Pacific Tree Frog - Green and Brown Color Morphs

Green and Brown Color Morphs

One of the most interesting features of these frogs is their ability to change color from brown to green. Previously, it was thought that there were two different fixed colors that an adult tree frog could be. Now it has been found that some of them are able to change between the two. They can also change from lighter to darker, shift from patterned markings to pure colors and vice versa, and even display combinations of colors, brown/green being the most frequent.

These color changing morphs are triggered not by color change in their environment, but a change in background brightness. This type of environmental change would be caused by seasonal fluctuation. A full change in the dorsal coloration of a color morph can take anywhere from weeks to months, but initial changes can occur in just a few hours. This has been shown to be a very useful cryptic survival feature for these frogs.

Skin color is produced via pigment cells called chromatophores. There are commonly three types of chromatophores found in amphibians: 1. Xanthophores - These contain yellow, orange, or red pigments and are found uppermost on the dermis; 2. Iridophores - These lie below the xanthophores and function by reflecting and scattering white light up through them; in the case of Pseudacris regilla and many other North American frogs, iridophores reflect blue light through the yellow pigment cells above to create a green frog; 3. Melanophores - These are the deepest pigment cells and are responsible for the presence of black and brown pigments.

A rare, recessive "blue morph" is known. There is one housed at the Humboldt State University Natural History Museum in Arcata, California. See link. It has been suggested that this mutation inhibits the xanthophores' ability to produce yellow pigments, thus the normally green frog (possibly of the non-color-changing type) appears blue.