2026-09-28 国立遺伝学研究所
図1．2011年の東日本大震災によって形成された湧水池と交雑集団
左：2011年の東日本大震災に伴う津波と地盤沈下によって岩手県大槌町に形成された湧水池（撮影：森誠一）。
中央：この池で発見されたイトヨとニホンイトヨの交雑集団（撮影：細木拓也）。
右：津波によって海洋性のニホンイトヨが、引き波によって河川上流の淡水性のイトヨが湧水池へ運ばれ、両種が接触し、異種間交雑が生じたと考えられる模式図（イラスト：木下ちひろ）
＜関連情報＞
津波による交雑後のトゲウオ集団におけるゲノム全体の急速な浄化 Rapid genome-wide purging following tsunami-induced hybridization in a stickleback population
Takuya K. Hosoki, Seiichi Mori, Kotaro Kagawa, Shotaro Nishida, Manabu Kume, Atsushi J. Nagano, Hiyu Kanbe, Ryo Kakioka, Kenta Nakamoto, Yuki Iino, Masafumi Kodama, Satoki Oba, Taekyoung Seong, Naoki Kabeya, Asano Ishikawa, Kohta Yoshida, Yo Y. Yamasaki & Jun Kitano
Nature Ecology & Evolution Published:25 September 2026
DOI:https://doi.org/10.1038/s41559-026-03184-1
Abstract
Speciation is the process by which barriers to gene flow evolve between populations. As speciation approaches completion, genome-wide divergence can be maintained in the face of hybridization. Because real-time observations of genomic changes following hybridization in natural populations remain rare, little is known about the processes and mechanisms by which introgressed genomes are purged in nature. 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. Elucidating the genetic mechanisms underlying genome-wide purging is crucial for understanding the factors that drive progress towards speciation completion.
