Species of Apatemon Szidat, 1928 and Australapatemon Sudarikov, 1959 (Trematoda: Strigeidae) from New Zealand: linking and characterising life cycle stages with morphology and molecules

Exploring Barbronia species diversity and phylogenetic relationship within Suborder Erpobdelliformes (Clitellata: Annelida)

Background

Barbronia, a genus of freshwater macrophagous leeches, belongs to Erpobdelliformes (Salifidae: Clitellata: Annelida), and B. weberi, a well-known leech within this genus, has a worldwide distribution. However, the systematics of Barbronia have not yet been adequately investigated, primarily due to a few molecular markers, and only 20 Barbronia sequences available in the GenBank database. This gap significantly limits our understanding of the Barbronia species identification, as well as the phylogenetic placement of the genus Barbronia within Salifidae.

Methods

Next-generation sequencing (NGS) was used to simultaneously capture the entire mitochondrial genome and the full-length 18S/28S rDNA sequences. The species boundary of Barbronia species was estimated using bGMYC and bPTP methods, based on all available Barbronia COI sequences. Uncorrected COI p-distance was calculated in MEGA. A molecular data matrix consisting of four loci (COI, 12S, 18S, and 28S rDNA) for outgroups (three Haemopis leeches) and 49 erpobdellid leeches, representing eight genera within the Suborder Erpobdelliformes was aligned using MAFFT and LocARNA. This matrix was used to reconstruct the phylogenetic relationship of Barbronia via Bayesian inference (BI) and the maximum likelihood (ML) method.

Results

The full lengths of the mitochondrial genome, 18S and 28S rDNAs of B. cf. gwalagwalensis, are 14847 bp, 1876 bp 1876 bp, and 2863 bp, respectively. Both bGMYC and bPTP results based on COI data are generally congruent, suggesting that the previously proposed taxa (B. arcana, B. weberi formosana, and B. wuttkei or Erpobdella wuttkei) are synonyms of B. weberi. The specimens listed in the B. gwalagwalensis group, however, are split into at least two Primary Species Hypotheses (PSHs). The p-distance of the first PSH is less than 1.3% but increased to 4.5% when including the secondary PSH (i.e., B. cf. gwalagwalensis). In comparison, the interspecific p-distance between the B. weberi group and the B. gwalagwalensis group ranged from 6.4% to 8.7%, and the intraspecific p-distance within the B. weberi group is less than 0.8%. Considering the species delimitation results and the sufficient large p-distance, the specimen sampled in China is treated as B. cf. gwalagwalensis. The monophyly of the four Erpobdelliformes families Salifidae, Orobdellidae, Gastrostomobdellidae sensu stricto and Erpobdellidae is well supported in ML and BI analysis based on a data of four markers. Within the Salifidae, a well-supported Barbronia is closely related to a clade containing Odontobdella and Mimobdella, and these three genera are sister to a clade consisted of Salifa and Linta. According to the results of this study, the strategy of simultaneous obtaining both whole mitochondria and nuclear markers from extensively sampled Salifids species using NGS is expected to fathom both the species diversity of B. gwalagwalensis and the evolutionary relationship of Salifidae.

First species record of Strigea falconis Szidat, 1928 (Trematoda, Strigeidae) from gyrfalcon Falco rusticolus in Iceland-pros and cons of a complex life cycle

Strigea falconis is a common parasite of birds of prey and owls widely distributed in the Holarctic. We aimed to characterise S. falconis from Iceland via integrative taxonomic approach and to contribute to the understanding of its circulation in the Holarctic. We recovered adult S. falconis from two gyrfalcons (Falco rusticolus) collected in 2011 and 2012 in Iceland (Reykjanes Peninsula, Westfjords) and characterised them by morphological and molecular genetic (D2 of rDNA, cox1, ND1 of the mDNA) methods. We provide the first species record of S. falconis in Iceland which to the best of our knowledge is its northernmost distributional range. The presence of S. falconis in Iceland is surprising, as there are no suitable intermediate hosts allowing completion of its life cycle. Gyrfalcons are fully sedentary in Iceland; thus, the only plausible explanation is that they acquired their infection by preying upon migratory birds arriving from Europe. Our data indicate that the most likely candidates are Anseriformes and Charadriiformes. Also, we corroborate the wide geographical distribution of S. falconis, as we found a high degree of similarity between our haplotypes and sequences of mesocercariae from frogs in France and of a metacercaria from Turdus naumanni in Japan, and adults from Buteo buteo and Circus aeruginosus from the Czech Republic. The case of Strigea falconis shows the advantages of a complex life cycle and also depicts its pitfalls when a parasite is introduced to a new area with no suitable intermediate hosts. In Iceland, gyrfalcons are apparently dead-end hosts for S. falconis.

Acanthocephalans of marine and freshwater fishes from Taiwan with description of a new species

During an ichthyoparasitological survey in 2017-2019, six species of acanthocephalans were found among Taiwan's freshwater (Cypriniformes: Xenocyprididae, Cyprinidae) and marine fishes (Scombriformes: Scombridae, Trichiuridae; Anabantiformes: Channidae; Carangaria/misc: Latidae): Micracanthorhynchina dakusuiensis (Harada, 1938), Rhadinorhynchus laterospinosus Amin, Heckmann et Ha, 2011, Pallisentis rexus Wongkham et Whitfield, 1999, Longicollum sp., Bolbosoma vasculosum (Rudolphi, 1819), and one new species, Micracanthorynchina brevelemniscus sp. n. All species are morphologically characterised and illustrated using light and scanning electron microscopy. The finding of R. laterospinosus, P. rexus and B. vasculosum is the first record for these species in Taiwan. Micracanthorhynchina brevelemniscus is similar to Micracanthorhynchina motomurai (Harada, 1935) and M. dakusuiensis in proboscis armature but differs from M. motomurai by larger eggs (53-59 × 15-16 µm vs 40 × 16 µm) and by the number of cement glands (6 vs 4) and from M. dakusuiensis by shorter body length (2.2-2.9 mm vs 4.0 mm in males and 2.9-4.1 mm vs 7.6 mm in females), by the location of the organs of the male reproductive system (from level of the posterior third of the proboscis receptacle in M. brevelemniscus vs in the posterior half of the trunk in M. dakusuiensis), and by length of lemnisci (lemnisci shorter than the proboscis receptacle vs lemnisci longer than the proboscis receptacle). Phylogenetic analyses of almost complete 18S rRNA gene revealed paraphyly of the family Rhadinorhynchidae suggested in previous studies. Micracanthorhynchina dakusuiensis and M. brevelemniscus formed a strongly supported cluster, which formed the earliest diverging branch to the rest of the rhadinorhynchids and transvenids.

Prey-mimetism in cercariae of Apatemon (Digenea, Strigeidae) in freshwater in northern latitudes

Cercariae, the free-living larval stages of trematodes, have adopted an amazing variety of transmission strategies. One of them is prey-mimetism, i.e. cercariae mimicking prey to attract motile hosts to be eaten. In a period between 2002 and 2019, we examined small planorbid snails, Bathyomphalus contortus, Gyraulus parvus and Planorbis planorbis from lakes in Finland and Iceland and from the Curonian Lagoon in Lithuania. Cercariae with conspicuously enlarged tails and unusual swimming behaviour, likely mimicking invertebrate prey, were detected and studied by the use of morphological and molecular (cox1, ITS1-5.8S-ITS2 and 28S rDNA) methods. Cercariae of two species belonging to the genus Apatemon (Strigeidae) were recognised. We consider Apatemon sp. 5 ex P. planorbis from the Curonian Lagoon identical to Cercaria globocaudata U. Szidat, 1940. Cercariae ex G. parvus from Iceland and ex B. contortus from Finland were conspecific, and we named them Apatemon sp. 6; these cercariae could not be associated with any known species. For the first time, we verified that cercariae of the Bulbocauda group belong to the genus Apatemon. We provide a mini-review on records of furcocercariae of the family Strigeidae with enlarged tails reported in freshwaters of the northern hemisphere and reveal that it is not only Apatemon but also Australapatemon and most likely Strigea which belong to the Bulbocauda group, rendering it a purely ecological assemblage. Understanding which invertebrate swimming behaviour these cercariae are mimicking will enhance our knowledge of the processes behind trematode transmission and will help to assess evolutionary pathways of host-finding strategies in trematodes.

Elucidating the life cycle of opossum parasites: DNA sequences reveal the involvement of planorbid snails as intermediate hosts of Rhopalias spp. (Trematoda: Echinostomatidae) in Brazil

Echinostomatid digeneans belonging to the genus Rhopalias are intestinal trematodes found mainly in opossums in the New World. The genus comprises seven species, but their life cycles and intermediate hosts have been unknown until now. During our long-term study carried out in freshwater habitats within the state of Minas Gerais, Southeast Brazil, echinostomatid cercariae lacking collar spines were found in planorbid snails Biomphalaria glabrata, Biomphalaria straminea, Drepanotrema lucidum and Gundlachia ticaga in six different batches of snail samples collected between 2010 and 2019. Morphologically, the larvae reported herein are morphologically consistent with each other and characterized by the presence of 2-3 large ovoid or spherical corpuscles in each main duct of the excretory system, resembling to Cercaria macrogranulosa previously described from the same region of Brazil. Partial sequences of the ITS (ITS1-5.8S-ITS2) region and 28S gene of the nuclear ribosomal RNA operon, and partial sequences of mitochondrial nad1 and cox1 genes were obtained and compared with the data available for members of the family Echinostomatidae. Nuclear markers indicate that all samples of cercariae evaluated in the present study can be assigned to Rhopalias, but distinct from North American isolates of Rhopalias macracanthus, Rhopalias coronatus and Rhopalias oochi (divergence 0.2-1.2% in 28S and 0.8-4.7% in ITS). The lack of differences verified in both 28S and ITS in 5 out 6 studied samples suggested that they belong to the same species. However, nad1 sequences revealed that our cercariae correspond to three distinct species of Rhopalias (interspecific divergence: 7.7-9.9%), named here as Rhopalias sp. 1, found in B. straminea and G. ticaga, Rhopalias sp. 2 found in B. glabrata and D. lucidum, and Rhopalias sp. 3 also found in D. lucidum. They also differ by 10.8-17.2% from a North American isolate of R. macracanthus sequenced in this study. The cox1 sequences obtained for Rhopalias sp. 1 and Rhopalias sp. 2 (but not Rhopalias sp. 3) reveal that they are distinct from North American isolates of R. macracanthus (genetic divergence 16.3-16.5% and 15.6-15.7%, respectively), R. coronatus (9.2-9.3% and 9.3-9.5%) and Rhopalias oochi (9.0% and 9.5-10.1%). Encysted metacercariae with general morphology similar to that of the body of cercariae were found in tadpoles of Rhinella sp. from the same stream where snails harbored Rhopalias sp. 2, suggesting that the amphibians could act as second intermediate hosts of species of Rhopalias. Data obtained provide the first insights into the life cycle of this unusual echinostomatid genus.

New specimens and molecular data provide validation of Apatemon jamiesoni n. sp. (Trematoda: Strigeidae) from water birds in New Zealand

A study published in 2016 reported on an undescribed species of Apatemon (Strigeidae) from New Zealand that was previously well known from its larval stages. Only a single specimen from a mallard duck was available at the time, which was described and given the provisional name Apatemon sp. “jamiesoni”. Specimens also obtained from a spotted shag were not in good enough condition to form the basis of a new species description. A black-backed gull has since been discovered with specimens of this strigeid, their identity confirmed by genetic similarity, allowing formal description and naming of this species. This paper provides a description of the new specimens from the black-backed gull, along with a comparison with the specimens from other bird hosts, reprises some data from Blasco-Costa et al. (Parasitol Res 115:271–289, 2016) and presents formally the name Apatemon jamiesonin. sp. This species differs from all other species of Apatemon in its small size, particularly that of the ovary and testes. It is most similar to A. jamesi from which it differs in the size of the oral and ventral suckers.

Gastrointestinal helminth parasites of the threatened Australasian crested grebe (Podiceps cristatus australis, Gould 1844) in New Zealand, with descriptions of Baruscapillaria kamanae n. sp. (Nematoda: Trichuridae) and Cryptocotyle micromorpha n. sp. (Trematoda: Opisthorchiidae)

The Australasian crested grebe Podiceps cristatus australis, Gould 1844 is restricted to Australia and New Zealand, where it is listed as Threatened and Nationally Vulnerable. For the first time in New Zealand, we report on the parasitic helminths infecting three individuals from Lake Wanaka, Otago, using morphological and molecular tools. Seven helminth species were found in the gastrointestinal tract: 2 nematodes (Contracaecum ovale and Baruscapillaria kamanaen. sp.), 4 trematodes (Australapatemon minor, Cryptocotyle micromorphan. sp., Tylodelphys darbyi and Neopetasiger neocomensis), and 1 cestode (Confluaria pseudofurcifera). Except for T. darbyi, all are new records for New Zealand. A change of orthography is proposed for Neopetasiger neocomensis and N. pseudoneocomensis. Cryptocotyle micromorphan. sp. (Opisthorchiidae) is distinguished from similar species by its small size, wholly extracaecal vitellaria and anteriorly looped uterus. Baruscapillaria kamanaen. sp. (Trichuridae) is distinguished from other freshwater species by a combination of vulva and spicule morphology. The helminth parasites found here are mostly the same as those from the grebe in the northern hemisphere, indicating that they have been carried with the host species in its spread to Australasia. However, the parasite fauna may be depauperate due to a diminishing reservoir of intermediate hosts in that geographical migration.

Molecular and morphological evidence suggests the reallocation from Parastrigea brasiliana (Szidat, 1928) Dubois, 1964 to Apharyngostrigea Ciurea, 1927 (Digenea: Strigeidae), a parasite of boat-billed heron (Cochlearius cochlearius) from the Neotropical region

Parastrigea brasiliana (Szidat, 1928) Dubois, 1964, was described from (Cochlearius cochlearius) in South America. The taxonomy of this species has been unstable due that it was described as a member of Strigea Abildgaard, 1790. However, the same author one year later transferred it to Apharyngostrigea Ciurea, 1927 and since then, it has been alternatively placed in the genus Apharyngostrigea or Parastrigea Szidat, 1928 from Strigeidae. In the current research, specimens identified as P. brasiliana were collected from type host in southeastern Mexico. We sequenced three molecular markers: the internal transcribed spacers ITS1 and ITS2 including the 5.8S gene (ITS region), the D1-D3 domains of the large subunit (LSU) from nuclear DNA and cytochrome c oxidase subunit I (cox 1) from mitochondrial DNA. These sequences were aligned with other sequences available in the GenBank dataset from Strigeidae. Maximum likelihood and Bayesian analyses inferred with three molecular markers consistently showed that P. brasiliana is not closely related to other members of the genus Parastrigea and are placed in a reciprocal monophyletic clade inside Apharyngostrigea, with very low genetic divergence, varying from 0 to 0.09% for the ITS, from 0 to 0.08% for the LSU and from 0.21 to 0.43% for cox 1. Consequently, we proposed to reallocate it to A. brasiliana. The phylogenetic analyses obtained are key and very useful for re-evaluate the morphology of A. brasiliana because this species share morphological characters with the genera Parastrigea (concentration of vitelline follicles distributed in two lateral expansions on the forebody) and Apharyngostrigea (absence of pharynx). Finally, the current record of A. brasiliana expands its distribution range in four countries, namely, the USA, Mexico, Venezuela and Brazil, in the Neotropical region.

Morphological and molecular assessment of the diversity of trematode communities in freshwater gastropods and bivalves in Los Tuxtlas tropical rainforest

Trematode life cycles involve molluscs as first intermediate hosts. The identification of trematodes based on the morphology of cercariae released from molluscs is challenging because the identification relies on adult forms obtained from their definitive hosts. Several studies have recently genetically characterized these larval forms establishing a link with adults sampled from their vertebrate hosts, allowing their identification at species level. In Los Tuxtlas tropical rainforest, in south-eastern Mexico, 57 species of trematodes have been reported from wildlife vertebrates; however, studies evaluating the diversity of trematode cercariae in molluscs are lacking. Here, we studied 11 species of molluscs to assess the diversity of cercariae in two lakes of Los Tuxtlas, Veracruz, Mexico; six of the 11 species were infected. Twelve cercarial morphotypes were collected and characterized morphologically. Sequences of the 28S ribosomal RNA gene were generated to allocate each morphotype into a family using the most recent phylogenetic classification of the Digenea as a framework; molecular work revealed 16 genetic lineages; some cercariae were identified up to genus (Apharyngostrigea, Ascocotyle, Centrocestus, Echinochasmus, Lecithodendrium and Posthodiplostomum), and some to species levels (Gorgoderina rosamondae, Langeronia macrocirra, Oligogonotylus manteri and Phyllodistomum inecoli) based on their phylogenetic position within the tree, and the genetic distance with respect to other sequenced congeners. Therefore, the cercarial morphotypes in the present study represent at least 16 putative species. Our study contributes to a better understanding of the trematode diversity in an area of high vertebrate species diversity, and to the knowledge of trematode life cycles.

Exploring the genetic structure of Parastrigea diovadena Dubois and Macko, 1972 (Digenea: Strigeidae), an endoparasite of the white ibis, Eudocimus albus, from the Neotropical region of Mexico

Parastrigea diovadena Dubois and Macko, 1972, is an allogenic trematode species that infects the intestine of white ibis. This widely distributed Neotropical species has been studied poorly, and nothing is known about its population genetic structure. In the current study, we attempt to fill this gap for the first time and to explore the genetic diversity in P. diovadena populations from three biogeographic provinces (Sierra Madre Oriental, Sierra Madre Occidental, and Sierra Madre del Sur) in the Neotropical region of Mexico. Newly generated sequences of the internal transcribed spacers (ITS) from ribosomal DNA and cytochrome c oxidase subunit 1 (cox 1) from mitochondrial DNA were compared with sequences available from the GenBank data set. Phylogenetic analyses performed with the ITS and cox 1 data sets using maximum likelihood and Bayesian inference unequivocally showed that new sequences of P. diovadena recovered from the white ibis formed a clade with other sequences of specimens previously identified as P. diovadena. The intraspecific genetic divergence among the isolates was very low, ranging from 0 to 0.38% for ITS and from 0 to 1.5% for cox 1, and in combination with the phylogenetic trees confirmed that the isolates belonged to the same species. The cox 1 haplotype network (star-shaped) inferred with 62 sequences revealed 36 haplotypes. The most frequent haplotype (H3, n = 18) corresponded to specimens from all the populations (except Tecolutla, Veracruz). In addition to the common haplotype, we identified four other shared haplotypes (H2, H9, H12, and H14) and 31 unique haplotypes (singlets). In addition, high haplotype diversity (Hd = 0.913), low nucleotide diversity (Pi = 0.0057), and null genetic differentiation or population structure (Fst = 0.0167) were found among the populations from the three biogeographic provinces. The results suggest that the biology of the definitive host has played a key role in the population genetic structure of Parastrigea diovadena in the Neotropical region of Mexico.

Crossing barriers of zoogeographical regions: Molecular evidence of vicariance of the only cestode parasite of loaches (Cobitidae) in the Indomalayan region, Paracaryophyllaeus lepidocephali (Cestoda: Caryophyllidea), and its redescription

Tapeworms of the genus Paracaryophyllaeus Kulakovskaya, 1961 (Cestoda: Caryophyllidea) are specific parasites of loaches (Cypriniformes: Cobitoidea) and occur almost exclusively in the Palaearctic region. The only exception and example of vicariance over the borders of two zoogeographical regions is Paracaryophyllaeus lepidocephali (Kundu, 1985), an insufficiently known species described from the Indomalayan region, with uncertain generic allocation. In the present paper, the species is redescribed based on new material collected from the type host, Lepidocephalichthys guntea, in West Bengal, India. Molecular data reveal this species as a member of Paracaryophyllaeus, within which it is the most closely related to P. cf. gotoi from Misgurnus anguillicaudatus in China and Japan on the basis of large subunit of ribosomal nuclear DNA (28S rDNA). Generic position of P. lepidocephali examined herein is also confirmed by morphology including cross sections, in particular, by a small, cylindrical body, medullary testes with testicular fields crossing the anterior margin of the cirrus sac, medullary vitelline follicles, with some follicles paramuscular, a shallow common genital atrium, short vagina and uterus not extending anteriorly beyond the cirrus sac. It differs from all Palaearctic congeners but Paracaryophyllaeus vladkae Scholz, Oros and Aydogdu, 2014 by the testicular field crossing the anterior margin of the cirrus sac. It differs from P. vladkae by more anterior position of the first vitelline follicles compared to the first testes. This species is a unique example of a fish tapeworm crossing the borders of the Palaearctic and Indomalayan zoogeographical regions.

Helminth parasites of shags (Phalacrocoracidae) from the Otago region of southern New Zealand

A total of 61 specimens representing five species of shag - Auckland Island shag Leucocarbo colensoi, little pied shag Microcarbo melanoleucos brevirostris, black shag Phalacrocorax carbo novaehollandiae, Otago shag Leucocarbo chalconotus and spotted shag Phalacrocorax punctatus - from the coast around Otago, South Island, New Zealand, were examined for helminths. A total of 18 helminth species was found: six nematodes (Anisakis pegreffi, Contracaecum rudolphii E, Baruscapillaria sp., Cosmocephalus jaenschi, Ingliseria cirrohamata, Desmidocercella australis), four trematodes (Apatemon sp. 'jamiesoni', Cardiocephaloides ovicorpus, Apophallus sp., Microphallidae gen. sp.), four cestodes (Microsomacanthus cormoranti, Microsomacanthus sp., Paradilepis urceina, Tetrabothrius sp.) and four acanthocephalans (Andracantha leucocarboi, A. sigma, Corynosoma hannae, Profilicollis novaezelandensis). Descriptions are provided for females of C. jaenschi and D. australis, which were previously undescribed. The data include 20 new host records and seven new locality records. New 18S ribosomal DNA and internal transcribed spacer (ITS1 and ITS2) DNA sequences have been provided where specimen conditions permitted. These data add considerably to our sparse knowledge of helminths in New Zealand shags, and provide a baseline for observations of change in the future.

Leeches as the intermediate host for strigeid trematodes: genetic diversity and taxonomy of the genera Australapatemon Sudarikov, 1959 and Cotylurus Szidat, 1928

Background

Leeches (Hirudinida) play a significant role as intermediate hosts in the circulation of trematodes in the aquatic environment. However, species richness and the molecular diversity and phylogeny of larval stages of strigeid trematodes (tetracotyle) occurring in this group of aquatic invertebrates remain poorly understood. Here, we report our use of recently obtained sequences of several molecular markers to analyse some aspects of the ecology, taxonomy and phylogeny of the genera Australapatemon and Cotylurus, which utilise leeches as intermediate hosts.

Methods

From April 2017 to September 2018, 153 leeches were collected from several sampling stations in small rivers with slow-flowing waters and related drainage canals located in three regions of Poland. The distinctive forms of tetracotyle metacercariae collected from leeches supplemented with adult Strigeidae specimens sampled from a wide range of water birds were analysed using the 28S rDNA partial gene, the second internal transcribed spacer region (ITS2) region and the cytochrome c oxidase (COI) fragment.

Results

Among investigated leeches, metacercariae of the tetracotyle type were detected in the parenchyma and musculature of 62 specimens (prevalence 40.5%) with a mean intensity reaching 19.9 individuals. The taxonomic generic affiliation of metacercariae derived from the leeches revealed the occurrence of two strigeid genera: Australapatemon Sudarikov, 1959 and Cotylurus Szidat, 1928. Phylogenetic reconstructions based on the partial 28S rRNA gene, ITS2 region and partial COI gene confirmed the separation of the Australapatemon and Cotylurus clades. Taking currently available molecular data and our results into consideration, recently sequenced tetracotyle of Australapatemon represents most probably Au. minor; however, unclear phylogenetic relationships between Au. burti and Au. minor reduce the reliability of this conclusion. On the other hand, on the basis of the obtained sequences, supplemented with previously published data, the metacercariae of Cotylurus detected in leeches were identified as two species: C. strigeoides Dubois, 1958 and C. syrius Dubois, 1934. This is the first record of C. syrius from the intermediate host.

Conclusions

The results of this study suggest the separation of ecological niches and life cycles between C. cornutus (Rudolphi, 1808) and C. strigeoides/C. syrius, with potential serious evolutionary consequences for a wide range of host–parasite relationships. Moreover, phylogenetic analyses corroborated the polyphyletic character of C. syrius, the unclear status of C. cornutus and the separate position of Cotylurus raabei Bezubik, 1958 within Cotylurus. The data demonstrate the inconsistent taxonomic status of the sequenced tetracotyle of Australapatemon, resulting, in our opinion, from the limited availability of fully reliable, comparative sequences of related taxa in GenBank.

How parasite exposure and time interact to determine Australapatemon burti (Trematoda: Digenea) infections in second intermediate hosts (Erpobdella microstoma) (Hirudinea: Erpodellidae)

Australapatemon spp. are cosmopolitan trematodes that infect freshwater snails, aquatic leeches, and birds. Despite their broad geographic distribution, relatively little is known about interactions between Australapatemon spp. and their leech hosts, particularly under experimental conditions and in natural settings. We used experimental exposures to determine how Australapatemon burti cercariae dosage (number administered to leech hosts, Erpobdella microstoma) affected infection success (fraction to encyst as metacercariae), infection abundance, host survival, and host size over the 100 days following exposure. Interestingly, infection success was strongly density-dependent, such that there were no differences in metacercariae load even among hosts exposed to a 30-fold difference in cercariae. This relationship suggests that local processes (e.g., resource availability, interference competition, or host defenses) may play a strong role in parasite transmission. Our results also indicated that metacercariae did not become evident until ~4 weeks post exposure, with average load climbing until approximately 13 weeks. There was no evidence of metacercariae death or clearance over the census period. Parasite exposure had no detectable effects on leech size or survival, even with nearly 1,000 cercariae. Complementary surveys of leeches in California revealed that 11 of 14 ponds supported infection by A. burti (based on morphology and molecular sequencing), with an average prevalence of 32% and similar metacercariae intensity as in our experimental exposures. The extended development time and extreme density dependence of A. burti has implications for studying naturally occurring host populations, for which detected infections may represent only a fraction of cercariae to which animals have been exposed. Future investigation of these underlying mechanisms would be benefical in understanding host-parasite relationships.

A new species of Atriophallophorus Deblock & Rosé, 1964 (Trematoda: Microphallidae) described from in vitro-grown adults and metacercariae from Potamopyrgus antipodarum (Gray, 1843) (Mollusca: Tateidae)

The adult and metacercaria life stages of a new species of the microphallid genus Atriophallophorus Deblock & Rosé, 1964 are described from specimens collected at Lake Alexandrina (South Island, New Zealand). In addition to molecular analyses of ribosomal and mitochondrial genes, metacercariae of Atriophallophorus winterbourni n. sp. from the snail host Potamopyrgus antipodarum (Gray) were grown in vitro to characterize internal and external morphology of adults using light and scanning electron microscopy and histological techniques. Atriophallophorus winterbourni n. sp. is readily distinguishable from Atriophallophorus coxiellae Smith, 1973 by having a different structure of the prostatic chamber, sub-circular and dorsal to genital atrium, rather than cylindrical, fibrous, elongate and placed between the seminal vesicle and the genital atrium. The new species is most similar to Atriophallophorus minutus (Price, 1934) with regards to the prostatic chamber and the morphometric data, but possesses elongate-oval testes and subtriangular ovary rather than oval and transversely oval in A. minutus. Phylogenetic analyses including sequence data for A. winterbourni n. sp. suggested a congeneric relationship of the new species to a hitherto undescribed metacercariae reported from Australia, both forming a strongly supported clade closely related to Microphallus and Levinseniella. In addition, we provide an amended diagnosis of Atriophallophorus to accommodate the new species and confirm the sinistral interruption of the outer rim of the ventral sucker caused by the protrusion of the dextral parietal atrial scale at the base of the phallus.

Molecular, morphological and experimental-infection studies of cercariae of five species in the superfamily Diplostomoidea (Trematoda: Digenea) infecting Biomphalaria straminea (Mollusca: Planorbidae) in Brazil

Trematodes belonging to the superfamily Diplostomoidea have complex life cycles involving birds, mammals and reptiles as definitive hosts, and gastropods and different groups of invertebrates and vertebrates as intermediate hosts. Molecular studies of these parasites are numerous, but data from larval stages in molluscs remain scarce, particularly in South America. The present study focused mainly on five morphotypes of longifurcate cercariae found in Biomphalaria straminea (Dunker, 1848) from Belo Horizonte, Minas Gerais, Brazil, collected between 2009 and 2017. In each morphotype, nuclear internal transcribed spacer (ITS1-5.8S ITS-2) rDNA and mitochondrial cytochrome c oxidase 1 (COI) genes were sequenced. Laboratory-reared fish, Poecilia reticulata Peters, 1859 or snails, Biomphalaria glabrata (Say, 1818) were exposed to cercariae to obtain metacercariae. The morphology of cercariae, experimentally obtained metacercariae, and phylogenetic analyses led to the identification of three species of Diplostomidae [Austrodiplostomum compactum (Lutz, 1928), Crassiphialinae gen. sp. and Hysteromorpha sp.] and two species of Strigeidae (Cotylurus sp., Apharyngostrigea sp.). Previously published sequences allowed species-level identification for only A. compactum, although provisional identifications were possible in two cases. First, the COI from cercariae of Apharyngostrigea sp. in Brazil matched those of metacercariae from naturally infected Cnesterodon decemmaculatus (Jenyns, 1842) in Argentina; although a positive identification is not possible, the material presents morphological similarities with larval stages previously described for A. simplex. Secondly, Cotylurus sp. resembles C. lutzi. Our analysis of previously published COI sequences suggests that Cotylurus cornutus (Rudolphi, 1808) has a Holarctic distribution. Both the morphology of experimentally obtained metacercariae and COI sequences indicate that Hysteromorpha sp. in Brazil is distinct from congeners in North America [Hysteromorpha corti (Hughes, 1929)] and Europe [Hysteromorpha triloba (Rudolphi, 1819)].

Morphological and molecular characterization of Apatemon sp. infecting killifish in Mozambique

Strigeid trematodes of the genus Apatemon Szidat, 1928 are intestinal parasites of fish-eating birds, utilizing various fish species as second intermediate hosts. In this study, we report morphometrical and molecular characterization of Apatemon sp. metacercariae parasitizing killifish Nothobranchius furzeri (Cyprinodontiformes: Nothobranchiidae) in south-east Mozambique. Metacercariae obtained from the cerebral cavity of killifish and two adult individuals isolated from experimentally infected ducklings were used for detailed morphological and molecular description, both resulting in generic affiliation to Apatemon. This is the first molecularly confirmed record of this trematode genus in Africa. Considering the morphological variability and wide host range of individual Apatemon species, the combination of both morphological and molecular analyses is indispensable for valid identification of this parasite. The results of our molecular analysis together with phylogenetic reconstruction indicated the presence of a new African lineage, reflecting potentially high diversity within the genus Apatemon comparable with other digenean genera.

Parasitological research in the molecular age

New technological methods, such as rapidly developing molecular approaches, often provide new tools for scientific advances. However, these new tools are often not utilized equally across different research areas, possibly leading to disparities in progress between these areas. Here, we use empirical evidence from the scientific literature to test for potential discrepancies in the use of genetic tools to study parasitic vs non-parasitic organisms across three distinguishable molecular periods, the allozyme, nucleotide and genomics periods. Publications on parasites constitute only a fraction (<5%) of the total research output across all molecular periods and are dominated by medically relevant parasites (especially protists), particularly during the early phase of each period. Our analysis suggests an increasing complexity of topics and research questions being addressed with the development of more sophisticated molecular tools, with the research focus between the periods shifting from predominantly species discovery to broader theory-focused questions. We conclude that both new and older molecular methods offer powerful tools for research on parasites, including their diverse roles in ecosystems and their relevance as human pathogens. While older methods, such as barcoding approaches, will continue to feature in the molecular toolbox of parasitologists for years to come, we encourage parasitologists to be more responsive to new approaches that provide the tools to address broader questions.

A fine-scale phylogenetic assessment of digenean trematodes in central Alberta reveals we have yet to uncover their total diversity

Despite over 100 years of digenean trematode parasite species descriptions, from a wide diversity of vertebrate and invertebrate host species, our ability to recognize the diversity of trematode species within a single lake remains an incredible challenge. The most challenging aspect is the identification of species from larval stages derived from intermediate hosts, due to the disjointed data of adult worm morphological descriptions, from which species are named, and links to corresponding molecular identifiers in depauperate databases. Cryptic species also play a significant role in the challenge of linking trematode larvae to adults, species identifications, and estimating diversity. Herein, we utilize a large, longitudinal dataset of snail first-intermediate host infection data from lakes in Alberta, Canada, to infer trematode larval diversity using molecular phylogenetics and snail host associations. From our assessments, we uncover a diversity of 79 larval trematode species among just five snail host species. Only 14 species were identified to a previously described species, while the other 65 species are either cryptic or otherwise unrepresented by mitochondrial genes in GenBank. This study currently represents the largest and most diverse singular molecular survey of trematode larval fauna composed of over one thousand mitochondrial sequences. Surprisingly, rarefaction analyses indicate we have yet to capture the complete diversity of trematodes from our sampling area.

Description of Tylodelphys darbyi n. sp. (Trematoda: Diplostomidae) from the threatened Australasian crested grebe (Podiceps cristatus australis, Gould 1844) and linking of its life-cycle stages

Species of the genus Tylodelphys (Diplostomidae) have a cosmopolitan distribution. Metacercariae of these species infect the eye, brain, pericardial sac or body cavity of fish second intermediate hosts, and the adults are found in piscivorous birds of many orders. An unnamed species of Tylodelphys from the eyes of bullies (Gobiomorphus cotidianus) was characterized molecularly and morphologically as a metacercaria in a previous study, in which it was predicted that the adult of this species would be found in the Australasian crested grebe. Two specimens of this bird became available and specimens of the unnamed Tylodelphys species were, indeed, found in them, confirmed by identity of genetic sequence data. Found to differ morphologically from its congeners, the new species is here described as Tylodelphys darbyi n. sp. Three species are closest to the new species in morphology: Tylodelphys glossoides, T. immer and T. podicipina robrauschi. Compared with T. darbyi n. sp. these three species are slightly larger and possess longer eggs. Tylodelphys glossoides also differs in having a wider oral sucker and T. podicipina robrauschi in having comma- or kidney-shaped pseudosuckers and an ovary that reaches a larger size, along with higher upper limits for body width, hind body and sucker width, holdfast and oesophagus length, and pharynx, pseudosucker and testes length and width. Tylodelphys immer also differs from T. darbyi n. sp. in having a shorter ventral sucker and the largest pseudosuckers of any Tylodelphys species.

Morphological and molecular characterization of six Indian Tetracotyle type metacercariae (Digenea: Strigeidae Railliet, 1919), using ribosomal and mitochondrial DNA

Strigeids have a cup-shaped fore body, containing a holdfast organ with two lobes and hind body. The species diversity of strigeids remains incomplete, especially in the Indian sub-continent. Here, we described six Tetracotyle type metacercariae (T. muscularis, T. fausti, T. lucknowensis, T. xenentodoni, T. mathuraensis and T. glossogobii) from five fresh water fish, collected at Lucknow (India). Next, we characterized these metacercariae using ribosomal (18S, 28S, ITS2) and mitochondrial DNA (COI) to determine their systematic and phylogenetic position. Molecular identification using inter-specific variation range for all four molecular markers revealed 1.9-4.9% (18S); 3.3-8.8% (28S); 6.8-12.9% (ITS2), and 3.5-9.4% (COI) among six Tetracotyle type metacercariae. In phylogenetic analysis, constructed by neighbour-joining (NJ) and maximum likelihood (ML) methods, T. fausti, T. glossogobii, T. xenentodoni, T. lucknowensis and T. mathuraenis nested as sister groups with the member of strigeids for all four markers used; T. muscularis, however, formed a basal clade. Furthermore, phylogenetic placement states the monophyly of the Tetracotyle type of metacercariae in all the markers (18S, 28S, COI), except ITS2.

Validity of the Diplostomoidea and Diplostomida (Digenea, Platyhelminthes) upheld in phylogenomic analysis

Higher systematics within the Digenea, Carus 1863 have been relatively stable since a phylogenetic analysis of partial nuclear ribosomal markers (rDNA) led to the erection of the Diplostomida Olson, Cribb, Tkach, Bray, and Littlewood, 2003. However, recent mitochondrial (mt) genome phylogenies suggest this order might be paraphyletic. These analyses show members of two diplostomidan superfamilies are more closely related to the Plagiorchiida La Rue, 1957 than to other members of the Diplostomida. A recent phylogeny based on partial cytochrome c oxidase I also indicates one of the groups implicated, the Diplostomoidea Poirier, 1886, is non-monophyletic. To determine if these results were robust to additional taxon sampling, we analyzed mt genomes from seven diplostomoids in three families. To choose between phylogenetic alternatives based on mt genomes and the prior rDNA-based topology, we analyzed hundreds of ultra-conserved genomic elements assembled from shotgun sequencing. The Diplostomida was paraphyletic in the mt genome phylogeny but supported in the ultra-conserved genomic element phylogeny. We speculate this mitonuclear discordance is related to ancient, rapid radiation in the Digenea. Both ultra-conserved genomic elements and mt genomes support the monophyly of the Diplostomoidea and show congruent relationships within it. The Cyathocotylidae Mühling, 1898 are early diverging descendants of a paraphyletic clade of Diplostomidae Poirier, 1886, in which are nested members of the Strigeidae Railliet, 1919; the results support prior suggestions that the Crassiphialinae Sudarikov, 1960 will rise to the family level. Morphological traits of diplostomoid metacercariae appear to be more useful for differentiating clades than those of adults. We describe a new species of Cotylurus Szidat, 1928, resurrect a species of Hysteromorpha Lutz, 1931, and find support for a species of Alaria Schrank, 1788 of contested validity. Complete rDNA operons from seven diplostomoid species are provided as a resource for future studies.

Molecular systematics of the digenean community parasitising the cerithiid gastropod Clypeomorus batillariaeformis Habe & Kusage on the Great Barrier Reef

A rich fauna of digenetic trematodes has been documented from the Great Barrier Reef (GBR), yet little is known of the complex life-cycles of these parasites which occur in this diverse marine ecosystem. At Heron Island, a small coral cay at the southern end of the GBR, the intertidal marine gastropod Clypeomorus batillariaeformis Habe & Kusage (Cerithiidae) is especially abundant. This gastropod serves as an intermediate host for 12 trematode species utilising both fish and avian definitive hosts. However, 11 of these species have been characterised solely with morphological data. Between 2015 and 2018 we collected 4870C. batillariaeformis from Heron Island to recollect these species with the goal of using molecular data to resolve their phylogenetic placement. We found eight of the 12 previously known species and two new forms, bringing the total number of digenean species known to parasitise C. batillariaeformis to 14. The families of this trematode community now include the Atractotrematidae Yamaguti, 1939, Bivesiculidae Yamaguti, 1934, Cyathocotylidae Mühling, 1898, Hemiuridae Looss, 1899, Heterophyidae Leiper, 1909, Himasthlidae Odhner, 1910, Microphallidae Ward, 1901, and Renicolidae Dollfus, 1939. Molecular data (ITS and 28S rDNA) were generated for all trematode species, and the phylogenetic position of each species was determined. The digenean community parasitising C. batillariaeformis includes several common species, as well as multiple species which are uncommon to rare. Although most of those trematodes in the community which exploit fishes as definitive hosts have remained common, the composition of those which utilise birds appears to have shifted over time.

Central European Strigeidae Railliet, 1919 (Trematoda: Strigeidida): Molecular and comparative morphological analysis suggests the reclassification of Parastrigea robusta Szidat, 1928 into Strigea Abildgaard, 1790

Strigeidae Railliet, 1919 are digenean parasites of birds and mammals that are characteristic by their cup-shaped forebody and bilobed holdfast organ. Despite that the family is taxonomically unsettled, particularly due to a very limited number of visible autapomorphic identification features, molecular phylogenetics have never been applied to analyze the relationships among European members of Strigeidae except for the genus Ichthyocotylurus. Here, we analyze the Strigeidae found during the examination of Czech birds performed from 1962 to 2017, and we provide comparative measurements and host spectra, including prevalence and intensity; we also provide and analyze sequences of four DNA loci of 12 of the Strigeidae species. We suggest the reclassification of Parastrigea robusta Szidat, 1928 as Strigea robusta (Szidat, 1928) Heneberg and Sitko, 2018 comb. n. The genera Strigea Abildgaard, 1790 and Parastrigea Szidat, 1928 appear paraphyletic, and morphological diagnostic features of genera within Strigeini Dubois, 1936 are invalid. The mute swan Cygnus olor hosts two Cotylurus spp., Cotylurus syrius Dubois, 1934 and a second species with molecular identification features shared in part with Cotylurus cornutus (Rudolphi, 1808) and Cotylurus gallinulae Lutz, 1928. New host records are provided for seven species. Analyses of non-European genera of the Strigeidae are needed to provide an updated key to Strigeini.

Detected trematodes inside blue-winged teals (Spatula discors) give insights on north-south flow of parasites through Cuba during migration

The Blue-winged Teal (Spatula discors) is known for engaging in long-distance North-South migrations and back in the Americas with Cuba being an important wintering ground. Teals serve as hosts for a wide range of parasite species that can be "discharged" at each end of the migration route. Here, we explore for the first time the diversity of trematodes that the Blue-winged Teal may be introducing to -or exporting from- Cuba. We found 15 digenean parasites in 65 sampled teals of which 13 represent first reports for Cuba with one species (Echinostoma revolutum) of zoonotic importance. Overall prevalence was very high (96.92%) whereas Trichobilharzia spp. resulted the most ubiquitous parasite. Highest intensities were recorded for Australapatemon sp. (arriving teals) and Levinseniella amnicolae (departing teals). Altogether, departing teals harboured the highest number of trematode species and abundance. The short development and lifespan, inside migratory birds, of adult stages of trematodes like Trichobilharzia sp., Cotylurus flabelliformis and Microphallus pygmaeus strongly suggest that the occurrence of these trematodes in the departing teals could be related to their long establishment in Cuban ecosystems. In a global scenario where parasitology, particularly wildlife parasitology, is mostly overlooked, there should be an increasing need of gathering information and increasing surveillance of wildlife diseases that might eventually become important for the health of ecosystems and of domestic animals and humans. The present study constitutes the first major attempt to explore trematode infection from S. discors in Cuba under the view of parasite flow via bird migration.

A hyper-diverse genus of acanthocephalans revealed by tree-based and non-tree-based species delimitation methods: Ten cryptic species of Neoechinorhynchus in Middle American freshwater fishes

The genus Neoechinorhynchus represents a hyper-diverse group of acanthocephalans, parasites of fresh and brackish water fish and freshwater turtles, with approximately 116 species described worldwide. Forty-nine species have been recorded in the Americas, nine of them in Middle America. Even though species delimitation methods using DNA sequences have been rarely used for parasitic helminths, the genetic library for species of Neoechinorhynchus has grown in the past few years, enhancing the possibility of using these methods for inferring evolutionary relationships and for establishing more robust species boundaries. In this study, we used non-tree-based and tree-based methods through a coalescent approach to explore the species limits of specimens of Neoechinorhynchus collected in 57 localities across Middle America. We sequenced a large number of individuals to build a comprehensive dataset for three genes: the mitochondrial cytochrome c oxidase subunit I (352 individuals), the internal transcribed spacers (330 individuals), and the D2 + D3 domains of the large subunit (278 individuals). Several species delimitation methods were implemented, i.e., Automatic Barcode Gap Discovery (ABGD), General Mixed Yule-Coalescent Model (GMYC), Bayesian species delimitation (BPP) and species tree (∗BEAST). Additionally, we conducted a detailed morphological study of the diagnostic traits associated with the proboscis of 184 males and 169 females. Overall, our analyses allowed us to validate nine nominal species of Neoechinorhynchus and to identify 10 additional genetic lineages herein regarded as candidate species. This unexpected genetic diversity and the lack of reliable morphological traits show that the genus Neoechinorhynchus includes a group of cryptic species, at least in Middle America.

Filling the gaps in the classification of the Digenea Carus, 1863: systematic position of the Proterodiplostomidae Dubois, 1936 within the superfamily Diplostomoidea Poirier, 1886, inferred from nuclear and mitochondrial DNA sequences

The Diplostomida Olson, Cribb, Tkach, Bray & Littlewood, 2003 is the less diverse order of the two orders within the subclass Digenea Carus, 1863 and is currently classified into three superfamilies, i.e. Brachylaimoidea Joyeux & Foley, 1930, Diplostomoidea Poirier, 1886, and Schistosomatoidea Stiles & Hassall, 1898. Although the suprageneric-level relationships have been elucidated with the use of molecular markers, the lack of representation of some groups obscure the phylogenetic relationships among families, rendering the classification unstable. Here, we tested the phylogenetic position of the family Proterodiplostomidae Dubois, 1936 based on partial 28S rDNA and complete 18S rDNA sequences for Crocodilicola pseudostoma (Willemoes-Suhm, 1870), a crocodile parasite that has been found as a progenetic metacercaria parasitising the pale catfish Rhamdia guatemalensis (Günther) in Mexico and in other siluruforms in the Neotropics. We augmented the representation of the species, genera and families within the Diplostomida, including mostly representatives of the superfamily Diplostomoidea, and assembled a dataset that contains 49 species for the 28S rRNA gene, and 45 species for the 18S rRNA gene. Additionally, we explored the phylogenetic signal of the mitochondrial gene cox1 in reconstructing the phylogenetic relationships of selected members of the superfamily. Our analyses showed that the family Proterodiplostomidae is the sister taxon to the paraphyletic Diplostomidae Poirier, 1886 and Strigeidae Railliet, 1919, with Cyathocotylidae Mühling, 1898 + Brauninidae Wolf, 1903 as their sister group. Analysis of concatenated 18S + 28S sequences revealed the Liolopidae Odhner, 1912 as the basal group of the superfamily Diplostomoidea, although analyses of independent datasets showed that the position of this family remains uncertain. Analysis based on cox1 unequivocally resolved the Proterodiplostomidae as the sister taxon to the Diplostomidae and Strigeidae, although the Cyathocotylidae was nested in a different clade, along with brachylaimoids and schistosomatoids.

Hiding in the swamp: new capillariid nematode parasitizing New Zealand brown mudfish

The extent of New Zealand's freshwater fish-parasite diversity has yet to be fully revealed, with host-parasite relationships still to be described from nearly half the known fish community. While advances in the number of fish species examined and parasite taxa described are being made, some parasite groups, such as nematodes, remain poorly understood. In the present study we combined morphological and molecular analyses to characterize a capillariid nematode found infecting the swim bladder of the brown mudfish Neochanna apoda, an endemic New Zealand fish from peat-swamp-forests. Morphologically, the studied nematodes are distinct from other Capillariinae taxa by the features of the male posterior end, namely the shape of the bursa lobes, and shape of spicule distal end. Male specimens were classified into three different types according to differences in the shape of the bursa lobes at the posterior end, but only one was successfully characterized molecularly. Molecular analysis indicated that the studied capillariid is distinct from other genera. However, inferences about the phylogenetic position of the capillariid reported here will remain uncertain, due to the limited number of Capillariinae taxa characterized molecularly. The discovery of this new capillariid, which atypically infects the swim bladder of its host, which itself inhabits a very unique ecosystem, underlines the very interesting evolutionary history of this parasite, which for now will remain unresolved.

Molecular and morphological evidence for nine species in North American Australapatemon (Sudarikov, 1959): a phylogeny expansion with description of the zygocercous Australapatemon mclaughlini n. sp

Zygocercous (aggregating) cercarial larvae were recently discovered emerging from a physid snail during a molecular survey of cercariae from molluscs in lakes in central Alberta, Canada. This manuscript delves into the characterization of these cercariae through morphological and molecular techniques and provides the first genetic information for a zygocercous larval trematode. Analyses of cytochrome c oxidase I of mitochondrial DNA and two partial regions of nuclear ribosomal DNA sequences revealed the zygocercous cercariae to belong to the genus Australapatemon Sudarikov, 1959. Further analyses of sequences of Australapatemon burti (Miller, 1923), from cercariae and adults collected from across North America, indicate a complex of nine genetically-distinct lineages within this species, a surprising level of diversity. The zygocercous cercariae, along with adult worms collected from ducks in Manitoba, Canada, and from Mexico, represent one of these lineages, and are herein described as Australapatemon mclaughlini n. sp. Seven lineages cannot yet be identified, but one is tentatively identified as Australapatemon burti.

Life History, Systematics and Evolution of the Diplostomoidea Poirier, 1886: Progress, Promises and Challenges Emerging From Molecular Studies

Members of the Diplostomoidea mature in amniotes and employ vertebrates, annelids and molluscs as second intermediate hosts. Diplostomoid life cycles generally follow a three-host pattern typical of digeneans, but novelties have arisen in some species, including obligate four-host life cycles, vertical transmission, and intracellular parasitism. In this review, we summarize the basic biology of diplostomoids with reference to molecular studies, and present challenges, gaps and areas where molecular data could address long-standing questions. Our analysis of published studies revealed that most molecular surveys find more diplostomoid species than expected, but this tendency is influenced by how much effort goes into examining specimens morphologically and the number of sequenced worms. To date, molecular work has concentrated disproportionately on intraspecific or species-level diversity of larval stages in the Diplostomidae in temperate northern regions. Although the higher taxonomy of the superfamily is recognized to be in need of revision, little molecular work has been conducted at this level. Our phylogenetic analysis indicates several families and subfamilies require reconsideration, and that larval morphotypes are more reflective of evolutionary relationships than definitive hosts. The host associations of adult diplostomoids result from host-switching processes, whereas molecular surveys indicate that larval diplostomoid metacercariae have narrow ranges of second intermediate hosts, consistent with coevolution. Molecular data are often used to link diplostomoid developmental stages, and we provide data from adult Neodiplostomum and Mesoophorodiplostomum that correct earlier misidentifications of their larval stages and propose alternatives to collecting definitive hosts.

Species delimitation in trematodes using DNA sequences: Middle-American Clinostomum as a case study

The recent development of genetic methods allows the delineation of species boundaries, especially in organisms where morphological characters are not reliable to differentiate species. However, few empirical studies have used these tools to delineate species among parasitic metazoans. Here we investigate the species boundaries of Clinostomum, a cosmopolitan trematode genus with complex life cycle. We sequenced a mitochondrial [cytochrome c oxidase subunit I (COI)] gene for multiple individuals (adults and metacercariae) from Middle-America. Bayesian phylogenetic analysis of the COI uncovered five reciprocally monophyletic clades. COI sequences were then explored using the Automatic Barcode Gap Discovery to identify putative species; this species delimitation method recognized six species. A subsample was sequenced for a nuclear gene (ITS1, 5·8S, ITS2), and a concatenated phylogenetic analysis was performed through Bayesian inference. The species delimitation of Middle-American Clinostomum was finally validated using a multispecies coalescent analysis (species tree). In total, five putative species are recognized among our samples. Mapping the second intermediate hosts (fish) onto the species tree suggests that metacercariae of these five species exhibit some level of host specificity towards their fish intermediate host (at the family level), irrespective of geographical distribution.

Digenean trematode cysts within the heads of threatened Galaxiella species (Teleostei : Galaxiidae) from south-eastern Australia

The dwarf galaxias (Galaxiella pusilla) and little galaxias (Galaxiella toourtkoourt) are both threatened freshwater fish from south-eastern Australia. Occasionally populations have been found with enlarged heads associated with the accumulation of ‘white balls’, but the cause of these deformities has not previously been investigated. In this study, histopathology and molecular techniques were employed to identify cysts extracted from the heads of Galaxiella species across six populations. Histopathology and DNA sequences from both mitochondrial (cytochrome c oxidase subunit I) and nuclear (ribosomal internal transcribed spacer 1) regions identified the cysts as metacercariae of Apatemon gracilis (Rudolphi, 1819), a cosmopolitan digenean trematode species. Heavy infestations of trematode metacercariae within Galaxiella populations are of concern due to the potential to cause increased mortality associated with altered behaviour of the fish host that increases the likelihood of predation. Direct mortality from infestations is also possible, but not quantified in this study.