La magie des couleurs : le caméléon géant de Madagascar révèle ses secrets

Cela vous intéressera aussiNous trouvons maintenant dans un biodiversity paradise: the island of Madagascar. Many species of animals and plants only live here, it is impossible to observe them anywhere else in the world other than on this piece of land bordered by the Indian Ocean. They are said to be endemic to the island of Madagascar. Life here has evolved in isolation, cut off from the rest of the world. And it has developed unexpectedly, spectacularly, offering an explosion of shapes and colors like no other. Color is what we are interested in today. Because the animal we are trying to observe is one of the few that has the extraordinary ability to change colors on command. From Antananarivo, the capital, we follow the road that leads to the North, in search of a gem: the primary forest of Madagascar. A primary forest is a place of exception. Preserved from all activity, these original forests are the refuge of countless species that can live there far from the noise and polluting activities of humans. It is in this forest, for example, that the ugliest orchid in the world, Gastrodia agnicellus, was discovered, its flower resembling a gaping, viscous mouth. Or, the species Brookesia nana, a tiny chameleon barely 1 cm long, the smallest in the world! Because, in Madagascar, nearly half of the known species of chameleons on Earth live. And today we have an appointment with one of them. Discover the podcast “Bêtes de Science” at the origin of this transcription. Click on the Play button and let yourself be carried away or click here to subscribe on your favorite application. © FuturaMeeting the Giant Chameleon of Madagascar Here we are: on its tree, in the humidity of the tropical climate, a silhouette reminiscent of a miniature dinosaur is coming into view. A large lizard basking in the sun, it’s a chameleon, of the species Furcifer oustaleti, the giant chameleon of Madagascar! This emblematic species can measure up to 70 cm long! It has a color that ranges from brown to green, speckled with white or yellow, and a crest runs along its body with small serrated spikes. Pay attention to its legs. Like us, this chameleon has five fingers, but they are arranged a little differently from ours. While in humans the thumb opposes the rest of the fingers to form a pinch – we simply say it is opposable – in our friend there are two fingers on one side and three fingers on the other to grip branches. It’s a bit like if you were grabbing a water bottle by placing your thumb and index finger on the same side! It may seem impractical to you, but for the chameleon, it’s completely natural. Ah… a daring butterfly approaches. It is taking a big risk, because chameleons love insects and can even engulf birds or small rodents. Be careful, little butterfly… the chameleon, with its prominent and independent eyes, which rotate in their sockets, is on the lookout. Nothing escapes it. In an instant, the chameleon’s tongue, sprung on springs, jumps out at lightning speed and swoops down on the butterfly. It cannot escape the attack, because this tongue is exceptionally long, and its sticky tip ensnares its prey. The little butterfly has already joined the depths of the lizard’s stomach. It may not move very fast on its branch, but when it comes to hunting, it is unbeatable.Chameleons are fascinating animals in more ways than one. But one of their abilities has made them famous: they can change color. For a long time, it was believed that this superpower allowed them to blend into any environment to stay incognito. In short, it served for camouflage purposes. But researchers have discovered that the reality is a bit more complex than that. To unravel the mysteries of chameleon coloration, we need to head to Arizona, in the United States. You will see that our extraordinary lizard has more than one trick up its sleeve…Fight and emotions: the hidden side of chameleon color changeTo better understand how and why chameleons change color, scientists at the University of Arizona organized a big boxing tournament between chameleons. Because chameleons are territorial animals, a meeting with another individual can quickly turn into a fight. For the purposes of the experiment, the researchers tested the reactions of 10 wild chameleons during a meeting with another individual. In this case, masked chameleons were chosen for the experiment. Originally from the mountains of Arabia, these chameleons have been introduced to the United States, specifically in the nearby state of Florida, which is quite convenient! They get their name from the hump that adorns their head, although this characteristic is shared by many chameleons. When two masked chameleons meet, a strange choreography unfolds. Each one inflates its body, abdomen, and tail to momentarily make themselves appear larger to their opponent. Then… the dance of colors begins. Each part of the chameleon’s body changes color, transitioning from green to red, yellow, or blue. The multicolored threat aims to deter the opponent.Eventually, how is the chameleon able to change color? To understand this, we must take a journey into the infinitely small, into the heart of the chameleon’s skin. Because the cells of its skin are equipped with a secret weapon: they contain nanocrystals, that is to say, crystals, like those of salt for example, so small that they are invisible to the naked eye! Depending on the biological state of the animal, these crystals either come closer or move away from each other. And they reflect light differently! Thus, when a chameleon is relaxed, the microscopic crystals in its skin are tight, they reflect the blue color that mixes with the yellow pigments naturally present in the chameleon’s skin. As a result, our little lizard sports a nice green color. But when the chameleon is agitated, things get more complicated…The colors of the chameleon’s body provide information about its health and intentionsThe masked chameleons participating in the experiment were placed in a large transparent box, facing each other, each on a branch. Then, the glass separating them was lifted to allow the chameleons to face each other. During this experiment, the researchers studied no less than 28 regions of the chameleons’ bodies. With the help of a camera, they didn’t miss a single detail of the fighters’ behavior during the tournament. And what they discovered exceeded their expectations. As the researchers imagined, when the two chameleons meet, they adopt a strategy of intimidation that involves changes in their bodies. They inflate themselves, as we saw, and the chameleon’s skin changes from a flamboyant green to shades of red, yellow, or blue. But what surprised them is that they discovered that these color changes actually have a purpose! Depending on the intensity and speed of color change in different regions of the chameleon’s body, the researchers discovered that they could predict the outcome of the fights! For example, the brighter and faster the colors of the stripes on the chameleon’s flanks change, the greater the probability that it will approach its opponent to fight. But there is even more impressive. The colors of the chameleon’s head can predict the winner of the fight. Yes, it’s true! Thus, while the chameleon’s stripes allow it to express its motivation, its head informs about its fighting abilities. All thanks to measuring the speed of color changes and their intensity. This is a very useful power for the chameleon! When it comes to fighting, chameleons turn slightly to the side, revealing their stripes to their opponents, a way of saying, “I’m ready to fight” or, on the contrary, “I’m a supporter of peace”. When the fight is confirmed, the two chameleons approach each other to engage in what is called a head-to
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