Characterization and phylogenetic implications of the first complete mitochondrial genome of Brachylaima sp. (Digenea: Brachylaimoidea).

Trematodes of the family Brachylaimidae infect birds and mammals, but mitochondrial (mt) genomic data for this group remain scarce. Here, we sequenced and characterised the complete mt genome of Brachylaima sp. recovered from the oriental turtle dove, Streptopelia orientalis, in China. The circular mt genome is 14,946 bp long and comprises 36 genes, including 12 protein-coding genes (PCGs), 22 transfer RNA (tRNA) genes, and 2 ribosomal RNA (rRNA) genes. All genes are encoded on the same strand and transcribed in the same direction. The mt genome is A + T-biased (62.49%) and shows negative AT-skew and positive GC-skew values. Codon usage analysis revealed a strong bias for A/T-ending codons. Among the 22 tRNAs, 20 were predicted to form canonical cloverleaf structures, whereas tRNA-SerAGN (trnS1) lacked the dihydrouridine (DHU) arm and tRNA-Cys (trnC) displayed a non-canonical secondary structure. Phylogenetic analyses based on the concatenated amino acid sequences of 12 mt PCGs using maximum likelihood and Bayesian inference yielded congruent topologies, placing Brachylaima sp. with Postharmostomum commutatum within Brachylaimidae. In the present mt dataset, Brachylaimidae was recovered as closely associated with Schistosomatidae; however, given the limited sampling of Brachylaimoidea, this relationship and the apparent non-monophyly of Diplostomida should be interpreted with caution. This study provides the first complete mt genome for the genus Brachylaima and a useful resource for molecular identification, comparative mitogenomics, and phylogenetic studies of brachylaimid trematodes.