Hidden Diversity of Madagascan Freshwater Crabs (Brachyura: Potamoidea) Revealed by Morphological and Molecular Studies

This study focuses on the freshwater crab fauna of the island of Madagascar. Relatively little is known about the species diversity of the island’s freshwater crabs and their phylogenetic relationships. Chapter 1 is based on a newly published molecular phylogeny that used the highest taxonomic sampling to date, including almost all of the island’s known freshwater crab genera and species. The phylogeny revealed a significant number of unidentified specimens that belong to several new lineages that potentially represent as many as 4 new genera and 10 new species. Chapters 2 and 3 focus on the taxonomic revision of the genus Foza, which was found to be polyphyletic because its four assigned species were positioned on three separate lineages within the tree. Chapter 4 reconstructs ancestral character states by mapping morphological characters onto the molecular phylogeny of the Malagasy freshwater crabs to better understand character evolution in these crabs. Character states of the mandibular palp, the ambulatory legs, and the gonopods were mapped onto the molecular phylogeny for all 24 species of Malagasy freshwater crabs. Patterns were interpreted in the context of monophyletic groups on the tree. The results indicated that the early ancestors of the Malagasy freshwater crabs likely had a mandibular palp with a medium sized anterior lobe, short ambulatory legs, and a first gonopod with a medium length terminal article that tapered to a pointed tip. Unusually long ambulatory legs belong to three different genera in unrelated lineages. This trait appears to be the result of convergent evolution