Integrated evidence reveals a new species of Cosmocerca (Ascaridomorpha: Cosmocercoidea) from the Asiatic toad Bufo gargarizans Cantor (Amphibia: Anura)

Cosmocerca goroensis n. sp. (Nematoda: Cosmocercidae) from South Africa and its phylogenetic relationships with other cosmocercids based on partial 28S sequences

Nematodes of the genus Cosmocerca are commonly found in various amphibians in South Africa and in most cases are identified as C. ornata. However, after detailed morphological studies and molecular approaches, three new species of the genus were recently described from three different frogs in South Africa. In present study, we describe another new species - Cosmocerca goroensis parasitising the Northern Pygmy Toad Poyntonophrynus fenoulheti in Soutpansberg mountains, Limpopo province, South Africa. The new species is characterised by prominent sex dimorphism, wide lateral alae, numerous somatic papillae in both sexes, and wide triangularly shaped gubernaculum and simple prominent spicules in males. Cosmocerca goroensis n. sp. distinguished from congeners, previously reported in Southern Africa by the shape of the gubernaculum and arrangement of somatic papillae in males. Morphological differences were confirmed by molecular analysis based on fragments of the 28S gene. Phylogenetic analysis based on the 28S gene fragments, including C. goroensis n. sp. and newly obtained sequence of C. ornata from Pelophylax lessonae from Ukraine, supported previously known data of closer relationships between species of Cosmocerca and Aplectana and more distant with Cosmocercoides spp.

Austraplectana extranes sp. n. (Nematoda: Cosmocercoidea) from Australian amphibians Mixophyes carbinensis Mahony, Donnellan, Richards & McDonald (Anura: Myobatrachidae) and Rhinella marina (Linnaeus) (Anura: Bufonidae)

The genus Austraplectana Baker, 1981 is a poorly known group of cosmocercoid nematodes. In the present study, a new species of Austraplectana, A. extranes sp. n., was described using both light and scanning electron microscopy, based on specimens collected from the carbine barred frog Mixophyes carbinensis Mahony, Donnellan, Richards & McDonald (Anura: Myobatrachidae) and the cane toad Rhinella marina (Linnaeus) (Anura: Bufonidae) in Australia. Austraplectana extranes sp. n. can be easily distinguished from its congener by the much longer and different morphology of tails in both sexes, the different number and arrangement of caudal papillae, the presence of single precloacal median heart-shaped papilla and large posterior protuberance with cuticular comb-like fringe in male.

Molecular data reveal a new species of Seuratascaris Sprent, 1985 (Nematoda: Ascaridoidea) from Quasipaa exilispinosa (Liu & Hu) (Amphibia: Anura)

The genus Seuratascaris Sprent, 1985 is a group of obligate nematode parasites of amphibians. In the present study, a new species of Seuratascaris, S. physalis sp. n. was described using light and scanning electron microscopy based on specimens collected from Quasipaa exilispinosa (Liu & Hu) (Amphibia: Anura) in China. The new species differs from S. numidica (Seurat, 1917) by the cuticle of the cervical region distinctly inflated to form a cephalic vesicle-like structure and the absence of single medio-ventral precloacal papilla. The molecular characterization of the nuclear large ribosomal DNA (28S) and internal transcribed spacer (ITS) and the mitochondrial cytochrome c oxidase subunit 1 (cox1), cytochrome c oxidase subunit 2 (cox2) and 12S small subunit ribosomal RNA gene of S. physalis sp. n., together with the 28S, cox2 and 12S of S. numidica are provided for the first time. Molecular analysis revealed the presence of high level of interspecific genetic variation between the two species in the ITS (5.50%), cox1 (13.3%), cox2 (10.6%) and 12S regions (10.5%), which strongly supported that S. physalis sp. n. represented a different species from S. numidica. Angusticaecum ranae Wang, Zhao & Chen, 1978 reported from the frog Quasipaa spinosa (David) (Anura: Dicroglossidae) in China was transferred into the genus Seuratascaris as S. ranae (Wang, Zhao & Chen, 1978) comb. n. based on the morphology of lips and the presence of very short and robust spicules without alae and small numbers of precloacal papillae. The present study provided useful genetic data for molecular identification of species of Seuratascaris and provides the foundation for being able to determine if S. numidica represents a species complex of some sibling species or a single species.

The first genome assembly of the amphibian nematode parasite (Aplectana chamaeleonis)

Cosmocercoid nematodes are common parasites of the digestive tract of amphibians. Genomic resources are important for understanding the evolution of a species and the molecular mechanisms of parasite adaptation. So far, no genome resource of Cosmocercoid has been reported. In 2020, a massive Cosmocercoid infection was found in the small intestine of a toad, causing severe intestinal blockage. We morphologically identified this parasite as A. chamaeleonis. Here, we report the first A. chamaeleonis genome with a genome size of 1.04 Gb. The repeat content of this A. chamaeleonis genome is 72.45%, and the total length is 751 Mb. This resource is fundamental for understanding the evolution of Cosmocercoid and provides the molecular basis for Cosmocercoid infection and control.

Morphological and molecular characterization of Cosmocercoides amapari n. sp. (Nematoda: Cosmocercidae), parasitic in hylid frogs from the Brazilian Amazon

Cosmocercoides Wilkie, 1930 are gastrointestinal parasites commonly found in amphibians and reptiles, with 4 species reported from the Neotropical region. In the present study, a new species of Cosmocercoides, namely Cosmocercoides amapari n. sp. is described using integrated approaches such as light and scanning microscopy, and DNA sequencing of the mitochondrial cytochrome c oxidase subunit 1 gene. The specimens were collected from the large intestine of 3 species of hylid frogs in Amapá, Brazil. The new species can be distinguished from its congeners by morphological traits, including the pattern of caudal papillae, absence of the gubernaculum, 2 poorly sclerotized spicules, presence of lateral alae and somatic papillae along the body. In addition, our molecular analyses and phylogenetic reconstructions strongly support the status of the new taxon, which clustered poorly with a large clade of Cosmocerca spp. Cosmocercoides amapari n. sp. is the 29th species of the genus, the 5th from the Neotropical region, the third reported in Brazil, the second described from the Amazon region and the first belonging to the Neotropical region with molecular data.

First molecular assessment on Cosmocerca spp. from Brazilian anurans and description of a new species of Cosmocerca (Ascaridomorpha: Cosmocercoidea) from the white-spotted humming frog Chiasmocleis albopunctata (Boettger, 1885) (Anura: Microhylidae)

Cosmocerca spp. are common nematode parasites of amphibians. We provide herein molecular data for two species of Cosmocerca and describe a new species, Cosmocerca albopunctata n. sp., using light microscopy and molecular data (cytochrome c oxidase subunit 1 - COI mtDNA). Cosmocerca albopunctata n. sp. can be easily distinguished from other congeneric species by the combination of characteristics such as body size, length of spicules and gubernaculum, and the arrangements and number of caudal papillae (7 + 1:1 + 1:6). The phylogenetic results based on the partial COI mtDNA sequences clustered the new species in a monophyletic clade along with the other sequences of Cosmocerca spp. Therefore, our results contribute to the knowledge about the species diversity and genetic data for Cosmocerca spp. in the Neotropical region.

Morphology, genetic characterization and molecular phylogeny of the poorly known nematode parasite Cissophyllus leytensis Tubangui & Villaamil, 1933 (Nematoda: Ascaridida) from the Philippine sailfin lizard Hydrosaurus pustulatus (Eschscholtz, 1829) (Reptilia: Squamata)

Background

The genus Cissophyllus (Cosmocercoidea: Kathlaniidae) is a rare group of nematodes parasitic in turtles and lizards. To date, only four species have been reported in Asia and North America. However, most of them are inadequately described. The species Cissophyllus leytensis has never been reported since it was originally described by Tubangui and Villaamil in 1933 from the Philippine sailfin lizard Hydrosaurus pustulatus (Eschscholtz, 1829) (Reptilia: Squamata). Furthermore, the systematic status of Cissophyllus/Cissophyllinae in the family Kathlaniidae of the superfamily Cosmocercoidea remains under debate.

Methods

The detailed morphology of C. leytensis was studied using light microscopy (LM) and, for the first time, scanning electron microscopy (SEM), based on newly collected specimens from the type host H. pustulatus. Six different genetic markers, including nuclear sequences [small ribosomal subunit (18S), internal transcribed spacer (ITS) and large ribosomal subunit (28S)], plus mitochondrial genes [cytochrome c oxidase subunit 1 (cox1), cytochrome c oxidase subunit 2 (cox2) and 12S small subunit ribosomal RNA gene] of C. leytensis were sequenced. Additionally, in order to test the validity of the subfamily Cissophyllinae and clarify the phylogenetic relationships of Cissophyllus and the other genera in the family Kathlaniidae, phylogenetic analyses based on 18S + 28S and ITS sequence data were performed using maximum likelihood (ML) and Bayesian inference (BI) analyses, respectively.

Results

Our observations using LM and SEM revealed some previously unreported morphological features, necessitating the redescription of this poorly known species. The presence of remarkable morphological variation in the isthmus and the position of excretory pore among different individuals was found. Molecular analysis showed no intraspecific nucleotide divergence detected in the 18S, ITS, 28S, cox2 and 12S regions among different individuals of C. leytensis, but a low level of intraspecific genetic variation was found in the cox1 (0.52%). Our phylogenetic results showed the representatives of the Cosmocercoidea divided into four large clades (Cosmocerca + Aplectana + Cosmocercoides representing the family Cosmocercidae, Cruzia representing the subfamily Cruzinae of Kathlaniidae, Falcaustra + Cissophyllus + Megalobatrachonema representing the subfamily Kathlaniinae of Kathlaniidae, and Orientatractis + Rondonia representing the family Atractidae). The genus Cissophyllus clustered together with the genus Megalobatrachonema in both the ML and BI trees using ITS sequence data, but displayed a sister relationship to the genus Falcaustra in the ML tree and to the genera Falcaustra + Megalobatrachonema in the BI tree using 18S + 28S sequence data.

Conclusions

Molecular phylogenetic results further confirmed that the family Kathlaniidae is not a monophyletic group. The subfamily Cruziinae should be moved from the hitherto-defined family Kathlaniidae and elevated as a separate family Cruziidae. The present phylogenetic results also negated the validity of the subfamily Cissophyllinae and supported the genus Cissophyllus assigned in the subfamily Kathlaniinae. Molecular analysis indicated that the morphological variation in the isthmus and position of excretory pore among different individuals should be considered as intraspecific variation. Moreover, some characters important for the specific diagnosis of C. leytensis are reported for the first time: the number of acuminate denticles (lamellae) on each lip, the chitinized pharynx with three flabellate pharyngeal plates, the presence of single medioventral precloacal papilla and the detailed morphology of caudal papillae. The present study is only the second record of C. leytensis.

Graphical Abstract

Three new species of Cosmocerca Diesing, 1861 (Nematoda: Cosmocercidae) parasitising frogs Cacosternum boettgeri Boulenger, 1882, Kassina senegalensis Dumeril and Bibron, 1841 and Phrynomantis bifasciatus Smith, 1847 from South Africa

Cosmocercid nematodes have been documented with much criticism due to the numerous inaccurate descriptions, redescriptions and synonymisation of found species. This is due to indistinguishable characters of females and the lack of male specimens found. Consequently, the species C. ornata is the most commonly found species worldwide and the only species of the genus reported in South Africa. In the present study, we found Cosmocerca in three different amphibian species, namely Cacosternum boettgeri, Kassina senegalensis and Phrynomantis bifasciatus. Based on differences in the shape of the gubernaculum and number of papillae, the found nematodes were assigned to three new species namely C. daly n. sp., C. monicae n. sp. and C. makhadoensis n. sp. Descriptions of species are followed by pairwise and phylogenetic analysis of partial ITS-28S sequences. All three species were found only in their host types from distant localities. Therefore, we hypothesise that host specificity of Cosmocerca from South African amphibians might be rather high and that the presence of C. ornata throughout South Africa is rather doubtful.

Morphology, genetic characterization and phylogeny of Aplectana dayaoshanensis n. sp. (Nematoda: Ascaridida) from frogs

Cosmocercoid nematodes are common parasites in the digestive tract of amphibians. However, our knowledge of the species diversity, genetic data and molecular phylogeny of the superfamily Cosmocercoidea are far from being well understood. In the present study, large numbers of cosmocercoid nematodes were collected from the fine-spined frog Sylvirana spinulosa (Smith) (Anura: Ranidae) and the white-spotted thigh tree-frog Polypedates megacephalus (Hallowell) (Anura: Rhacophoridae) in Guangxi Province, China. Integrated morphological and genetic evidence reveals these nematode specimens to be a new species of the genus Aplectana, A. dayaoshanensis n. sp. (Cosmocercoidea: Cosmocercidae). The molecular characterization of small ribosomal DNA (18S), internal transcribed spacer (ITS) and large ribosomal DNA (28S) of A. dayaoshanensis n. sp., together with the 28S of A. chamaeleonis (Baylis, 1929) (collected from Hyperolius kivuensis Ahl in Rwanda), were reported for the first time. Moreover, phylogenetic analyses using maximum likelihood (ML) inference based on 18S + 28S and ITS sequence data, respectively, both supported the family Cosmocercidae to be a monophyletic group and the family Kathlaniidae to be a paraphyletic group. Our phylogenetic results rejected the monophyly of the genus Aplectana. The present results contribute to the knowledge of the species diversity and genetic data of cosmocercoid nematodes, and preliminarily revealed the phylogenetic relationships of the major families and some genera in the Cosmocercoidea.

Taxonomic assessment of the genus Procamallanus (Nematoda) in Middle American cichlids (Osteichthyes) with molecular data, and the description of a new species from Nicaragua and Costa Rica

Procamallanus is a species-rich genus of parasitic nematodes of marine, brackish, and freshwater fishes, occurring also occasionally in amphibians and reptiles. In the Neotropical region, this genus is highly diverse, with species described from a wide range of fish families. In this study, we reassess the taxonomic status of Procamallanus rebecae with molecular and morphological data and describe a new species endemic to Nicaragua and Costa Rica. We analyzed all Procamallanus isolated from fish from the Nicaraguan lakes and some rivers in Costa Rica after an exhaustive analysis of their freshwater fish endoparasite fauna. Procamallanus rebecae is a host-specific parasite of Middle American cichlids, previously reported in southern Mexico, Nicaragua, and Costa Rica. We therefore compared these Central American specimens with individuals of P. rebecae collected in cichlids from southeastern Mexico using two genomic regions (28S rDNA and mitochondrial cytochrome oxidase subunit 1, COI). We found high levels of sequence divergence between Procamallanus from the two geographical regions, with up to 9.8 and 10.5% for both genetic markers, respectively. We also analyzed their morphology and found conspicuous differences in the shape of the mouth and the structure of the female cauda. We therefore describe the specimens of Procamallanus from Central American cichlids as a new species. Both Procamallanus species occur in different cichlid species and are allopatrically distributed. The host specificity and ancient association patterns between cichlids and Procamallanus and the jointly colonization of both hosts and parasites during their northern dispersal from South America are briefly discussed.

Description of a new species of Aplectana (Nematoda: Ascaridomorpha: Cosmocercidae) using an integrative approach and preliminary phylogenetic study of Cosmocercidae and related taxa

BACKGROUND

Nematodes of the family Cosmocercidae (Ascaridomorpha: Cosmocercoidea) are mainly parasitic in the digestive tract of various amphibians and reptiles worldwide. However, our knowledge of the molecular phylogeny of the Cosmocercidae is still far from comprehensive. The phylogenetic relationships between Cosmocercidae and the other two families, Atractidae and Kathlaniidae, in the superfamily Cosmocercoidea are still under debate. Moreover, the systematic position of some genera within Cosmocercidae remains unclear.

METHODS

Nematodes collected from Polypedates megacephalus (Hallowell) (Anura: Rhacophoridae) were identified using morphological (light and scanning electron microscopy) and molecular methods [sequencing the small ribosomal DNA (18S), internal transcribed spacer 1 (ITS-1), large ribosomal DNA (28S) and mitochondrial cytochrome c oxidase subunit 1 (cox1) target regions]. Phylogenetic analyses of cosmocercoid nematodes using 18S + 28S sequence data were performed to clarify the phylogenetic relationships of the Cosmocercidae, Atractidae and Kathlaniidae in the Cosmocercoidea and the systematic position of the genus Aplectana in Cosmocercidae.

RESULTS

Morphological and genetic evidence supported the hypothesis that the nematode specimens collected from P. megacephalus represent a new species of Aplectana (Cosmocercoidea: Cosmocercidae). Our phylogenetic results revealed that the Cosmocercidae is a monophyletic group, but not the basal group in Cosmocercoidea as in the traditional classification. The Kathlaniidae is a paraphyletic group because the subfamily Cruziinae within Kathlaniidae (including only the genus Cruzia) formed a seperate lineage. Phylogenetic analyses also showed that the genus Aplectana has a closer relationship to the genus Cosmocerca in Cosmocercidae.

CONCLUSIONS

Our phylogenetic results suggested that the subfamily Cruziinae should be moved from the hitherto-defined family Kathlaniidae and elevated as a separate family, and the genus Cosmocerca is closely related to the genus Aplectana in the family Cosmocercidae. The present study provided a basic molecular phylogenetic framework for the superfamily Cosmocercoidea based on 18S + 28S sequence data for the first time to our knowledge. Moreover, a new species, A. xishuangbannaensis n. sp., was described using integrative approach.