By HFSP Program Grant holder Matthew D. Shawkey and Michaël Nicolaï
While much is known about the structural mechanisms leading to colouration, much less is known about the cascade from gene to colour. Even less is known about the mechanisms resulting in colour change – in particular the molecular mechanisms. Here we used transcriptomic analyses to explore colour production in the lizard Agama atra that changes quickly from brown to blue, and show that colour change is highly influenced by changes in genes related to melanin and light-reflecting crystals.
With functions as diverse as communication, protection and thermoregulation, colouration is one of the most important traits in animals. The ability to change colour as a function of varying social and environmental conditions is thus an important innovation, but not much is known about the mechanisms behind it. Agama lizards in southern Africa can change from dull brown to deep blue colouration. Traditionally, such colour change was attributed to migration of pigments (in particular melanin) in the skin, comparable to how humans become tan. More recent work has shown that nanoscale changes in the configuration of small light reflecting crystals present in skin, called iridophores, can produce a wide palette of colours.
Agama atra lizard (photo byMichaël Nicolaï)
Here we used a combination of gene expression analyses, together with microscopic identification of iridophores and pigments. The former analyses allowed us to see which genes are “switched on”, expressed or “off”, not expressed, in colour changing animals versus animals that changed colour less. We then compared these differentially expressed genes with previously published genes that are associated with specific colour producing mechanisms, including the melanin pathway (the series of genes involved in the production of melanin) and genes involved in iridophore production, as well as pathways from other pigments. We found differential expression in genes related to both the melanin production pathway and the iridophore pathway, but no genes related to other pigments. Indeed, microscopic analyses confirmed that there were differences in both melanin and iridophore densities and organisation in animals with the deep blue colour. As such, we showed that colour change in Agamas is the result of a complex interaction between both changes in iridophore configuration and pigment (melanin) production and transportation. Furthermore, this work demonstrates the power of combining genotypic (gene expression) and phenotypic (microscopy) information for addressing physiological questions, providing a basis for future studies of colour change.
Our HFSP project focuses on uncovering how colours produced by nanostructured arrangements of materials grow in animals. How do these materials become so precisely organised at such a small scale? This paper is a step forward in answering this question, and shows that the answer is not likely to be straightforward, involving multiple genes that control multiple aspects of morphology. This work was started before our HFSP project began, but with a focus on the effects of diet quality on colour. Halfway through that experiment, we discovered that “food-restricted” lizards were sneaking food from other sources and were thus eating as well as control lizards! Rather than giving up, we realized that the colour change from brown to blue that these lizards underwent provided an excellent opportunity to study how coloured nanostructures form, regardless of any differences in food. Thanks to our HFSP project, we were able to run the gene expression analyses needed to complete the study. Concurrently, we published a similar analysis comparing gene expression in feathers from African starlings that are coloured either by nanostructures or pigments (Rubenstein et al. 2021), with comparably complex results. We continue to dive into this topic, and look forward to new discoveries.
As part of our HFSP project, we are developing biomimetic replicas of these nanostructures that grow using low-cost processes similar to those we observe in animals. This could pave the way for new coloured materials that require fewer costly pigments and energy to produce.
Reference
Untangling the structural and molecular mechanisms underlying colour and rapid colour change in a lizard, Agama atra.
Nicolaï, M.P.J., D’Alba, L., Goldenberg, J., Gansemans, Y., Van Nieuwerburgh, F., Clusella-Trullas, S. and Shawkey, M.D. (2021). Mol Ecol, 30: 2262-2284.
FAQs
Lizards can darken their color by dispersing melanin throughout the cells that contain it, or lighten their color by concentrating the same melanin into a small area of each cell. Color change often involves several cell types.
How do lizards change color? ›
Melanophores are the pigment cells that permit colour change, and the concentration of pigment granules within these cells determine the type of colour that is produced. In general, the animal appears lighter coloured when pigment is concentrated and dark when pigment is dispersed throughout the cells.
Why do lizards change from green to brown? ›
This change in color depends on temperature, humidity, mood, and overall health of the lizard. When green, they are active and usually in bright light. They change to brown when they reduce their activity and when they are in moist and cool conditions.
What lizard has the ability to change color? ›
Chameleons can change skin color based on their surroundings. A new 'smart' skin, designed to use the same principles as chameleon tissues, can shift hue in response to light.
Do lizards change color when stressed? ›
Similarly, stress has been shown to alter both the size and luminance of dark coloration in birds (Almasi et al., 2008; Roulin et al., 2008) and other lizard species (San‐Jose & Fitze, 2013).
Why do lizards turn from green to black? ›
In general, dark color is a response to heightened stress, although a variety of other factors—including predation attempts, temperature, and light levels—also affect color in A. carolinensis (reviewed in Jenssen et al., 1995; Greenberg, 2003).
Why do lizards' necks turn red? ›
The lizard is also known for its pigmented neck skin, which becomes bright red or pink when males expand a 'dewlap' — an air pouch similar to a pelican's throat pouch—to mark their territory.
Why do lizards turn blue? ›
Agama lizards in southern Africa can change from dull brown to deep blue colouration. Traditionally, such colour change was attributed to migration of pigments (in particular melanin) in the skin, comparable to how humans become tan.
What are the little green lizards that turn brown? ›
Abundance: Green anoles are generally common in almost all habitats. Notes: The anole's ability to change color has given it the nickname chameleon; however, this species' color changing abilities are not nearly as sophisticated as the true chameleons which inhabit the old world.
What does it mean when lizards are brown? ›
For instance, if the lizard is cold, it may turn from the vivid green to the dark brown in hopes of absorbing more heat. Finally, the last reason that they would change colors is for camouflage. Small lizards are easily predated upon and being able to change color in order to hide can help the little critters survive!
Lizard Lifespan
The lifespan of a Lizard depends on the species of Lizards. Geckos survive for about 10-15 years in a typical home, the Chameleons are known to survive for around 5-7 years, the Iguanas survive for about 20 years, and the Komodo Dragons, the biggest of the reptiles, live for an average of 40 years.
Can all lizards lose their tails? ›
Most lizards with long tails (and many with short tails) can also detach that tail, the more tail the more likely it is a predator will grab them by it, allowing them to drop the tail and escape.
Can lizards see all colors? ›
Reptiles can see color. Most reptiles are tetrachromats, which means they have 4 types of cones (humans only have 3 – red, green, and blue). This means that they can see the entire rainbow that humans can see, and more.
What colors are lizards afraid of? ›
When Putman wore red, the lizards ran away sooner, and she was less likely to catch them. And surprisingly, the lizards responded similarly to red and gray shirts, even though gray is a more muted, neutral color than red.
How do lizards show anger? ›
Hissing. Hissing is one of the common behaviors your beardie will show when angry. This is a sign that they are feeling uncomfortable or threatened. It is usually accompanied by an open mouth and a flared beard and can be quite surprising.
Do any lizards have emotions? ›
We found that reptiles were assumed to be capable of the following emotions and states; anxiety, distress, excitement, fear, frustration, pain, stress, and suffering, in 37 articles. We also found four articles that explored and found evidence for the capacity of reptiles to feel pleasure, emotion, and anxiety.
What makes lizards camouflage? ›
New research shows wild Aegean wall lizards found on Greek islands choose to sit on rocks that better match their individual colouring. This improves camouflage and so reduces the risk of being attacked by birds when they sit out in the open, raising the intriguing question of how the lizards know what colour they are.
Can lizards change body colour? ›
It is not possible to change your natural skin color permanently, as it is determined by genetics and the amount of melanin in your skin.
Do lizards change color when they mate? ›
In the case of mating, females will often use their coloration to signal that they are ready to mate. Males have a flap of skin under their neck called a Dewlap that turns to a vivid pinkish color when trying to attract mates. The next reason that they may change colors is due to individual stress.
How do geckos change color? ›
Geckos try to blend in, not only to avoid predators, but also, to catch prey. Chameleons do it to communicate or convey emotions and result in becoming even more conspicuous. The color change occurs when cells with different color pigments beneath the lizard's transparent skin expands or contracts.
