Adaptive radiations are are a composite phenomenon, characterized by a complex series of successive processes, starting with invasion followed by adaptation and speciation, and ending with evolutionary community assembly into many sympatric species as four critical stages that lead to a fully fledged adaptive radiation. We use next generation sequencing, bioinformatics and population genomic modeling to investigate genetic constraint and facilitation of the four critical stages in a single analytical and conceptual framework. We study adaptive radiation processes in stickleback and cichlid fish, having occurred over different time scales: from 100 years (Swiss invasive sticklebacks), to several tens of thousands of years (older clades of Lake Victoria cichlids). Sticklebacks and haplochromine cichlids share an unusual propensity to rapid speciation, orders of magnitude faster than in most other animals. Yet haplochromines and sticklebacks markedly differ in their ability to generate sympatric species diversity. Stickleback have radiated into hundreds of very young species distributed over all the coastal regions of the northern hemisphere. However, most species pairs diverged just a few thousand years ago, while older species are very rare, and there are never more than two species in any one site. On the other hand, haplochromine cichlids have also radiated into hundreds of species, but tens or hundreds of species, often not much older than the stickleback species, can be found sympatrically at a single site. We are investigating genomic variation, its origins and the architecture of adaptation and reproductive isolation in these two taxa.
