The phylogenetic position of Anacanthorus (Monogenea, Dactylogyridae) parasitizing Brazilian serrasalmids (Characiformes)

Molecular identification of Mymarothecium viatorum and Anacanthorus penilabiatus in extensive native fish farming systems of the Peruvian Amazon

Piaractus brachypomus (Pacú) is the main native fish species cultivated in Peru and holds great potential for growth in aquaculture from the Peruvian Amazon. Between October 2021 and January 2022 in two fish producing farms in the Amazon region of San Martín in Peru, P. brachypomus individuals were examined for parasite evaluation. A total of 6366 monogeneans were isolated from the gills of 30 fish, revealing a prevalence of 100%, with an abundance and mean intensity of 212 parasites per fish. Monogeneans were morphologically identified as Mymarothecium viatorum and Anacanthorus penilabiatus. The genetic divergence in the 28S rDNA gene found among A. penilabiatus sequences was 0.1% and among Anacanthorus spp. it ranged from 0.9% to 7.5%. The genetic divergence found among the M. viatorum sequences was 0.3%. These finding represents the first molecular data of M. viatorum and A. penilabiatus in Peru using the 28S rDNA gene of these monogeneans. The new sequences obtained will contribute to future studies on the phylogenetic relationships among dactylogyrids. However, further research with a broader range of host-parasite samples and additional genetic markers is needed to clarify these relationships and provide stronger support for the phylogenetic positions.

Integrative Taxonomy of Urocleidoides spp. (Monogenoidea, Dactylogyridae) Parasites of Pseudanos trimaculatus (Characiformes: Anostomidae) from Eastern Amazon, Brazil

Two new species of Urocleidoides are described from the gills of Pseudanos trimaculatus (Characiformes: Anostomidae) from the coastal drainages of the Eastern Amazon, Brazil. Urocleidoides itabocaensis n. sp. is characterized by having a sclerotized, tubular, sigmoid male copulatory organ (MCO), a circular sclerotized tandem brim associated with the base of the MCO; an accessory piece articulated with the MCO, a V-shaped, divided into two subunits, distal subunit spoon-shaped; and a vaginal pore dextroventral with opening marginal. Urocleidoides omphalocleithrum n. sp. is characterized by presenting a C-shaped or sigmoid MCO; an accessory piece articulated with the MCO, L-shaped, divided into two subunits, distal subunit gutter-shaped; a vaginal pore dextroventral with opening marginal; and a ventral bar broadly V-shaped, with anteromedial projection. Molecular phylogenetic analysis based on partial 28S rDNA and COI mtDNA genes indicate that U. itabocaensis n. sp. and U. omphalocleithrum n. sp. are closely related and appear as a sister group to other Urocleidoides species (U. paradoxus, U. digitabulum and U. sinus) parasitizing anostomid fishes. This study represents the first record of monogenoids from the gills of P. trimaculatus for the Eastern Amazon.

Geographic range, distribution patterns and interactions of Monogenea Van Beneden 1858, with species of native host freshwater fishes from Brazil

This paper investigated information on monogenean species using 312 scientific papers, to search for infection and geographic distribution patterns in native freshwater fish from Brazil. We used 1,698 samples of 296 fish species of 28 families distributed into Characiformes, Siluriformes, Cichliformes, Gymnotiformes, Perciformes, Mugiliformes, Osteoglossiformes and Clupeiformes, in addition to four hybrid fish. Among the hosts of the different orders and families, the greatest numbers of parasite-host associations were found for species of the families Serrasalmidae, Characidae, Loricariidae, Curimatidae and Anostomidae. The 578 species of monogeneans used in parasite-host interactions were distributed in 86 genera of six five families (Dactylogyridae, Gyrodactylidae, Diplectanidae, Microcotylidae, Ancylodiscoididae and Ancyrocephalidae), but with great predominance of Dactylogyridae species. There was variation in prevalence, intensity and abundance levels of monogeneans species among host fish species, as well as in infection sites that occurred predominantly in external organs. Positive correlations of prevalence, intensity and abundance with body length of hosts were observed. There was geographic distribution pattern of monogeneans limited mostly to two hydrographic basins those being the Amazon River and Paraná River. Just approximately 6% of potential monogeneans have been explored thus far, showing a clear need for further studies on this interesting group of parasites.

Molecular phylogeny of Cosmetocleithrum Kritsky, Thatcher & Boeger, 1986 (Monogenoidea: Dactylogyridae), gill parasites of Neotropical catfishes (Siluriformes)

Cosmetocleithrum Kritsky, Thatcher & Boeger, 1986 (Dactylogyridae) represents one of the most species-rich groups (22 species currently recognized as valid) of all dactylogyrid parasites infecting Neotropical catfishes. Species of Cosmetocleithrum exhibit a remarkable affinity towards catfishes of the Doradidae and the Auchenipteridae. However, phylogenetic relationships between members of this genus have not been yet analysed. This study analysed newly obtained partial sequences of the 28S ribosomal RNA gene of seven species of Cosmetocleithrum, including its type species C. gussevi Kritsky, Thatcher & Boeger, 1986, along with several other dactylogyrids infecting siluriform, gymnotiform, perciform and characiform fishes. Cosmetocleithrum appeared as an evolutionary recent group, composed of two well-defined lineages: lineage 1 includes parasites of doradids - namely, C. bulbocirrus, C. confusum, C. parvum and C. bifurcum - whereas lineage 2 is composed of species from doradids - that is, C. rarum, C. gussevi, C. gigas, C. trachydorasi and C. falsunilatum - together with parasites of auchenipterids - namely, C. laciniatum and C. baculum. The search for synapomorphies to characterize taxonomic groups within Cosmetocleithrum appears challenging, since the morphology of their haptoral elements is quite conservative, and that of the copulatory complex is highly variable between species. The results of the present study support the recent synonymization of Paracosmetocleithrum Acosta, Scholz, Blasco-Costa, Alves & Silva, 2018 with Cosmetocleithrum. Whereas the 28S ribosomal DNA data resolved Cosmetocleithrum as monophyletic, the statistical support for the lineage was low, rendering its phylogenetic position between other Neotropical dactylogyrids yet undefined.

Dactylogyridae 2022: a meta-analysis of phylogenetic studies and generic diagnoses of parasitic flatworms using published genetic and morphological data

Dactylogyridae is one of the most studied families of parasitic flatworms with more than 1000 species and 166 genera described to date including ecto- and endoparasites. Dactylogyrid monogeneans were suggested as model organisms for host-parasite macroevolutionary and biogeographical studies due to the scientific and economic importance of some of their host lineages. Consequently, an array of phylogenetic research into different dactylogyrid lineages has been produced over the past years but the last family-wide study was published 16 years ago. Here, we provide a meta-analysis of the phylogenetic relationships of Dactylogyridae including representatives of all genera with available molecular data (n=67). First, we investigate the systematic informativeness of morphological characters widely used to diagnose dactylogyrid genera through a parsimony analysis of the characters, character mapping, and phylogenetic comparative methods. Second, we provide an overview of the current state of the systematics of the family and its subfamilies, and summarise potentially poly- and paraphyletic genera. Third, we elaborate on the implications of taxonomic, citation, and confirmation bias in past studies. Fourth, we discuss host range, biogeographical, and freshwater-marine patterns. We found two well-supported macroclades which we assigned to the subfamilies Dactylogyrinae and Ancyrocephalinae. These subfamilies further include 16 well-supported clades with only a few synapomorphies that could be deduced from generic diagnoses in the literature. Furthermore, few morphological characters considered systematically informative at the genus level display a strong phylogenetic signal. However, the parsimony analysis suggests that these characters provide little information on the relationships between genera. We conclude that a strong taxonomic bias and low coverage of DNA sequences and regions limit knowledge on morphological and biogeographical evolutionary patterns that can be inferred from these results. We propose addressing potential citation and confirmation biases through a 'level playing field' multiple sequence alignment as provided by this study.