The complete mitochondrial genome of Argiope ocula (Araneae: Araneidae) and its phylogeny.

The complete mitochondrial genome of Argiope ocula (GenBank accession number MN331657) is a circular molecule of 14,079 bp in length, comprising of 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes, and a control region. Ten intergenic spacer regions and 19 reading frame overlaps were found in the mitogenome of A. ocula. Ten tRNAs (trnD, trnF, trnK, trnR, trnT, trnW, trnE, trnG, trnL1 , and trnM) lacked the TΨC arm stem, whereas three tRNAs (trnA, trnS1 , and trnS2 ) lost the dihydrouracil (DHU) arm. Phylogenetic analysis suggested that A. ocula had the closest evolutionary relationship with A. perforata.

The orb-weaver spider, Argiope ocula (Araneae: Araneidae), is a major predator of many economical agricultural pests and distributed widely in farmland and orchard (Levi 2004; Platnick 2015). In this study, adult species of A. ocula were collected from Maolan Nature Reserve in Libo county, Guizhou Province, China (N25°18′, E107°52′), and deposited in the spider specimen room of Guiyang University with an accession number GYU-GZML-01. The complete mitochondrial genome of A. ocula (GenBank accession number MN331657) is a circular molecule of 14,079 bp in length, comprising of 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), two ribosomal RNA genes (rrnL and rrnS), and a putative control region. All genes have the similar location and strands with that of other determined spiders (Li et al. 2016; Yang et al. 2019). The overall base composition of A. ocula mitogenome was biased towards A and T, with 75.07% of A + T content (A = 36.35%, T = 38.72%, C = 9.57%, G = 15.36%). The AT-skew and GC-skew of this genome were −0.032 and 0.232, respectively.

Fifteen genes was transcribed on the minority strand, whereas the others were oriented on the majority strand. Gene overlaps in the A. ocula mitogenome were found at 19 gene junctions and involved a total of 180 bp, the longest 13 bp overlapping located between trnE and trnF. There are 10 intergenic spacer regions in a total of 55 bp and the largest spacer (8 bp) resided between trnA and trnN. Eight PCGs start with the typical ATN codons (ATT for cob, nad2, nad5, and atp8; ATA for atp6, nad3, nad4, and nad4L), three PCGs (cox2, cox3, and nad6) start with TTG, and two PCGs (cox1 and nad1) use TTA as initiation codon. Eleven PCGs (atp6, atp8, cob, cox1, cox2, cox3, nad1, nad2, nad4, nad4L, and nad6) use the canonical termination codons (TAA or TAG), while nad3 and nad5 stop with the incomplete termination signal T. The length of 22 tRNAs ranged from 52 bp (trnA) to 69 bp (trnI), A + T content ranged from 62.26% (trnR) to 83.64% (trnG). Thirteen tRNAs lacked the potential to form the cloverleaf-shaped secondary structure. Ten of them (trnD, trnF, trnK, trnR, trnT, trnW, trnE, trnG, trnL, and trnM) lacked the TΨC arm stems, three tRNAs (trnA, trnS and trnS) lost the dihydrouracil (DHU) arm. The rrnL was located between trnL and trnV, while the rrnS resided between trnV and trnQ. The lengths of rrnL and rrnS were 1,018 bp and 694 bp, and their A + T contents were 78.78% and 76.95%, respectively. The control region was located between trnQ and trnM with 492 bp long and 79.47% A + T content.

To validate the evolutionary position of A. ocula, a neighbor-joining phylogenetic tree inferred from mitochondrial 13 PCGs of 15 spiders was constructed by MEGA 7.0 (Kumar et al. 2016). The result showed that A. ocula had a sister relationship with A. perforata (Figure 1), which was in accordance with conventional morphological classification.

Figure 1.

Phylogenetic tree showing the relationship between Argiope ocula and 14 other spiders based on neighbor-joining method. GenBank accession numbers used in the study are the following: Araneus ventricosus (KM588668), Argiope perforata (MK512574), Carrhotus xanthogramma (NC_027492.1), Cyclosa argenteoalba (KP862583), Habronattus oregonensis (AY571145), Heptathela hangzhouensis (AY309258), Hypsosinga pygmaea (KR259803), Liphistius erawan (NC_020323.1), Neoscona theisi (NC_026290.1), Pardosa laura (NC_025223.1), Pirata subpiraticus (NC_025523.1), Plexippus paykulli (NC_024877.1), Telamonia vlijmi (NC_024287.1), Tetrancychus urticae (EU345430.1), and Wadicosa fidelis (NC_026123.1). T. urticae was used as an outgroup. Spider determined in this study was underlined.