Influence of Thermal Fluctuations on the Post-Metamorphic Morphological Traits of Rhinella diptycha

Abstract

Daily thermal fluctuations (DTF) represent a significant challenge for ectotherms, as the non-linear relationship between temperature and physiological processes leads to increased metabolic demands at higher temperatures. These conditions can result in energetic trade-offs that affect growth and development. This study experimentally evaluated the effect of DTF on the duration of the larval period and the morphology of metamorphic individuals of Rhinella diptycha, comparing these effects with those observed under constant temperature conditions. Six treatments were established: three with fluctuating temperatures (24–26 °C, 24–30 °C, and 24–34 °C) and three with constant temperatures (26 °C, 30 °C, and 34 °C). Twenty larvae were raised per treatment, from Gosner stage 26 to metamorphosis, with temperature regulated every 12 hours using automatic heaters. Nine morphological variables, body mass, and time to metamorphosis were recorded.

Analyses included principal component analysis to reduce dimensionality, MANOVA to assess effects on morphological traits and body mass, and ANOVA to evaluate the effect of temperature on larval development time. Results showed that DTF had a positive effect on the morphology of metamorphic individuals compared to constant temperatures. Specifically, the lengths of forelimbs and hindlimbs, as well as radio-ulna distance, were greater under fluctuating conditions. These findings highlight the importance of considering both thermal fluctuations and average temperatures when assessing the effects of thermal environments on amphibian development, providing key insights into ectothermic responses to climate change scenarios.