Phylogeny And Phylochronology Of Brachyura

The Brachyura is one of the most species-rich lineages within the Decapoda. Brachyuran crabs are extremely diverse both morphologically and ecologically, which makes it complicated for addressing its phylogenetic relationships. The major controversies have focused on the status of Podotremata and the internal relationships within Eubrachyura since the classification of the brachyuran taxa was proposed by Guinot (1977,1978). With the deepening of the study, the monophyletic of the Heterotremata has been questioned. To resolve the controversy, we present entire sequences of the complete mitochondrial genome of Ilyoplax deschampsi (Brachyura: Thoracotremata:Ocypodoidea). Based on it and Sinopotamon yangtsekiense (Brachyura:Heterotremata:Potamoidea) which sequenced by our team and other available mitochondrial genomes, we evaluate the usefulness of PCGs in resolving deep phylogenetic relationships of the Brachyura. Our phylogenetic analyses suggest the position of Potamoidea and Ocypodoidea within the Brachyura were totally unexpected. Potamoidea was identified as the sister group of Thoracotremata (Ocypodoidea and Varunidae) with high nodal supports, which makes the subsection Heterotremata paraphyletic. Notably, three families within the Thoracotremata have the following relationship:(Ocypodidae+Varunidae)+Grapsidae, suggesting that Grapsioidea is not monophyletic. We also investigate the phylochronology of Brachyura and support the post-Gondwana hypothesis. Our results imply that a common ancestor of the taxa of Heterotremata and Potamidae divergenced during Cretaceous, and then evolved independently in two directions. One of them has evolved to the modern Thoracotremata and the other divergenced to the modern Potamidae during the Tertiary which we consider as a relation with the transgression and regression.