Take it from Carlos Taboada, postdoc in the Johnson Lab. He and his collaborators have published a deep dive into frogs’ green coloration in PNAS, “Multiple Origins of Green Coloration in Frogs Mediated by a Novel Biliverdin-Binding Serpin.” While most species of frogs produce their color in the usual way, by chromatophores or pigment-carrying cells in the skin, a subset has very few chromatophores. These species, which are mostly treefrogs, have transparent skin as well as a phenomenal excess of bilirubin, a normally toxic yellow byproduct from the breakdown of old red blood cells. Carlos and his fellow researchers found that a protease inhibitor, biliverdin-binding serpin, binds the bilirubin, making it less toxic, more blue-green and more reflective. This helps the treefrogs to disappear in the foliage. The team also determined that this process of “physiological chlorosis” has evolved more than 40 separate times in widely-separated populations of frogs.
As co-author Sönke Johnson said, the paper is a “tour-de-force” bridging the fields of molecular biology, biochemistry and ecology. Congratulations to Carlos and all for bringing such a complex project to fruition!