Global diversity of crabs (Crustacea: Decapoda: Brachyura) in freshwater

The apparent biotic affinities between the mainland and the island in the Western Ghats-Sri Lanka biodiversity hotspot have been interpreted as the result of frequent migrations during recent periods of low sea level. We show, using molecular phylogenies of two invertebrate and four vertebrate groups, that biotic interchange between these areas has been much more limited than hitherto assumed. Despite several extended periods of land connection during the past 500,000 years, Sri Lanka has maintained a fauna that is largely distinct from that of the Indian mainland. Future conservation programs for the subcontinent should take into account such patterns of local endemism at the finest scale at which they may occur.

The phylogenetic relationships among the southern African freshwater crab species were examined using partial sequence data from three mitochondrial genes (12S rRNA, 16S rRNA, and mtDNA COI) 26 morphological characters and 14 allozyme loci. The aims of the present study were firstly to determine whether freshwater crab species that live in the same geographic region share a close phylogenetic relationship. Secondly, to investigate whether hybridizing species are genetically closely related and thirdly, to test for the validity of subgenera based on the genetic data sets. Phylogenetic analysis based on sequence data revealed largely congruent tree topologies and some associations had consistently high bootstrap support, and these data did not support Bott's subgeneric divisions. The morphological data were less informative for phylogenetic reconstruction while the allozyme data generally supported patterns recovered by the sequence data. A combined analysis of all the data recovered two monophyletic clades, one comprised of small-bodied mountain stream species and the other clade consisting of large-bodied riverine species. The combined analyses reflected clear biogeographic patterning for these river crabs. In addition, there was a clear correlation between genetic distance values and the ability of sympatric species to hybridize.