Phenotypic divergence and eco-evolutionary dynamics in moor frog tadpoles

Quentin Corbel , Mariella Kaiser, Jelena Mausbach, Anssi Laurila, Katja Räsänen

In the face of rapid environmental change, persistence of natural populations often relies on evolutionary rescue. Such rapid evolution can, in turn, affect ecosystem properties (i.e. cause evo-to-eco effects), as recently documented across taxa and ecosystems. Amphibians often act as keystone species, making them ideal candidates for studying eco-evolutionary dynamics, yet empirical studies remain rare. We aimed to bridge this gap in the moor frog (Rana arvalis), known for adaptive phenotypic plasticity and local adaptation to environmental acidification. To investigate context-dependent phenotypic divergence and potential for ecosystem feedbacks we performed an outdoor mesocosm experiment on R. arvalis tadpoles. We used a full-factorial design, rearing tadpoles from two different population origins (pH 4 vs 7) in two contrasting environments (pH 4.3 vs 8.4). Additionally, we included no-tadpole mesocosms in each pH environment to assess population origin effects relative to a no-tadpole baseline. We found that tadpoles exhibited substantial phenotypic plasticity in physiological and life-history traits (higher corticosterone levels, faster development, larger metamorphic size, and different diets in the pH 4.3  as compared to pH 8.4 environments) and environment dependent divergence between populations: acid-origin tadpoles had higher survival in the pH 4.3 environment, larger metamorphic size in both pH environments, and relatively longer guts in the pH 8.4 environment than neutral-origin tadpoles. Additionally, tadpole presence reduced light penetration in pH 4.3, and decreased zooplankton density while increasing phytoplankton density in pH 8.4. Finally, in the pH 4.3 environment, acid-origin tadpoles reduced phytoplankton (relative to neutral origin tadpoles), whereas in the pH 8.4 environment neutral origin tadpoles reduced periphyton while acid origin tadpoles reduced vegetation biomass (relative to the no-tadpole baseline). These results demonstrate marked phenotypic plasticity and divergence in R. arvalis tadpoles under ecologically relevant conditions, the central ecological role of tadpoles in ecosystems, and the potential for their evolutionary divergence of tadpoles to alter ecosystem function. These results indicate that plastic and/or evolved trait divergence of tadpoles can reshape eco-evolutionary dynamics in freshwater ecosystems. In light of global amphibian declines, understanding such context-dependent eco-evolutionary dynamics is vital for predicting ecosystem responses and informing conservation strategies.