Phylogenetic relationships of the nematode subfamily Phascolostrongylinae from macropodid and vombatid marsupials inferred using mitochondrial protein sequence data

Abstract

Background: The subfamily Phascolostrongylinae (Superfamily Strongyloidea) comprises nematodes that are parasitic in the gastrointestinal tracts of macropodid (Family Macropodidae) and vombatid (Family Vombatidae) marsupials. Currently, nine genera and 20 species have been attributed to the subfamily Phascolostrongylinae. Previous studies using sequence data sets for the internal transcribed spacers (ITS) of nuclear ribosomal DNA showed conflicting topologies between the Phascolostrongylinae and related subfamilies. Therefore, the aim of this study was to validate the phylogenetic relationships within the Phascolostrongylinae and its relationship with the families Chabertiidae and Strongylidae using mitochondrial amino acid sequences.

Methods: The sequences of all 12 mitochondrial protein-coding genes were obtained by next-generation sequencing of individual adult nematodes (n = 8) representing members of the Phascolostrongylinae. These sequences were conceptually translated and the phylogenetic relationships within the Phascolostrongylinae and its relationship with the families Chabertiidae and Strongylidae were inferred from aligned, concatenated amino acid sequence data sets.

Results: Within the Phascolostrongylinae, the wombat-specific genera grouped separately from the genera occurring in macropods. Two of the phascolostrongyline tribes were monophyletic, including Phascolostrongylinea and Hypodontinea, whereas the tribe Macropostrongyloidinea was paraphyletic. The tribe Phascolostrongylinea occurring in wombats was closely related to Oesophagostomum spp., also from the family Chabertiidae, which formed a sister relationship with the Phascolostrongylinae.

Conclusion: The current phylogenetic relationship within the subfamily Phascolostrongylinae supports findings from a previous study based on ITS sequence data. This study contributes also to the understanding of the phylogenetic position of the subfamily Phascolostrongylinae within the Chabertiidae. Future studies investigating the relationships between the Phascolostrongylinae and Cloacininae from macropodid marsupials may advance our knowledge of the phylogeny of strongyloid nematodes in marsupials.

Keywords: Macropodid marsupials; Mitochondrial DNA; Phascolostrongylinae; Vombatid marsupials.

Fig. 1

Nucleotide diversity (Pi) across 12 concatenated mitochondrial protein-coding genes (y-axis) of eight genera of Phascolostrongylinae, two genera of Strongylidae and one genus each of Oesophagostominae, Chabertiinae and Syngamidae. Nucleotide diversity was calculated in DnaSP version 6 software using a window of 100 bp and 25-bp steps. The nucleotide position (base pairs) is indicated on the x-axis next to the boundaries between mitochondrial protein-coding genes. CO1 – 3 = Cytochrome c oxidase subunit 1 – 3; ND1 – 6, 4L = Nicotinamide adenine dinucleotide hydrogen dehydrogenase subunits 1 – 6 and 4L; ATP6 = Adenosine triphosphate synthase subunit 6; COB = Cytochrome B

Fig. 2

Topology of the Bayesian inference phylogenetic analyses inferred from the concatenated alignment of 12 mitochondrial protein-coding genes of the genera of Phascolostrongylinae, Oesophagostominae, Chabertiinae (Chabertiidae) and Strongylidae. Nodal support is indicated as posterior probabilities of the Bayesian inference analysis. Syngamus trachea from the family Syngamidae was used as the outgroup. The host families (Macropodidae or Vombatidae) in which the species of Phascolostrongylinae occur are represented by icons. The scale bar indicates the number of inferred substitutions per amino acid site