Mitochondrial genome characteristics of six Phylloscopus species and their phylogenetic implication

The mitochondrial genomes of six Phylloscopus species-small insectivores belonging to the Phylloscopidae family-were obtained using the Illumina sequencing platform. The mitogenomes were closed circular molecules 16,922-17,007 bp in size, containing 13 protein-coding genes, 22 tRNA genes, two rRNA genes, and two control regions (CR1 and remnant CR2). The gene orders were conserved in 35 sampled Phylloscopus mitogenomes in the GenBank database, with a gene rearrangement of cytb-trnT-CR1-trnP-nad6-trnE-remnant CR2-trnF-rrnS. The average base compositions of the six Phylloscopus mitogenomes were 29.43% A, 32.75% C, 14.68% G, and 23.10% T, with the A+T content slightly higher than that of G+C. ATG and TAA were the most frequent initiating and terminating codons, respectively. Several conserved boxes were identified in CR1, including C-string in domain I; F, E, D, and C boxes, as well as bird similarity and B boxes, in domain II; and CSB1 in domain III. Tandem repeats were observed in remnant CR2 of the Phylloscopus fuscatus and Phylloscopus proregulus mitogenomes. A phylogenetic analysis with maximum likelihood (ML) and Bayesian inference (BI) methods, based on 13 protein-coding genes and two rRNA genes, indicated that the Phylloscopus species was divided into two larger clades, with a splitting time approximately 11.06 million years ago (mya). The taxa of Phylloscopus coronatus/Phylloscopus burkii and Phylloscopus inornatus/P. proregulus were located at the basal position of the different clades. The phylogenetic result of the cox1 gene showed that Seicercus was nested within Phylloscopus. The complete set of mitogenomes of the Phylloscopus species provides potentially useful resources for the further exploration of the taxonomic status and phylogenetic history of Phylloscopidae.