Relaxed purifying selection pressure drives accelerated and dynamic gene rearrangements in thrips (Insecta: Thysanoptera) mitochondrial genomes.

Insect mitochondrial genomes (mitogenome) generally present a typical gene order, which is considered as the ancestral arrangement. All sequenced mitogenomes in the Thysanoptera display high levels of gene rearrangement. Due to limited number of thrips mitogenomes sequenced, how gene rearrangement may be shaped by evolution remain unclear. Here, we analyzed 33 thrips mitogenomes, including 14 newly sequenced. These mitogenomes were diverse in organization, nucleotides substitution and gene arrangements. We found 28 highly rearranged gene orders with the breakpoints of gene rearrangements from 25 to 33. Reconstruction of the ancestors mitochondrial gene arrangements states indicated that Tubulifera have more complex pathways than Terebrantia in the gene order evolution. Molecular calibration estimated that divergence of two suborders occurred in the middle Triassic while the radiation of thrips was associated with the arose and flourish of angiosperm. Our evolutionary hypothesis testing suggests that relaxation of selection pressure enabled the early phase of Thysanoptera evolution, followed by a stronger selective pressure fixed diversification. Our analyses found gene inversion increases the nonsynonymous substitution rates and provide an evolutionary hypothesis driving the diverse gene orders.