Characterization of four new mitogenomes from Ocypodoidea & Grapsoidea, and phylomitogenomic insights into thoracotreme evolution

Four new complete mitochondrial genomes (mitogenomes) from the two superfamilies Ocypodoidea and Grapsoidea were sequenced, which represented Uca (Gelasimus) borealis (Ocypodidae: Ucinae), Dotilla wichmani (Dotillidae), Metopograpsus quadridentatus (Grapsidae: Grapsinae), and Gaetice depressus (Varunidae: Gaeticinae). All of the mitogenomes shared the complete set of 37 mitochondrial genes. Mitogenome lengths were 15,659, 15,600, 15,517, and 16,288 bp, respectively, with A + T contents of 69.41%, 68.46%, 70.30%, and 72.96%, respectively. Comparative genomic analyses suggested that they exhibited different genomic rearrangements. In particular, G. depressus shared a major rearrangement pattern present in Eriocheir crabs, while the remainder shared the brachyuran ground genomic rearrangement patterns. Phylomitogenomic inferences provided new evidence for the strongly supported nesting of Thoracotremata within Heterotremata clades. A close phylogenetic relationship was observed between Varunidae and Macrophthalmidae crabs, and between Dotillidae and Grapsidae crabs, which was consistent with mitochondrial genomic rearrangement similarities. Altogether, these results suggest the presence of reciprocal paraphyly for Ocypodoidea and Grapsoidea.