Comparative Mitogenomes And Molecular Phylogenetic Analysis Of Delphacinae(hemiptera: Delphacidae)

The planthopper subfamily Delphacinae（Hemiptera:Delphacidae）is the most specious group in Delphacidae,distributing in all Zoogeographical Regions over the world.Members in this subfamily are terraneous and phloem-feeding,some are known as plant pathogen vectors which always cause significant losses for agricultural crops.This subfamily includes3 tribes up to date,358 genera and 1842 species have been reported in the world so far,in which 170 genera and more than 370 species are known in Chinese fauna,representing the richest species diversity of this group worldwide.Although the phylogenetic relationship of this group have been conducted in previous studies,the division of subtribes and relationships among generic taxa await further investigation;in addition,the origin of the subfamily,the divergence time of the tribes and host plant direction of transitions remain poorly understood,more exploration are still needed about this subfamily.In this study,four gene segments（28S r DNA,16S r DNA,cox1 and cytb）of 123Delphacinae specimes were sequenced to reconstruct the ML and BI trees.In addition,mitogenomes of 23 species in Delphacinae and one species of Stenocraninae were sequenced by the next generation DNA sequencing to reconstruct the phylogeny and explore the comparative mitogenomes.Based on these the structural traits,nucleotide composition,usage of start and stop codon,rearrangement of gene order and pairwise distances were studied.The results as follows:（1）The mitogenomes of Delphacinae is between 15331-16729 bp.Delphacini（16007-16729 bp）is generally longer than Tropidocephalini（15531-16231 bp）;（2）The mitogenomes of Delphacinae are small,double stranded,circular DNA molecules,comprising thirty-seven genes（13 protein-coding,22 transfer RNA,and 2ribosomal RNA genes）,and a control region（A+T-rich region）that is thought as a source of length variation in the genome;（3）The mitogenomes of the subfamily are heavily biased toward the A and T nucleotides;（4）Five kind of start codons and three of stop codons have been used in protein coding genes;（5）The gene arrangement is conserved in Delphacinae,and an inversion was happened between t RNA^Cys and t RNA^Trp,and an inverse transposition occurred between t RNA^Thr and nad6.This study reveals the evolutionary process from Cixiidae to Stenocraninae,and then to Delphacinae based on mitogenomes comparison;（6）The gene nad2 is recommended as a molecular marker in further population genetic studies.The combined dataset of four genes and mitogenomes yield similar topologies of Delphacinae,but the support values of node has more advantages in mitogenomes phylogenetic trees.The optimal dataset of mitogenomes is the one consist of position 1 and2.The results of phylogenetic analyses are as follows:（1）The topologies support the monophyly of Delphacinae and its basal split into three tribes,Saccharosydnini and Tropidocephalini were recovered as sister groups;（2）This study supports the subdivision of Delphacini into three subtribes,i.e.Toyoidina,Numatina and Delphacina;（3）There are probably two subtribes.i.e.Bambusiphagina and Tropidocephalina in the tribe Tropidocephalini;（4）The monophyly of Bambusiphaga Huang&Ding is here indicated;（5）The genus Paranectopia Ding&Tian is recommended to transfer from Tropidocephalini to Delphacini;（6）The genus Harmalia Fennah is regarded as a junior synonym of Opiconsiva Distant;（7）The subfamily Delphacinae can be traced back to the Cretaceous period（90 Mya）,and the tribe Saccharosydnini diverged from Tropidocephalini at 82 mya;（8）The ancestors of Delphacinae,Tropidocephalini and Delphacini may feed on C₃grasses,and then host shifts from C₃ to C₄ grasses happened many times in Delphacinae independently.