Evolutionary History of True Crabs (Crustacea: Decapoda: Brachyura) and the Origin of Freshwater Crabs

Abstract

Crabs of the infra-order Brachyura are one of the most diverse groups of crustaceans with approximately 7,000 described species in 98 families, occurring in marine, freshwater, and terrestrial habitats. The relationships among the brachyuran families are poorly understood due to the high morphological complexity of the group. Here, we reconstruct the most comprehensive phylogeny of Brachyura to date using sequence data of six nuclear protein-coding genes and two mitochondrial rRNA genes from more than 140 species belonging to 58 families. The gene tree confirms that the "Podotremata," are paraphyletic. Within the monophyletic Eubrachyura, the reciprocal monophyly of the two subsections, Heterotremata and Thoracotremata, is supported. Monophyly of many superfamilies, however, is not recovered, indicating the prevalence of morphological convergence and the need for further taxonomic studies. Freshwater crabs were derived early in the evolution of Eubrachyura and are shown to have at least two independent origins. Bayesian relaxed molecular methods estimate that freshwater crabs separated from their closest marine sister taxa ~135 Ma, that is, after the break up of Pangaea (∼200 Ma) and that a Gondwanan origin of these freshwater representatives is untenable. Most extant families and superfamilies arose during the late Cretaceous and early Tertiary.

The complete mitochondrial genome of the semiterrestrial crab, Chiromantes neglectum (Eubrachyura: Grapsoidea: Sesarmidae)

“…Combining sequences of 13 PCGs from 25 brachyurans, both maximum likelihood and Bayesian analyses place the C. neglectum within an intermingled 'Grapsoidea & Ocypodoidea' clade ( Figure 1). It confirm the results of previous analyses (Schubart et al 2006;Tsang et al 2014) that monophyles of these two superfamilies were negative in their current compositions. In addition, the heterotreme crabs appear paraphyletic in our analyses, with potamoid taxa being more closely related to thoracotreme crabs than to the remaining heterotremes.…”

“…This confirms the result obtained from similar dataset by Ji et al (2014). Whereas phylogenetic trees of Tsang et al (2014) suggested that freshwater crabs align with Heterotremata rather than Thoracotremata. This difference in tree topologies may result from taxon sampling unevenly (Sheffield et al 2009).…”

The complete mitochondrial genome of Grapsus tenuicrustatus (Herbst, 1783) (Decapoda, Grapsidae)

“…Families Grapsidae and Varunidae have sister group relationship and Xenograpsidae early branched in the superfamily Grapsoidea (Figure 1). Similar results were observed in previous nuclear and mitochondrial gene-based molecular study (Tsang et al 2014). This mitochondrial genome data provide genetic markers for phylogenetic of the grapsid crabs, which will be a part of mitochondrial genome library for provide evolutionary and systematic studies.…”

Complete mitochondrial genome of Leptodius sanguineus (Decapoda, Xanthidae)

“…The phylogenetic study showed that L. sanguineus positioned in the family Xanthidae and it has sister group relationship with a lineage including the families Portunidae and Menippidae in the subsection Heterotremata (Figure 1). Similar results showed previously by the combination of the six nuclear genes-and two mitochondrial genes-based molecular studies (Tsang et al 2014). This is the first report for L. sanguineus complete mitochondrion sequence information.…”