The Mitochondrial Genome of Cylicocyclus elongatus (Strongylida: Strongylidae) and Its Comparative Analysis with Other Cylicocyclus Species

The complete mitochondrial genome of Cylicocyclus ultrajectinus (Ihle, 1920)

In this study, the mitochondrial genome of Cylicocyclus ultrajectinus (Ihle, 1920) was sequenced for the first time using next-generation sequencing technology, and its compositional characteristics, structure, and phylogenetic relationship with other strongylid nematodes were analyzed by biological software. The results showed that these sequences contained 12 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and 2 non-coding regions, all exhibiting a significant AT bias. Phylogenetic studies showed that C. ultrajectinus formed a distinct branch form other Cylicocyclus nematodes. This study contributes to the mitochondrial genome database of Strongylidae, laying a foundation for genetic variation, molecular classification, and evolutionary studies of strongylid nematodes.

Characterisation of the mitochondrial genome and phylogenetic analysis of Toxocara apodemi (Nematoda: Ascarididae)

We first sequenced and characterised the complete mitochondrial genome of Toxocara apodeme, then studied the evolutionary relationship of the species within Toxocaridae. The complete mitochondrial genome was amplified using PCR with 14 specific primers. The mitogenome length was 14303 bp in size, including 12 PCGs (encoding 3,423 amino acids), 22 tRNAs, 2 rRNAs, and 2 NCRs, with 68.38% A+T contents. The mt genomes of T. apodemi had relatively compact structures with 11 intergenic spacers and 5 overlaps. Comparative analyses of the nucleotide sequences of complete mt genomes showed that T. apodemi had higher identities with T. canis than other congeners. A sliding window analysis of 12 PCGs among 5 Toxocara species indicated that nad4 had the highest sequence divergence, and cox1 was the least variable gene. Relative synonymous codon usage showed that UUG, ACU, CCU, CGU, and UCU most frequently occurred in the complete genomes of T. apodemi. The Ka/Ks ratio showed that all Toxocara mt genes were subject to purification selection. The largest genetic distance between T. apodemi and the other 4 congeneric species was found in nad2, and the smallest was found in cox2. Phylogenetic analyses based on the concatenated amino acid sequences of 12 PCGs demonstrated that T. apodemi formed a distinct branch and was always a sister taxon to other congeneric species. The present study determined the complete mt genome sequences of T. apodemi, which provide novel genetic markers for further studies of the taxonomy, population genetics, and systematics of the Toxocaridae nematodes.

Description and phylogenetic analysis of the complete mitochondrial genome in Eulaelaps silvestris provides new insights into the molecular classification of the family Haemogamasidae

In this study, the mitochondrial genome of Eulaelaps silvestris, which parasitizes Apodemus chevrieri, was sequenced and assembled to fill the gap in understanding the molecular evolution of the genus Eulaelaps. The E. silvestris mitochondrial genome is a double-stranded DNA molecule with a length of 14 882 bp, with a distinct AT preference for base composition and a notably higher AT content than GC content. The arrangement between genes is relatively compact, with a total of 10 gene intergenic regions and 12 gene overlap regions. All protein-coding genes had a typical ATN initiation codon, and only 2 protein-coding genes had an incomplete termination codon T. Out of the 13 protein-coding genes, the 5 most frequently used codons ended in A/U, with only 1 codon ending in G/C had an relative synonymous codon usage value >1. Except for trnS1 and trnS2, which lacked the D arm, all other tRNAs were able to form a typical cloverleaf structure; and there were a total of 38 mismatches in the folding process of tRNA genes. Unlike the gene arrangement order of the arthropod hypothetical ancestor, the E. silvestris mitochondrial genome underwent fewer rearrangements, mainly near tRNA genes and control regions. Both the maximum likelihood tree and the Bayesian tree showed that the family Haemogamasidae is most closely related to the family Dermanyssidae. The results not only provide a theoretical basis for studying the phylogenetic relationships of the genus Eulaelaps, but also provide molecular evidence that the family Haemogamasidae does not belong to the subfamily Laelapidae.