The phylogenetics of Anguillicolidae (Nematoda: Anguillicoloidea), swimbladder parasites of eels

Morphological and molecular characterization of larval Echinocephalus sp. (Spirurida: Gnathostomatidae), a parasite of the greater lizard fish (Saurida undosquamis) and red porgy or common seabream (Pagrus pagrus)

Larvae of an unidentified Echinocephalus species were obtained from two fish species: red porgy or common seabream (Pagrus pagrus) and greater lizard fish (Saurida undosquamis) from the Red Sea. The prevalence of Echinocephalus sp. larvae in P. pagrus was 4.92% and 4.98% in S. undosquamis. The length, width, cephalic bulb, and spine shape and pattern of the larvae resembled Echinocephalus overstreeti. SSU gene sequences of larvae from P. pagrus and S. undosquamis were identical. Comparison of the SSU sequence to those available in GenBank showed that the larvae from P. pagrus and S. undosquamis are diagnosably distinct. Based on sequence similarity and published phylogenetic analysis, these larvae are most similar to an unknown species of Echinocephalus from an Australian sea snake (Hydrophis peronii). Despite morphological similarities of the Red Sea larvae to E. overstreeti, the SSU sequence differences show that they are not the same species.

Advancing the knowledge of the nematode Echinocephalus pseudouncinatus (Gnathostomatidae, Spirurida): morphological and molecular identification, new host, and host specificity in two coexisting pen shells (Bivalvia: Pinnidae)

The life cycle of Echinocephalus pseudouncinatus has not been described in detail to date, as is also the case of other species in the genus. This study contributes to the information available about the life history of the genus, particularly E. pseudouncinatus, by (1) using molecular techniques (small subunit rRNA gene [SSU rRNA] sequences) to identify larvae of this species; (2) describing the most conspicuous morphological characteristics that distinguish the species by scanning electron microscopy; (3) describing histological characteristics of the internal anatomy of larvae and the lesions caused by them in the gonads of hosts; (4) reporting new host and reporting evidence of host specificity of E. pseudouncinatus between two species of edible pen shells coexisting in the northern Pacific of Mexico; and (5) analyzing the frequency of infested gonads by host sex, size, and gonadal development stage. The molecular analysis confirmed the morphological and histological diagnosis of E. pseudouncinatus larvae infesting gonads of Atrina maura and Pinna rugosa in Ojo de Liebre and San Ignacio lagoons. The morphological characterization of larvae provides internal details of the cephalic bulb (including rows of hooks and ballonets), neural chord, and cell types of the body wall. Histopathological findings such as degenerated and atretic gametes and the displacement of gonadal tissue in hosts infested with E. pseudouncinatus larvae are discussed in terms of temperature anomalies caused by the "Godzilla El Niño." The frequency of infestation increased with shell length and gonadal development in A. maura, with a higher infestation frequency in females versus males observed at both study sites. Our findings expand the list of hosts of E. pseudouncinatus, which was previously unknown as a parasite of P. rugosa. In P. rugosa, infestation frequencies are noticeably lower (<1%) compared with those observed in A. maura (>30%) at both study sites, suggesting host-specific requirements or preferences in E. pseudouncinatus larvae.

Review of the metazoan parasites of the economically and ecologically important African sharptooth catfish Clarias gariepinus in Africa: Current status and novel records

One of the most widely distributed African freshwater fish is the African sharptooth catfish Clarias gariepinus (Burchell) that is naturally distributed in 8 of the 10 ichthyofaunal regions of this continent. Clarias gariepinus is a highly valued and cheap staple to local communities and an ideal aquaculture species. Consequently, interest in the parasitic communities of C. gariepinus has increased as parasites may accidentally be ingested by humans when eating uncooked fish or can be introduced into culture systems through fish stocks supplied from local rivers which affect yield, growth, and marketability. This review provides an overview of the ∼107 metazoan parasite species known to parasitise C. gariepinus in Africa and their general life cycles, morphology, paratenic and post-cyclic infections, and the biogeography and validity of records are discussed. A brief overview is included on the application of some of these parasites in environmental studies and their link to human health.

Large-scale genetic investigation of nematode diversity and their phylogenetic patterns in New Zealand's marine animals

Nematodes constitute one of the most speciose metazoan groups on earth, and a significant proportion of them have parasitic life styles. Zooparasitic nematodes have zoonotic, commercial and ecological significance within natural systems. Due to their generally small size and hidden nature within their hosts, and the fact that species discrimination using traditional morphological characteristics is often challenging, their biodiversity is not well known, especially within marine ecosystems. For instance, the majority of New Zealand's marine animals have never been the subject of nematode studies, and many currently known nematodes in New Zealand await confirmation of their species identity with modern taxonomic techniques. In this study, we present the results of an extensive biodiversity survey and phylogenetic analyses of parasitic nematodes infecting New Zealand's marine animals. We used genetic data to differentiate nematodes to the lowest taxonomic level possible and present phylogenies of the dominant clades to illustrate their genetic diversity in New Zealand. Our findings reveal a high diversity of parasitic nematodes (23 taxa) infecting New Zealand's marine animals (62 of 94 free-living animal species investigated). The novel data collected here provide a solid baseline for future assessments of change in diversity and distribution of parasitic nematodes.

A molecular characterization of marsupial filarioid nematodes of the genus Breinlia

Here we present the genetic relationships of 26 specimens of the genus Breinlia (Nematoda: Filarioidea) from a range of Australian marsupials using markers in the small subunit of nuclear ribosomal RNA and mitochondrial cytochrome c oxidase subunit 1 (cox1) genes and compare them with morphological determinations. The molecular data support the validity of most of the morpho-species included in the study and provide provisional insights into the phylogeny of the genus in Australian mammals, with dasyuroid marsupials appearing to be the original hosts. The recent discovery of Breinlia annulipapillata in the eye of a human brings this genus of parasites into the group of emerging infectious parasitic diseases.

Genetic characterisation of Echinocephalus spp. (Nematoda: Gnathostomatidae) from marine hosts in Australia

We genetically characterised larval and adult specimens of species of Echinocephalus Molin, 1858 (Gnathostomatidae) collected from various hosts found within Australian waters. Adult specimens of Echinocephalus were collected from a dasyatid stingray [Pastinachus ater (Macleay); n = 2] from Moreton Bay, Queensland and larvae from a hydrophiine sea snake [Hydrophis peronii (Duméril); n = 3] from Cape York Peninsula, Queensland, from an octopus (Octopus djinda Amor & Hart; n = 3) from Fremantle, Western Australia and from a lucinid bivalve [Codakia paytenorum (Iredale); n = 5] from Heron Island, Queensland Australia. All nematode samples were identified morphologically and genetically characterised using the small subunit nuclear ribosomal DNA (SSU). Some morphological differences were identified between previous studies of Echinocephalus spp. and those observed herein but the significance of these differences remains unresolved. Molecular phylogenetic analyses revealed that larval Echinocephalus sp. from H. peronii and C. paytenorum in Australia were very similar (with strong nodal support) to larval Echinocephalus sp. infecting two fish species from Egypt, Saurida undosquamis (Richardson) (Synodontidae) and Pagrus pagrus (Linnaeus) (Sparidae). The SSU sequences of larval Echinocephalus sp. from O. djinda and adults from P. ater formed a well-supported clade with that of adult E. overstreeti Deardorff and Ko, 1983 from the Port Jackson shark, Heterodontus portusjacksoni (Meyer), as well as that of the larval Echinocephalus sp., from the common carp (Cyprinus carpio Linnaeus) from Egypt. This study extends the intermediate host range of Echinocephalus larvae by including a sea snake for the first time. Findings of this study highlight the importance of genetic characterisation of larval and adult specimens of Echinocephalus spp. to resolve the current difficulties in the taxonomy of this genus.

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Historical morphological descriptions of larval forms of Echinocephalus provide inadequate species identification.

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Larval stages of Echinocephalus species from various hosts found within Australian waters were characterised.

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Intermediate host range of Echinocephalus larvae was extended to include a reptile.

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Future studies should include genetic characterisation of Echinocephalus spp. to resolve taxonomic inaccuracies.

Genetic characterisation of Tanqua (von Linstow, 1879) (Nematoda: Gnathostomatidae) larval forms including new host and locality records

In an unrelated study of spotted snakehead fish Channa punctata (Bloch) of family Channidae (N = 103) from Bangladesh, ten fish had taupe and clear coloured cysts attached to the intestinal mesentery. Investigation of the cysts revealed larval nematodes. The larvae were damaged and not suitable for detailed morphological study, however, key features such as tooth like projections of the pseudolabia and lateral pseudolabium were observed in specimens with undamaged cephalic regions. Molecular characterisation was undertaken and although the parasite genetic material was poor, five of the twelve nematode larvae through sequencing of the 18S ribosomal RNA gene, showed 98.17% match with sequences assigned for Tanqua tiara (accession number JF934728) deposited in GenBank. The prevalence of infection was 9.7% and the mean intensity 2.70. Tanqua has not previously been identified in fish, or from the definitive host, the Asian water monitor Varanus salvator (Laurenti, 1768) of family Varanidae (class Reptilia), in Bangladesh. Therefore, this study represents a new host and locality record for this nematode species. In many previous reports from this region, nematode larvae have been identified morphologically and assigned to a diverse range of nematode genera. Some confusion therefore exists regarding their accuracy and further investigations are required using molecular methodology to clarify the species of larval nematodes which infect edible fish in Bangladesh.

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Tanqua species identified from Channa punctata.

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New host and region record for Tanqua species in Bangladesh.

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Tanqua species identified using molecular methodology.

Towards an in-situ non-lethal rapid test to accurately detect the presence of the nematode parasite, Anguillicoloides crassus, in European eel, Anguilla anguilla

Anguillicoloides crassus is an invasive nematode parasite of the critically endangered European eel, Anguilla anguilla, and possibly one of the primary drivers of eel population collapse, impacting many features of eel physiology and life history. Early detection of the parasite is vital to limit the spread of A. crassus, to assess its potential impact on spawning biomass. However accurate diagnosis of infection could only be achieved via necropsy. To support eel fisheries management we developed a rapid, non-lethal, minimally invasive and in situ DNA-based method to infer the presence of the parasite in the swim bladder. Screening of 131 wild eels was undertaken between 2017 and 2019 in Ireland and UK to validate the procedure. DNA extractions and PCR were conducted using both a Qiagen Stool kit and in situ using Whatman qualitative filter paper No1 and a miniPCR DNA Discovery-System™. Primers were specifically designed to target the cytochrome oxidase mtDNA gene region and in situ extraction and amplification takes approximately 3 h for up to 16 individuals. Our in-situ diagnostic procedure demonstrated positive predictive values at 96% and negative predictive values at 87% by comparison to necropsy data. Our method could be a valuable tool in the hands of fisheries managers to enable infection control and help protect this iconic but critically endangered species.

Integrative taxonomy suggests that South American freshwater nematodes Echinocephalus and their host stingrays co-originated in late Oligocene to early Miocene

Nematoda of the genus Echinocephalus Molin, 1858 include species from the Gnathostomatidae family, the adult stages of which parasitize the stomach and spiral intestine of elasmobranchs as their final hosts. In the present study, we describe Echinocephalus spinosus n. sp. found parasitizing the spiral valve of the freshwater stingray Potamotrygon motoro from the Tapajós River, in the Amazon Basin, in the state of Pará, Brazil. In the study we performed morphological (light and scanning electron microscopy) and molecular (small subunit ribosomal ribonucleic acid (SSU rDNA) and mitochondrial cytochrome c oxidase I sequencing) analyses. E. spinosus n. sp. is only the second species of the Echinocephalus genus described from a strictly freshwater environment. The SSU rDNA based phylogenetic analyses showed Echinocephalus clade as a sister lineage of Gnathostoma, and that the new species arises as a sister to Echinocephalus cf. pseudouncinatus. Time-calibrated phylogenetic analysis revealed that the origin of the freshwater Echinocephalus coincides with the recently proposed origin of the freshwater host potamotrygonin stingray, namely the late Oligocene to early Miocene, when the western Amazon was dominated by the Pebas wetlands, an epicontinental marine/freshwater system.

Anguillicola (Anguillicoides) crassus: Morphometric characteristics and pathogenicity in eels (Anguilla anguilla) in Greece

Anguillicola (Anguillicoides) crassus is a swimbladder nematode parasite of Anguilla anguilla (Linnaeus, 1758). The present study investigates the morphology and pathogenicity of A. crassus in European eel, as well as, the effects of different aquatic environments on the infection of A. crassus, in Greece. A total of 268 nematodes were collected from four estuarine systems in Greece. In all collected parasites, measurements carried out to define the morphological characteristics of parasites: parasite length and width, oesophagus max length and max width. Τhe mean parasite length was 23.50 mm (95% CI: 22.42-24.58) for females, 12.95 mm (95% CI: 12.25-13.64) for the males and 6.39 mm (95% CI: 5.27-7.50) for the juveniles. The mean parasite width was 1.99 mm (95% CI: 1.88-2.10) for females, 0.93 mm (95% CI: 0.86-1.00) for males and 0.51 mm (95% CI: 0.39-0.64) for juveniles. In total, the mean intensity was found 3.15 (95% CI: 2.53-3.78), while the highest mean intensity per eel was 8.00 (95% CI: 0.00-29.51) in Tholi Lagoon and the lowest was 2.20 (95% CI: 0.36-4.04) in Amvrakikos Gulf. Longitudinal and transverse histological sections of two adults A. crassus and two swimbladders were carried out. Multiple granules were observed, as a tissue reaction of the organism to swath around the 4th stage larvae (L4) that have entered the swimbladder. Molecular analysis was performed on three female adults A. crassus derived from eel specimens coming from the Vistonis estuarine system. The high reproductive capacity of the parasite reveals that A. anguilla has low effective defense mechanisms against the parasite. Also, the morphometric variations of the A. crassus seems to have a plastic feature which is being differently expressed when exposed to various environments.

Detection of Breinlia sp. (Nematoda) in the Leadbeater's possum (Gymnobelideus leadbeateri)

The Leadbeater's possum (Gymnobelideus leadbeateri) is a critically endangered marsupial in south-eastern Australia. Among other conservation efforts, free-ranging animals in the two remaining geographically separate populations (highland and lowland) have been extensively studied; however, little is known about their health and mortality. Although some wild populations are frequently monitored, cadavers are rarely recovered for post mortem examination. In June 2019, a recently deceased, wild, adult male lowland Leadbeater's possum was collected from a nest box and a comprehensive post mortem examination was conducted. Microfilariae of a filarioid nematode were observed in testes, liver, lung and skin samples in tissue impression smears and upon histopathological examination. No gross or histological changes were seen associated with the parasites, except for a focal area of tissue damage in the skin, suggesting that the possum is a natural host. Using a PCR-coupled sequencing method the filarioid was identified as a species of Breinlia. Species of Breinlia occur in other Australian marsupials and rodents.

Symbiosis of the millipede parasitic nematodes Rhigonematoidea and Thelastomatoidea with evolutionary different origins

Background

How various host–parasite combinations have been established is an important question in evolutionary biology. We have previously described two nematode species, Rhigonema naylae and Travassosinema claudiae, which are parasites of the xystodesmid millipede Parafontaria laminata in Aichi Prefecture, Japan. Rhigonema naylae belongs to the superfamily Rhigonematoidea, which exclusively consists of parasites of millipedes. T. claudiae belongs to the superfamily Thelastomatoidea, which includes a wide variety of species that parasitize many invertebrates. These nematodes were isolated together with a high prevalence; however, the phylogenetic, evolutionary, and ecological relationships between these two parasitic nematodes and between hosts and parasites are not well known.

Results

We collected nine species (11 isolates) of xystodesmid millipedes from seven locations in Japan, and found that all species were co-infected with the parasitic nematodes Rhigonematoidea spp. and Thelastomatoidea spp. We found that the infection prevalence and population densities of Rhigonematoidea spp. were higher than those of Thelastomatoidea spp. However, the population densities of Rhigonematoidea spp. were not negatively affected by co-infection with Thelastomatoidea spp., suggesting that these parasites are not competitive. We also found a positive correlation between the prevalence of parasitic nematodes and host body size. In Rhigonematoidea spp., combinations of parasitic nematode groups and host genera seem to be fixed, suggesting the evolution of a more specialized interaction between Rhigonematoidea spp. and their host. On the other hand, host preference of Thelastomatoidea spp. was not specific to any millipede species, indicating a non-intimate interaction between these parasites and their hosts.

Conclusions

The two nematode superfamilies, Rhigonematoidea and Thelastomatoidea, have phylogenetically distinct origins, and might have acquired xystodesmid millipede parasitism independently. Currently, the two nematodes co-parasitize millipedes without any clear negative impact on each other or the host millipedes. Our study provides an example of balanced complex symbioses among parasitic nematodes and between parasitic nematodes and host millipedes, which have been established over a long evolutionary history.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-021-01851-4.

Pseudodactylogyrus anguillae (Yin & Sproston, 1948) from the giant mottled eel Anguilla marmorata Quoy & Gaimard, 1824, in the Phongolo River, South Africa: an invader on the African continent

The global invasive anguillid gill parasite Pseudodactylogyrus anguillae (Yin and Sproston, 1948) has only recently been documented from eels in South Africa. As there is no known eel trade in South Africa, the source of introduction of this parasite has been debated, and its status as an alien parasite was rendered uncertain. We report on the first infection of Pseudodactylogyrus anguillae from the giant mottled eel Anguilla marmorata from the Phongolo River (South Africa) using classic morphological and molecular methodologies and clarify the introduction status category of this parasite as alien and invasive.

The wild world of Guinea Worms: A review of the genus Dracunculus in wildlife

Nematodes are an extremely diverse and speciose group of parasites. Adult dracunculoid nematodes (Superfamily Dracunculoidea) occur in the tissues and serous cavities of mammals, fish, reptiles, amphibians and birds. Of the dracunculid group, perhaps best known is Dracunculus medinensis, the human Guinea Worm. Considerable work has been done on D. medinensis; however recent infections in peri-domestic dogs and the finding of naturally-infected paratenic hosts (previously unreported for D. medinensis) indicate we still have much to learn about these parasites. Furthermore, among eight species in the Old World and six species in the New World there is a lack of general life history knowledge as well as questions on species occurrence, host diversity, and transmission dynamics. Herein, we provide a comprehensive review of the genus Dracunculus, in order of a theoretical evolutionary progression from reptilian to mammalian hosts. Species descriptions, where available, are provided but also show where gaps occur in our knowledge of various species. Additionally, many first reports of Dracunculus spp. were done prior to the development and use of molecular tools. This is especially important for this group of parasites as speciation based on morphology is only applicable to males of the genus, and males, given their size, are notoriously difficult to recover from definitive hosts. Therefore, we also discuss current molecular tools used in the investigation of this group of parasites. Given recent host-switching events, the dracunculids are of increasing importance and require further work to expand our understanding of this genus.

Light microscopic study of four plagiorchiid trematodes infecting marine fish in the south-eastern Mediterranean Sea, Alexandria City, with descriptions of two new species

During the present investigation, a total of 220 fish specimens belonging to three different species, namely, little tunny Euthynnus alletteratus, African snook Lates niloticus, and striped red mullet Mullus surmuletus, were collected from January-November 2016 from the coasts off Abu Qir landing site, Alexandria City, south-eastern Mediterranean Sea, Egypt. The collected fish samples were dissected and examined for the presence of helminth parasites. Twenty-three out of 220 (10.45%) fish specimens were found to be naturally infected with four species of trematode parasites belonging to three different families of the order Plagiorchiida. The recovered parasite species were collected and identified by applying light microscopic examinations. The present study recorded two new parasite species, namely, Stephanostomum alletterani sp. nov. and Bathycreadium mulli sp. nov., belonging to the families Acanthocolpidae and Opecoelidae and infecting E. alletteratus and M. surmuletus, respectively and re-descriptions of the two remaining species, namely, Acanthostomum spiniceps and Aponurus mulli of the families Acanthostomatidae and Opecoelidae, respectively, to clarify the measurements of some body parts. Morphological and morphometric characterizations revealed some differences between the present species and other related species detected previously. Future studies are recommended to include advanced molecular characteristics for these species.

A molecular phylogeny of the Rhigonematomorpha De Ley & Blaxter, 2002 as inferred from SSU and LSU rDNA sequences

A molecular hypothesis of the Infraorder Rhigonematomorpha is presented. The phylogeny recovered using combined SSU and LSU markers suggests that the Rhigonematomorpha is nested within a larger clade that includes Ascaridomorpha, Spiruromorpha and Oxyuridomorpha and is strongly supported by maximum likelihood (ML) bootstrap support values (BS) and Bayesian posterior probabilities (BPP). SSU and LSU ML and Bayesian analyses recovered Rhigonematomorpha as a paraphyletic clade. In the ML and Bayesian analyses of a combined matrix of complete to partial sequences of SSU and LSU, respectively, Rhigonematomorpha is recovered as a monophyletic clade with moderate BPP but low BS. Highly supported BS and BPP of a combined SSU and LSU matrix support a hypothesis of a monophyletic Superfamily Ransomnematoidea that includes the families Carnoyidae, Hethidae, Ransomnematidae plus a Brumptaemilius, Cattiena, Insulanema clade, and a monophyletic Superfamily Rhigonematoidea that probably includes the paraphyletic families Rhigonematidae and Ichthyocephalidae. It is suggested that the future inclusion of more families and genera might help resolve the monophyly of the Infraorder Rhigonematomorpha as advanced here.

Morphological and molecular characterization of cucullanid nematodes including Cucullanus opisthoporus n. sp. in freshwater fish from the Brazilian Amazon

Molecular and morphological characterization of two species of Cucullanidae from freshwater fish in Brazil are provided, one of which represented an undescribed taxon. Cucullanus opisthoporus n. sp. was collected in Cichla melaniae from River Xingu, State of Pará, and in C. pinima from River Jamarí, State of Rondônia. Nematodes referable to Cucullanus grandistomis were collected in Oxydoras niger from River Xingu. The new species has an appendage in the tail tip, ventrally covered by small spines, which is an exclusive feature of Cucullanus tucunarensis. However, C. tucunarensis differs from C. opisthoporus n. sp. based upon the relative position of deirids and the excretory pore, which are more posterior from the oesophageal end in the new species. Observations of C. tucunarensis type specimens also revealed features that were wrongly or not reported in the original description. Type specimens of C. grandistomis were observed, although they were poorly preserved. After evaluation of newly collected specimens of C. grandistomis, features unreported in the original description were observed for the first time, including the presence of an intestinal caecum. Thus, C. grandistomis was transferred to Dichelyne. Sequences of the 18S and 28S rRNA genes revealed high genetic similarity between the specimens of C. opisthoporus n. sp. from the two different hosts as well as their genetic distance from Dichelyne grandistomis n. comb. Phylogenetic reconstructions using representatives of Cucullanidae suggested the artificiality of the current morphological system adopted to separate the genera, since most genera were not monophyletic, although the availability of genetic data is still fragmented.

First report on nematode parasite infection in the yellowbar angelfish Pomacanthus maculosus (Perciformes: Pomacanthidae) from the Iraqi coral reef, with description of a new species of Cucullanus (Nematoda: Ascaridida) using the integrated approaches

The yellowbar angelfish Pomacanthus maculosus (Forsskål) (Perciformes: Pomacanthidae) is a beautiful, marine ornamental fish with very important commercial value. However, to date, no information is available on nematode parasite infection in P. maculosus. In the present study, the integrated approaches including light and scanning electron microscopy, and sequencing and analysing ribosomal [small ribosomal DNA (18S) and internal transcribed spacer (ITS)] and mitochondrial [cytochrome c oxidase subunit 1 (cox1)] target regions, respectively, were employed for the systematic evaluation of the nematode parasites firstly isolated from P. maculosus in the Iraqi coral reef. The results revealed that these nematodes represent a new species of Cucullanus (Ascaridida: Cucullanidae). The phylogenetic analyses based on 18S, ITS and cox1 sequences were constructed, respectively, to assess the phylogenetic relationships between the new species and the other cucullanids, and the monophyly of Cucullanus, as well as some its related genus-level taxa. The results supported C. extraneus n. sp. appear to be sister to C. hainanensis, and the genera Cucullanus, Dichelyne and Truttaedacnitis may be not monophyletic assemblages. This is the first report of the occurrence of nematode parasites in P. maculosus.

The Hsp70 response of Anguillicola species to host-specific stressors

The present study is based on infection experiments of two different swim bladder parasite species, Anguillicola crassus Kuwahara et al., 1974 and Anguillicola novaezelandiae Moravec and Taraschewski, 1988, which were experimentally transferred to the two eel species Anguilla anguilla Linnaeus, 1758 and Anguilla japonica Temmink and Schlegel, 1846, respectively. The host-parasite groups were selected due to their different grades of mutual adaptation. The main aim of this study was to analyze the stress responses within the parasites, which were confronted with different hosts, i.e. with different stressors related to the respective host. For this purpose, mean intensities, recovery rates, larvae output, and levels of synthesized heat shock proteins (Hsp70) were determined in nematodes of each infection group. Increased stress responses were detected in the endemic system of A. crassus parasitizing A. japonica and A. crassus in its recently acquired host A. anguilla, which seems to be associated with the immune response of the particular host species and the expenditure of energy on producing larvae. A. novaezelandiae showed overall weak activities in its unknown host species A. japonica, with the lowest recovery rate of all examined groups neither featuring elevated Hsp responses, nor a high mean intensity, nor any reproductive output. On the contrary, in A. anguilla, the parasite reached higher recovery rates, mean intensities, and reproductive output, but no increased Hsp70 levels could be detected. The four considered factors proved partially interdependent, whereas few results did not follow a clear pattern.

Comparison of five methods for delimitating species in Ophion Fabricius, a diverse genus of parasitoid wasps (Hymenoptera, Ichneumonidae)

DNA taxonomy has been proposed as a method to quickly assess diversity and species limits in highly diverse, understudied taxa. Here we use five methods for species delimitation and two genetic markers (COI and ITS2) to assess species diversity within the parasitoid genus, Ophion. We searched for compensatory base changes (CBC's) in ITS2, and determined that they are too rare to be of practical use in delimiting species in this genus. The other four methods used both COI and ITS2, and included distance-based (threshold analysis and ABGD) and tree-based (GMYC and PTP) models. We compared the results of these analyses to each other under various parameters and tested their performance with respect to 11 Nearctic species/morphospecies and 15 described Palearctic species. We also computed barcode accumulation curves of COI sequences to assess the completeness of sampling. The species count was highly variable depending on the method and parameters used, ranging from 47 to 168 species, with more conservative estimates of 89-121 species. Despite this range, many of the Nearctic test species were fairly robust with respect to method. We concluded that while there was often good congruence between methods, GMYC and PTP were less reliant on arbitrary parameters than the other two methods and more easily applied to genetic markers other than COI. However, PTP was less successful at delimiting test species than was GMYC. All methods, as well as the barcode accumulation curves, indicate that several Palearctic species remain undescribed and that we have scarcely begun to appreciate the Nearctic diversity within this genus.

Size does matter-a closer look on Anguillicola morphology

The present study deals with morphological differences between two closely related parasitic nematode species (Anguillicola crassus Kuwahara et al., 1974 and Anguillicola novaezelandiae Moravec & Taraschewski, 1988) in two different experimentally infected eel species (Anguilla anguilla Linnaeus, 1758 and Anguilla japonica Temminck & Schlegel, 1847). Furthermore, it considers the question whether size differences between those two species are ontogenetically determined or host species-dependent. In order to analyse these questions, experimental infections with the four possible host-parasite systems have been performed, followed by precise morphometric measurements related to body size and head structures of all resulting nematodes 120 days post infection. Body size measurements (length and width) of A. crassus generally exceeded those of A. novaezelandiae, while both Anguillicola species turned out to be smaller in Japanese eels than in European eels. Comparative measurements of neck width, maximum oesophagus width, and posterior head end width were found to be highly significant with regard to the different host-parasite systems. Shape and width of neck have been identified as reliable discriminating factors for species distinction. Generally, the relation of anterior head end width and neck width proved to be distinctly species-specific and can thus serve as a decisive and easily measureable distinguishing feature.

Competing invaders: Performance of two Anguillicola species in Lake Bracciano

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Two Anguillicola spp. occurring as nonindigenous species are compared in the review.

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Both species differ in their life cycles.

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Anguillicola crassus replaced Anguillicola novaezelandiae in Lake Bracciano.

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Possible reasons for the disappearance of A. novaezelandiae are discussed.

Anguillicola crassus is one of the most successful parasitic invasive species as it has spread from its original habitat in East Asia throughout the world and has acquired five new eel host species in the course of its invasion within the last three decades. Records from an Italian lake indicate that this species has even displaced an established population of its close relative A. novaezelandiae originating from New Zealand. In order to analyze the reasons for its high invasive potential, this review highlights recent studies, which substantiate the selective advantages of A. crassus over A. novaezelandiae.

Laboratory infection experiments revealed that A. crassus features a less synchronized development compared to A. novaezelandiae in the European eel, which enables this species to emit eggs over a longer period of time. Differences in the time period required for first egg output and in the maturation process of second stage larvae in intermediate hosts could also be detected, which may lead to differences in infection potential. Finally, microsatellite analyses have shown that hybridization processes are possible, but might only occur between A. crassus males and A. novaezelandiae females. Taken as a whole, the sum of minor selective advantages and differences in life cycle traits could have considerably contributed to a replacement of one species by the other.

Transcriptome analyses of Anguillicola crassus from native and novel hosts

Anguillicola crassus is a swim bladder nematode of eels. The parasite is native to the Asian eel Anguilla japonica, but was introduced to Europe and the European eel Anguilla anguilla in the early 1980s. A Taiwanese source has been proposed for this introduction. In the new host in the recipient area, the parasite appears to be more pathogenic. As a reason for these differences, genetically fixed differences in infectivity and development between Taiwanese and European A.crassus have been described and disentangled from plasticity induced by different host environments. To explore whether transcriptional regulation is involved in these lifecycle differences, we have analysed a “common garden”, cross infection experiment, using deep-sequencing transcriptomics. Surprisingly, in the face of clear phenotypic differences in life history traits, we identified no significant differences in gene expression between parasite populations or between experimental host species. From 120,000 SNPs identified in the transcriptome data we found that European A. crassus were not a genetic subset of the Taiwanese nematodes sampled. The loci that have the major contribution to the European-Taiwanese population differentiation show an enrichment of synonymous and non-coding polymorphism. This argues against positive selection in population differentiation. However, genes involved in protein processing in the endoplasmatic reticulum membrane and genes bearing secretion signal sequences were enriched in the set of genes most differentiated between European and Taiwanese A. crassus. These genes could be a source for the phenotypically visible genetically fixed differences between European and Taiwanese A. crassus.

Morphological and molecular evidence for a new species of the genus Dichelyne Jägerskiöld, 1902 (Ascaridida: Cucullanidae) from marine perciform fishes in the South China Sea

A new cucullanid nematode, Dichelyne (Dichelyne) breviculus n. sp., collected from the intestine of the goatee croaker Dendrophysa russelii (Cuvier) (Perciformes: Sciaenidae), the burrowing goby Trypauchen vagina (Bloch & Schneider) and the tropical sand goby Acentrogobius caninus (Valenciennes) (Perciformes: Gobiidae) in the South China Sea, is described using both light and scanning electron microscopy. The new species differs from its congeners in the size of body (2.16-2.96 mm in male), the position of the excretory pore and deirids, the length of the spicules (0.90-1.32 mm, representing 32.4-51.9% of body length), the arrangement of the caudal papillae and the morphology of the tail. In addition, in order to primarily assess the validity of the new species genetically, the specimens of D. breviculus n. sp. collected from the three different hosts were also characterised using molecular methods by sequencing and analysing ribosomal [small ribosomal subunit (18S rDNA) and internal transcribed spacer (ITS)] and mitochondrial [cytochrome c oxidase subunit 1 (cox1)] target regions. The molecular analyses support the validity of the new species based on the morphological observations.

SSU rDNA divergence in planktonic foraminifera: molecular taxonomy and biogeographic implications

The use of planktonic foraminifera in paleoceanography requires taxonomic consistency and precise assessment of the species biogeography. Yet, ribosomal small subunit (SSUr) DNA analyses have revealed that most of the modern morpho-species of planktonic foraminifera are composed of a complex of several distinct genetic types that may correspond to cryptic or pseudo-cryptic species. These genetic types are usually delimitated using partial sequences located at the 3'end of the SSUrDNA, but typically based on empirical delimitation. Here, we first use patristic genetic distances calculated within and among genetic types of the most common morpho-species to show that intra-type and inter-type genetic distances within morpho-species may significantly overlap, suggesting that genetic types have been sometimes inconsistently defined. We further apply two quantitative and independent methods, ABGD (Automatic Barcode Gap Detection) and GMYC (General Mixed Yule Coalescent) to a dataset of published and newly obtained partial SSU rDNA for a more objective assessment of the species status of these genetic types. Results of these complementary approaches are highly congruent and lead to a molecular taxonomy that ranks 49 genetic types of planktonic foraminifera as genuine (pseudo)cryptic species. Our results advocate for a standardized sequencing procedure allowing homogenous delimitations of (pseudo)cryptic species. On the ground of this revised taxonomic framework, we finally provide an integrative taxonomy synthesizing geographic, ecological and morphological differentiations that can occur among the genuine (pseudo)cryptic species. Due to molecular, environmental or morphological data scarcities, many aspects of our proposed integrative taxonomy are not yet fully resolved. On the other hand, our study opens up the potential for a correct interpretation of environmental sequence datasets.

The evolution of parasitism in Nematoda

Nematodes are abundant and diverse, and include many parasitic species. Molecular phylogenetic analyses have shown that parasitism of plants and animals has arisen at least 15 times independently. Extant nematode species also display lifestyles that are proposed to be on the evolutionary trajectory to parasitism. Recent advances have permitted the determination of the genomes and transcriptomes of many nematode species. These new data can be used to further resolve the phylogeny of Nematoda, and identify possible genetic patterns associated with parasitism. Plant-parasitic nematode genomes show evidence of horizontal gene transfer from other members of the rhizosphere, and these genes play important roles in the parasite-host interface. Similar horizontal transfer is not evident in animal parasitic groups. Many nematodes have bacterial symbionts that can be essential for survival. Horizontal transfer from symbionts to the nematode is also common, but its biological importance is unclear. Over 100 nematode species are currently targeted for sequencing, and these data will yield important insights into the biology and evolutionary history of parasitism. It is important that these new technologies are also applied to free-living taxa, so that the pre-parasitic ground state can be inferred, and the novelties associated with parasitism isolated.

Preferential host switching and codivergence shaped radiation of bark beetle symbionts, nematodes of Micoletzkya (Nematoda: Diplogastridae)

Host-symbiont systems are of particular interest to evolutionary biology because they allow testable inferences of diversification processes while also providing both a historical basis and an ecological context for studies of adaptation. Our investigations of bark beetle symbionts, predatory nematodes of the genus Micoletzkya, have revealed remarkable diversity of the group along with a high level of host specificity. Cophylogenetic analyses suggest that evolution of the nematodes was largely influenced by the evolutionary history of beetles. The diversification of the symbionts, however, could not be attributed to parallel divergence alone; our results indicate that adaptive radiation of the nematodes was shaped by preferential host shifts among closely related beetles along with codivergence. Whereas ecological and geographic isolation have played a major role in the diversification of Micoletzkya at shallow phylogenetic depths, adaptations towards related hosts have played a role in shaping cophylogenetic structure at a larger evolutionary scale.

Can differences in life cycle explain differences in invasiveness? - A study on Anguillicola novaezelandiae in the European eel

Anguillicola crassus is the most invasive species of its genus and it is a successful colonizer of different eel species worldwide. It is so far the only species of the genus Anguillicola whose life cycle has been studied completely. To analyse whether differences in life cycle may explain differences in invasiveness, we infected European eels with Anguillicola novaezelandiae under laboratory conditions. Anguillicola novaezelandiae shows a synchronized development in the European eel. Eggs with second-stage larvae appeared 120 days after infection. No density-dependent effect in parasite development could be found for A. novaezelandiae. The present study shows that the life cycle of A. novaezelandiae differs on final host level compared with A. crassus in ways which result in a less successful invasion of new host species.

Evolutionary divergence of the swim bladder nematode Anguillicola crassus after colonization of a novel host, Anguilla anguilla

Background

Anguillicola crassus, a swim bladder nematode naturally parasitizing the Japanese eel, was introduced about 30 years ago from East Asia into Europe where it colonized almost all populations of the European eel. We conducted a common garden experiment under a reciprocal transfer design infecting both European and Japanese eels with populations of A. crassus from Germany, Poland and Taiwan. We tested, whether differences in infectivity, developmental dynamics and reproductive output between the European and Asian parasite populations occur while harboured in the specimens of native and colonized eel host, and if these differences are genetically based or are plastic responses to the new environment.

Results

Under common garden conditions an evolutionary change in the both European parasite populations of A. crassus compared with their Taiwanese conspecifics was observed for infectivity and developmental dynamics, but not for reproductive output. When infecting the European eel, current European populations of the parasite were less infective and developed faster than their Taiwanese conspecifics. In the reciprocally infected Japanese eel the genetically induced differences between the parasite strains were less apparent than in the European eel but higher infectivity, faster development and higher larval mortality of the European parasite populations could be inferred.

Conclusions

The differences in infectivity and developmental dynamics between European and Taiwanese populations of A. crassus found in our study suggest rapid genetic divergence of this parasite after a successful host switch in Europe.

Natural Anguillicola novaezelandiae infection--is there seasonality in New Zealand?

Knowledge of natural Anguillicola infections of Short-finned eels (Anguilla australis) in New Zealand is very limited. So far, no study contains data on all life cycle stages of Anguillicola novaezelandiae in naturally infected eels. In order to study the frequency of A. novaezelandiae in New Zealand Short-finned eels, we examined eels of the North and the South Island for the presence of the swim bladder parasite. The results show that A. novaezelandiae is a common parasite of the Short-finned eel. The parasite was present in both regions. Eels from both localities show differences in their infection status with respect to prevalence, abundance and intensity. While eels of the South Island were only infected with larval stages, adult and preadult stages could be detected in eels of the North Island. Nevertheless, infrapopulations at both sites were dominated by larval parasite stages. This unique composition of infrapopulations has never been described for any Anguillicola species before and suggests a seasonal occurrence as a possible reason. Export of live eels should be handled cautiously to prevent the spread of A. novaezelandiae throughout other eel populations.

Merging species? Evidence for hybridization between the eel parasites Anguillicola crassus and A. novaezelandiae (Nematoda, Anguillicolidea)

Background

The eel parasitic nematodes Anguillicola crassus (originating from Asia) and Anguillicola novaezelandiae (originating from New Zealand) were both introduced to Europe, but occurred in sympatry only in Lake Bracciano in Italy, where they both infected the European eel (Anguilla anguilla). A. novaezelandiae was introduced to the lake in 1975 and disappeared soon after A. crassus was also found there in 1993. We tested the hypothesis if hybridization of the two species might be an explanation for the findings at Lake Bracciano.

Findings

After laboratory infection of one European eel with 10 third stage larvae of each parasite, two living female and 4 male adults of each species were found to co-occur in the swim bladder after 222 days post exposure. In 9 out of 17 eggs, isolated in total from uteri of the two A. novaezelandiae females, alleles were detected by microsatellite analysis that are characteristic for A. crassus, suggesting the hybrid origin of these eggs. In contrast, none of the eggs isolated from A. crassus females possessed alleles different from those found in A. crassus adults, but it was revealed that one female can be inseminated by several males.

Conclusion

Our results show that A. crassus and A. novaezelandiae can co-infect a single eel and can mature together in the same swim bladder. We also provide evidence for the possibility of hybridization of A. crassus males with A. novaezelandiae females. Therefore, hybridization might be an explanation for the disappearance of A. novaezelandiae from Lake Bracciano.