Japan tsunami triggered rapid evolution in stickleback fish

A study published in Nature Ecology & Evolution reveals how the 2011 tsunami in Japan triggered an unprecedented hybridization event between two stickleback fish species. The disaster created new coastal lagoons in Otsuchi, forcing the marine species Gasterosteus nipponicus and the freshwater species Gasterosteus aculeatus to coexist after being separated for approximately 680,000 years.

Researchers tracked the population for nine years, observing rapid evolutionary changes. While 38% of the fish analyzed in 2012 were hybrids, by 2020, the population had shifted almost entirely toward the genetic makeup of the freshwater species, Gasterosteus aculeatus. This shift suggests that natural selection quickly eliminated marine genetic traits that were less suited to the freshwater environments formed in the post-tsunami lagoons.