2025-10-23 京都大学
京都大学の研究チームは、サケ科魚類ヤマメの生態を対象に、流域全体における「生き方の多様性」を定量的に解明した。源流から本流までの複数河川で大規模調査を実施した結果、同じ川でも環境条件や季節性の違いにより、定住型・降海型・成長速度などが多様化していることが分かった。こうした個体群の多様性が、流域全体の適応力や環境変化へのレジリエンスを支えているという。本研究は、生態的多様性を「進化的保険」として位置づけ、河川生態系の保全戦略に新たな視点を提示するものである。成果は『Journal of Animal Ecology』誌に掲載。
河川流域で育まれるヤマメの多様な生き方の概要
<関連情報>
- https://www.kyoto-u.ac.jp/ja/research-news/2025-10-23
- https://www.kyoto-u.ac.jp/sites/default/files/2025-10/2510_JoAniEco_Sato-Shida_relj%20web_-a715a6b905fe6b9dae450c35f06e9416.pdf
- https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2656.70141
河川景観において階層的に維持されるサケ科⿂類の⽣活史変異:季節的な成⻑機会と成熟意思決定の関連性 Hierarchical organization of life-history variation in a salmonid fish across riverscape: Relevance of seasonal growth opportunity and maturation decision-window
Takeya Shida, Takuya Sato
Journal of Animal Ecolog Aceeptid:11 August 2025
DOI:10.1111/1365-2656.70141
abstract
- Understanding life-history variation maintained across landscapes is crucial for revealing the spatial scale at which adaptation and population stability manifest. Previous studies have often focused on population mean life history and its differences between habitats, overlooking variation within local habitats and its relative contribution to life-history variation at the landscape scale.
- By integrating a year-round survey of spatial heterogeneity in stream temperature and prey resource dynamics with a life-history survey for a masu salmon Oncorhynchus masou masou inhabiting a large watershed, we examined here how relative phenologies of seasonal growth and the maturation decision window have potentially shaped within-habitat and between-habitat variation in life history across the watershed.
- We found that fast-life individuals tended to dominate downstream reaches, characterized by warmer temperature, abundant aquatic invertebrate prey, and fewer terrestrial invertebrate inputs. On the other hand, slow-life individuals were more prevalent in upstream reaches, characterized by colder temperature, fewer aquatic invertebrate prey, but relatively abundant terrestrial invertebrate subsidies. However, there was considerable variation in the age of mature fish in all reaches except the most downstream and upstream reaches. The variation partitioning for the age of mature fish across the watershed revealed that the proportional contribution of within-habitat variation was unexpectedly higher (84% in females, 88% in males) than that of between-habitat variation in both sexes (16% in females, 12% in males).
- These results highlight the need to acknowledge the hierarchical structure of life-history variation, especially within-habitat variation, to fully understand the spatial scales at which the life-history variation is maintained and its functions, such as population stabilization and adaptive evolution, are operated.
