Description, biology and molecular characterisation of Serpentirhabdias moi n. sp. (Nematoda: Rhabdiasidae) from Chironius exoletus (Serpentes: Colubridae) in Brazil

Morphology, complete mitochondrial genome, and molecular phylogeny of Rhabdias macrocephalum n. sp. (Nematoda: Rhabdiasidae) from Diploderma splendidum (Reptilia: Agamidae)

Species of the genus Rhabdias Stiles & Hassall, 1905 are common parasitic nematodes occurring in the lungs of amphibians and reptiles worldwide. In the present study, Rhabdias macrocephalum n. sp. is described using integrated morphological methods (light and scanning electron microscopy) and molecular approaches (sequencing of the nuclear 28S and ITS regions, and mitochondrial cox1, cox2, and 12S genes) based on specimens collected from the green striped tree dragon Diploderma splendidum (Barbour & Dunn) (Reptilia: Agamidae) in China. The complete mitochondrial genome of R. macrocephalum n. sp. was sequenced and annotated: it is 14,819 bp in length, including 12 protein coding genes (missing atp8), 22 tRNA genes, 2 rRNA genes and three non-coding regions. The gene arrangement of R. macrocephalum n. sp. is different from all of the currently available mitogenomes of nematodes and represents a novel type of mitochondrial gene arrangement reported in Nematoda. Molecular phylogenetic results based on the ITS + 28S data support the monophyly of Entomelas, Pneumonema, Serpentirhabdias, and Rhabdias, and showed R. macrocephalum n. sp. forming a most basal lineage in Rhabdias.

Molecular phylogeny of the family Rhabdiasidae (Nematoda: Rhabditida), with morphology, genetic characterization and mitochondrial genomes of Rhabdias kafunata and R. bufonis

BACKGROUND

The family Rhabdiasidae (Nematoda: Rhabditida) is a globally distributed group of nematode parasites, with over 110 species parasitic mainly in amphibians and reptiles. However, the systematic position of the family Rhabdiasidae in the order Rhabditida remains unsolved, and the evolutionary relationships among its genera are still unclear. Moreover, the present knowledge of the mitochondrial genomes of rhabdiasids remains limited.

METHODS

Two rhabdiasid species: Rhabdias kafunata Sata, Takeuchi & Nakano, 2020 and R. bufonis (Schrank, 1788) collected from the Asiatic toad Bufo gargarizans Cantor (Amphibia: Anura) in China, were identified based on morphology (light and scanning electron microscopy) and molecular characterization (sequencing of the nuclear 28S and ITS regions and mitochondrial cox1 and 12S genes). The complete mitochondrial genomes of R. kafunata and R. bufonis were also sequenced and annotated for the first time. Moreover, phylogenetic analyses based on the amino acid sequences of 12 protein-coding genes (PCGs) of the mitochondrial genomes were performed to clarify the systematic position of the family Rhabdiasidae in the order Rhabditida using maximum likelihood (ML) and Bayesian inference (BI). The phylogenetic analyses based on the 28S + ITS sequences, were also inferred to assess the evolutionary relationships among the genera within Rhabdiasidae.

RESULTS

The detailed morphology of the cephalic structures, vulva and eggs in R. kafunata and R. bufonis was revealed using scanning electron microscopy (SEM) for the first time. The characterization of 28S and ITS regions of R. kafunata was reported for the first time. The mitogenomes of R. kafunata and R. bufonis are 15,437 bp and 15,128 bp long, respectively, and both contain 36 genes, including 12 PCGs (missing atp8). Comparative mitogenomics revealed that the gene arrangement of R. kafunata and R. bufonis is different from all of the currently available mitogenomes of nematodes. Phylogenetic analyses based on the ITS + 28S data showed Neoentomelas and Kurilonema as sister lineages, and supported the monophyly of Entomelas, Pneumonema, Serpentirhabdias and Rhabdias. Mitochondrial phylogenomic results supported Rhabdiasidae as a member of the superfamily Rhabditoidea in the suborder Rhabditina, and its occurrance as sister to the family Rhabditidae.

CONCLUSIONS

The complete mitochondrial genome of R. kafunata and R. bufonis were reported for the first time, and two new gene arrangements of mitogenomes in Nematoda were revealed. Mitogenomic phylogenetic results indicated that the family Rhabdiasidae is a member of Rhabditoidea in Rhabditina, and is closely related to Rhabditidae. Molecular phylogenies based on the ITS + 28S sequence data supported the validity of Kurilonema, and showed that Kurilonema is sister to Neoentomelas. The present phylogenetic results also indicated that the ancestors of rhabdiasids seem to have initially infected reptiles, then spreading to amphibians.

Serpentirhabdias mexicanus n. sp. (Nematoda: Rhabdiasidae), a parasitic lungworm of the nauyaca viper Bothrops asper (Serpentes: Viperidae) in the Mexican Neotropics

Serpentirhabdias mexicanus n. sp. (Nematoda: Rhabdiasidae) is described from the lung of the nauyaca viper Bothrops asper in Puebla State, central Mexico. This new species is the fifth of the genus described having onchia. Among the species included in this group, the new species is morphologically closest to S. viperidicus and S. atroxi. However, it differs from both species mainly by having only one excretory gland (compared to two present in S. viperidicus and S. atroxi). In addition, S. mexicanus n. sp. can be separated of S. viperidicus by tail length, shape of vulval lips, geographic distribution and host species and from S. atroxi by body length, number of papillae in the cephalic region, as well as the host species and geographic distribution. In the present study, we propose the new species based on morphological, host spectrum and genetic evidence. Phylogenetic analysis indicated Serpentirhabdias as a monophyletic group, with two subgroups that are congruent with the presence/absence of onchia in the esophagostome, host association and other relevant morphological characters.

A new species of Serpentirhabdias Tkach, Kuzmin et Snyder, 2014 (Nematoda: Rhabdiasidae) parasitic in the herald snake, Crotaphopeltis hotamboeia (Laurenti) (Reptilia: Serpentes: Colubridae) in South Africa

Serpentirhabdias mamlambo n. sp. is described from the lung of the herald snake, Crotaphopeltis hotamboeia (Laurenti) in KwaZulu-Natal Province, South Africa. The new species is characterised by the small lips, the absence of the buccal capsule, the large excretory glands (1.5-2.3 times longer than the oesophagus), and the numerous eggs in uteri. Serpentirhabdias mamlambo n. sp. differs from other Serpentirhabdias spp. in the presence of M-shaped cuticular folds on dorsal and ventral sides of apical surface, the eye-shaped internal labial papillae, and the distinct dilatation of the oesophagus at its mid-length. Morphological differentiation of S. mamlambo n. sp. from its congeners is supported by molecular evidence based on cox1 mitochondrial gene, and ITS and partial 28S region of nuclear rDNA. Serpentirhabdias mamlambo n. sp. is the first species of the genus Serpentirhabdias described from the Afrotropical Realm.

Description, molecular characterization and life cycle of Serpentirhabdias mussuranae n. sp. (Nematoda: Rhabdiasidae) from Clelia clelia (Reptilia: Colubroidea) in Brazil

Serpentirhabdias mussuranae n. sp. is described from the lungs of the mussurana, Clelia clelia (Daudin, 1803), from vicinities of Lábrea, Amazonas State, Brazil. The species is characterized by the triangular oral opening, the presence of teeth (onchia) in the oesophastome, the excretory glands longer than the oesophagus and the tail abruptly narrowing in its anterior half and gradually tapering in posterior half. Among the Neotropical representatives of the genus, three species are known to possess the onchia in the oesophastome: S. atroxi, S. moi and S. viperidicus. Serpentirhabdias mussuranae n. sp. differs from S. atroxi and S. viperidicus by its triangular shape of the oral opening and the oesophastome in apical view, vs. round in the latter two congeners. Additionally, S. viperidicus has a larger oesophastome, 13-22 micrometers wide and 13-23 micrometers deep. The new species has relatively longer excretory glands than S. moi. The new species is morphologically and genetically close to S. atroxi, S. moi and S. viperidicus, all parasitic in Brazilian snakes, based on the presence of onchia and the comparison of nucleotide sequences of nuclear ribosomal DNA and mitochondrial cox1 gene (differences varied between 3.8% and 7.1%). Data on the life cycle of S. mussuranae n. sp. is provided, and the life cycle is typical of the genus Serpentirhabdias, with the combination of direct development and heterogony. Free-living larval stages and the adults of amphimictic free-living generation are described. The results of molecular phylogenetic analysis based on nuclear ribosomal internal transcribed spacer (ITS) + partial 28S region and partial mitochondrial cox1 gene are provided.

Rhabdias glaurungi sp. nov. (Nematoda: Rhabdiasidae), parasite of Scinax gr. ruber (Laurenti, 1768) (Anura: Hylidae), from the Brazilian Amazon

The genus Rhabdias Stiles & Hassal, 1905 includes about 83 species of nematodes parasitic in amphibians and reptiles worldwide. Herein, we describe Rhabdias glaurungi sp. nov. from the hylid frog Scinax gr. ruber (Laurenti, 1768) in the Gunma Ecological Park, Santa Bárbara municipality, state of Pará, Brazil. This species has six small lips, an inflated cuticle along the entire body and a cup-shaped buccal capsule with smooth internal surface of its anterior part and irregularly folded internal surface of its posterior part in apical view. From the 17 valid species recognized in the Neotropical realm, the new species can be distinguished by the number of lips, the morphology and size of its buccal capsule, as well as the extent and shape of its cuticular inflation; in addition, there are molecular differences. Sequences of the mitochondrial Cytochrome c Oxidase subunit I gene strongly support the status of this form as a separate species. Molecular phylogenetic analysis shows R. glaurungi sp. nov. nested within the R. pseudosphaerocephala Kuzmin, Tkach & Brooks, 2007 species complex. Rhabdias glaurungi sp. nov. is the second species of the genus described from hosts of the family Hylidae in the Neotropical realm. We conclude that the diversity of Rhabdias within the Neotropics is likely largely underestimated.