Hahn, B. & M.-O. Rödel

Thermal relationships in the habitat use of Bombina variegata tadpoles. pp. 206-214.

Abstract. If ectothermic animals live in habitats where temperatures reach their upper thermal limit, global warming may be problematic, particularly if the animals cannot escape from their respective habitats. Tadpoles of the Yellow-bellied Toad, Bombina variegata, develop in small, temporary water bodies that are exposed to the sun and prone to short-term temperature fluctuation, extreme heat events, and high risk of desiccation. Thermoregulation should be essential for the successful development of the tadpoles because metabolism, developmental time, heat stress and death, and desiccation are temperature dependent. Thus, already small temperature differences within ponds may have important physiological and developmental consequences for tadpoles and should therefore influence their habitat use. We investigated the thermal relationships in the habitat use of B. variegata tadpoles in semi-natural outdoor experiments, providing a natural day/night cycle of temperature and light and natural temperature gradients and ranges. In experimental puddles, equipped with temperature loggers, we recorded the distribution of the tadpoles with time-lapse videos. We then compared their positions to the respective temperature data. The thermal relationships detected in our field experiment were similar to thermal preferences observed in previous laboratory experiments with artificial temperature gradients. We found the tadpoles more frequently in cooler zones when the water temperature was above their thermal preference range, and in warmer zones when water temperature was below. The number of tadpoles increased in the shallow and warmer water in the cool forenoon, and the deep and cooler water in the warm afternoon. At higher temperatures, tadpoles accumulated in small, shaded areas. Apparently, B. variegata tadpoles use even limited opportunities to compensate for temperature fluctuations to avoid heat stress.

Key words. Amphibia, Anura, Bombinatoridae, daily movement, ectotherms, ephemeral water, thermoregulation, thermal limits, thermotaxis, temperature stress, thermal preference, shade preference.