Ancient and modern genome shuffling: Reticulate mito-nuclear phylogeny of four related allopatric species of Gyrodactylus von Nordmann, 1832 (Monogenea: Gyrodactylidae), ectoparasites on the Eurasian minnow Phoxinus phoxinus (L.) (Cyprinidae)

Description of three new species of Gyrodactylus von Nordmann, 1832 (Monogenea: Gyrodactylidae) on bitterling fishes (Acheilognathinae) from China

Three new species of Gyrodactylus are described from three species of bitterling in Donghu Lake, China: Gyrodactylus ocellorhodei n. sp. from Rhodeus ocellatus; G. sinenorhodei n. sp. from Rhodeus sinensis; and G. acheilorhodei n. sp. from Acheilognathus macropterus. All the three new species showed similar opisthaptor morphology, especially the marginal hooks: all had a slender and perpendicular sickle shaft, and flat sickle base with distinct heel and inner arch which was different from the G. rhodei-group species parasitic on bitterling. Multivariate analyses based on hamulus and marginal hooks suggested that these three new species cannot be completely distinguished, despite some morphology divergence observed in certain less reliable morphometric features, such as hamulus root length, ventral bar total length and process shape. These three new species shared an identical 18S ribosomal RNA gene sequence, while the variation in the Internal Transcribed Spacers (ITS1-ITS2) sequence among them (8.4-11.2%, K2P) far exceeded the 1% ITS sequence difference that had been suggested as a threshold for species delimitation of Gyrodactylus. Phylogenetic analysis based on ITS1-ITS2 showed that all these sequenced Gyrodactylus spp. parasitic on the subfamily Acheilognathinae host formed a monophyletic group. However, a clear differentiation (18.9-20.9%, K2P of ITS1-ITS2) could be found between the subgroup from China (G. ocellorhodei n. sp., G. sinenorhodei n. sp. and G. acheilorhodei n. sp.) and that from Europe (G. rhodei).

Identification of a new species of Gyrodactylus von Nordmann, 1832 (Monogenoidea Gyrodactylidae) isolated from Diptychus maculatus in Yarkand River, Xinjiang, China

To investigate Gyrodactylus infection of fish in the river system of Xinjiang (China), Gyrodactylus individuals were isolated from specimens of Diptychus maculatus. Morphological characterization and phylogenetic analysis based on ITS1-5.8S-ITS2 rDNA locus revealed that the gyrodactylids belong to new species. Gyrodactylus diptychi n. sp. differs significantly in the morphology of the haptoral structures from 12 known species of Gyrodactylus found in fishes of the subfamily Schizothoracinae. In particular, G. diptychi n. sp. has a relatively short dorsal bar with thick and large ends, flat and straight hamuli roots, and small ventral bar processes. Furthermore, G. diptychi n. sp. is the only representative of Gyrodactylus found on D. maculatus. Using the BLASTn search of ITS1-5.8S-ITS2 rDNA sequences in GenBank and the Bayesian Information and Maximum Likelihood methods, we constructed phylogenetic trees for G. diptychi n. sp. As a result, our studies clearly identified that G. diptychi n. sp. was the first Gyrodactylus monogenean isolated from D. maculatus and a new species belonged to the subgenus Limnonephrotus.

Geography, phylogeny and host switch drive the coevolution of parasitic Gyrodactylus flatworms and their hosts

BACKGROUND

Gyrodactylus is a lineage of monogenean flatworm ectoparasites exhibiting many features that make them a suitable model to study the host-parasite coevolutionary dynamics. Previous coevolutionary studies of this lineage mainly relied on low-power datasets (a small number of samples and a single molecular marker) and (now) outdated algorithms.

METHODS

To investigate the coevolutionary relationship of gyrodactylids and their fish hosts in high resolution, we used complete mitogenomes (including two newly sequenced Gyrodactylus species), a large number of species in the single-gene dataset, and four different coevolutionary algorithms.

RESULTS

The overall coevolutionary fit between the parasites and hosts was consistently significant. Multiple indicators confirmed that gyrodactylids are generally highly host-specific parasites, but several species could parasitize either multiple (more than 5) or phylogenetically distant fish hosts. The molecular dating results indicated that gyrodactylids tend to evolve towards high host specificity. Speciation by host switch was identified as a more important speciation mode than co-speciation. Assuming that the ancestral host belonged to Cypriniformes, we inferred four major host switch events to non-Cypriniformes hosts (mostly Salmoniformes), all of which occurred deep in the evolutionary history. Despite their relative rarity, these events had strong macroevolutionary consequences for gyrodactylid diversity. For example, in our dataset, 57.28% of all studied gyrodactylids parasitized only non-Cypriniformes hosts, which implies that the evolutionary history of more than half of all included lineages could be traced back to these major host switch events. The geographical co-occurrence of fishes and gyrodactylids determined the host use by these gyrodactylids, and geography accounted for most of the phylogenetic signal in host use.

CONCLUSIONS

Our findings suggest that the coevolution of Gyrodactylus flatworms and their hosts is largely driven by geography, phylogeny, and host switches.

Morphological and genetic variability of the cryptic Gyrodactylus sphinx and Gyrodactylus gerasevi n. sp. (Platyhelminthes: Monogenea) from the Mediterranean Sea and Black Sea: two new members of the cross-ocean distributed Gyrodactylus orecchiae species group

Gyrodactylus sphinx Dmitrieva & Gerasev, 2000 is the only species of Gyrodactylus originally described from Aidablennius sphynx (Valenciennes) in the Black Sea. In the present study, monogeneans similar to G. sphinx are reported from the same host and from two other species of Blenniidae from the Black Sea, as well as from the Mediterranean Sea. This study aims to verify the taxonomic status of the specimens found in different hosts and localities, other than the type ones of G. sphinx. Twenty-two measurements of the haptoral structures of 169 gyrodactylids were used for the morphological study. Morphometric variability between different samples was analysed using analysis of variance, multivariate analysis of variance (MANOVA) and principal component analysis (PCA). Molecular studies were carried out using the nuclear internal transcribed spacer 2 and 5.8S ribosomal DNA regions. Network, Bayesian phylogenetic and species delimitation analyses were performed to infer the number of taxonomic units and the phylogeographic relationships occurring within and among them. MANOVA revealed a significant dependence of the morphometry of hamuli and marginal hooks on host species and regions, but a clear differentiation between samples was not confirmed by PCA. Moreover, the ranges of all dimensions overlapped between samples. However, molecular analyses suggested the occurrence of at least two taxonomic entities. The most common entity was present in individuals of the Black and Mediterranean seas, and is described here as Gyrodactylus gerasevi n. sp., whereas a second entity recognized as a G. sphinx was found only in individuals from two localities off Crimea. The monophyletic cluster grouping of these two species was placed within a large clade that also included a separate sister cluster with seven other species of the Gyrodactylus orecchiae cross-ocean species group.

Description of Gyrodactylus banmae n. sp. (Monogenea, Gyrodactylidae) parasitic on zebrafish, Danio rerio

A new species of Gyrodactylus was described on the body surface of zebrafish (Danio rerio) in China. Basing on morphological characteristics and ITS sequence, we identified the parasite as a new member of the Gyrodactylus-wageneri group. Morphologically, Gyrodactylus sp. nov. is greatly similar to "G. zebrae", another species parasitic on zebrafish: both have moderately stout hamulus, marginal hook sickle with a prominent heel and toe, as well as a curved blade. However, distinct haptoral shape differences were detected between these two species. The dorsal bar is straight in Gyrodactylus sp. nov. but strongly curved in "G. zebrae", and the sickle shaft in Gyrodactylus sp. nov. is approximately perpendicular to the base, but in "G. zebrae" it is slanted downwards. The ITS1-5.8S-ITS2 sequence also indicate that Gyrodactylus sp. nov. exhibits the highest similarity to "G. zebrae": 95.7% sequence identity suggests interspecific differentiation. Phylogenetic analysis of the ITS1-ITS2 sequence showed that Gyrodactylus sp. nov. formed a sister clade with "G. zebrae", and exhibited a relatively close phylogenetic relationship with G. kobayashii, G. gurleyi, and G. longoacuminatus, all of which parasitise on goldfish, Carassius auratus. To test the susceptibility of zebrafish and goldfish to the Gyrodactylus sp. nov., ten gyrodactylids were inoculated to the caudal fin of zebrafish and goldfish. The gyrodactylids exhibited the ability to attach themselves to the goldfish, and some gyrodactylids reproduced a few days after the inoculation. On day 9, however, the mean abundance sharply decreased to zero on goldfish and increased to more than 30 on zebrafish. The result suggested that golfish is an unsuitable host for Gyrodactylus sp. nov. Therefore, on the basis of morphology, molecular sequence similarity, and host susceptibility, we conclude that the gyrodactylid found on the zebrafish is a new species, which we named Gyrodactylus banmae.

A variant of Gyrodactylus mediotorus King, Marcogliese, Forest, McLaughlin and Bentzen, 2013 (Monogenea) identified from weed shiner (Notropis texanus) in Wisconsin portions of the upper Mississippi River

Gyrodactylus mediotorus King, Marcogliese, Forest, McLaughlin and Bentzen, 2013, previously described from the spottail shiner Notropis hudsonius (Clinton) in the St. Lawrence River, Quebec, was identified from weed shiner Notropis texanus (Girard) in Wisconsin. The parasite was primarily observed to infect the fins and, to a lesser extent, the skin. BLASTn searches of a 436 bp partial 18S rRNA gene and 1066 bp targeting the ITS region were highly similar (100%; 98.75%, respectively) to Canadian specimens of G. mediotorus. The slight genetic difference coupled with nearly identical morphology led us to conclude the Wisconsin specimens on weed shiner were a variant of G. mediotorus. This species also shares a prominent anteromedial knob on the ventral bar (and noticeable similarity in overall form of the haptoral hard parts and male copulatory organ) with G. campostomae Wellborn, 1967, G. laruei Kritsky and Mizelle, 1968, G. protuberus Rogers and Wellborn, 1965, G. rhinichthius Wood and Mizelle, 1957, G. spathulatus Mueller, 1936 and G. stunkardi Kritsky and Mizelle, 1968. It seems likely these knob-bearing species are members of a gyrodactylid lineage that has radiated among leuciscid and catostomid host fishes endemic to North America, although whether this knob is a shared or independent character remains unsolved.

Species delimitation of Gyrodactylus (Monogenea: Gyrodactylidae) infecting the southernmost cyprinids (Actinopterygii: Cyprinidae) in the New World

The genus Gyrodactylus von Nordmann, 1832 represents one of the most diverse and widespread taxa within Monogenea, with approximately 500 species described worldwide. Thirty-three species of Gyrodactylus have been recorded in Mexico, and in the last two decades, at least 26 new species have been described mainly from freshwater fish families such as poeciliids, goodeids, profundulids, characids, and cichlids. In this study, we describe two new species of Gyrodactylus infecting freshwater cyprinids based on morphological and molecular characteristics. Gyrodactylus ticuchi n. sp. and Gyrodactylus tobala n. sp. were recovered from Notropis moralesi de Buen and N. imeldae Cortés, respectively, captured in five localities from the State of Oaxaca, Mexico. The new species differ slightly from their congeners in the morphology of the haptoral hard parts and the male copulatory organ. Sequences of the Internal Transcribed Spacers rDNA (ITS1-5.8S-ITS2), cytochrome oxidase subunit I (cox1), and the D2 + D3 domains of the large subunit (28S rDNA) were obtained from multiple specimens and analyzed using Maximum Likelihood (ML) and Bayesian Inference (BI). Phylogenetic hypotheses using ITS rDNA, cox1, and 28S rDNA genes recovered two new species of Gyrodactylus from N. moralesi and N. imeldae; we briefly discuss their phylogenetic relationship with other congeners. These gyrodactylids represent the first species described in species of Notropis from southern Mexico, the cyprinids exhibiting the southernmost distribution in the New World.

Morphological and molecular studies of Eudiplozoon nipponicum (Goto, 1891) and Eudiplozoon kamegaii sp. n. (Monogenea; Diplozoidae)

Eudiplozoon nipponicum (Goto, 1891) Khotenovsky, 1985 (Monogenea: Diplozoidae), is known to parasitise Cyprinus carpio Linnaeus and species of Carassius. In this study, we conducted a taxonomic re-examination of E. nipponicum using genetic analysis and morphological comparisons from different host species from a single water system. rDNA nucleotide sequences of the internal transcription spacer 2 (ITS-2) region (645 bp) showed interspecific-level genetic differences among diplozoids from species of Carassius and C. carpio (p-distance: 3.1-4.0%) but no difference among those from different species of Carassius (0-0.4%) or between those from C. carpio collected in Asia and Europe (0-1.1%). Large variation was observed among 346 bp cytochrome c oxidase subunit I (COI) sequences (0.3-16.0 %); the topology of the phylogenetic tree showed no relationship to host genera or geographical regions of origin. Morphological observation showed that average clamp size of diplozoids from C. carpio was larger than those from Carassius spp. The number of folds on the hindbody was 10-25 for diplozoids from C. carpio and 12-19 for those from Carassius spp. Thus, our ITS-2 sequence and morphological comparison results indicate that diplozoids from C. carpio and species of Carassius belong to different species. The scientific name E. nipponicum should be applied to the species infected to the type host, Carassius sp. of Nakabo (2013) (Japanese name ginbuna). The diplozoid infecting C. carpio (Eurasian type) should be established as a new species: Eudiplozoon kamegaii sp. n. A neotype of E. nipponicum is designated in this report because the original E. nipponicum specimens are thought to have been lost.

Alien parasites on an alien fish species: monogeneans from the black bullhead Ameiurus melas (Siluriformes) in the Lake Srebarna Biosphere Reserve, Bulgaria, with the first record of Gyrodactylus nebulosus in the Palaearctic

Black bullhead Ameiurus melas (Actinopterygii: Siluriformes) is an alien fish species of North American origin, which has expanded its invasive geographical range in Europe. In 2017-2019, 32 black bullhead specimens from the Lake Srebarna Biosphere Reserve, Bulgaria, were examined for monogenean parasites. Two species of monogeneans were recorded and identified on the basis of morphological and molecular data: Ligictaluridus pricei (Ancyrocephalidae), with prevalence 100% and intensity 2-32 (mean 13.3 ± 6.8), and Gyrodactylus nebulosus (Gyrodactylidae), with prevalence 72.0% and intensity 1-15 (mean 7.4 ± 4.3). Partial 18S rDNA and the ITS1 region of L. pricei were sequenced. For G. nebulosus, sequenced genes included the partial 18S rDNA and the entire ITS1-5.8S rDNA-ITS2 region as well as the mitochondrial COI gene. Both recorded monogenean species are specific parasites of North American ictalurid fishes and alien to Europe. The present study is the first record of L. pricei from Bulgaria and the first record of G. nebulosus from Europe and the Palaearctic Region.

Revision of Gyrodactylus salaris phylogeny inspired by new evidence for Eemian crossing between lineages living on grayling in Baltic and White sea basins

In this research, grayling-specific Gyrodactylus salarisMalmberg, 1957 isolates from Baltic Sea basin were collected in Sweden for the first time. Samples were obtained in three drainage systems: Kalixälven (River Kaitum), Ljungan (River Sölvbacka strömmar), and Umeälven (River Juktån). Three molecular markers were analysed: nuclear ITS rDNA (Internal Transcribed Spacer) and ADNAM1 (Anonymous DNA Marker 1), and mitochondrial cox1 gene. As a result, four new mitochondrial haplotypes were identified (III-C1tt, III-C1tt_ht, IX-A1tt and X-A1tt). The ADNAM1 analyses resulted in revealing two new alleles (WS4 and BS9) and two new genotypes (T6 and T7). T7 seems to be an indicator of ancient crossing between Baltic and White Sea lineages of the parasite which happened during a first 3000-year period of Eemian interglacial about 130,000 years ago in the connection between Baltic and White Sea. Molecular clock estimates were adjusted, revealing the mean substitution rate and the divergence rate among branches of 3.6% (95% HPD: 2.2%–5.2%) and 7.2% per million years, respectively. As a result, cox1 phylogeny rooted with the introgressed haplotypes has been revised and altered in accordance to new data, revealing fourteen equidistant lineages five of which have been excluded from the study. Based on the new phylogenetic approach, including the molecular clock, this work suggests an overall revision of G. salaris phylogeny and attempts at precisely drawing the division of lineages within this polytypic species as well as proposes unification in nomenclature for its strains.