Morphology and genetic characterization of Physaloptera sibirica Petrow & Gorbunov, 1931 (Spirurida: Physalopteridae), from the hog-badger Arctonyx collaris Cuvier (Carnivora: Mustelidae), with molecular phylogeny of Physalopteridae
Authors: Chen Hui-Xia , Zeng Jia-Lu , Gao Yun-Yun , Zhang Dong , Li Yang , Li Liang 
Published: July 2023

Background

Nematodes of the family Physalopteridae (Spirurida: Physalopteroidea) commonly parasitize the alimentary canal of all major vertebrate groups. However, many physalopterid species are not adequately described, especially regarding the detailed morphology of the cephalic end. The current genetic database forPhysalopteraspecies is still very limited, which seriously hampers molecular-based species identification. Additionally, the systematic status of some genera and the evolutionary relationships of the subfamilies in the Physalopteridae remain under debate.

Methods

New morphological data forPhysaloptera sibiricawas gathered using light and scanning electron microscopy based on newly collected specimens from the hog badgerArctonyx collarisCuvier (Carnivora: Mustelidae) in China. Six different genetic markers, including nuclear small ribosomal DNA (18S), large ribosomal DNA (28S) and internal transcribed spacer (ITS), mitochondrial cytochrome c oxidase subunit 1 (cox1) and subunit 2 (cox2), and the 12S small subunit ribosomal RNA gene ofP. sibiricawere sequenced and analyzed for the first time to our knowledge. Additionally, to construct a basic molecular phylogenetic framework for the Physalopteridae, phylogenetic analyses were performed based on thecox1 and 18S + cox1 genes using maximum likelihood (ML) and Bayesian inference (BI) methods.

Results

Scanning electron microscopy (SEM) observation displayed the details of the cephalic structures, deirids, excretory pore, caudal papillae, vulva, phasmids and egg ofP. sibiricafor the first time to our knowledge. Pairwise comparison of the sequences obtained forP. sibiricadid not reveal intraspecific divergence regarding the 18S, 28S,cox1 and 12S genetic markers and a low level of divergence in the ITS (0.16%) andcox2 (2.39%) regions. Maximum likelihood and Bayesian inference analyses showed that the representatives of Physalopteridae formed two major clades (species of Physalopterinae + Thubunaeinae parasitic in terrestrial vertebrates and Proleptinae only occurring in marine or freshwater fishes).Turgida turgidawas found nested among representatives ofPhysaloptera.Physaloptera sibiricaclustered together withP. rara. Physalopteroidessp. (Thubunaeinae) formed a sister relationship to the physalopterineAbbreviata caucasica.

Conclusions

Physaloptera sibiricawas redescribed, which is the fourth nematode parasite reported from the hog badgerA. collaris, andA. collarisrepresents a new host forP. sibirica. The phylogenetic results challenged the validity of the subfamily Thubunaeinae and of the genusTurgidaand supported dividing the family Physalopteridae into two subfamilies, Physalopterinae and Proleptinae. However, we do not make any immediate systematic changes in the Physalopteridae, because a more rigorous study with broader representation of the Physalopteridae is required. These present findings contribute to morphologically identifyingP. sibiricamore accurately and provide new insights into the systematics of the Physalopteridae.

Graphical Abstract