Urbanisation and eutrophication as drivers of morphological and physiological divergence among riverine fish populations

Abstract

Abstract Freshwater ecosystems are highly impacted by human activities, but the effects of human‐induced perturbations on fish phenotypic divergence remain poorly understood, especially in riverine systems. In this study, we tested the effects of urbanisation and eutrophication on several morphological and physiological traits in 17 gudgeon populations of Gobio occitaniae from South of France. We first demonstrated that eutrophication gradient was associated with changes in morphology and energy reserves, while urbanisation was associated with changes in body condition. More specifically, fish from highly eutrophic sites had deeper bodies and larger jaws, and a higher lipid content in their muscles. Urban fish had a higher body condition compared to their rural counterparts. The phenotypic divergence (Pst) among sites was significantly higher than the neutral genetic differentiation (Fst), suggesting that these morphological and physiological differences cannot be explained by neutral genetic drift alone. This study thus suggests that eutrophication and urbanisation are major drivers of phenotypic divergence in riverine fish populations, and calls for further experimental studies investigating the ecological and evolutionary effects of human activities on riverine fish populations.