Factors Controlling Color Change in the Tree Frog, Hyla versicolor Wiech

Abstract

Hyla versicolor responds to light by melanophore expansion, and to darkness by contraction. The completenes of contraction depends upon duration of the period of dark-adaptation, generally more than 72 hours are required for all frogs to turn green. The change to brown after dark-adaptation is variable and no consistent relationship has been found between length of darkness and length of recovery period. Temperatures of 3-5° C darken frogs as does light. Light and cold appear to be stimuli which cause release of mel-anophorotropic hormone (ACTH?) from the pituitary gland. Light-induced changes, opposite to those shown by other frogs, seem explicable on the basis of natural selection during the diurnal period when these frogs are inactive.