Effects of background color on pigmentation, morphological traits, and behavior in the European tree frog (Hyla arborea, Hylidae, Anura) tadpoles

Amphibian tadpoles are capable of avoiding threats (predators, uv radiation, etc.) through changes in coloration, behavior, and shape. In this paper, we tested how quickly European tree frog (Hyla arborea) tadpoles can change body pigmentation to achieve crypsis and whether color change is reversible. Additionally, we tested how different environmental background colorations affect the body length, shape, and ontogenetic trajectories of tadpoles. We also analyzed if tadpoles can relate to their coloration and choose the appropriate background to enhance crypsis. For this purpose, we reared tadpoles on white and black backgrounds for 36 days. Halfway through the experiment, half of the tadpoles from each treatment were placed on the alternative background. Our results suggest that H. arborea tadpoles are capable of rapidly responding to color changes in their environment, however, color-matching with the white background is poor. These quick color changes are reversible. Rearing in different background coloration and rapid color changes do not affect tadpoles' length variation but affect tadpoles' shape. Tadpoles introduced to the white background at the start of the experiment developed deeper tail fins and more pronounced snouts. We also found that H. arborea tadpoles actively choose an appropriate background to achieve maximum crypsis. This study represents the basis for the future analysis of adaptive coloration in tadpoles as it has a very complex function in anurans.