Local differences of thermal preferences in European common frog (Rana temporaria Linnaeus, 1758) tadpoles

Physiological functions of ectotherms and thus their performance depend on environmental temperatures. Many ectotherms are capable of active thermoregulation, e.g. by selecting suitable microhabitats. However, this may be constrained by unavailability of favourable microhabitats or high energetic costs of thermoregulation. Thus, to achieve the optimal performance levels, adaptations to local thermal environments are of great importance. Due to the inability of leaving their aquatic habitat, larval anurans should especially benefit from local thermal adaptations. Rana temporaria is a widely distributed European anuran species, inhabiting a range of microhabitats, which makes it an excellent model to study the potential of local thermal adaptation. We raised R. temporaria tadpoles from Germany and Croatia under respective natural temperature fluctuations and three constant temperatures (15°, 20° and 25 °C), and tested dependency of their thermal preferences on the developmental stage and temperature regime, and the population origin. Tadpoles of both origins selected higher temperatures towards the end of the developmental period, and their thermal preferences were affected by the developmental temperature. However, regardless of the developmental stage or treatment, tadpoles from warmer Croatia selected higher temperatures than tadpoles from colder Germany. This demonstrates the tendency of adjusting the sensitivity of physiological processes to local thermal conditions.