MECHANISMS OF PHENOTYPIC PLASTICITY IN AMPHIBIANS EXPOSED TO RAPID TEMPERATURE FLUCTUATIONS IN BREEDING HABITATS

Abstract

Amphibians are increasingly exposed to rapid and unpredictable temperature fluctuations in breeding habitats due to climate change, yet the underlying mechanisms enabling phenotypic plasticity remain poorly understood. This study investigated the developmental, physiological, behavioral, and molecular responses of Rana temporaria larvae reared under three temperature regimes: constant (18°C), diel fluctuation (15–21°C), and high-amplitude thermal spikes (15–25°C). Larvae exposed to fluctuating temperatures developed significantly faster but metamorphosed at smaller sizes and exhibited reduced survival rates, particularly under thermal spikes. Metabolic assays revealed elevated basal and maximum oxygen consumption in fluctuating groups, indicating increased physiological demands, while aerobic scope remained relatively stable. Whole-body corticosterone (CORT) levels were significantly higher under thermal variability, especially in the spike group, suggesting stress-induced hormonal regulation. Gene expression analyses demonstrated pronounced upregulation of Hsp70, Dio2, and Crhbp, linking molecular stress responses and hormonal modulation to environmental variability. Behavioral assessments further revealed increased hiding, feeding latency, and activity levels in fluctuating environments, with the most intense behaviors observed under spike conditions. Collectively, these results reveal an integrative suite of plastic responses spanning morphological, endocrine, and genetic levels that enable amphibians to partially buffer the effects of temperature variability. However, the trade-offs in growth and survival underscore the potential limits of this plasticity under extreme or prolonged stress. This study provides novel empirical evidence for mechanistic plasticity in amphibians and highlights the importance of incorporating thermal variability—not just mean temperature changes—into ecological models and conservation strategies aimed at predicting amphibian responses to climate change.