Characterization of the complete mitochondrial genome of Tylorida striata (Araneae: Tetragnathidae) and phylogenetic analysis.

The complete mitochondrial genome of Tylorida striata (GenBank accession number MN615900) is 14,422 bp in length with a high AT bias of 71.73%. It contains 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), 2 ribosomal RNA (rRNA) genes, and a putative control region. The gene order of T. striata was identical to other spider mitogenomes. Eleven tRNAs (trnW, trnY, trnC, trnD, trnG, trnL2 , trnR, trnF, trnP, trnI, and trnL1 ) lose the TΨC-stems, whereas two tRNAs (trnS1 and trnS2 ) lack the dihydrouracil (DHU) arm. Phylogenetic tree based on concatenated amino acid sequences of 13 PCGs showed that T. striata is clustered with two Tetragnathidae species and recovered as sister of other two Tetragnathids.

The big-jawed spider Tylorida striata belongs to the family of Tetragnathidae, which includes about 9000 described species in 50 genera (Kulkarni and Yadav 2015; Platnick 2015). Most of these spiders are important predators of several insects and usually live in grassy places and swamps (Zhang et al. 2002). In this study, adult species of T. striata were collected from Maolan Nature Reserve in Libo County, Guizhou Province, China (N25°16′, E107°58′), and preserved in spider specimen room of Guiyang University with an accession number GYU-GZML-23.

The complete mitogenome sequence of T. striata is deposited in GenBank under accession number MN615900. It is a circular molecule of 14,422 bp in length and contains sets of genes, including 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), 2 ribosomal RNA genes (12S rRNA and 16S rRNA), and a putative control region (Boore 1999; Yan et al. 2019). The gene order of T. striata was identical with other spider mitogenomes (Li et al. 2016; Yang et al. 2019). Fourteen genes were transcribed on the minor strand (N-strand), while the others were oriented on the major strand (J-strand). The overall base composition of T. striata mitogenome is A (31.27%), C (10.19%), G (18.08%), and T (40.46%), with a high AT bias of 71.73%. The AT-skew and GC-skew of this genome were −0.128 and 0.279, respectively.

There were 5 intergenic spacer regions comprising a total length of 23 bp and the largest spacer (8 bp) was located between nad1 and trnL. Gene overlaps were found at 23 gene junctions, the longest 35 bp overlapping located between trnE and trnF. The length of 22 tRNAs varied between 48 bp (trnC) and 77 bp (trnM), with a mean length of 59 bp. Thirteen tRNAs could not be folded into typical cloverleaf-shaped secondary structures. Among them, eleven tRNAs (trnW, trnY, trnC, trnD, trnG, trnL, trnR, trnF, trnP, trnI, and trnL) lost the TΨC-stem and two tRNAs (trnS and trnS) lacked the dihydrouracil (DHU) arm. The 16S rRNA (1014 bp) is located between trnL and trnV, and 12S rRNA (691 bp) reside between trnV and trnQ, and their A + T contents were 76.23 and 78.00%, respectively. The control region is located between trnQ and trnM with a length of 895 bp long and the A + T content is 75.87%. Ten PCGs initiate with typical ATN start codons (ATT for atp8, nad1, nad2, nad4L, nad5, and nad6; ATA for nad4 and cob; ATG for atp6 and nad3), two PCGs (cox2 and cox3) use TTG and cox1 is initiated with TTA. Ten PCGs use the typical termination codons TAA and TAG in T. striata, while only three PCGs (nad4L, nad5, and cob) stop with the incomplete termination single T.

Based on the concatenated amino acid sequences of 13 PCGs from T. striata and 14 other spiders, the neighbor-joining method was used to reveal the phylogenetic relationship among these spiders. The result showed that T. striata is clustered with two Tetragnathidae species (Figure 1). Within the Tetragnathidae clade, T. striata is recovered as sister to the other two Tetragnathids.

Figure 1.

Phylogenetic tree showing the relationship between Tylorida striata and 14 other representative spiders based on neighbor-joining method. GenBank accession numbers used in the study are the following: Araneus angulatus (KU365988), Argiope bruennichi (NC_024281), Carrhotus xanthogramma (NC_005942), Neoscona adianta (KR259805), Neoscona nautica (KR259804), Pardosa laura (KM272948), Pholcus phalangioides (NC_020324), Pholcus sp. (KJ782458), Pirata subpiraticus (NC_025523), Plexippus paykulli (NC_024877), Telamonia vlijmi (NC_024287), Tetragnatha maxillosa (KP306789), Tetragnatha nitens (KP306790), Tetrancychus urticae (EU345430), Wadicosa fidelis (NC_026123). Tetrancychus urticae was used as an outgroup. The spider determined in this study is underlined.