Mitogenomic phylogenies support the validity of the family Micracanthorhynchinidae (Acanthocephala: Echinorhynchida), with novel gene arrangement in the mitogenomes of Micracanthorhynchina hemirhamphi and Rhadinorhynchus laterospinosus.

BACKGROUND

The family Rhadinorhynchidae is a common group of acanthocephalans parasitizing various marine and freshwater fishes. The current knowledge of the pattern of mitogenomic evolution of the rhadinorhynchid acanthocephalans is still extremely limited. The monophyly of the Rhadinorhynchidae and the phylogenetic status of several of its included genera and subfamilies remain under debate.

METHODS

The complete mitogenomes of Micracanthorhynchina hemirhamphi and Rhadinorhynchus laterospinosus were sequenced and annotated for the first time on the basis of the specimens collected from the Asian pencil halfbeak Hyporhamphus intermedius (Cantor) (Beloniformes: Hemiramphidae) and the frigate tuna Auxis thazard (Lacepède) (Scombriformes: Scombridae), respectively. Phylogenetic analyses of Acanthocephala were performed on the basis of the concatenated amino acid sequences of 12 protein-coding genes (PCGs) of mitogenomes using maximum likelihood (ML) and Bayesian inference (BI), respectively.

RESULTS

The complete mitogenomes of M. hemirhamphi and R. laterospinosus are 17,272 bp and 13,567 bp in length, which both include 36 genes, containing 12 PCGs (missing atp8), 22 transfer RNA (tRNA) genes, and two ribosomal RNAs (rrnS and rrnL), plus two noncoding regions. Additionally, several tRNA gene rearrangement events occurred in the mitogenomes of both M. hemirhamphi and R. laterospinosus. Phylogenetic results supported the traditional rhadinorhynchid genus Micracanthorhynchina as a distinct lineage from Rhadinorhynchidae and Cavisomatidae.

CONCLUSIONS

The mitogenome of M. hemirhamphi represents the largest mitogenome of acanthocephalan reported so far. The mitogenome of R. laterospinosus is the smallest mitogenome of the order Echinorhynchida, which also represents the first mitogenomic data for the genus Rhadinorhynchus and also for the Rhadinorhynchidae sensu stricto. Comparative mitogenomic analyses revealed the gene arrangements of R. laterospinosus and M. hemirhamphi represent two new types of mitochondrial gene arrangement reported in Acanthocephala. Moreover, mitogenomic phylogenies further confirmed the validity of the family Micracanthorhynchinidae and suggested a sister relationship Micracanthorhynchinidae + (Rhadinorhynchidae + Cavisomatidae) within Echinorhynchida.