A tree frog can change its body color to match the brightness of its background. In cold weather and in cold water, green color absorbs more light and heat from the sun. When it gets hotter and drier, and on land, brown color is beneficial: it absorbs less solar radiation. The change from green to brown or mottled brown, or the reverse, can start within a few hours, but takes several weeks to be total.
How does it happen? Beneath the upper level of skin (the epidermis) lies the dermis. Here, in the top layer of the dermis are cells with pigment granules. Xanthophores contain yellow, orange or red pigments. Iridophores reflect blue light, which coming through the yellow pigment creates green color. Melanophores contain melanin, the black or brown pigments, in granules called the melanosomes.
The melanosomes are connected by tiny threads, microtubules. When the frog is brown, the melanosomes are scattered throughout the cell. If the microtubules are stimulated by the proper hormonal signal, they pull all the melanosomes into a tight ball in the center of the cell. Now the yellow and blue colors can shine through to create the green color.
Ranging from Northern Humboldt County to Southern Oregon are some frogs who lack the ability to make the yellow pigments. As a consequence, they are not green but blue.
First, the frog takes a deep breath, filling his lungs. Then, he closes his mouth and nostrils.
Eve Broughton lives in Whitethorn and has degrees from U.C. Berkeley.
This column is sponsored by the Lost Coast Interpretive Association as part of their environmental education mission. For information about the organization, visit facebook or the website, lostcoast.org. Interested in submitting an article? Email email@example.com.
Blue tree frog