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This brown chameleon lizard has had trouble evolutionarily, and they have little room for evolution.
Picture note: A Cuban brown chameleon lizard. (Photo: Charles Sharp)
Brown chameleon lizards are one of the most successful species in the world, and these animals are so tenacious that they have settled in much of the Western Hemisphere, and they have even traveled to Hawaii and Singapore on ships that transport ornamental plants across the Pacific Ocean. In the southeastern United States, brown chameleons have effectively replaced the local indigenous green chameleons, and they have even herded natives to trees. From gloomy forests to sun-drenched beaches, there are traces of these cold-blooded animals, and they seem to be able to play anywhere on the planet!
"This animal is very common in the Bahamas and it can surprise you with its prevalence. You pick up a random kind of bush on the side of the road, and then take a closer look, and I bet you'll see a brown chameleon lizard, of course, possibly three. Said Michael Logan, a postdoctoral fellow at the Smithsonian Institute for Tropical Research in Panama City. Logan studied these color-changing lizards.
You might think that with so many brown chameleon lizards and covering so many parts of the planet, there should be a lot of genetic variation in this species. Yes, some chameleon lizards will become larger or smaller, move faster or slower, and may have a lighter or darker appearance, that is, chameleon lizards in different places may occasionally adapt to new challenges, such as climate change, and they will pass these characteristics on to the younger generation, then the next generation should be more tolerant of climate. But a new study suggests that this is not the case.
Illustration: Brown chameleon lizard. (Photo: Thomas Brown)
The study was published in the recently published Proceedings of the Royal Society B. The study will have a major impact on the future of all cold-blooded animals. These cold-blooded animals include lizards, other reptiles, amphibians, and fish, whose body temperature changes with changes in the environment. Because the lives of these species, known as cold-blooded animals, are so closely linked to fluctuations in temperature, studying these species could help scientists better understand the dangers of global warming.
"It is indeed surprising that the characteristics of these genetic variants are not obvious under the influence of climate change. For example, if one of the fastest color-changing lizards in brown chameleons has less obvious genetic variation in their body temperature, this trait is important to escape predators. Now the question arises, if brown chameleon lizards lack the necessary conditions for genetic adaptation, how can they adapt to the environment in different parts of the planet? Logan said.
There is now an explanation that generations of chameleon lizards face environmental challenges, and the species evolves to meet those challenges, but genetic adaptation can also go like a dead end. This explanation is also possible, but there is still no definite answer to the above question. What's happening now is that there are some subtle changes within the brown chameleon lizard species, "but time goes by, and some traits have very limited variability, so the effect of evolution is limited." Logan explained.
"As I said earlier, there are some traits that have very limited variability, which is like a quadruped animal with only four legs, and these traits are completely determined by genes. Because these genes do not change between individuals, almost all tetrapods are born with four legs, so the selection cannot be applied to features that do not have variation," Logan said.
Michael Logan collects research data on brown chameleons on Greater Exuma Island in the Bahamas. (Photo: Christine Miller)
Scientists have captured adult lizards from two very different habitats, a cool woodland and a hot and well-lit peninsula. The researchers allowed the lizards to reproduce in captivity and then reared the offspring of both color-changing lizards in the same laboratory environment.
"Differences between populations are entirely determined by genetics. Now, we're going to provide the same growth conditions for two different color-changing lizards, just to see if the 'growth conditions' are working. Logan explained. Although the offspring of both grew up under the same conditions, there is a clear distinction between lizards in cold regions and lizards in warm regions. Logan said.
The researchers first exposed the two color-changing lizards to different temperatures and then used high-speed cameras to record them running on a wooden stick. The researchers also used gel packs and heating lamps to create an environment of 21 to 48 degrees Celsius and recorded the reactions of the chameleon lizards with a video camera. As the researchers expected, the lizards that originally grew in warmer environments performed better in higher temperature conditions, but the two groups of lizards did not show many genetic variants.
"Our findings suggest that in order for these populations to adapt to their thermal environment in the first place, natural selection may have exhausted all available genetic variation, so that as the global climate continues to change, these chameleon lizards have no more room for evolution," Logan said
Illustration: Brown chameleon lizard. (Photo: Pixabay)
The study shows that traits that adapt to heat have a genetic basis, "because when we exert control over the influence of the environment, there are differences between these two color-changing lizards," Logan added. "But we also show that within both populations of chameleon lizards, these traits lack genetic variation, which means they can no longer evolve in the face of natural selection."
"Although color-changing lizards have proven to be more vulnerable than expected, brown color-chameleon lizards are large in number, and they also have the ability to adapt to new environments, and it seems unlikely that they will be vulnerable to the effects of climate change," Logan said. The study also raises the troubling question of what will happen to other species in an environment of global warming.
"Other species tend to cover areas with more limited coverage than brown chameleon lizards and are more likely to live in only one thermal environment," Logan said. "Brown chameleon lizards are a successful intruder around the world, but if even they lack the genetic variation necessary to evolve quickly, other creatures may be even worse." Logan said. "In the face of natural selection, relatively rare, more specialized species should have less chance of genetic variation."
Shane Campbell-Staten, an evolutionary biologist and postdoctoral researcher at the University of Montana, said the study builds a key link between cold-blooded animals coping with changing temperatures. Campbell was not involved in the study.
Caption: Ring-necked lizard. (Photo: Pixabay)
"Until now, there have been several studies that suggest that extreme weather events and rapid changes in the environment cause selective events, such as organisms that are more resistant to drought, heat or cold snaps are more likely to survive and pass genes on to the next generation," says Campbell Staten. In any case, the study points out that while evolution can occur across generations, there is a condition that traits that allow organisms to continue to survive can be passed on to offspring. In the case of brown chameleon lizards, traits selected in high-temperature environments do not seem to be effectively passed on to the next generation, which means that the adaptive evolution of these traits may occur at a much slower rate than would be expected by global warming, in short, the rate of biological evolution cannot keep up with the rate of climate change. Campbell Staten added.
"This mismatch could be a disastrous combination," Campbell Staten said. "This means that as the climate warms, the heat tolerance requirements of the organism increase by adaptation, that is, more individuals will die in a certain generation, and the survivors will not be much better off, and they may be slightly more adaptable to rising temperatures, but may also have no advantage at all." The end result of this mismatch is that if temperatures continue to rise, species will inevitably go extinct. Campbell Staten said.
While the study doesn't apply directly to warm-blooded animals, "it's clear that there are many species in the world, including the plants we depend on because plants provide food and oxygen, as well as insects that pollinate plants, and many cold-blooded animals that act as important players in ecological health are likely to be greatly affected." Campbell Staten said.
The world is warming, but small ranges of species lack the ability to migrate, so evolution is "their main escape route," Logan said. But the study "suggests that many species we love and care about may not be able to respond rapidly to the evolution of climate change." ”
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