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<p>As global warming progresses, many tropical and subtropical species are now observed in temperate regions, including the Japanese Archipelago. Similar range shifts are also expected within species, with increasing influxes of individuals from southern populations, potentially altering their population genetic structures. The flagtail <i>Kuhlia marginata</i> and <i>Kuhlia rupestris</i> (Perciformes: Kuhliidae) are catadromous fishes distributed across the tropical and subtropical western Pacific and adjacent areas. They are believed to reproduce around the Ryukyu Islands in Japan as well. Carried by warm currents, such as the Kuroshio Current, they appear in the Japanese Archipelago, but are generally thought to die during winter. However, recent reports suggest their successful overwintering in certain areas in the archipelago. Global warming may enable such individuals to reproduce around the Japanese Archipelago or increase the influx of individuals from more southern regions to both the Japanese Archipelago and the Ryukyu Islands, raising the possibility of changes in population structures in Japan. To explore such potential changes, we investigated the current population genetic structure of these two species in Japan. Population analyses based on partial mitochondrial DNA sequences (including publicly available data) and genome-wide polymorphism data obtained by the MIG-seq method supported the hypothesis that each species constitutes a single population within Japan. In addition, there was no significant difference in the genetic diversity indices between regional samples from the Japanese Archipelago and the Ryukyu Islands. These results propose two possible scenarios: <i>K. marginata</i> and <i>K. rupestris</i> reproduce in the Ryukyu Islands and a significant number of juveniles born from genetically unbiased parentals are transported to the Japanese Archipelago by the Kuroshio Current, sufficient to maintain the genetic diversity of the original population; or these species reproduce mainly in more southern regions, not even around the Ryukyu Islands, and the individuals born in the former are transported to Japan. In addition, the subtle population structure observed exclusively in the mtDNA of <i>K. rupestris</i> across the western Pacific suggests that ecological differences between <i>K. marginata</i> and <i>K. rupestris</i> have contributed to their different population structures, and may further lead to divergent changes in their future population structures.</p>

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Genetic population structure of two catadromous flagtail species, Kuhlia marginata and Kuhlia rupestris, in Japan

  • 期刊论文

  • 发表日期：

    2026年3月25日

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  • Jo Hamahashi,
  • Yoshimitsu Takada,
  • Katsutoshi Watanabe

摘要

As global warming progresses, many tropical and subtropical species are now observed in temperate regions, including the Japanese Archipelago. Similar range shifts are also expected within species, with increasing influxes of individuals from southern populations, potentially altering their population genetic structures. The flagtail Kuhlia marginata and Kuhlia rupestris (Perciformes: Kuhliidae) are catadromous fishes distributed across the tropical and subtropical western Pacific and adjacent areas. They are believed to reproduce around the Ryukyu Islands in Japan as well. Carried by warm currents, such as the Kuroshio Current, they appear in the Japanese Archipelago, but are generally thought to die during winter. However, recent reports suggest their successful overwintering in certain areas in the archipelago. Global warming may enable such individuals to reproduce around the Japanese Archipelago or increase the influx of individuals from more southern regions to both the Japanese Archipelago and the Ryukyu Islands, raising the possibility of changes in population structures in Japan. To explore such potential changes, we investigated the current population genetic structure of these two species in Japan. Population analyses based on partial mitochondrial DNA sequences (including publicly available data) and genome-wide polymorphism data obtained by the MIG-seq method supported the hypothesis that each species constitutes a single population within Japan. In addition, there was no significant difference in the genetic diversity indices between regional samples from the Japanese Archipelago and the Ryukyu Islands. These results propose two possible scenarios: K. marginata and K. rupestris reproduce in the Ryukyu Islands and a significant number of juveniles born from genetically unbiased parentals are transported to the Japanese Archipelago by the Kuroshio Current, sufficient to maintain the genetic diversity of the original population; or these species reproduce mainly in more southern regions, not even around the Ryukyu Islands, and the individuals born in the former are transported to Japan. In addition, the subtle population structure observed exclusively in the mtDNA of K. rupestris across the western Pacific suggests that ecological differences between K. marginata and K. rupestris have contributed to their different population structures, and may further lead to divergent changes in their future population structures.