Morphology and molecules reveal the alien Posthodiplostomum centrarchi Hoffman, 1958 as the third species of Posthodiplostomum Dubois, 1936 (Digenea: Diplostomidae) in Europe

Comparative Analysis of Parasite Load on Recently Established Invasive Pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) in Europe

PURPOSE

The aim of this study was the comparative analysis of the parasite communities of new populations of invasive pumpkinseed (Lepomis gibbosus) in western Ukraine with pumpkinseed from Czechia, where populations have rapidly expanded over the last two decades.

METHODS

Sampling took place at three localities in the western part of Ukraine (i.e. Dobrotvir Reservoir (Vistula basin), Burshtyn Reservoir (Dniester basin), Mynai Pond (Danube basin)) and four in Czechia (i.e. Oxbow D2, Heršpický Pond (Danube basin), and Kolín oxbow and Římov Reservoir (Elbe basin).

RESULTS

In total, 11 parasite taxa were recorded in Ukraine and 17 in Czechia. Four species were co-introduced from North America with their host, i.e. the myxosporean Myxobolus dechtiari, the monogeneans Onchocleidus dispar and Onchocleidus similis, and metacercariae of a trematode Posthodiplostomum centrarchi. High dominance indices were related to a high abundance of co-introduced parasites, i.e. O. similis in Mynai pond and P. centrarchi in Dobrotvir Reservoir. Overall abundance of acquired parasites was generally low.

CONCLUSION

This study shows that parasite communities in recently established pumpkinseed populations in the western part of Ukraine and Czechia are less diverse than those established in Europe for decades. The generally low parasite load in these new populations may play an important role in their ability to successfully establish and create strong populations by providing a competitive advantage over local species.

Other Schistosomatoidea and Diplostomoidea

Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis (schistosomiasis) affecting more than 200 million people in tropical and subtropical countries, and infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The "Aporocotylidae" sensu lato are pathogenic in fish, "Spirorchiidae" sensu lato in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in mollusks and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.

Differential Strigeid Infection Patterns in Male Morphotypes of Bluegill Sunfish (Lepomis macrochirus)

PURPOSE

Behavioral variation among conspecific organisms can have substantial ecological impacts, particularly affecting parasite infection. Bluegill sunfish (Lepomis macrochirus) exhibit multiple male reproductive morphotypes that differ in their size, feeding dynamics, and reproductive behavior. This study investigated how these morphological and ecological differences contribute to the patterns of infection by strigeid trematodes.

METHODS

A total of 1961 L. macrochirus was collected from 14 lakes and ponds in northwestern Virginia, USA, and were necropsied to identify and enumerate three common strigeid parasites, white grub (Posthodiplostoum spp.), black grub (Uvulifer ambloplitis), and yellow grub (Clinostomum marginatum) infecting the fish and determine if there were different infection patterns among sexes and morphotypes.

RESULTS

Strigeid infections in L. macrochirus α-males were in greater abundance compared to females and β-males. Additionally, α-males had greater strigeid infection in the kidneys and fins, while females and β-males accumulated more parasites in the liver and body tissues.

CONCLUSIONS

Increased nesting responsibilities and potential interaction with snail intermediate hosts by α-males may lead to the differences in infection patterns. The distinction of morphotypes revealed significant differences in abundance and distribution of parasite infections between the sexes of L. macrochirus, trends that were masked when male morphotypes are combined.

Population genetic structure, parasite infection and somatic condition of pumpkinseed Lepomis gibbosus (Actinopterygii: Centrarchidae) in the Oder river basin

In Poland, distribution of non-native pumpkinseed Lepomis gibbosus (Centrarchidae) is strictly limited to the Oder river basin, where it was introduced in the early 20th century. Recently, several populations have been found in waterbodies adjacent to the Oder, particularly in its lower reaches. In this study, we compare the genetic relatedness of populations in the Oder basin with other European populations using nuclear (microsatellite) and mitochondrial (partial cytochrome c oxidase subunit I; cox1) markers. Microsatellite analysis indicated that four populations in the lower Oder form a separate cluster, while one in the middle Oder clustered with Danubian populations, from where probably having been introduced. Microsatellite data suggested that the lower Oder populations differ from other non-native European populations, making it impossible to estimate the source of introduction. Nevertheless, analysis of cox1 indicated that Oder pumpkinseeds belong to the same haplotype as the vast majority of European populations. Parasitological examination confirmed the presence of two North American species, the monogenean Onchocleidus dispar and trematode Posthodiplostomum centrarchi, in the lower Oder, both previously unknown in the region. Fifteen other parasite species were acquired, including glochidia of invasive Sinanodonta woodiana. In the middle Oder, parasite infection was more limited. Fish from the Gryfino Canal, considered one of the most invasive populations in Europe, showed the highest parasite abundance and diversity, and the highest somatic condition and growth rate due to warm water released from the Dolna Odra power plant. Our results highlight significant differences in somatic condition and parasite infection in long-established non-native pumpkinseed populations in the same river system, reflecting mainly environmental conditions.

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.

First integrative study of the diversity and specificity of metacercariae of Posthodiplostomum Dubois, 1936 from native and introduced fishes in the Caribbean

Metacercariae of the genus Posthodiplostomum are often recorded in freshwater fish hosts. While the diversity and taxonomy of this genus are receiving increasing attention in molecular phylogenetic studies, available data remain geographically biased. Most molecular studies of Posthodiplostomum and morphologically similar (neascus) worms originate in North America and Europe and Asia (more than 60% of DNA sequences are from USA and Canada), with few data currently available from the Neotropics, where high host diversity suggests high and under-sampled parasite diversity. In this study, we report molecular and morphological data from metacercariae of Posthodiplostomum in fish in Puerto Rico, where only a single species has been previously reported. Partial sequences of cytochrome c oxidase subunit 1 from metacercariae from Dajaus monticola (native to Puerto Rico) and the introduced fishes Poecilia reticulata, Parachromis managuensis, Lepomis macrochirus and Micropterus salmoides revealed 7 genetically distinct species-level lineages, of which 4 were novel. We report novel molecular life-cycle linkages in Posthodiplostomum macrocotyle (metacercariae in muscle of the cichlid Pa. managuensis), a species previously known only from adults in birds from South America; and in Posthodiplostomum sp. 23 (metacercariae in poeciliids), which has recently been found in Ardea herodias in Georgia, USA. We also report the first molecular data from Posthodiplostomum sp. 8 in M. salmoides in the Caribbean. Metacercariae of most species were morphologically distinguished and all displayed narrow specificity for fish hosts, with no indication of parasite sharing among introduced and native fishes.

Marine parasite in a freshwater wetland: new host and geographical records of Progrillotia dasyatidis (Cestoda: Trypanorhyncha) from Gasterosteus aculeatus (Actinopterygii: Gasterosteidae) in Bulgaria, with comments on its life-cycle

Plerocerci of the trypanorhynch cestode Progrillotia dasyatidis Beveridge, Neifar & Euzet, (Progrillotiidae) were isolated from the gallbladder of the three-spined stickleback Gasterosteus aculeatus from a small freshwater marsh in the Lake Atanasovsko Wetlands, a coastal area adjacent to the Black Sea coast, Bulgaria. The parasite was recorded in five out of 134 fish individuals studied (prevalence 3.73%, intensity 1-7, mean intensity 2.40 ± 1.17 and mean abundance 0.09 ± 0.06). A description of the plerocerci is presented, expanding data on intraspecific variation. The present report is the first record of P. dasyatidis from G. aculeatus (new host record) and from Bulgaria (new geographical record). Recording only plerocerci with evaginated scoleces in the sticklebacks is consistent with the hypothesis that teleosts are paratenic hosts and not intermediate hosts of P. dasyatidis.

Assessing the genetic diversity of the metacercariae of Posthodiplostomum minimum (Trematoda: Diplostomidae) in Middle American freshwater fishes: one species or more?

Trematode taxonomy is mainly based on the morphological traits of adults. The identification of metacercariae is challenging because such traits are not developed in larval forms, and they even may show some level of morphological variability. Studies testing the potential correspondence between morphological differences and genetic variation of parasites are still lacking. The metacercariae of Posthodiplostomum minimum are probably the diplostomids more widely distributed in North and Middle American freshwater fish, and their intraspecific morphological variability has been attributed to the effect exerted by the host. Here, we tested the hypothesis whether they represent a single species, or a species complex by assessing the genetic divergence and phylogenetic relationships of metacercariae sampled from several host species in a wide geographical range across Middle America. The internal transcribed spacers (ITS1-5.8S-ITS2), and the mitochondrial COI gene were sequenced for 124 and 55 metacercariae, respectively. Phylogenetic analysis inferred from ITS sequences uncovered six well-supported monophyletic lineages. The six lineages show no correspondence to any Posthodiplostomum species for which sequences are available thus far in GenBank. Lineages exhibit some degree of host specificity; Lineages I, II, IV and V are primarily parasites of cyprinodontiforms of the families Poeciliidae, Goodeidae, Profundulidae and Fundulidae. In poeciliids there are at least four candidate species of Posthodiplostomum, some of them occurring in sympatry; instead, Lineages II and VI are exclusively parasites of cichlids. This study contributes to our understanding of the diversity of larval forms of diplostomids and provides an opportunity to further study their life cycles.

Unravelling the diversity of the Crassiphialinae (Digenea: Diplostomidae) with molecular phylogeny and descriptions of five new species

Crassiphialinae Sudarikov, 1960 is a large subfamily of the Diplostomidae Poirier, 1886 with a complex taxonomic history. It includes a diversity of species parasitic in the intestines of avian and mammalian definitive hosts worldwide. Posthodiplostomum Dubois, 1936 is a large and broadly distributed crassiphialine genus notorious for its association with diseases in their fish second intermediate hosts. In this study, we generated partial 28S rDNA and cytochrome c oxidase subunit 1 (cox1) mtDNA gene sequences of digeneans belonging to seven crassiphialine genera. The 28S sequences were used to study the interrelationships among crassiphialines and their placement among other major diplostomoidean lineages. Our molecular phylogenetic analysis and review of morphology does not support subfamilies currently recognized in the Diplostomidae; therefore, we abandon the current subfamily system of the Diplostomidae. Molecular phylogenetic analyses suggest the synonymy of Posthodiplostomum, Ornithodiplostomum Dubois, 1936 and Mesoophorodiplostomum Dubois, 1936; morphological study of our well-fixed adult specimens and review of literature revealed lack of consistent differences among the three genera. Thus, we synonymize Ornithodiplostomum and Mesoophorodiplostomum with Posthodiplostomum. Our phylogenetic analyses suggest an Old World origin of Posthodiplostomum followed by multiple dispersal events among biogeographic realms. Furthermore, our analyses indicate that the ancestors of these digeneans likely parasitized ardeid definitive hosts. Four new species of Posthodiplostomum collected from birds in the New World as well as one new species of Posthodiplostomoides Williams, 1969 from Uganda are described.

Evidence of the American Myxobolus dechtiari was introduced along with its host Lepomis gibbosus in Europe: Molecular and histological data

The American pumpkinseed Lepomis gibbosus, was introduced to Europe more than one hundred years ago. Currently it is a common fish in European freshwaters but relatively few specific parasites infect this fish in this new habitat. In Europe only a single species, Myxobolus dechtiari seems to represent the American myxosporean fauna of centrarchid fishes. M. dechtiari was found in both Portugal and Hungary. This species forms plasmodia with elongated shape inside the cartilaginous rays of gill filaments. In the advanced stage of infection, after disruption of plasmodia, small groups of myxospores remain enclosed in the cartilaginous gill rays causing distortions in the filaments. Myxospores were ellipsoidal in frontal view and lemon-shape in sutural, length 12.5 ± 0.46 (12-13.4) μm, width 10 ± 0.37 (9.6-10.4) μm, and thickness 7.4 ± 0.37 (7-8) μm; the polar capsules were pyriform, equal in size, length 5.6 ± 0.21 (5.3-6) μm, width 3.2 ± 0.16 (3-3.6) μm; Seven to eight polar tube coils were arranged perpendicularly to the capsule length. There was a small, round, 0.4 ± 0.1 (0.3-05) (N = 50) intercapsular appendix in the spores. The small subunit ribosomal DNA (ssrDNA) of M. dechtiari differed from other myxozoans sequenced to date. Phylogenetic analysis of the ssrDNA gene sequence placed this species in a clade including actinospores and Myxobolus species: Raabeia type1, Triactinomyxon sp., and Myxobolus osburni infecting the same host fish. The focus of our study was to prove that the pumpkinseed, a fish originated from North-America introduced one of its myxosporean parasite to Europe. Emphasis was put on to demonstrate the unique feature of this parasite causing infection in the cartilaginous gill rays.

Intercontinental distributions, phylogenetic position and life cycles of species of Apharyngostrigea (Digenea, Diplostomoidea) illuminated with morphological, experimental, molecular and genomic data

When subjected to molecular study, species of digeneans believed to be cosmopolitan are usually found to consist of complexes of species with narrower distributions. We present molecular and morphological evidence of transcontinental distributions in two species of Apharyngostrigea Ciurea, 1924, based on samples from Africa and the Americas. Sequences of cytochrome c oxidase I and, in some samples, internal transcribed spacer, revealed Apharyngostrigea pipientis (Faust, 1918) in Tanzania (first known African record), Argentina, Brazil, USA and Canada. Sequences from A. pipientis also match previously published sequences identified as Apharyngostrigea cornu (Zeder, 1800) originating in Mexico. Hosts of A. pipientis surveyed include definitive hosts from the Afrotropic, Neotropic and Nearctic, as well as first and second intermediate hosts from the Americas, including the type host and type region. In addition, metacercariae of A. pipientis were obtained from experimentally infected Poecilia reticulata, the first known record of this parasite in a non-amphibian second intermediate host. Variation in cytochrome c oxidase I haplotypes in A. pipientis is consistent with a long established, wide-ranging species with moderate genetic structure among Nearctic, Neotropic and Afrotropic regions. We attribute this to natural dispersal by birds and find no evidence of anthropogenic introductions of exotic host species. Sequences of CO1 and ITS from adult Apharyngostrigea simplex (Johnston, 1904) from Egretta thula in Argentina matched published data from cercariae from Biomphalaria straminea from Brazil and metacercariae from Cnesterodon decemmaculatus in Argentina, consistent with previous morphological and life-cycle studies reporting this parasite-originally described in Australia-in South America. Analyses of the mitochondrial genome and rDNA operon from A. pipientis support prior phylogenies based on shorter markers showing the Strigeidae Railliet, 1919 to be polyphyletic.

First record of the American cestode Proteocephalus ambloplitis (Leidy, 1887) (Proteocephalidae) in Europe

Here, we report the first record of pleroceroids of the Nearctic tapeworm Proteocephalus ambloplitis (Leidy, 1887) in European fresh waters. The plerocercoids were found encapsulated in the internal organs of the invasive pumpkinseed Lepomis gibbosus (Linnaeus, 1758) in a pond in Bègles Plage, Bordeaux, France. This parasite species was not observed in L. gibbosus collected from two nearby localities, Bordeaux Lac and a pond in the Parc de Fontaudin. Species identification was confirmed using molecular data and morphological characteristics.

Phylogenetic Affinities of Uvulifer Spp. (Digenea: Diplostomidae) in the Americas with Description of Two New Species from Peruvian Amazon

Uvulifer Yamaguti, 1934, is a genus of diplostomoidean digeneans that parasitizes kingfishers worldwide. Species have a Neascus-type metacercaria that encysts in or on fish intermediate hosts, often causing black spot disease. Only 3 prior studies published DNA sequence data for Uvulifer species with only 1 including a single named species (Uvulifer spinatus López-Jiménez, Pérez-Ponce de León, & García-Varela, 2018). Herein we describe 2 new species of Uvulifer from the green-and-rufous kingfisher, Chloroceryle inda (Linnaeus), collected in Peru ( Uvulifer batesi n. sp. and Uvulifer pequenae n. sp.). Both new species are readily differentiated from their New World congeners by a combination of morphological characters including distribution of vitelline follicles and prosoma:opisthosoma length ratios. In addition, we used newly generated nuclear 28S rRNA and mitochondrial COI gene sequence data to differentiate among species and examine phylogenetic affinities of Uvulifer. This includes the 2 new species and Uvulifer ambloplitis (Hughes, 1927), as well as Uvulifer elongatus Dubois, 1988 , Uvulifer prosocotyle (Lutz, 1928), and Uvulifer weberi Dubois, 1985 , none of which have been part of prior molecular phylogenetic studies. Our data on Uvulifer revealed 0.1-2.2% interspecific divergence in 28S sequences and 9.3-15.3% in COI sequences. Our 28S phylogeny revealed at least 6 well-supported clades within the genus. In contrast, the branch topology in the COI phylogenetic tree was overall less supported, indicating that although COI sequences are a great tool for species differentiation, they should be used with caution for phylogenetic inference at higher taxonomic levels. Our 28S phylogeny did not reveal any clear patterns of host association between Uvulifer and particular species of kingfishers; however, it identified 2 well-supported clades uniting Uvulifer species from distant geographical locations and more than 1 biogeographic realm, indicating at least 2 independent dispersal events in the evolutionary history of the New World Uvulifer. Our results clearly demonstrate that the diversity of Uvulifer in the New World has been underestimated.

New record of metacercariae of the North American Posthodiplostomum centrarchi (Digenea, Diplostomidae) in pumpkinseed (Lepomis gibbosus) in Hungary

Two species of the genus Posthodiplostomum (Digenea: Diplostomatidae) (Posthodiplostomum brevicaudatum Nordmann, 1832 and Posthodiplostomum cuticola Nordmann, 1832) are known as parasites of Hungarian native fishes. Metacercariae of P. cuticola are widespread in Europe and cause black spot disease. Several species of Posthodiplostomum were described also from North America but none of them has been isolated in Hungary up to now. Posthodiplostomum centrarchi Hoffman, 1958 has been detected recently in pumpkinseeds (Lepomis gibbosus L., 1758) in several European countries. Posthodiplostomum centrarchi was isolated for the first time in Hungary from pumpkinseeds caught in the Maconka water reservoir in 2015. Thereafter, several natural waters (e.g. the River Danube, Lake Balaton and the Sió channel) were sampled in order to determine its presence and distribution. Only the native species P. cuticola was detected in Lake Balaton on cyprinids but a relatively high infection rate of P. centrarchi was observed in the Sió channel close to the lake. Pathological changes were absent, and metacercariae were mostly attached to the surface of the liver, kidney and heart. The phylogenetic analysis of the ITS and COI sequences of P. centrarchi and P. cuticola clustered into two distinct branches, which was in agreement with the morphological results.

Infections of Digenetic Trematode Metacercariae in Wrestling Halfbeak, Dermogenys pusilla from Bangkok Metropolitan Region in Thailand

This study aimed to investigate metacercarial infections in the wrestling halfbeak, Dermogenys pusilla, collected from Bangkok metropolitan region of Thailand. A total of 4,501 fish from 78 study sites were commonly examined with muscle compression and digestion methods (only head part of fish) during September 2017 to July 2018. The overall prevalence of metacercarial infection was 86.1% (3,876/4,501 individuals), and the mean intensity was 48.9 metacercariae per fish infected. Four species, i.e., Posthodiplostomum sp., Stellantchasmus falcatus, Cyathocotylidae fam. sp., and Centrocestus formosanus, of digenetic trematode metacercariae (DTM) were detected. The prevalences were 65.8%, 52.0%, 2.1%, and 1.2%, respectively and their mean intensities were 23.1, 51.6, 1.4, and 3.2 per fish infected, respectively. The seasonal prevalences were 81.0% in winter, 87.8% in summer and 87.4% in rainy, and the mean intensities were 38.9, 46.6, and 55.2 metacercariae per fish infected, respectively. Conclusively, it was confirmed that the wrestling halfbeak play the role of second intermediate hosts of 4 species of digenetic trematodes including S. falcatus and Posthodiplostomum sp. in Bangkok metropolitan region. And then the metacercariae of C. formosanus and Cyathocotylidae fam. sp. are to be first found in the wrestling halfbeak by this study.

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)].

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.

Schistosomatoidea and Diplostomoidea

Trematodes of the order Diplostomida are well known as serious pathogens of man, and both farm and wild animals; members of the genus Schistosoma (Schistosomatidae) are responsible for human schistosomosis affecting more than 200 million people in tropical and subtropical countries, infections of mammals and birds by animal schistosomes are of great veterinary importance. The order Diplostomida is also rich in species parasitizing other major taxa of vertebrates. The Aporocotylidae are pathogenic in fish, Spirorchiidae in reptiles. All these flukes have two-host life cycles, with asexually reproducing larvae usually in molluscs and occasionally in annelids, and adults usually live in the blood vessels of their vertebrate hosts. Pathology is frequently associated with inflammatory reactions to eggs trapped in various tissues/organs. On the other hand, the representatives of Diplostomidae and Strigeidae have three- or four-host life cycles in which vertebrates often serve not only as definitive, but also as intermediate or paratenic hosts. Pathology is usually associated with migration of metacercariae and mesocercariae within the host tissues. The impact of these trematode infections on both farm and wild animals may be significant.

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.

Limited parasite acquisition by non-native Lepomis gibbosus (Actinopterygii: Centrarchidae) at two ponds in the Upper Rhine basin, Germany

Metazoan parasite communities of Lepomis gibbosus (Centrarchidae), one of the most successfully introduced fish species in Europe, were studied at two isolated ponds (Knielingen, Tropfen) along the Upper Rhine in Germany. Nine parasite taxa were observed, including North American species co-introduced to Europe (ancyrocephalid monogeneans, diplostomid trematodes), circumpolar species infecting L. gibbosus in both their native and non-native ranges (bothriocephalid cestodes) and locally acquired parasitic nematodes. Both parasite communities consisted predominantly of North American species. Acquisition of local parasites was not observed at Tropfen, where the fish community comprised just two species, with L. gibbosus dominant. Low prevalence and abundance of acquired parasites was found at Knielingen, which supported a diverse fish community. At Tropfen, a high abundance of the North American parasite Posthodiplostomum centrarchi probably contributed to the lower condition index, hepatomegaly and splenomegaly observed. Due to low local parasite competency, L. gibbosus appears to have no significant impact on parasite dynamics in affected habitats.

Infection patterns and molecular data reveal host and tissue specificity of Posthodiplostomum species in centrarchid hosts

Posthodiplostomum minimum utilizes a three-host life cycle with multiple developmental stages. The metacercarial stage, commonly known as 'white grub', infects the visceral organs of many freshwater fishes and was historically considered a host generalist due to its limited morphological variation among a wide range of hosts. In this study, infection data and molecular techniques were used to evaluate the host and tissue specificity of Posthodiplostomum metacercariae in centrarchid fishes. Eleven centrarchid species from three genera were collected from the Illinois portion of the Ohio River drainage and necropsied. Posthodiplostomum infection levels differed significantly by host age, host genera and infection locality. Three Posthodiplostomum spp. were identified by DNA sequencing, two of which were relatively common within centrarchid hosts. Both common species were host specialists at the genus level, with one species restricted to Micropterus hosts and the other preferentially infecting Lepomis. Host specificity is likely dictated by physiological compatibility and deviations from Lepomis host specificity may be related to host hybridization. Posthodiplostomum species also differed in their utilization of host tissues. Neither common species displayed strong genetic structure over the scale of this study, likely due to their utilization of bird definitive hosts.

Molecular data reveal high diversity ofUvulifer(Trematoda: Diplostomidae) in Middle America, with the description of a new species

Members of the genusUvuliferare distributed worldwide and infect aquatic snails and freshwater fishes as first and second intermediate hosts, respectively, and fish-eating birds (kingfishers) as definitive hosts. Metacercariae ofUvuliferspp. were collected from the fins and skin of 20 species of freshwater fishes in Mexico, Guatemala, Honduras, Nicaragua and Costa Rica, and the adults were recovered from the intestine of kingfishers in four localities of Mexico. The genetic divergence among 76 samples (64 metacercariae and 12 adults) was estimated by sequencing the 28S and 5.8S nuclear genes, as well as the internal transcribed spacers ITS1 and ITS2, and one mitochondrial gene (cox1). Maximum likelihood and Bayesian inference analyses inferred with each dataset showed a high genetic diversity within the genusUvuliferacross Middle America, revealing the existence of four genetic lineages that exhibit some level of host specificity to their second intermediate hosts. The metacercariae of lineage 1 were associated with characids and cyprinids in central and northern Mexico. Metacercariae of lineages 2 and 3 were associated with cichlids distributed widely across Middle America. The lack of adults of these lineages in kingfishers, in lineages 2 and 3, or the fact that just a few adult specimens were recovered, as in lineage 1, prevented a formal description of these species. The metacercariae of lineage 4 were found in poeciliids, across a distribution range comprising Mexico, Guatemala, Honduras and Nicaragua, and the adult was found in the green kingfisher in Mexico. The number of specimens sampled for lineage 4, for both gravid adults and metacercariae, allowed us to describe a new species,Uvulifer spinatusn. sp. We describe the new species herein and we discuss briefly the genetic diversity inUvuliferspp. and the importance of using DNA sequences to properly characterize parasite diversity.

Occurrence and effect of trematode metacercariae in two endangered killifishes from Greece

We report digeneans (Diplostomidae, Crassiphialinae) in the endangered freshwater fishes Valencia letourneuxi and Valencia robertae, endemics of Western Greece. Digenean metacercariae occurred in two forms in the abdominal cavity, excysted and encysted, the latter attached to the gonads, liver and alimentary tract. Parasites were, using morphological and molecular techniques, identified as two representatives of Crassiphialinae, specifically part of the Posthodiplostomum-Ornithodiplostomum clade. The spatial, seasonal, and age class variation in parasite prevalence was examined. Autumn parasite prevalence varied between the six populations sampled (18.2 to 100%). Seasonal prevalence at the two sites sampled quadannually peaked in autumn and reached its lowest value in spring; prevalence increased with size to 100% in young adult fish. We did not find a correlation between prevalence and host sex. Overall parasites' weight averaged 0.64% of the host's, while parasite weight increased with host weight. A comparison of relative condition and hepatosomatic and gonadosomatic indices of infected and metacercariae-free specimens showed that infection did not have a significant effect on host body condition and reproduction. Regarding the parasite's life cycle, planorbid gastropods are proposed as potential first intermediate hosts in view of the host's diet and occurrence data of molluscs in the ecosystem. This is the first record of a diplostomid digenean in valenciid fishes and of representatives of the Posthodiplostomum-Ornithodiplostomum clade in a native Greek freshwater fish. Our findings are discussed in conjunction to fish conservation interventions, since parasites may contribute to the decline of endangered species.

European distribution for metacercariae of the North American digenean Posthodiplostomum cf. minimum centrarchi (Strigeiformes: Diplostomidae)

Metacercariae of a North American digenean Posthodiplostomum cf. minimum centrarchi (Strigeiformes: Diplostomidae), have been reported from seven localities in Europe, with cysts recorded in the mesentery and internal organs of two invasive non-indigenous fishes (Lepomis gibbosus and Micropterus salmoides) from sites in Bulgaria, the Czech Republic and Portugal. Analysis of rDNA locus ITS1-ITS2-28S confirmed a closer relationship to the American Posthodiplostomum species than the common European species P. cuticola or P. brevicaudatum. Our data indicate limited potential of this parasite for switch to local fish fauna and confirm the occurrence at distant sites across Europe, suggesting that birds as definitive parasite hosts may play an important role for parasite dispersal. Further detailed studies are needed to confirm the actual means of introduction to Europe.

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.