Madagascar is a global biodiversity hotspot with an exceptional level of endemism across every organism group, terrestrial as well as aquatic. The proportion of endemic species in different groups is usually correlated with dispersal ability. Diving beetles (fam. Dytiscidae) is the largest family of aquatic beetles (c. 4300 species) and is one of four major generalist predators in freshwater ecosystems and Madaglymbus, with around 20 species, represents the largest readiation of species in Madagascar waterbeetles. For different groups of animals that have speciated on the island divergent patterns have been found regarding the geographical mode and process of speciation. For some groups larger rivers seems to constitute dispersal barriers whilst others seems to have speciated over climatic gradients. In this study, part of a VR-grant (621-2013-5170 to Johannes Bergsten), we will reconstruct the phylogeny of Madaglymbus to investigate the geographical and temporal pattern of diversification. This will be the first such study on a freshwater radiation on Madagascar. For phylogenetic reconstruction, RAD-seq method have proved efficiency in closely related group of species. We have selected about 3-4 individuals per species spread geographically. There is little knowledge of the genome size of diving beetles in general but some estimates by flow cytometry measures have been found in the literature varying from 700Mb to 2.5 Gb. There have not been any dated studies on the subfamily Copelatinae to which Madaglymbus belong so the age of the genus is unknown. Recent analyses suggest its sister group is the South American Agaporomorphus which suggest an old stem group. But a similar radiation of a related Copelatinae genus in stream habitats, Exocelina, in Papua New Guinea and Australia was analyzed and dated to not more than 15 million years old and over 140 species. However, as the dating was done with a mitochondrial clock rate this may be an underestimate.