Green Frog

While out at the pond the other day, I came across an unusual Green Frog. It caught my attention because of its' vivid blue coloring; something I have not come across before. Borrowing Michaela's little net, I captured the frog for closer inspection, and then set out to find the answer to my question: why was this green frog, blue?

Frogs have a complex arrangement of cells which provide them the ability to adjust their hue to their surroundings and blend in with their environment. Within their skin are three types of pigment cells (chromatophores) stacked on top of each other. The bottom layer are melanophores, which contain the dark pigment melanin. The middle layer consists of iridophores, which are packed with highly reflective bundles of purine crystals. On top are the xanthophores, which are usually packed with yellowish pteridine pigments.

Each type of cell can change shape, and control the intensity and character of transmitted or reflected light by moving the pigment within them. A wide range of colors can be produced by manipulating all three types of pigment cells, though normally their coloration ranges from bright green to various shades of brown and grey.

Light penetrates to the iridophores, which reflect mostly blue light back into the xanthophores above them. The xanthophores act as yellow filters, causing the light escaping the skin surface to appear green to us. This particular frog lacks the yellow xanthophore cells, which (ahh) causes it to appear blue. Science broken down into a simple color mixing fomula: an artistic anomoly in the pond - but a beautiful one indeed.