The comparative mitogenomics and phylogenetics of the two grouse-grasshoppers (Insecta, Orthoptera, Tetrigoidea)

A new species of the genus Xistra (Orthoptera: Tetrigoidea: Metrodorinae) with comments on the characters of mitochondrial genome

A new species from Jiangxi Province of China, Xistra zhengi Deng, sp. nov. is described and illustrated. Meanwhile, the complete mitochondrical genome of the new species was determined and annotated. It has the typical invertebrate mitochondrial gene arrangement, the size of the sequenced mitogenomes is 18148 bp. The constructed phylogenetic tree showed that the new species was placed in Metrodorinae, and formed a separate clade from other species of Metrodorinae.

The mitogenome data of Holothuria (Mertensiothuria) leucospilota (Brandt,1835) from Malaysia

White threads fish Holothuria (Mertensiothuria) leucospilota (Brandt, 1835) or locally known as bat puntil is a neritic marine organism, and it is widely distributed in Indo Pacific. They serve many important roles in ecosystem services and were discovered to contain many bioactive compounds that are useful for medicinal value. However, despite its abundance in Malaysian seawater, there is still a lack of records on H. leucospilota mitochondrial genome (mitogenome) from Malaysia. The mitogenome of H. leucospilota originating from Sedili Kechil, Kota Tinggi, Johor, Malaysia, is presented here. Whole genome sequencing was successfully sequenced using Illumina NovaSEQ6000 sequencing system and the mitochondrial-derived contigs were assembled using de novo approach. The size of the mitogenome is 15,982 bp which consists of 13 protein-coding genes (PCGs), 21 transfer RNAs, and 2 ribosomal RNAs. The overall composition of nucleotide bases was estimated to be 25.8% for T, 25.9% for C, 31.8% for A and 16.5% for G (with A + T content of 57.6%). Maximum likelihood phylogenetic tree analysis revealed that the mitochondrial Protein-Coding Genes (PCGs) sequence data from our H. leucospilota is closely related to H. leucospilota from accession number MK940237 and H. leucospilota from accession number MN594790, followed by H. leucospilota from accession number MN276190, forming sister group with H. hilla (MN163001), known as Tiger tail sea cucumber. The mitogenome of H. leucospilota will be valuable for genetic research, mitogenome reference and future conservation management of sea cucumber in Malaysia. The mitogenome data of H. leucospilota from Sedili Kechil, Kota Tinggi, Johor, Malaysia is available in the GenBank database repository with accession number ON584426.

Mitochondrial genomes of eight Scelimeninae species (Orthoptera) and their phylogenetic implications within Tetrigoidea

Scelimeninae is a key member of the pygmy grasshopper community, and an important ecological indicator. No mitochondrial genomes of Scelimeninae have been reported to date, and the monophyly of Scelimeninae and its phylogenetic relationship within Tetrigidae is still unclear. We sequenced and analyzed eight nearly complete mitochondrial genomes representing eight genera of Scelimeninae. These mitogenomes ranged in size from 13,112 to 16,380 bp and the order of tRNA genes between COII and ATP8 was reversed compared with the ancestral order of insects. The protein-coding genes (PCGs) of tetrigid species mainly with the typical ATN codons and most terminated with complete (TAA or TAG) stop codons. Analyses of pairwise genetic distances showed that ATP8 was the least conserved gene within Tetrigidae, while COI was the most conserved. The longest intergenic spacer (IGS) region in the mitogenomes was always found between tRNASer(UCN) and ND1. Additionally, tandem repeat units were identified in the longest IGS of three mitogenomes. Maximum likelihood (ML) and Bayesian Inference (BI) analyses based on the two datasets supported the monophyly of Tetriginae. Scelimeninae was classified as a non-monophyletic subfamily.

MtOrt: an empirical mitochondrial amino acid substitution model for evolutionary studies of Orthoptera insects

BACKGROUND

Amino acid substitution models play an important role in inferring phylogenies from proteins. Although different amino acid substitution models have been proposed, only a few were estimated from mitochondrial protein sequences for specific taxa such as the mtArt model for Arthropoda. The increasing of mitochondrial genome data from broad Orthoptera taxa provides an opportunity to estimate the Orthoptera-specific mitochondrial amino acid empirical model.

RESULTS

We sequenced complete mitochondrial genomes of 54 Orthoptera species, and estimated an amino acid substitution model (named mtOrt) by maximum likelihood method based on the 283 complete mitochondrial genomes available currently. The results indicated that there are obvious differences between mtOrt and the existing models, and the new model can better fit the Orthoptera mitochondrial protein datasets. Moreover, topologies of trees constructed using mtOrt and existing models are frequently different. MtOrt does indeed have an impact on likelihood improvement as well as tree topologies. The comparisons between the topologies of trees constructed using mtOrt and existing models show that the new model outperforms the existing models in inferring phylogenies from Orthoptera mitochondrial protein data.

CONCLUSIONS

The new mitochondrial amino acid substitution model of Orthoptera shows obvious differences from the existing models, and outperforms the existing models in inferring phylogenies from Orthoptera mitochondrial protein sequences.

Evolutionary rates of and selective constraints on the mitochondrial genomes of Orthoptera insects with different wing types

Orthoptera is the most diverse order of polyneopterans, and the forewing and hindwing of its members exhibit extremely variability from full length to complete loss in many groups; thus, this order provides a good model for studying the effects of insect flight ability on the evolutionary constraints on and evolutionary rate of the mitochondrial genome. Based on a data set of mitochondrial genomes from 171 species, including 43 newly determined, we reconstructed Orthoptera phylogenetic relationships and estimated the divergence times of this group. The results supported Caelifera and Ensifera as two monophyletic groups, and revealed that Orthoptera originated in the Carboniferous (298.997 Mya). The date of divergence between the suborders Caelifera and Ensifera was 255.705 Mya, in the late Permian. The major lineages of Acrididae seemed to have radiated in the Cenozoic, and the six patterns of rearrangement of 171 Orthoptera mitogenomes mostly occurred in the Cretaceous and Cenozoic. Based on phylogenetic relationships and ancestral state reconstruction, we analysed the evolutionary selection pressure on and evolutionary rate of mitochondrial protein-coding genes (mPCGs). The results indicated that during approximately 300 Mya of evolution, these genes experienced purifying selection to maintain their function. Flightless orthopteran insects accumulated more non-synonymous mutations than flying species and experienced more relaxed evolutionary constraints. The different wing types had different evolutionary rates, and the mean evolutionary rate of Orthoptera mitochondrial mPCGs was 13.554 × 10^-9 subs/s/y. The differences in selection pressures and evolutionary rates observed between the mitochondrial genomes suggested that functional constraints due to locomotion play an important role in the evolution of mitochondrial DNA in orthopteran insects with different wing types.