Chameleon Color Changing Abilities Debunked

Chameleons are fascinating creatures! From how they climb trees, curl their tail, shoot their long tongue to their darting eyes, they are a marvel of nature. But perhaps the most mesmerizing characteristic of this reptile is its uncanny ability to change color. So how do chameleons change color radically and in such a short period?

The Misconception

It has been long assumed that chameleons change color through the dispersion and aggregation of pigment-containing organelles in their chromatophores. With all factors considered, this assumption was not that far off the mark – i.e. based on the prevailing scientific data. In fact, the dispersion/aggregation of pigments is a technique used by other color-changing animals such as the octopus, cuttlefish, and squid. A microscopic dissection of an octopus’ skin reveals thousands of elastic pigment-containing cells (chromatophores) that are linked to their nervous system (this is why their color rapidly changes with moods). An octopus changes color depending on how far or close these pigment sacks are positioned.

The scientific world assumed that chameleons change color in a similar way to these cephalopods. However, a 2015 study published in Nature Communications suggests otherwise. The findings of the research explain how chameleons are able to alter their exterior color so swiftly, and it’s not through chromatophores – the answer has more to do with physics.

Light Is The Key To Chameleons Changing Colors

The secret to the color changing ability of chameleons lies in a layer of special cells (iridophores), which contain reflecting nanocrystals within the animal’s skin. This is according to a cross-disciplinary team of Swiss scientists who used photonic band-gap modeling, photometric videography, and microscopy to determine the facts behind the color shifts in a chameleon’s skins. The study by Teyssier et al. (2015) used a sample of 4 juvenile, 4 adult male, and 5 adult male Furcifer pardalis (Panther Chameleons). They conclude that chameleons change color through the “active tuning of a lattice of guanine nanocrystals within a superficial thick layer of dermal iridophores” (Teyssier et al., 2015, para. 1).

What Are Iridophores, And How Do They Work?

Simply speaking, iridophores are light-reflecting cells within the chameleon’s skin. They contain guanine nanocrystals, which are arranged in a crisscross pattern forming a lattice i.e. they have different shapes, organizations, and sizes. When light from the environment hits the lattices, the nanocrystals reflect back different wavelength of light depending on their position (how closely they are packed in the lattice). According to geneticist Michel Milinkovitch, who was a lead scientist in the study above, a chameleon has two different types of iridophores as highlighted below:

S-iridophores– They are responsible for the chameleon’s color changing ability by modifying the spacing of nanocrystals. Highly concentrated in mature male chameleons. D-iridophores– Deeper placed iridophores that reflect a broader spectrum of light, and are responsible for temperature regulation by reflecting infrared radiation.

Figure 1: Images of the guanine nanocrystal lattice in an excited and relaxed state, and the corresponding optical response.

The combination of this layer along with the upper layers of a chameleon’s skin results in the spellbinding colors we see – see figure 2 and 3. As shown in figure 1 above, a chameleon has the ability to change the structural arrangement of these cells by exciting or relaxing their skin. Consider the following examples:

Green Chameleon– When the lattice is tightly packed, they reflect shorter wavelengths of light such as blue (Remember, different frequencies produce different spectral color). This is achieved when the chameleon’s skin is relaxed, and the nanocrystals are close to each other as shown in figure 1. However, the blue color may bounce through yellow pigments on the layer above resulting in a green color – See figure 2 below. Think of it as mixing yellow and blue paint.

Figure 2: Simplified diagram of the inner mechanisms of a chameleon changing color to Green.

Orange chameleon: When the skin of a chameleon is excited, the crisscross pattern loosens as the distance between the nanocrystals increases. This causes the nanocrystal-containing iridophore cells to reflect longer wavelengths of light such as red, orange, or yellow. The reflected color may be visible as either a red color or orange color (if it combines with the yellow pigments) – see figure 3 below.

Figure 3: Simplified diagram of the inner mechanisms of a chameleon changing color to Orange.

Why Do Chameleons Change Color?

We now know the science behind the enthralling color changing ability of chameleons and how do chameleons change color, but why do they do it? And no, it’s not primarily for camouflage against predators – that only applies to the cephalopods described above. The reason for chameleons changing colors is actually linked to their feelings.

The color of a chameleon often reflects its mood. When a male chameleon wants to intimidate its rival, attract mates, or show its intentions to predators, it changes color. For example, when a male chameleon is attempting to court a prospective mate or fight off competition, its skin becomes excited and the lattices loosen. The nanocrystals reflect longer wavelengths, which give the red, orange, or yellow color we see in such circumstances.