Complete mitochondrial genome of bamboo grasshopper, Ceracris fasciata, and the phylogenetic analyses and divergence time estimation of Caelifera (Orthoptera)

The bamboo grasshopper Ceracris fasciata is regarded as a major pest species because of the damage it causes to bamboo, and its classification within the families and subfamilies of the suborder Caelifera remains unclear. Thus, we attempted to resolve these questions using molecular biology methods and analyses. Our results are as follows: (1) the complete mitochondrial genome of C. fasciata is 15,569 bp in length. The mitochondrial genome contains a standard set of 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes and an A + T-rich region in the same order as those of the other analysed Caeliferan species. The putative start codon for the COX1 gene in C. fasciata is ACC, although it is not defined in other genes. The presence of tandem repeats of different sizes in the A + T-rich region may lead to size differences in other mitochondrial genomes. The mitochondrial genome of C. fasciata harbours the typical 37 genes and an A + T-rich region, and it shows similar characteristics to those of other grasshopper species. Characterization of the mitochondrial genome has enriched our knowledge of the mitochondrial genomes of Orthoptera around the world. Therefore, the phylogenetic relationships in Orthoptera can be re-examined. (2) In phylogenetic analyses, the monophyly of Orthoptera and its two suborders (Caelifera and Ensifera) has been consistently recovered based on most of the datasets selected, regardless of the optimal criteria. Our results do not support the monophyly of the subfamily Oedipodinae of Caelifera. We found that Phlaeoba albonema of the Acridinae is sorted into a clade with Ceracris in all our phylogenetic trees, and field experiments show that Phlaeoba always lives with Ceracris in the same ecotopes. Therefore, we suggest that Phlaeoba should be classified as a member of the Oedipodinae. We found that C. fasciata always clustered with Ceracris kiangsu, and both were sisters to Ceracris versicolor. Therefore, the genetic relationship between C. fasciata and C. kiangsu is closer than that between C. fasciata and C. versicolor. (3) The oldest estimated time of divergence of Ensifera in this context was determined to be 146.16 million years ago (Mya), or around the late Jurassic or early Cretaceous. We estimated that katydids (Grylloidea) likely diverged from other groups in the early Cretaceous. According to our divergence time analyses, we concluded that the ancestral Acrididae probably originated in the early Paleogene, and it is likely that the major diversification events happened at the middle Paleogene, well into the next geologic time. We estimated that crickets (Tettigoniidae) likely diverged from other groups in the early Cretaceous. Acrididae and Romaleinae group, Pyrgacrididae and Ommexechidae group, the youngest two clades we observed, were estimated to have diverged 58.79 Mya, between the middle and early Paleogene. C. versicolor is a sister to the group containing C. kiangsu and C. fasciata. First, C. versicolor diverged from the sister group (C. kiangsu + C. fasciata) around 44.81 Mya, and then the C. kiangsu and C. fasciata group separated at 43.04 Mya.