Interplay of Diet, Heat Stress, and the Microbiome Shapes Health and Escape Behaviour in Amphibian Larvae.

Diet influences animal health and their microbiomes, potentially affecting how they cope with environmental stressors such as rising temperatures and altered food quality associated with climate change. Using a multifactorial experiment, larvae of the frog Rana temporaria were reared on three diets differing in protein, fat, and animal-derived components (low-, intermediate-, and high-quality), at two temperatures (18°C and 24.5°C), and either exposed or not to a simulated heatwave (28°C for 48 h). We examined how these treatments and associated shifts in gut bacterial indicators and predicted microbial metabolic pathways related to nutrient assimilation, host health (body condition and developmental rate), and escape behaviour. Larvae maintained body condition and developed faster at 24.5°C, with higher diet quality further accelerating development. An intermediate-quality diet reduced responsiveness to an aversive stimulus at 24.5°C, although this effect disappeared following heatwave exposure. Heatwave conditions were associated with increased abundance of Klebsiella and a predicted increase in the myo-inositol degradation pathway, which may influence membrane dynamics and signalling and may increase attention levels. Despite microbial shifts, host performance remained similar across most treatments, suggesting substantial microbiome plasticity and the presence of functionally redundant enterotypes that help buffer environmental stress.