Japan's 2011 tsunami sparked fish hybridization, but species boundaries largely held

Key Points:

• A 2011 tsunami in northeastern Japan brought two closely related stickleback fish species, Gasterosteus nipponicus and Gasterosteus aculeatus, into contact, resulting in hybridization within newly formed freshwater habitats.
• A nine-year study tracked this hybrid population and found that the proportion of G. nipponicus genomic regions rapidly declined, with the population returning to almost entirely G. aculeatus genetics within about 10 generations.
• Genomic regions linked to major reproductive isolation traits such as freshwater adaptation, migration, mate choice, and hybrid male sterility were purged quickly, but numerous weak genetic incompatibilities across the genome also contributed to the elimination of foreign DNA.
• The findings suggest that a combination of strong reproductive barriers and many weak genetic incompatibilities may be a general mechanism maintaining species boundaries despite hybridization.
• This study, published in Nature Ecology & Evolution, provides rare direct evidence from a natural population on how species boundaries are maintained through the progressive removal of foreign genomic regions after hybridization.