Japan’s 2011 tsunami sparked fish hybridization, but species boundaries largely held
[post_content]
Disclaimer: This article has been automatically aggregated from
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.
As mechanisms preventing gene exchange between populations, known as reproductive isolation, accumulate, populations can eventually diverge into separate species. When reproductive isolation is incomplete, however, environmental changes can bring closely related species into contact and lead to hybridization. For species boundaries to persist despite extensive hybridization, many of the genomic regions introduced from another species must be eliminated. Yet how rapidly this process occurs in nature, and which reproductive isolation mechanisms contribute to the removal of foreign genomic regions, have remained poorly understood.
A tsunami brings two species together
The tsunami triggered by the Great East Japan Earthquake in 2011 dramatically altered habitats along the Pacific coast of northeastern Japan. Otsuchi Town in Iwate Prefecture was struck by a tsunami exceeding 10 meters (33 feet) in height.
The tsunami and subsequent backwash are thought to have brought the marine Japan Sea stickleback, Gasterosteus nipponicus, from the sea and a freshwater population of the threespine stickleback, Gasterosteus aculeatus, from upstream into newly formed freshwater habitats in the town center. This brought the two closely related fish species into contact and resulted in interspecific hybridization.
Hybrid ancestry declines over nine years
A research team comprising scientists from the National Institute of Genetics (NIG), Hokkaido University, Gifu Kyoritsu University, Kyoto University, Ishinomaki Senshu University, Nagoya University, Keio University, The University of Tokyo, and Tokyo University of Marine Science and Technology tracked this hybrid population for nine years. In 2012, 38% of the individuals sampled were hybrids.
Over the following years, however, genomic regions derived from G. nipponicus rapidly declined across the genome, and by 2020 the population had returned to an almost entirely G. aculeatus genomic composition. Because the generation time of this population is approximately one year, most of the G. nipponicus-derived genome was eliminated within about 10 generations.
The study is published in the journal Nature Ecology & Evolution.
Strong barriers and weaker incompatibilities
Genomic regions containing major reproductive isolation loci associated with freshwater adaptation, migration to the sea, mate choice, and hybrid male sterility showed particularly rapid declines in G. nipponicus ancestry. However, these major loci alone could not explain the genome-wide removal observed over 10 generations. Individual-based simulations suggested that numerous weak genetic incompatibilities distributed throughout the genome may also have contributed to the rapid elimination of G. nipponicus ancestry.
“There were two major surprises in this study,” said Takuya Hosoki and Jun Kitano. “First, we did not expect genomic regions associated with major reproductive barriers to be purged so rapidly. Second, we were surprised that most of the foreign genome continued to disappear over subsequent generations. An important next question is whether this combination of a few strong reproductive barriers and many weak genetic incompatibilities represents a general mechanism by which species boundaries are maintained after hybridization.”
This study is one of the few to track genomic changes in a natural population from immediately after interspecific hybridization through approximately 10 generations. By directly observing the progressive removal of foreign genomic regions, the study reveals how multiple reproductive barriers can work together to maintain species boundaries following extensive hybridization.
Publication details
Takuya K. Hosoki et al, Rapid genome-wide purging following tsunami-induced hybridization in a stickleback population, Nature Ecology & Evolution (2026). DOI: 10.1038/s41559-026-03184-1
Provided by
Research Organization of Information and Systems
Citation:
Japan’s 2011 tsunami sparked fish hybridization, but species boundaries largely held (2026, September 27)
retrieved 27 September 2026
from https://phys.org/news/2026-09-japan-tsunami-fish-hybridization-species.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.
for informational purposes only. We do not claim ownership, accuracy, or liability for the content provided. All rights belong to the original publisher.