Characterization of the complete mitochondrial genome of Chinese Triops granarius and implications for species delimitation

Abstract

The mt genome of T. granarius (15.121 bp), containing 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (rRNAs) and one control region, present the typical pattern of phyllopod mt genomes from the perspective of gene content and order. All PCGs initiate with standard start codon of ATN and share the complete stop codon of TAA or TAG, whereas nd1 initiates with GTG, nd2 terminates with AGA and nd4 terminates with a single T. The secondary structures of rrnL and rrnS comprise of 48 helices and 32 helices, respectively. The patterns of evolutionary rate heterogeneity were observed at different levels in Triops. Phylogenetic analyses were performed based on the nucleotide sequences and amino acid sequences showed that Asian T. granarius was a sister group to (T. longicaudatus + T. australiensis), and T. cancriformis was the basal clade of Triops. Furthermore, we investigated the genetic diversity and phylogenetic relationships of different T. granarius s.l. populations. Ten phylogenetic lineages are separated on species level by mean maximum likelihood distance ≥ 12.2% in the cox1 gene. While the six populations occurring in Inner Mongolia of China, Mongolia and Russia, investigated for haplotypes belonged to the same haplotype networks.