Mitochondrial genome of Helice tientsinensis (Brachyura: Grapsoidea: Varunidae): Gene rearrangements and higher-level phylogeny of the Brachyura.

The mitochondrial genome (mt genome) provides important information for understanding molecular evolution and phylogeny. The further understand the molecular evolution and phylogeny of Helice tientsinensis, the complete mt genome was determined. It is 16,212bp long and includes 13 protein-coding genes (PCGs), 22 tRNA genes, two rRNA genes and a control region. The genome composition of H. tientsinensis was highly A+T biased 69.0% and showed negative AT skew (-0.017) and GC skew (-0.289). One PCG, all rRNAs and 12 of the tRNAs appeared to be rearranged with respect to the pancrustacean ground pattern gene order. Tandem duplication, followed by random deletion, is widely considered to explain translocation of mitochondrial genes. Consecutive recombinations events could explain inversions of genes. The phylogenetic analyses showed that H. tientsinensis has close relationships with Eriocheir japonica sinensis, E. j. hepuensis and E. j. japonica; this indicated that H. tientsinensis belongs in the Grapsoidea, part of the Varunidae family. This study provides evidence for a better understanding of gene rearrangements, as well as the evolutionary status of H. tientsinensis and related species.