Characterization of the complete mitochondrial genome and phylogenetic analysis of Leucauge celebesiana (Araneae: Tetragnathidae).

The complete mitogenome of Leucauge celebesiana (GenBank accession number MN296353) is 13,901 bp in size, and harbours 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), 2 ribosomal RNAs, and an A + T-rich region. The base composition of the mitogenome comprised A (33.80%), C (8.82%), G (14.42%), and T (42.96%), with a total A + T content of 76.76%. Eleven tRNAs (trnK, trnP, trnL1 , trnD, trnF, trnG, trnH, trnR, trnT, trnW, and trnV) lacked the TΨC arm stem, while three tRNAs (trnA, trnS1 , and trnS2 ) lost the dihydrouracil (DHU) arm. Phylogenetic analysis suggests that L. celebesiana has a close phylogenetic relationship with Tetragnatha maxillosa, which agree with the traditional taxonomy.

The orb-weaving spider, Leucauge celebesiana (Araneae: Tetragnathidae), is an important predator of many agricultural pests (Nasir et al. 2016). This species is widely distributed in China, India, Japan, Indonesia, and New Guinea, and usually lives in paddy fields, waterside plants and shurblands (Li et al. 2011). In this study, adult individuals of L. celebesiana were collected from the Maolan Nature Reserve in Libo county, Guizhou Province, China (N25°18′, E107°52′). Samples were preserved in 95% ethanol and stored in the spider specimen room of Guiyang University with an accession number GYU-GZML-18.

The complete mitochondrial genome of L. celebesiana (GenBank accession number MN296353) is 13,901 bp in size, harbouring 37 typical animal mitochondrial genes which include 13 protein-coding genes (PCGs), 22 transfer RNAs (tRNAs), 2 ribosomal RNAs (rrnL and rrnS), and an A + T-rich region (Boore 1999). The gene content and orientation of L. celebesiana were consistent with those observed in other spider mitogenomes (Wang et al. 2016; Xu et al. 2019). Sixteen genes were transcribed on the minority strand (N-strand), while the others were encoded on the majority strand (J-strand). The overall base composition of L. celebesiana mitogenome comprised A (33.80%), C (8.82%), G (14.42%), and T (42.96%), with a total of A + T content of 76.76%. The AT-skew and GC-skew of this genome were −0.119 and 0.241, respectively. A total of 208 bp overlaps were found at 27 gene junctions in L. celebesiana mitogenome, and the length of overlaps are ranging from 1 to 28 bp. Intergenic spacers were present in five positions and involved a total of 19 bp, the longest intergenic spacer was located between trnF and nad5.

The length of 22 tRNAs ranged from 51 bp (trnS and trnV) to 118 bp (trnC), A + T content ranged from 66.13% (trnM) to 88.14% (trnC). Fourteen tRNAs lacked the potential to form the cloverleaf secondary structure. Eleven tRNAs (trnK, trnP, trnL, trnD, trnF, trnG, trnH, trnR, trnT, trnW, and trnV) lacked the TΨC arm stem, while three tRNAs (trnA, trnS, and trnS) lost the dihydrouracil (DHU) arm. The rrnL was 1,026 bp long with A + T content of 80.60%, and the rrnS was 694 bp long with A + T content of 82.71%. The rrnL was located between trnL and trnV, and rrnS resided between trnV and trnQ. The A + T-rich region was located between trnQ and trnM genes with a length of 377 bp long and the A + T content was 83.29%.

Nine PCGs start with typical ATN codons (ATT for nad1, nad2, nad4L, and atp8; ATA for atp6, nad3, nad4, and nad5; ATG for cob). However, three genes (cox2, cox3, and nad6) start with TTG, and cox1 uses TTA as initiation codon. Ten PCGs terminate with conventional stop codons (TAA or TAG), and the remaining PCGs including nad5, nad4L, and cob use a single T as termination codon. According to the relative synonymous codon usage analyses of 13 PCGs, ATA (M), TTT (F), ATT (I), TTA (L) and were the four most frequently used codons. Methionine, phenylalanine, isoleucine, and leucine are the most frequent the amino acid of 13 PCGs. Based on the concatenated amino acid sequences of 13 PCGs, the neighbour-joining method was used to construct the phylogenetic relationship of L. celebesiana with 16 other representative spiders. The result showed that L. celebesiana is closely related to Tetragnatha maxillosa (Figure 1), which agree with the traditional taxonomy.

Figure 1.

Phylogenetic tree showing the relationship between Leucauge celebesiana and 16 other representative spiders based on neighbour-joining method. GenBank accession numbers of each species were listed in the tree. Spider determined in this study is labelled with triangle. Tetranychus urticae was used as an outgroup.