First report of mitochondrial genome of family Bombyliidae, Geron pallipilosus (Diptera: Bombyliidae)

Abstract

The species of genus Geron are easily to be found in arid area, more species were reported from Afrontropical than other regions. Their potential use as important pollinators and natural enemy insect, especially in the desert and semidesert region. In this study, the mitochondrial DNA (mtDNA) of the bee fly, Geron pallipilosus, has been annotated for the first time in the family. The circular genome is 15,588 bp in length with an A + T content of 75.5%, and contains 13 protein-coding genes, 22 transfer RNAs, two ribosomal RNAs and a partial control region (633 bp). All genes have the similar locations and strands with that of other published Diptera. It is the first time to published the whole mitochondrial DNA for the family. Phylogenetic analysis suggests that G. pallipilosus is closely related to Leptogaster longicauda and Satanas sp. which belong to the family Asilidae. Our results show the location of Bombyliidae in the Brachycera, and provide data for further study of phylogeny in Diptera.

Keywords:

• Bombyliidae
• Geron pallipilosus
• mitochondrial genome
• phylogenetics

Genus Geron Meigen, 1820 belongs to the family Bombyliidae, which comprising over 150 described species and distributed worldwide. They are generally small to medium black flies, and are readily recognized by the presence of only three posterior cells (M₂ absent), the basally stout, conically tapered abdomen which is a little compressed laterally, the humpbacked mesonotum, and the characteristic antenna. The elongate third antennal segment is strongly tapered from base to apex so that it ends acutely and much attenuate with apical stylus (Hull 1973; Greathead and Evenhuis 1997). The species G. pallipilosus was firstly found and described by Yang et Yang in 1992 (Yang and Du 1992; Yang, Yao and Cui 2012; Evenhuis and Greathead 2015). It is reported that Geron sp. is one of the most important pollinating insects of Commelina erecta L. and Tradescantia roseolens Small (Commelinaceae) (Deyrup 1988). Geron is also recorded for its parasitization of Fumea sp. Stephens and Solenobia walshella Clemens (Lepidoptera, Psychidae) (Meigen 1820; Mik 1896; Donahue 1968). In this study, we assembled and characterized the mitochondrial genome of G. pallipilosus by high-throughput sequencing method for the first time. The sequence is accessible from GenBank with the accession number MG732929. This study would supply important basis for conservation genetics of G. pallipilosus, and promote the phylogenetic analysis of Bombyliidae.

The male adult sample of G. pallipilosus was collected from Hexi, Tongxin, Ningxia, China in 2016. The thorax muscle of the specimen was used to extract total genomic DNA. Vouchers consisting of the remaining bee fly were deposited in the Entomological Museum of China Agricultural University, Beijing, China. The mitogenomes were amplified and sequenced as described in these studies. The sequence reads into contigs by using the program Geneious version 10.2.2 and BioEdit version 7.0.5.3 (Hall 1999). tRNA genes were identified by using the tRNAscan-SE (Lowe and Eddy 1997) and checked manually. Two rRNA genes and all protein-coding genes (PCGs) were identified by BLAST searches in NCBI (http://www.ncbi.nlm.nih.gov). Strand asymmetry was measured using the formulas: AT skew = [A − T]/[A + T] and GC skew = [G − C]/[G + C] (Perna and Kocher 1995).

The G. pallipilosus circular genome is more than 15,588 bp in length with an A + T content of 75.5%, and like other animals G. pallipilosus mitogenome is circular and contains 37 genes, including 13 protein-coding genes, 22 transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs) and a control region (could not sequence the entirely control region in this study). The control region is more than 633 bp in length and located between srRNA and tRNA^Ile genes. All genes of G. pallipilosus mitogenomes have the similar locations and strands with that of other published Brachycera. The composition of the mitogenome is biased toward A and T (75.5%), with A 40.1%, T 35.4%, C 14.8% and G 9.7%. The A + T content of PCGs, tRNAs and rRNAs are 73.5%, 77.2% and 80.0%, respectively. The total length of all 13 PCGs in G. pallipilosus is 11,118 bp. Five PCGs (COI, ND5, ND4L, ND6 and ND1) used ATT as start codon, while five PCGs (ND2, COII, COIII, ND4 and CytB) used ATG as start codon, and three PCGs (ATP8, ATP6 and ND3) used ATC as start codon. Meanwhile, 10 PCGs used the typical termination codons TAA, while two PCGs (ND4 and CytB) used TAG as termination codons, and only one PCGs stopped with the incomplete termination signal T. The 22 tRNA genes size varies from 63 to 73 bp and all tRNAs could be folded into typical clover-leaf structures, except tRNA^Ser(AGN) without steam on the DHU arm. The lengths of 12S and 16S rRNA genes are 807 and 1338 bp, respectively. In addition to the control region, there were 252 nucleotides dispersed in 20 intergenic spacers, ranging from 1 to 42. The longest non-coding intergenic spacer is located between ND2 and tRNA^Met. Gene overlaps are also found at 10 gene junctions involving 36 nucleotides with the longest overlap (eight nucleotides) between tRNA^Cys and tRNA^Tyr.

Based on published mitogenome sequences of Diptera species, phylogenetic analyses were performed with respect to the nucleotide sequences of 13 PCGs and two rRNAs. Phylogenetic trees (Figure 1) based on the mitogenome data were inferred by both maximum-likelihood (ML) and Bayesian methods (BI). The results phylogenetic analysis show that all infraorders of Brachycera are monophyletic, and it shows G. pallipilosus (Bombyliidae) has very closely related to Leptogaster longicauda and Satanas sp. which belong to the family Asilidae. In this monophyletic bombyliidae and Asilidae was assigned to be a sister group, and Dolichopodidae and Empididae were herein corroborated to be a sister group, this result is supported by previous studies base on morphological characters (Yeates and Wiegmann 2007; Lambkin et al. 2013).

Figure 1. Phylogenetic tree of Brachycera families based on mt genome data.

In summary, the mitochondrial genome of G. pallipilosus (Bombyliidae) will provide important molecular data for further evolutionary analysis for the phylogeny status of the family, the genome data will also provide fundamental information for the conservation, pollinating and natural enemy of this important species.

Acknowledgements

The authors are very grateful to Mr. Xuankun Li (Canberra) for collecting the specimens, our thanks also goes to Mrs Qianqian Yang (Hangzhou) for her help in using the software. This research is supported by the National Natural Science Foundation of China [31301670] and China Postdoctoral Science Foundation [2015M581205].

Disclosure statement

The authors report no conflict of interest.