The genomics of organismal diversification illuminated by adaptive radiations

• We review progress in understanding adaptive radiation based on genomic approaches.
• Features of genome architecture promoting diversification have not been identified.
• Access to ancient genetic variation emerges as a key driver of diversification.
• Convergent evolution facilitates the detection of adaptation genes.

Adaptive radiation is the rapid and extensive ecological diversification of an organismal lineage to generate both phenotypic disparity (divergence) and similarity (convergence). Demonstrating particularly clear evidence of the power of natural selection, adaptive radiations serve as outstanding systems for studying the mechanisms of evolution. We review how the first wave of genomic investigation across major archetypal adaptive radiations has started to shed light on the molecular basis of adaptive diversification. Notably, these efforts have not yet identified consistent features of genomic architecture that promote diversification. However, access to a pool of ancient adaptive variation via genetic exchange emerges as an important driver of adaptive radiation. We conclude by highlighting avenues for future research on adaptive radiations, including the discovery of ‘adaptation genes’ based on genome scans using replicate convergent populations.