Adaptation of the tree frog, <i>Hyla cinerea</i>, to colored backgrounds, and the rôle of the three chromatophore types

Abstract

Abstract Measurements have been made of the spectral reflectance of the dorsal skin of living tree frogs, Hyla cinerea . The colors assumed by the frogs when placed on backgounds of different col‐ors varied with respect to both dominant wavelength (565–580 nm), purity (42–58%) and lightness (2–19%). A certain adaptation to the lightness of the background took place, whereas adaptation to hue and purity seems almost negligible. On the basis of reflection measurements of single chromatophores and chro‐matophore associationa, a model is proposed for the color generation in the chromatophores, assuming an absorption of short‐wave light in the xantho‐phores, a reflection of short‐and medium‐wave light (blue, green) from the iridophores, and almost total absorption of all light in the melanophores, and a uniform, but subtotal, reflection of light of all wavelenghts from the connective tissue. It is suggested that the states of dispersion of the three types of chro‐matophores may be related to simple parameters which can be calculated from the reflectance spectra. Using these parameters it was found that mela‐nophores, xanthophores and iridophores all play an active part in the color change, and an explanation is presented on how the observed frog colors are generated by means of changes in the chromatophores. The three types of chromatophores probably are able to react independently of each other, thus indicating that the unihumoral theory fails to explain the color changes in Hyla cinerea .