Mitochondrial genome characterization of Gryllodes sigillatus (Orthoptera: Gryllidae) and its phylogenetic implications

Abstract Gryllodes sigillatus is a cricket widely distributed throughout the world. In this study, we reported the first complete mitogenome sequence of Genus Gryllodes and inferred its phylogeny. The mitogenome of G. sigillatus was 16,369 bp and consisted of a control region and a typical set of 37 genes. It was AT-rich with strong codon usage bias and possessed a gene arrangement of trnE-trnS1-trnN. Phylogenetic analysis indicated G. sigillatus was sister species to Velarifictorus hemelytrus, together belonging to the Family Gryllidae. Our findings would contribute to understanding mitogenomic evolution and phylogeny of Ensifera.

Gryllodes sigillatus (Walker), a field cricket, also known as tropical house cricket, belongs to the Family Gryllidae with a wide distribution throughout the world (Otte 2006). It is a pest but sometimes also kept as a pet or animal feed in addition to a promising protein source for human diet (Ma et al. 2019;Daniso et al. 2020). G. sigillatus was first described in 1869 and then classified into different genera many times (Otte 2006). Insect mitogenome sequences have been extensively used to infer the evolution and phylogeny of metazoan at both deep and shallow taxonomic levels due to its fast mutation rate, conservation among conspecifics and lack of recombination (Cameron 2014;Li et al. 2019;Shaoli et al. 2018). Here, we reported the complete mitogenome sequence of G. sigillatus, the first in the Genus Gryllodes, which would contribute to evolution and phylogeny of Ensifera.
The complete mitogenome of G. sigillatus was a circular DNA molecule of 16,369 bp in length. It comprised of a control region (also called AT-rich or D-loop region) and a typical set of 37 genes coding for 13 proteins (PCGs), two ribosomal RNA and 22 transfer RNA. Similar to mitogenomes of other Gryllidae species (Ma and Li 2018;Ma et al. 2019), G. sigillatus possessed a unique gene arrangement of trnE-trnS1-trnN. Twenty genes were encoded on the majority strand (Jstrand). The overall AT content was 70.40%. AT-and GC-skew were 0.07 and À0.31, respectively, indicating that the mitogenome of G. sigillatus was AT-rich and adenine was preferred. For PCGs, all started with ATN except the cox1 with TCG as the start codon, and terminated with TAA, TAG or T. The AT percentage of 80.17% at the third codon position was higher than that at other two positions. Moreover, Leu was the most abundant (15.53%) among the used 20 amino acids and codon usage biases were strong with range of relative synonymous codon usage from 0.00 (AGG) to 3.22 (TTA).
The topology of ML, MP and BI trees were highly consistent only with slightly difference for support values at some nodes ( Figure 1). The results indicated that G. sigillatus was sister species to Velarifictorus hemelytrus and belonged to Gryllinae subfamily in the Family Gryllidae. Oecanthus and Truljalia genera grouped together at the base of Gryllidae. It was identical with the result of Ma et al. (Ma et al. 2019).
Moreover, the Family Gryllidae, Phalangopsidae and Trigonidiidae clustered a monophyly sharing a gene arrangement of trnE-trnS1-trnN, whereas Gryllotalpoidea was at the base of Grylloidea with a trnN-trnS1-trnE gene arrangement.

Funding
This study was supported by the Key Scientific Research Project of Wannan Medical College (Grant No. WK2020Z08) and College students Innovation and Enterprise Training Foundation of Anhui Province (Grant No. s201910368003 and s201910368016).

Data availability statement
The mitogenom sequence data are openly available in GenBank of NCBI at (https://www.ncbi.nlm.nih.gov/) under the accession no. MW365703. The associated BioProject, Bio-Sample, and SRA numbers are PRJNA693646, SAMN17393255, and SRR13495188, respectively.

Disclosure statement
No potential conflict of interest was reported by the authors.