Abstract
The colors and color adaptation of the European tree frog, Hyla arborea, have been investigated by means of reflectance microspectrophotometry. The results are compared to those previously published on Hyla cinerea.
The two species have a number of colors in common (yellow green, light green, green, dark green, blackβgreen, and olive green), while grey colors are assumed only by Hyla arborea and lemon yellow (olive yellow) only by Hyla cinerea. The physical qualities of these colors and the corresponding states of the chromatophores are presented and discussed.
Hyla arborea apparently adapts better, and thus more predictably to its background than Hyla cinerea (as judged with the eyes of man). Both adapt to a certain degree to the lightness of the background, but the former also shows a certain adaptation to the purity, and it has a greater ability to change its hue, although a definite adaptation to background hue could not be determined.
In Hyla arborea, the changes in the xanthophores seem to be paralleling those of the iridophores, but the changes in the melanophores appear to be independent. For this species, as well as for Hyla cinerea, more than one factor must therefore be regulating the adaptive color change. A number of possibilities are discussed.