species demonstrated the general structure of parasite-host relationships. Nyctalus noctula has the highest diversity of ectoparasite communities and the model of the log-normal distribution of species abundance confirmed this. In terms of species composition, the parasite communities of Nyctalus noctula and N. lasiopterus were the most similar, while the parasite communities of Nyctalus noctula and N. leisleri were the least similar. The key components involved in the differentiation of ectoparasitic communities were the following species: Spinturnix acuminatus, S. kolenatii, Steatonyssus spinosus, and Macronyssus flavus, which have different infestation values in their hosts. Co-occurrence analysis revealed a strong positive relationship for 28 ectoparasite species pairs and a strong negative relationship for 26 species, which may be explained by weakened competitive relations between the ectoparasites. The observed assortativity of parasite species among themselves has been discussed.

First study on the metazoan parasite community of Crenicichla strigata (Cichliformes: Cichlidae).

This study provides the first report of metazoan parasites in Crenicichla strigata. From 31 hosts caught in the Jari River basin, in the eastern Amazon region of Brazil, a total of 1454 parasites were collected: Sciadicleithrum araguariensis, Sciadicleithrum joanae, Sciadicleithrum satanopercae, Posthodiplostomum sp., Genarchella genarchella, Contracaecum sp., Spirocamallanus peraccuratus, Acarina gen. sp. and Dolops geayi. However, the community was dominated by the three species of Sciadicleithrum (Monogenea) and there was similar presence of parasites in the larval and adult stages. The total prevalence was 100% and each of the hosts was parasitized by two or three species, which presented random dispersion. Brillouin diversity, parasite species richness, Berger-Parker dominance index and evenness were low. There was positive correlation between the abundance of Posthodiplostomum sp. the hosts' length, while the abundance of S. peraccuratus showed negative correlation with the body weight of fish. The abundance of S. araguariensis, S. joanae and S. satanopercae showed negative correlation with the hosts' length. The parasite community of C. strigata was characterized by low diversity, low richness, low intensity and low abundance of species.

Parasite Fauna and Coinfections in Urban Rats Naturally Infected by the Zoonotic Parasite Angiostrongylus cantonensis.

When the zoonotic parasite of rodents that can cause human neuroangiostrongyliasis, i.e., Angiostrongylus cantonensis, is found in its natural definitive hosts, it is usually reported in isolation, as if the rat lungworm were the only component of its parasite community. In this study, we report the coinfections found in rats naturally infected by A. cantonensis in urban populations of Rattus norvegicus and Rattus rattus in Valencia, Spain. In addition to the rat lungworms, which were found in 14 of the 125 rats studied (a prevalence of 11.20%), 18 other parasite species (intestinal and tissular protists, microsporidia and helminths) were found, some of them with high burdens. Fourteen of these nineteen species found are potential zoonotic parasites, namely Blastocystis, Giardia duodenalis, Cryptosporidium spp., Enterocytozoon bieneusi, Encephalitozoon hellem, Toxoplasma gondii, Brachylaima spp., Hydatigera taeniaeformis s.l. larvae, Hymenolepis nana, Hymenolepis diminuta, Angiostrongylus cantonensis, Calodium hepaticum, Gongylonema neoplasticum and Moniliformis moniliformis. The total predominance of coinfected rats as well as their high parasite loads seem to indicate a trend towards parasite tolerance.

Profiling pathogenic protozoan and their functional pathways in wastewater using 18S rRNA and shotgun metagenomics

Despite extensive research, little is known about the composition of eukaryotic protists in environmental samples. This is due to low parasite concentrations, the complexity of parasite diversity, and a lack of suitable reference databases and standardized protocols. To bridge this knowledge gap, this study used 18S rRNA short amplicon and shotgun metagenomic sequencing approaches to profile protozoan microbial communities as well as their functional pathways in treated and untreated wastewater samples collected from different regions of South Africa. Results demonstrated that protozoan diversity (Shannon index P-value = 0.03) and taxonomic composition (PERMANOVA, P-value = 0.02) was mainly driven by the type of wastewater samples (treated & untreated) and geographic location. However, these WWTPs were also found to contain a core community of protozoan parasites. The untreated wastewater samples revealed a predominant presence of free-living, parasitic, and potentially pathogenic protists typically found in humans and animals, ranging from Alveolata (27 %) phylum (Apicomplexa and Ciliophora) to Excavata (3.88 %) (Discoba and Parasalia) and Amoebozoa (2.84 %) (Entamoeba and Acanthamoeba). Shotgun metagenomics analyses in a subset of the untreated wastewater samples confirmed the presence of public health-importance protozoa, including Cryptosporidium species (3.48 %), Entamoeba hystolitica (6.58 %), Blastocystis hominis (2.91 %), Naegleria gruberi (2.37 %), Toxoplasma gondii (1.98 %), Cyclospora cayetanensis (1.30 %), and Giardia intestinalis (0.31 %). Virulent gene families linked to pathogenic protozoa, such as serine/threonine protein phosphatase and mucin-desulfating sulfatase were identified. Additionally, enriched pathways included thiamine diphosphate biosynthesis III, heme biosynthesis, Methylerythritol 4-Phosphate Pathway, methyl erythritol phosphate (MEP), and pentose phosphate pathways. These findings suggest that protozoan pathogens may possess metabolic and growth potential within WWTPs, posing a severe risk of transmission to humans and animals if inadequately disinfected before release. This study provides a baseline for the future investigation of diverse protozoal communities in wastewater, which are of public health importance.

Gastrointestinal parasite community structure in horses after the introduction of selective anthelmintic treatment strategies

A relatively new method to study the species richness and diversity of nematode parasites in grazing animals is to perform deep sequencing on composite samples containing a mixture of parasites. In this work, we compared species composition of strongyles in two groups of horses as a function of egg count and age, based on a DNA barcoding approach. Faecal egg counts and larval cultures were obtained from nearly 300 horses, i.e., domestic horses (n = 167) and trotters (n = 130) sampled nationwide. The second internal transcribed spacer region (ITS2) of strongyle nematodes in the larval cultures was first amplified using barcoded universal primers and then sequenced on the PacBio platform. Subsequently, bioinformatic sequence analysis was performed using SCATA to assign operational taxonomic units (OTU). Finally, species occurrence and composition were assessed using R. ITS2 sequences were found in the majority (89%) of larval samples. Sequencing yielded an average of 140 (26 to 503) reads per sample. The OTUs were assigned to 28 different taxa, of which all but three could be identified as species. The average relative abundance of the seven most abundant species (all Cyathostominae) accounted for 87% of the combined data set. The three species with the highest prevalence in both horse groups were Cyathostomum catinatum, Cylicocyclus nassatus and Cylicostephanus calicatus, and they were frequently found in different combinations with other species regardless of horse group. Interestingly, this result is largely consistent with a previous Swedish study based on morphological analysis of adult worms. In addition, two migratory strongylids (Strongylus vulgaris and S. edentatus) occurred in few domestic horses and trotters. Except for C. minutus and C. nassatus, which decreased with age, and C. catinatum and S. vulgaris, which increased, no specific trends were observed with respect to horse age. Taken together, these results are broadly consistent with data obtained before the introduction of selective targeted treatment in Sweden in 2007. All in all, our results suggest that this treatment strategy has not led to a significant change in strongyle nematode community structure in Swedish horses. The study also confirms that nemabiome analysis in combination with diversity index analysis is an objective method to study strongyle communities in horses.

Climate heterogeneity, season variation, and sexual dimorphism modulate the association between MHC II diversity and parasite variation in striped hamster

AbstractParasite‐mediated selection is widely believed to play a crucial role in maintaining the diversity of the major histocompatibility complex (MHC) genes, which is thought to be maintained through heterozygote advantage, rare‐allele advantage, and fluctuating selection. However, the relationship between parasite pressure and MHC diversity has yielded inconsistent findings. These inconsistencies may arise from the influence of environmental factors and individual variations in traits on host–parasite interactions. To address these issues, our study extensively investigated populations of striped hamsters inhabiting regions characterized by environmental heterogeneity. The primary objective was to examine the universality of parasite‐mediated selection mechanisms. Our observations revealed the presence of multiple parasite infections, accompanied by spatial and temporal variations in parasite communities and infection patterns among individual hamsters. Specifically, the temperature was found to influence all four parasite indices, while the presence of gamasid mites and parasite richness decreased with increasing precipitation. We also noted significant seasonal variation in parasite dynamics. Moreover, a significant sexual dimorphism was observed with males exhibiting a considerably higher parasite burden compared to their female counterparts. Lastly, we identified the maintenance of MHC polymorphism in striped hamsters as being driven by the heterozygote advantage and fluctuating selection mechanisms. This study underscores the significance of ecological processes in comprehending host–parasite systems and highlights the necessity of considering environmental factors and individual traits when elucidating the mechanisms underlying MHC diversity mediated by parasites.

First data on parasites of the invasive brown bullhead Ameiurus nebulosus (Siluriformes: Ictaluridae) in Ukraine.

This study describes the parasite community of non-native brown bullhead, Ameiurus nebulosus (Actinopterygii: Ictaluridae), collected at three sites in the river Vistula Basin (Lake Svitiaz, Lake Pisochne, and Lake on Plastova) and one site in the river Diester Basin (Lake Stryiska), in Ukraine. Our data represent the first comprehensive study of parasite community in this fish species in Europe. Sixteen parasite taxa were found, including species co-introduced from North America and species acquired in the European range. Maximum parasite richness (13 spp.) was recorded in Lake Svitiaz situated in a Natural Protected Area, while lowest species richness (3 spp.) was observed at Lake on Plastova, an artificial pond in the city of Lviv. Three co-introduced monogenean species, Gyrodactylus nebulosus, Ligictaluridus pricei and Ligictaluridus monticellii, are recorded in Ukraine for the first time, widening the knowledge of the European distribution of these North American parasites. Metric features for hard parts of invasive and native monogeneans showed overlap in ligictalurid parasites, but slightly smaller metrics in Ukrainian G. nebulosus, possibly reflecting water temperature during fish sampling. Though prevalence and abundance of acquired parasites was relatively low, infection parameters for metacercariae of Diplostomum spp. were relatively high at Lake Svitiaz and the natural Lake Stryiska in Lviv. In two lakes in the Vistula basin, we found high prevalence and abundance of Anguillicola crassus, an Asian nematode infecting eels, possibly supporting the invasional meltdown hypothesis. Our study confirms both further spread of non-native parasites in Europe and use of non-native fish as competent hosts for local native and introduced parasites.

Unravelling the mosquito-haemosporidian parasite-bird host network in the southwestern Iberian Peninsula: insights into malaria infections, mosquito community and feeding preferences.

Vector-borne diseases affecting humans, wildlife and livestock have significantly increased their incidence and distribution in the last decades. Because the interaction among vectors-parasite-vertebrate hosts plays a key role driving vector-borne disease transmission, the analyses of the diversity and structure of vector-parasite networks and host-feeding preference may help to assess disease risk. Also, the study of seasonal variations in the structure and composition of vector and parasite communities may elucidate the current patterns of parasite persistence and spread as well as facilitate prediction of how climate variations may impact vector-borne disease transmission. Avian malaria and related haemosporidian parasites constitute an exceptional model to understand the ecology and evolution of vector-borne diseases. However, the characterization of vector-haemosporidian parasite-bird host assemblages is largely unknown in many regions. Here, we analyzed 5859 female mosquitoes captured from May to November in five localities from southwestern Spain to explore the composition and seasonal variation of the vector-parasite-vertebrate host network. We showed a gradual increase in mosquito abundance, peaking in July. A total of 16 different haemosporidian lineages were found infecting 13 mosquito species. Of these assemblages, more than 70% of these vector-parasite associations have not been described in previous studies. Moreover, three Haemoproteus lineages were reported for the first time in this study. The prevalence of avian malaria infections in mosquitoes varied significantly across the months, reaching a maximum in November. Mosquito blood-feeding preference was higher for mammals (62.5%), whereas 37.5% of vectors fed on birds, suggesting opportunistic feeding behavior. These outcomes improve our understanding of disease transmission risk and help tovector control strategies.

Very low prevalence of haemosporidian parasites in two species of marsh terns

Vector-transmitted haemosporidians are among the most common parasites in birds, but our knowledge of the inter-specific patterns of infection rates and the parasite community composition is far from complete because of the unequal distribution of the screening effort across bird families and genera. To assess infection rates and the diversity of haemosporidians from the genera Plasmodium, Haemoproteus, and Leucocytozoon in marsh terns, which represent poorly explored in this regard genus of the family gulls, terns, and skimmers (Laridae), we screened two species: the Whiskered Tern (Chlidonias hybrida) and the Black Tern (Chlidonias niger). We sampled these long-distance migratory birds on breeding grounds: the Whiskered Tern in south-central Poland and north-central Ukraine, and the Black Tern—in north-central Ukraine. We found that birds from both species were infected only sporadically, with prevalence at the population level not exceeding 3.4%. Only parasites from the genera Plasmodium and Leucocytozoon were detected. There was neither an inter-specific difference nor a difference between populations of the Whiskered Tern in infection rates. In total, we registered three lineages—one Plasmodium and two Leucocytozoon—that were previously recorded in other bird species, and two unidentified Plasmodium infections. One of the lineages (Leucocytozoon LARCAC02) represents a specialist parasite with the host range restricted to larids and geographic range restricted to Poland, and two others (Plasmodium SGS1 and Leucocytozoon CIAE02) represent generalist parasites with very broad host and geographic ranges. This study reinforces the existing evidence that terns host parasites from genera Haemoproteus, Plasmodium, and Leucocytozoon only sporadically.

Parasites as indicators of habitat preferences by hybrids between estuarine and freshwater congeneric silversides (Atherinopsidae)

Silversides of the genus Odontesthes are characterized by their conserved morphology and vast phenotypic plasticity. They have developed complex population structures, promoting hybridization and speciation phenomena and often leading to intricate taxonomies. Within this genus, O. argentinensis, an originally marine species and O. bonariensis, a freshwater species, coexist in Mar Chiquita Coastal Lagoon (central Argentina). This lagoon has an inlet to the sea, creating a saline gradient that promotes highly variable conditions throughout the system. While O. argentinensis has established a resident population inside the lagoon, O. bonariensis is only sporadically found, inhabiting mainly tributary streams. Notably, hybrids between the two have been found in the lagoon. Parasites can significantly influence hybridization in host species, either promoting or hindering the process. From an evolutionary standpoint, parasites can impact hybridization by altering host immune responses, affecting host ecology and fitness. As a result, parasites can be valuable indicators of hybrid host ecology and their evolutionary trajectories. The present study analyzes the parasite communities of these sympatric Odontesthes and their hybrids, and determines their habitat preferences. While O. argentinensis showed evidence of marine parasites, O. bonariensis had a dominance of freshwater species as expected. And, although parasites of hybrids displayed similarities with both parental species, they indicated a preference of these hosts by freshwater habitats or longer periods of permanence in the oligohaline areas of Mar Chiquita. The presence of pure parental species, the differences in habitat use found between them and hybrids, and the conditioning effect of environmental heterogeneity over the hybridization event support a mosaic model for this hybrid zone. Finally, studies of parasitism in hybrid zones may contribute to understand the evolutionary history and stability of boundaries or possible biological barriers between host species, and they also provide insight on how natural selection and evolution drive speciation, colonization and habitat use in transitional environments.

Parasites of juvenile Salminus brasiliensis and Brycon orbignyanus (Characiformes, Bryconidae) in the middle Paraná River, Argentina

Piscivorous Salminus brasiliensis and herbivorous/omnivorous Brycon orbignyanus often form mixed schools in the same habitats. The aims of this study were: (a) to analyze and compare ecto- and endoparasite communities in juvenile S. brasiliensis and B. orbignyanus in the Middle Paraná River, Argentina; and (b) to evaluate the possible relationships between degree of parasitic infestation and body condition (Kn) of the fish. Fish necropsy was performed in search of endo- and ectoparasites, which were mounted in permanent or semi-permanent preparations for taxonomic study using helminthological techniques. A total 24 macroparasite taxa were recorded from the two host species. The parasitic infracommunities of both hosts were competitively structured. Ectoparasite communities were more similar than endoparasite communities. The abundance of parasitic species was not correlated with the standard length, weight and Kn of host individuals, except for the abundance of the copepod E. lacusauratus in the host S. brasiliensis, which was positively related to fish condition. New records of parasites were observed for native hosts, extending the geographic range of several species already known in the Upper Paraná River. The general structure of parasite communities can be determined by several factors, such as parasite-host relationship, host trophic level, and environment. In concordance with the similarity in habitat preferences, and the strong differences in trophic preferences, ectoparasite communities were found to be more similar than endoparasite communities between the two host species.

The functional traits of host fish can act as good predictors for parasite composition in a neotropical floodplain.

Parasite diversity can be influenced by the interaction of environmental factors and host traits, but understanding which traits can be decisive for the establishment of the parasite may provide subsidies fora better understanding of the host-parasite relationship. In this study, we investigated whether functional traits, diet, and host phylogeny can predict the similarity of the endoparasite composition of a fish assemblage in a Brazilian floodplain. Of the three evaluated components, the host's diet was the factor that showed the greatest influence on the composition and similarity of endoparasites, demonstrating the highest value of the explanation. The functional traits and phylogeny, despite presenting significant values (unique effect and global effect), showed low explainability in the composition of the endoparasites. When analyzing the joint effects, all components showed significant influence. Hosts that live in the same environment that are phylogenetically related and have a similar ecology have a certain degree of homogeneity in their parasite assemblages and, because they are endoparasites (which are acquired trophically along the chain), diet is the main driver of parasite richness and similarity. Overall, host traits can be one of the main determinants of parasite composition, so studies that address the functional traits of the host provide a representation of local diversity and define the possible patterns of these parasite communities.

Loss of species and genetic diversity during colonization: Insights from acanthocephalan parasites in northern European seals.

Studies on host-parasite systems that have experienced distributional shifts, range fragmentation, and population declines in the past can provide information regarding how parasite community richness and genetic diversity will change as a result of anthropogenic environmental changes in the future. Here, we studied how sequential postglacial colonization, shifts in habitat, and reduced host population sizes have influenced species richness and genetic diversity of Corynosoma (Acanthocephala: Polymorphidae) parasites in northern European marine, brackish, and freshwater seal populations. We collected Corynosoma population samples from Arctic, Baltic, Ladoga, and Saimaa ringed seal subspecies and Baltic gray seals, and then applied COI barcoding and triple-enzyme restriction-site associated DNA (3RAD) sequencing to delimit species, clarify their distributions and community structures, and elucidate patterns of intraspecific gene flow and genetic diversity. Our results showed that Corynosoma species diversity reflected host colonization histories and population sizes, with four species being present in the Arctic, three in the Baltic Sea, two in Lake Ladoga, and only one in Lake Saimaa. We found statistically significant population-genetic differentiation within all three Corynosoma species that occur in more than one seal (sub)species. Genetic diversity tended to be high in Corynosoma populations originating from Arctic ringed seals and low in the landlocked populations. Our results indicate that acanthocephalan communities in landlocked seal populations are impoverished with respect to both species and intraspecific genetic diversity. Interestingly, the loss of genetic diversity within Corynosoma species seems to have been less drastic than in their seal hosts, possibly due to their large local effective population sizes resulting from high infection intensities and effective intra-host population mixing. Our study highlights the utility of genomic methods in investigations of community composition and genetic diversity of understudied parasites.