Tree-climbing mangrove crabs, a case of convergent evolution

Several crab species of the families Sesarmidae and Grapsidae (Crustacea: Brachyura: Grapsoidea) are known to climb mangrove trees. They show different degrees of dependence on arboreal life, with only a few of them thriving in the tree canopies and feeding on fresh leaves. Some of the sesarmid tree-dwelling crabs share a number of morphological characters and therefore have been considered to be of monophyletic origin. A phylogeny derived from 1038 base pairs of the mitochondrial DNA encoding the small and large ribosomal subunits was used to examine the evolutionary origin of tree-climbing behaviour within the Grapsoidea, and to determine whether morphological and ecological similarities are based on convergence or common ancestry. The analysis included African, American and Asian arboreal crab species plus several representatives of ground-living forms. Our results suggest that the very specialized arboreal lifestyle evolved several times independently within grapsoid mangroves crabs, providing another striking example of the likelihood of convergence in evolutionary biology and the degree of phenetic and ecological potential to be found among marine organisms.