Morphology, genetic characterization and molecular phylogeny of pinworm Skrjabinema longicaudatum n. sp. (Oxyurida: Oxyuridae) from the endangered Tibetan antelope Pantholops hodgsonii (Abel) (Artiodactyla: Bovidae)

Abstract

Background: The Tibetan antelope Pantholops hodgsonii (Abel) (Artiodactyla: Bovidae) is an endangered species of mammal endemic to the Qinghai-Tibetan Plateau. Parasites and parasitic diseases are considered to be important threats in the conservation of the Tibetan antelope. However, our present knowledge of the composition of the parasites of the Tibetan antelope remains limited.

Methods: Large numbers of nematode parasites were collected from a dead Tibetan antelope. The morphology of these nematode specimens was observed using light and scanning electron microscopy. The nuclear and mitochondrial DNA sequences, i.e. small subunit ribosomal DNA (18S), large subunit ribosomal DNA (28S), internal transcribed spacer (ITS) and cytochrome c oxidase subunit 1 (cox1), were amplified and sequenced for molecular identification. Moreover, phylogenetic analyses were performed using maximum likelihood (ML) inference based on 28S and 18S + 28S + cox1 sequence data, respectively, in order to clarify the systematic status of these nematodes.

Results: Integrated morphological and genetic evidence reveals these nematode specimens to be a new species of pinworm Skrjabinema longicaudatum (Oxyurida: Oxyuridae). There was no intraspecific nucleotide variation between different individuals of S. longicaudatum n. sp. in the partial 18S, 28S, ITS and cox1 sequences. However, a high level of nucleotide divergence was revealed between the new species and its congeners in 28S (8.36%) and ITS (20.3-23.7%) regions, respectively. Molecular phylogenetic results suggest that the genus Skrjabinema should belong to the subfamily Oxyurinae (Oxyuroidea: Oxyuridae), instead of the subfamily Syphaciidae or Skrjabinemiinae in the traditional classification, as it formed a sister relationship to the genus Oxyuris.

Conclusions: A new species of pinworm Skrjabinema longicaudatum n. sp. (Oxyurida: Oxyuridae) is described. Skrjabinema longicaudatum n. sp. represents the first species of Oxyurida (pinworm) and the fourth nematode species reported from the Tibetan antelope. Our results contribute to the knowledge of the species diversity of parasites from the Tibetan antelope, and clarify the systematic position of the genus Skrjabinema.

Keywords: Genetic data; Morphology; Nematoda; Parasite; Phylogeny; Tibetan antelope.

Fig. 1

Skrjabinema longicaudatum n. sp. (Oxyurida: Oxyuridae) from the endangered Tibetan antelope Pantholops hodgsonii (Abel) (Artiodactyla: Bovidae) in China. a Anterior part of female, lateral view. b Cephalic extremity of female, apical view. c Anterior part of male, dorsal view. d Region of vulva, lateral view. e Spicule. f Posterior extremity of female, lateral view. g Posterior extremity of male (phasmids arrowed), ventral view. h Posterior extremity of male, lateral view. i Egg. Scale-bars: a, f, 500 μm; b, e, g, h, i, 50 μm; c, 100 μm; d, 200 μm

Fig. 2

Scanning electron micrographs of Skrjabinema longicaudatum n. sp. (Oxyurida: Oxyuridae) from the endangered Tibetan antelope Pantholops hodgsonii (Abel) (Artiodactyla: Bovidae) in China. a Anterior part of female (lateral ala and depressed region around excretory pore arrowed), lateral view. b Magnified image of depressed region and excretory pore (excretory pore arrowed). c Magnified image of the original position of lateral ala. d Anterior part of female (lateral alae arrowed), dorsal view. e Magnified image of transverse annulations in the anterior part of body. f Posterior extremity of female (anus arrowed), ventral view. g Magnified image of anus. h Magnified image of the ending position of caudal ala. i Magnified image of eggs in uterus in different views

Fig. 3

Scanning electron micrographs of Skrjabinema longicaudatum n. sp. (Oxyurida: Oxyuridae) from the endangered Tibetan antelope Pantholops hodgsonii (Abel) (Artiodactyla: Bovidae) in China. a Cephalic region of female, sub-apical view. b Cephalic region of female (amphidial pores arrowed), apical view. c Cephalic region of female, lateral view. d Cephalic region of male, apical view. e Magnified image of vulva. f Magnified image of egg, lateral view

Fig. 4

Maximum likelihood (ML) tree constructed from the partial 28S gene data showing the phylogenetic relationships of representatives of the family Oxyuridae. Pseudonymus spirotheca (Oxyurida: Pseudonymidae) was chosen as the outgroup

Fig. 5

Maximum likelihood (ML) tree constructed from the partial 18+28S+cox1 gene data showing the phylogenetic relationships of representatives of the family Oxyuridae. Pseudonymus spirotheca (Oxyurida: Pseudonymidae) was chosen as the outgroup