Thermal ecology and swimming performance of native tadpoles Dryophytes femoralis in central Florida

Abstract

Urbanization and climate warming have contributed to global amphibian declines in recent decades, and amphibians are particularly vulnerable to warming because temperature influences their physiological processes across all life stages. Tadpole responses to warming in tropical climates are relatively understudied, and previous studies demonstrated species-specific responses to warming temperature. Warming ponds may quicken tadpole development and increase thermal tolerances, but increasing local temperatures push populations towards their physiological limits. Specifically, baseline responses of thermal ecology traits of pinewoods tree frog (Dryophytes femoralis) tadpoles in Florida to warming temperature are unknown. Herein, we tested if the thermal ecology and swimming performance of a native Florida tadpole varied with rearing temperature to determine if these traits exhibit plasticity. We collected eggs from wild populations of D. femoralis in Central Florida and utilized common garden experiments to assess critical thermal maximum (CT_max), minimum (CT_min), thermal safety margins (T_sm), thermal preference (T_set), and swimming performance across different rearing temperatures. Importantly, variation in traits was better explained by clutch ID, indicating the role of maternal effects. Increases in critical thermal thresholds and thermal safety margins at warmer rearing temperatures suggest plasticity in these traits and potential to adapt to rising temperatures. While thermal preference appeared fixed, complex interactions between rearing temperature and test temperature predicted swimming performance. These results demonstrate that although D. femoralis tadpoles have the ability to adjust their thermal thresholds – the responses of other critical traits, like swimming performance are less clear, at least within the temperature range tested in this study. However, warming ponds may soon exceed the temperatures tadpoles can tolerate, even via phenotypic plasticity. Our findings emphasize the need to prioritize the conservation of cooler habitats and fill in gaps in our understanding of species-specific responses to a warming environment, to ensure the survival of vulnerable amphibian populations.