Evidence item

Here we report a 9-year genomic monitoring of a tsunami-induced hybrid stickleback population, revealing rapid genome-wide purging within only a few generations. On 11 March 2011, a devastating tsunami struck the Tohoku Region, Japan, creating new stickleback habitats and inducing hybridization between freshwater Gasterosteus aculeatus and marine Gasterosteus nipponicus. Within the first few generations, G. nipponicus alleles were purged at major loci responsible for reproductive isolation, including ancestral-X and neo-X chromosomes. These loci are involved in freshwater survival, migratory divergence associated with habitat choice, sexual isolation and hybrid sterility. Subsequently, G. nipponicus alleles were purged across the genome except at several loci. We provide direct evidence from a natural population that rapid genome-wide purging allows species identity to persist even after extensive introgression.