ABSTRACT
The phylogeny of the Asian freshwater crabs of the family Gecarcinucidae is investigated using the mitochondrial large subunit rRNA gene and the nuclear encoded histone 3 gene. The results confirm the monophyly of the Gecarcinucidae. A division into two families, Gecarcinucidae and Parathelphusidae, is not supported. Therefore, and in consideration of the unresolved family relationships, all Old World freshwater crabs are assigned to one superfamily, the Potamoidea. The evolution of structures of the second gonopod within the Gecarcinucidae is shown to involve convergent reduction of a complex-type groove to a simple-type groove or its complete absence. Gecarcinucids without a frontal triangle are shown to form a paraphyletic group. Thus, these morphological characters are of minor importance for clarifying phylogenetic relationships within the Gecarcinucidae. Genetically, the Gecarcinucidae can be differentiated and separated into seven monophyletic lineages and an assemblage of as yet unresolved Indian groups. We identify the Malay Peninsula and Borneo (particularly Sabah and Sarawak), where representatives of four of these lineages occur, as a hotspot of gecarcinucid diversity. In agreement with our phylogenetic results, an early radiation of the Gecarcinucidae on the Indian subcontinent is postulated along with several dispersal events from Sundaland into the Malesian (Malaysian) Archipelago.
