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<p>Mechanisms of adaptive phenotypic divergence between populations in discrete or contrasting environments have been well studied. However, species and populations often experience continuous environmental variability, such as gradual shifts in prey composition and availability across habitats. In populations inhabiting continuously heterogeneous environments with migration and gene flow, phenotypic patterns can be complex due to admixture of individuals under diverse selection pressures. Here, we investigated morphological variation, habitat use, diet, and fine-scale genetic structure in a benthic freshwater fish, <i>Pseudogobio esocinus</i>, widely distributed in Japan, focusing on the population in the Yura River, a system characterized by high environmental heterogeneity. We found that (1) despite migration and gene flow, individuals diverged in feeding and locomotion traits among habitat types; (2) even within habitats, individuals exhibited continuous phenotypic variation correlated with diet composition; and (3) these phenotypic patterns were partly influenced by gene flow from an artificially introduced lake population. Overall, our findings suggest that, even under migration across heterogeneous environments, diverse phenotypic variation can arise and persist at multiple spatial scales as local adaptations. This diversity highlights the flexible potential of generalist populations to thrive across ecological contexts by leveraging genetic variation introduced through immigration to facilitate adaptive diversification.</p>

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Eco-morphological variation with gene flow in a benthic fish across heterogeneous riverine habitats

  • 期刊论文

  • 发表日期：

    2026年7月8日

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  • Chiharu Endo,
  • Hikaru Nakagawa,
  • Katsutoshi Watanabe

摘要

Mechanisms of adaptive phenotypic divergence between populations in discrete or contrasting environments have been well studied. However, species and populations often experience continuous environmental variability, such as gradual shifts in prey composition and availability across habitats. In populations inhabiting continuously heterogeneous environments with migration and gene flow, phenotypic patterns can be complex due to admixture of individuals under diverse selection pressures. Here, we investigated morphological variation, habitat use, diet, and fine-scale genetic structure in a benthic freshwater fish, Pseudogobio esocinus, widely distributed in Japan, focusing on the population in the Yura River, a system characterized by high environmental heterogeneity. We found that (1) despite migration and gene flow, individuals diverged in feeding and locomotion traits among habitat types; (2) even within habitats, individuals exhibited continuous phenotypic variation correlated with diet composition; and (3) these phenotypic patterns were partly influenced by gene flow from an artificially introduced lake population. Overall, our findings suggest that, even under migration across heterogeneous environments, diverse phenotypic variation can arise and persist at multiple spatial scales as local adaptations. This diversity highlights the flexible potential of generalist populations to thrive across ecological contexts by leveraging genetic variation introduced through immigration to facilitate adaptive diversification.