Japan's 2011 tsunami sparked fish hybridization, but species boundaries largely held
How are species boundaries maintained in the face of environmental disturbance? This is not only a fundamental question in evolutionary biology but also an increasingly important one as human activities and climate change alter habitats and bring previously separated species into contact.
In 2011, Japan's tsunami inundated coastal habitats, transporting marine stickleback and freshwater threespine stickleback into newly formed freshwater environments near Otsuchi Town. This ecological disturbance led to the hybridization of these closely related fish species. Following the event, a research team monitored a hybrid population for nine years, observing that 38% of individuals were hybrids in 2012.
Over the subsequent years, foreign genetic material from the marine stickleback rapidly diminished, with the population returning to a nearly pure composition of the freshwater species by 2020. The study, published in Nature Ecology & Evolution, found that major reproductive isolation loci, including those related to freshwater adaptation and hybrid male sterility, experienced significant loss of G. nipponicus ancestry.
However, the removal of foreign genetic material was not solely driven by these strong reproductive barriers. Instead, numerous weak genetic incompatibilities throughout the genome also contributed to the rapid elimination of G. nipponicus ancestry, suggesting a complex interplay between several genetic factors in maintaining species boundaries following hybridization events.
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