Morphological and molecular data on Pseudozoogonoides ugui Shimazu, 1974 (Digenea: Microphalloidea: Zoogonidae) ex Pseudaspius hakonensis (Günther, 1877) and taxonomic problems in Zoogoninae genera

New morphological and molecular data were generated for trematodes recovered from the intestines of the fish Pseudaspius hakonensis from two locations in the south of the Russian Far East. Morphologically, these trematodes are identical to Pseudozoogonoides ugui (Microphalloidea: Zoogonidae) from Japan. According to results of phylogenetic analysis based on 28S rDNA sequence data, P. ugui was closely related to Zoogonoides viviparus, and P. subaequiporus appears as a sister taxon to these two species. Genetic distance values, calculated based on both 28S rDNA and ITS2 rDNA, between P. ugui and Z. viviparus represents an interspecific differentiation level. Our results have an ambiguous explanation, indicating that the implication of the presence of one or two compact vitellarial aggregations for the differentiation of Zoogonoides and Pseudozoogonoides should be reconsidered or that our results open up the question of the taxonomical status of trematodes previously denoted as Z. viviparus and P. subaequiporus.

A report on the complete mitochondrial genome of the trematode Azygia robusta Odhner, 1911, its new definitive host from the Russian Far East, and unexpected phylogeny of Azygiidae within Digenea, as inferred from mitogenome sequences

New data on the complete mitochondrial genome of Azygia robusta (Azygiidae) were obtained by the next-generation sequencing (NGS) approach. The mitochondrial DNA (mtDNA) of A. robusta had a length of 13 857 bp and included 12 protein-coding genes, two ribosomal genes, 22 transfer RNA genes, and two non-coding regions. The nucleotide sequences of the complete mitochondrial genomes of two A. robusta specimens differed from each other by 0.12 ± 0.03%. Six of 12 protein-coding genes demonstrated intraspecific variation. The difference between the nucleotide sequences of the complete mitochondrial genomes of A. robusta and Azygia hwangtsiyui was 26.95 ± 0.35%; the interspecific variation of protein-coding genes between A. robusta and A. hwangtsiyui ranged from 20.5 ± 0.9% (cox1) to 30.7 ± 1.2% (nad5). The observed gene arrangement in the mtDNA sequence of A. robusta was identical to that of A. hwangtsiyui. Codon usage and amino acid frequencies were highly similar between A. robusta and A. hwangtsiyui. The results of phylogenetic analyses based on mtDNA protein-coding regions showed that A. robusta is closely related to A. hwangtsiyui (belonging to the same suborder, Azygiida) that formed a distinct early-diverging branch relative to all other Digenea. A preliminary morphological analysis of paratypes of the two azygiid specimens studied showed visible morphological differences between them. The specimen extracted from Sakhalin taimen (Parahucho perryi) was most similar to A. robusta. Thus, we here provide the first record of a new definitive host, P. perryi, for A. robusta and also molecular characteristics of the trematode specimens.

Molecular-genetic approaches to species identification of platyhelminthes of the genus <i>Ligophorus</i> (Monogenea) parasitising flathead mullet

Mugil cephalus L., 1758 (flathead mullet) is a valuable commercial fish and a promising object of artificial breeding in the Black Sea and the Sea of Azov, and the study of its parasite fauna is important for fishery and mariculture. Monogeneans of the genus Ligophorus are common ectoparasites dwelling on the gills of mullets. Two representatives of this genus parasitise flathead mullet in the Azov-Black Sea region, namely Ligophorus mediterraneus Sarabeev, Balbuena et Euzet, 2005 and Ligophorus cephali Rubtsova, Balbuena, Sarabeev, Blasco- Costa et Euzet, 2006. Morphological identification of these species requires spending much time and a high level of experience in monogenean taxonomy. For quick and correct species identification of these parasites, we have developed a genotyping approach based on the polymerase chain reaction of allele-specific gene sites for various Monogenea species. A fragment of the 28S ribosomal gene, which includes conserved and variable sites, was chosen as a genetic marker. Three approaches were used as follows: amplified fragment length analysis, allelespecific PCR with endpoint detection and allele-specific real-time PCR using SYBR Green intercalating dye. The first approach was by obtaining PCR products of different lengths that were specific either to L. mediterraneus or to L. cephali. This approach was implemented due to the presence of several variable sites located at a distance from each other. The PCR mixture contained three primers: one forward and two reverse. The forward primer was complementary to the conserved site, which did not differ between species. Reverse primers were speciesspecific and, for each species, they were complementary to different DNA regions located 100 bp apart. As a result, L. mediterraneus was characterized by shorter amplicons than L. cephali. For the second and third approaches, a pair of primers was designed according to the following principle: the forward primer was complementary to both species, since it was selected for the conserved gene region. Reverse primers were species-specific and were designed for the 28S variable region. The two parasite species were distinguished by three-point mutations. Thus, one pair of primers was complementary to L. mediterraneus, the other, to L. cephali. The amplified fragment length analysis and the allele-specific real-time PCR demonstrated 100 % coincidence of genotyping results compared with Sanger sequencing. The developed genotyping protocols can be used not only to distinguish two species of Ligophorus from flathead mullet in ecological studies and veterinary practice but also for further development of similar approaches for other monogeneans, among which there are many pathogenic species.

New species and new genus of Pseudohaploporinae (Digenea): Pseudohaploporus pusitestis sp. n. and Parahaploporus elegantus n. g., sp. n. (Digenea: Pseudohaploporinae) from Vietnamese mullet fish

Two new species of Pseudohaploporinae, Pseudohaploporus pusitestis sp. n. and Parahaploporus elegantus n. g., sp. n., are described from intestines of the Vietnamese mullet fish Moolgarda seheli and Osteomugil cunnesius, respectively. Pseudohaploporus pusitestis sp. n. differs from two known Pseudohaploporus species, P. vietnamensis and P. planiliza, by the absence of a diverticulate hermaphroditic duct and muscular sphincters at the proximal end of the hermaphroditic sac. Metrically, P. pusitestis sp. n. is close to P. vietnamensis and differs from this species and from P. planilizum by lower maximum sizes of most parameters. Parahaploporus elegantus n. g., sp. differs from representatives of Pseudohaploporus by the presence of a single testis and the armament of hermaphroditic duct and is morphologically close to trematodes of the genus Haploporus. However, P. elegantus n. g differs from all known Haploporus species from mugilids of the Indo-West Pacific by the structure of the armament of the hermaphroditic duct and also by size of body, organs and eggs. The validity of designating two new species and a new genus of trematodes is supported by ITS and 28S rDNA sequence data. Phylogenetic reconstructions showed that the new trematodes belong to the Pseudohaploporinae, which formed a well-supported cluster within the monophyletic Haploporidae.

Phylogenetic relationships of Hemiuridae (Digenea: Hemiuroidea) with new morphometric and molecular data of Aphanurus mugilis Tang, 1981 (Aphanurinae) from mullet fish of Vietnam

Adult Aphanurus mugilis Tang, 1981 worms were detected in the intestine of Moolgarda engeli in the shallow waters off Cat Ba Island, Vietnam. Tang (1981) first described this species in Mugil cephalus off China. The worms in Vietnamese mullet were identical to Chinese specimens in a number of morphometric characteristics, with the exception of body and ovary size. In the present study, morphological characteristics, and the first molecular data for A. mugilis are provided. Additionally, molecular phylogenetic analysis of the family Hemiuridae was performed. The results of our molecular phylogenetic study indicate that the presence or absence of an ecsoma was not associated with molecular data for hemiurid subfamilies differentiation. The basal position of Bunocotylinae on the molecular-based phylogenetic tree indicated a primordial nature of ecsoma of hemiurid trematodes. Considerable molecular differentiation of Bunocotylinae from other hemiurids indicated the possibility of the recognition of the family Bunocotylidae Dollfus, 1950. Assuming that Machidatrema chilostoma is considered within the Bunocotylinae, the paraphyly of the Lecithasterinae was supported.

[Divergence of paralogous growth-hormone-encoding genes and their promoters in Salmonidae]

In many fish species, including salmonids, the growth-hormone is encoded by two duplicated paralogous genes, gh1 and gh2. Both genes were already in place at the time of divergence of species in this group. A comparison of the entire sequence of these genes of salmonids has shown that their conserved regions are associated with exons, while their most variable regions correspond to introns. Introns C and D include putative regulatory elements (sites Pit-1, CRE, and ERE), that are also conserved. In chars, the degree of polymorphism of gh2 gene is 2-3 times as large as that in gh1 gene. However, a comparison across all Salmonidae species would not extent this observation to other species. In both these chars' genes, the promoters are conserved mainly because they correspond to putative regulatory sequences (TATA box, binding sites for the pituitary transcription factor Pit-1 (F1-F4), CRE, GRE and RAR/RXR elements). The promoter of gh2 gene has a greater degree of polymorphism compared with gh1 gene promoter in all investigated species of salmonids. The observed differences in the rates of accumulation of changes in growth hormone encoding paralogs could be explained by differences in the intensity of selection.

[Fish growth-hormone genes: functionality evidence of paralogous genes in Levanidov's charr]

In the genome of most vertebrates growth-hormone gene is presented in a single copy, while in salmonids after one of the duplication events many genes were multiplied, including growth hormone gene. In salmonids, the growth-hormone gene exists as two independently inherited functional paralogues, gh1 and gh2. In this study, we performed a comparative analysis of gh1 and gh2 growth-hormone genes and their adjacent sequences in Levanidov's charr Salvelinus levanidovi to determine their functionality and define the potential differences. We found that both genes have the same gene structure and are composed of six exons (I-VI) and five introns (A, B, C, D, E). However, the respective gene sequences differ in length. A comparison of exons showed that the size of each exon is identical in both paralogues. The overall length of genes differs due to the varying lengths of introns. Coding sequence of both genes contains an open reading frame for 210 amino acids. We identified regulatory elements in the promoter region of both genes: TATA box, A/T-rich regions that contain binding sites for pituitary-specific transcriptional activator Pit-1, and regions responsible for interaction with other transcriptional activators and initiators, in particular hormone receptors. The obtained data indicate that both genes are functional.

[Molecular genetic characterization of the Far Eastern trematode Skrjabino lecithum spasskii Belous, 1954 (Digenea: Haploporidae)), a parasite of mullets]

Intraspecific genetic differentiation of the trematode Skrjabinolecithum spasskii and its phylogenetic relationships with other species of the family Haploporidae were studied by comparing the nucleotide sequences of a part of the 28S rRNA gene and the ITS1-5.8S-ITS2 rDNA region. Trematodes were isolated from so-iuy mullet Liza haematocheila fishes collected in rivers of Primorye and flathead grey mullet Mugil cephalus fishes collected in water bodies of Vietnam (27 fishes in total). A phylogenetic analysis showed that S. spasskii is close to species of the genus Capitimitta of the subfamily Waretrematinae. By intraspecific variation of rDNA sequences, trematodes were divided into three groups with tree different genotypes, which had fixed nucleotide substitutions. Genotype I was found in trematodes from fishes collected in Primorye. Genotype II was detected in trematodes from M. cephalus fishes collected in the Tonkin Bay, Cat Ba Island, Vietnam. Genotype III was found in five trematodes from L. haematocheila collected in the Kievka River, Primorye. The genetic distances between genotypes I and III from Primorye were 0.4 and 0.65% by 28S and ITS rDNA sequences, respectively. The lowest genetic distances were observed between genotypes II (Vietnam) and III (Primorye), 0.1 and 0.33% by 28S and ITS rDNA sequences, respectively. Possible causes of genetic differentiation of S. spasskii from different geographic locations and different definitive host species are discussed.

Life-cycle and genetic characterization of Astiotrema odhneri Bhalerao, 1936 sensu Cho & Seo 1977 from the Primorsky Region (Russian Far East)

Adult Astiotrema odhneri Bhalerao, 1936 sensu Cho & Seo 1977 were found in the intestine of a freshwater turtle, Pelodiscus sinensis (Wiegmann), from the Komissarovka River Basin, Primorsky Region, Russia. It was established that the first intermediate host of this parasite is a snail, Anisus centrifugops, and that the second intermediate hosts include the snails, Helicorbis sujfunensis and A. centrifugops, tadpoles of the frog Rana dybowskii, and the fish Perccottus glenii. The development of A. odhneri includes the formation of sporocyst and xiphidiocercariae, which is typical for species belonging to Plagiorchioidea. Phylogenetic analysis based on 28S rRNA gene sequences showed that A. odhneri, together with Astiotrema monticellii, form a monophyletic clade that was closer to Opisthorchioidea than to any other taxon represented in the tree. However, phylogenetic analysis without outgroup taxon indicated a high degree of differentiation of Astiotrema from both Plagiorchioidea and Opisthorchioidea.

THE FIRST RECORD OF DIMEROSACCUS ONCORHYNCHI (TREMATODA: OPECOELIDAE) IN FISHES FROM RIVERS OF PRIMORSKY TERRITORY, RUSSIA, WITH A DISCUSSION ON ITS TAXONOMIC POSITION USING MORPHOLOGICAL AND MOLECULAR DATA

The opecoelid trematode Dimerosaccus oncorhynchi (Eguchi, 1931) Shimazu, 1980, hitherto known only from the Japanese archipelago, has been found in three species of freshwater salmonid fish (Oncorhynchus masou, Brachymystax tumensis, Salvelinus curilus) from rivers of Primorsky Territory, the Sea of Japan basin, Russia. This is the first record of the parasite in the continental part of Asia. Fishes B. tumensis and S. curilus are new hosts for D. oncorhynchi. The ecological notes, morphological description and drawings of the found trematodes clarifying the morphology of the male reproductive system are given. In the present study phylogenetic relationships of the species D. oncorhynchi with the related taxa were revealed using partial sequences of the 28S rDNA. Obtained results indicate the validity of D. oncorhynchi as the member of the subfamily Opecoelinae, which was closely related to the genus Opecoeloides, a representative of this subfamily.

[Fish growth hormone genes: divergence of intron sequence in charrs of Salvelinus genus]

Sequences of the two large introns (C and D) from two paralogous growth hormone genes, GH1 and GH2, were compared in eight charr species of the Salvelinus genus (Osteichthes, Salmonidae). It was demonstrated that the rates of intron divergence in these two genes were remarkably different. Introns in the GH1 gene appeared to be more conservative, while the rate of intron variations was considerably higher in the GH2 gene. These data suggest that noncoding regions of nuclear genes are shaped by selective pressure. The lower congruence of phylogenetic scheme constructed based on an analysis of the GH1 introns compared to that based on the GH2 data, as well as with the traditional views on the evolution of charr species, also favors the supposition on contrasted patterns of selective pressure in noncoding intronic sequences.

[Molecular genetic evidences of a deep phylogenetic discontinuity between Asian and European races of pygmy wood mouse based on the data of mtDNA cytochrome b gene variability]

The variability of mitochondrial DNA (mtDNA) cytochrome b gene sequences of pygmy wood mouse Sylvaemus uralensis (Pallas, 1811) from local populations of European regions of Russia, West Siberia, and neighboring countries (Moldova, Kazakhstan, Uzbekistan, and Turkmenistan) have been studied. Phylogenetic analysis both our results and data from GenBank revealed two clusters of haplotypes: "western" with reliable subdivision into two sequence groups and "eastern" without valid differentiation. Clusters correspond exactly to European and Asian races of pygmy wood mouse recognized earlier on the basis of biochemical and karyological variability. We suppose that Asian race can be considered as independent allopatric species. This is supported by following evidences: high divergence level (which proposes more than 1 mya of divergent evolution) between races, absence of common haplotypes and hiatus between main peaks of mismatch distribution, differences in frequencies of codon usage, fixed nucleotide substitutions in cyt b gene, and also changes in amino acid sequences of cytochrome b. Only specimens of the western phylogenetic linage can be considered as S. uralensis (Pallas, 1811) while according to the first description S. tokmak (Severtzov, 1873) may be considered as species united specimens of eastern phylogenetic linage.

[Analysis of genetic variation and differentiation in the pygmy wood mouse Sylvaemus uralensis (Rodentia, Muridae) aided by RAPD-PCR method]

The present work ascertains distinct differentiation of the pygmy wood mouse into two groups of populations, which correspond to the European and Asian races, but can not, however, be considered valid species due to the low values of genetic distances between them. Neither of the used statistical methods explicitly verifies genetic isolation of the East-European and South-European chromosomal forms, which are close to one another and together constitute the European race. However, polymorphism of these chromosomal forms/races of the pygmy wood mouse differs each of them from the others, that can be explained both by the history of their formation (the degree of proximity to the ancestral population complex, isolation, etc.) and by unequal current environmental conditions.

[Genetic variation and differentiation in striped field mouse Apodemus agrarius inferred from RAPD-PCR analysis]

Genetic variation and differentiation of the trans-Palearctic species Apodemus agrarius (striped field mouse), whose range consists of two large isolates-European-Siberian and Far Eastern-Chinese, were examined using RAPD-PCR analysis. The material from the both parts of the range was examined (41 individual of A. agrarius from 18 localities of Russia, Ukraine, Moldova, and Kazakhstan); the Far-Eastern part was represented by samples from the Amur region, Khabarovsk krai, and Primorye (Russia). Differences in frequencies of polymorphic RAPD loci were found between the European-Siberian and the Far Eastern population groups of striped field mouse. No "fixed" differences between them in RAPD spectra were found, and none of the used statistical methods permitted to distinguish with absolute certainty animals from the two range parts. Thus, genetic isolation of the European-Siberian and the Far Eastern population groups of A. agrarius is not strict. These results support the hypothesis on recent dispersal of striped field mouse from East to West Palearctics (during the Holocene climatic optimum, 7000 to 4500 years ago) and subsequent disjunction of the species range (not earlier than 4000-4500 years ago). The Far Eastern population group is more polymorphic than the European-Siberian one, while genetic heterogeneity is more uniformly distributed within it. This is probably explained by both historical events that happened during the species dispersal in the past, and different environmental conditions for the species in different parts of its range. The Far Eastern population group inhabits the area close to the distribution center of A. agrarius. It is likely that this group preserved genetic variation of the formerly integral ancestral form, while some amount of genetic polymorphism could be lost during the species colonization of the Siberian and European areas. To date, the settlement density and population number in general are higher than within the European-Siberian isolate, which seems to account for closer interpopulation associations, intense genetic exchange, and "smoothing" of polymorphism within the Far Eastern population group of A. agrarius.