Originally, the “18 generations of ancestors” were all fond of meat, but in less than 40 years, they began to switch to vegetarianism, and even grew a new body structure for vegetarianism. This time, let’s talk about a creature that can rapidly evolve and adapt to the environment – the Italian wall lizard.
Unconventional Italian wall lizard
Five pairs of Italian wall lizards from the island of Pod Kopiste (left) near Croatia were brought to Pod Mrcaru and began to evolve towards vegetarianism
The Italian wall lizard (Podarcis siculus) is a small reptile with a body length of less than 13 cm. Their hometown is in the Mediterranean region of Europe. They are carnivores, and their favorite food is various arthropods, such as insects. Because of their cute appearance and amazing numbers, they are not only regarded as pets, but also important experimental subjects for researchers.
But who could have guessed that this little thing that looks like it can only blink would dare to go against Darwin’s classical evolution theory, and grow a new body structure out of nothing in a short period of time, and embark on a meat like Fat Da. The evolutionary path of transgenics.
Things have to start in 1971. That year, Duncan Irschick, a biologist at the University of Massachusetts, and his colleagues came to Croatia to do a project. They caught five pairs of Italian wall lizards on the southern Adriatic island of Pod Kopiste and brought them to the nearby island of Pod Mrcaru.
However, an accident occurred.
The Croatian War of Independence broke out. The war lasted for about 20 years, and it didn’t come to an end until the mid-1990s. Because of the war, the researchers had to interrupt their studies and leave the lizards on the island.
The accident of this human society has brought the accident of evolution.
In 2004, Croatia resumed tourism on the island of Pod-Makalu, and researchers were able to land on the island to retrieve the original experiment. At first, the researchers weren’t sure if the lizards were doing well, or even if they were still alive. But the sight of the island took them by surprise.
”The island was full of lizards,” recalls Irschick. That wasn’t a big deal, since Pod-Makalu has its own lizard species: the Dalmatian wall lizard (Podarcis melisellensis). But genetic analysis of the Pod-Makalu Island lizards revealed that none of these lizards were Dalmatian wall lizards, but all descended from the original five pairs of Italian wall lizards.
The researchers also discovered another surprising thing: the more than 5,000 descendants of these carnivorous lizards are now all vegetarian. Keep in mind that on the lizard’s home island of Pod Kopiste, vegetarian diets make up a negligible portion (less than 7 percent). But the Italian wall lizards on Pod-Makalu are not only vegetarian, they’re also very good at eating: Vegetarian food makes up 34 percent of their rations in the spring, and becomes a staple in the summer, reaching 61 percent.
It’s unusual for carnivores to be vegetarians
Ruminant cattle have a large digestive tract (meal)
In the eyes of most biologists, the sudden ability of a meat-eating animal to become a vegetarian and to digest the ultra-refractory cellulose and lignin is an incredible thing, since very few microbes on Earth (such as white rot fungi) can break it down these complex organic polymers.
In the Carboniferous period (about 300 million years ago), it was because there was no living thing that could decompose plants, so that the incorruptible plant carcasses were slowly turned into coal underground. And now animals on earth cannot directly digest plant fibers, and herbivores such as cattle and horses need to use microbial fermentation, so they need to grow a huge digestive tract that acts as a fermenter.
Because of this, many researchers thought that switching from a meat-eating diet to a vegetarian diet required growing a larger body to accommodate a larger stomach. In addition, the body temperature of vegetarian animals needs to reach the high temperatures required for microbial activity. In short, before becoming a vegetarian, it has to grow into a carbon-based petri dish. These two conditions are very harsh for ectothermic lizards.
So why are these Italian wall lizards suddenly able to digest vegetarian food? It turned out that they grew a gut structure that their ancestors did not have – the ileocecal valve. The ileocecal valve is a sphincter muscle valve that regulates the rate of food digestion, allowing gut bacteria sufficient time to ferment the plant and convert it into fatty acids that the lizard can absorb and utilize.
The ileocecal valve itself is not a new product in evolution, but it is rare in the wall lizard family. In fact, less than 1% of the scaly lizards to which the Italian wall lizard belongs have an ileocecal valve. While other vertebrates, such as Panda, have been documented carnivorous and vegetarian, this rarely happens in scaly lizards.
That is to say, the Italian wall lizard has evolved a new body structure in at most 30 generations and 37 years, and changed from carnivorous to vegetarian. Irschick uses an analogy: It’s like humans growing a new appendix (the original function of the appendix as a plant fermenter) over a few hundred years.
In order to be vegetarian, their bodies not only grew new sphincter muscles, but also “outsourced” the work of handling plants to their supporting teammates: a belly of “gu”. In fact, the Pod-Makalu wall lizard’s gut is full of bacteria and nematodes that digest plant fiber, but its native lizard species doesn’t, which is surprising.
Of course, to better “graze”, these lizards also had larger and wider heads and larger bodies, as theory predicted.
In general, it takes millions of years to completely change eating habits, these researchers commented. But it took these lizards less than 40 years to acclimate, which is quite bizarre. “This rate of evolution is unprecedented,” says Irschick. Biologist Andrew Hendry of McGill University in Canada agrees: “It’s pretty amazing.”
Changes in the body also bring changes in behavior and group structure. Since they no longer need to pursue their prey, their hind legs become shorter and their speed is slower. Furthermore, now everyone loves to eat “grass”, and there are many plants on the island. These lizards have weakened territorial awareness and live closer. They give birth to more small lizards, making the population density very high. .
Disrupted ecological balance
The changes in the body of the Italian wall lizard also broke the local ecological balance. The island’s original lizard colony was completely defeated in the Italian wall lizard’s switch to a vegetarian diet. While the researchers don’t know how this process happens, the exotic lizards now completely occupy the native lizard’s habitat.
This amazing study was published in 2008 in the Proceedings of the National Academy of Sciences (PNAS). The discovery also changed researchers’ understanding of evolution. The paper suggests that rapid evolution may be a general phenomenon, rather than a rare exception, as traditional Darwinism thinks.
However, a guy who can evolve into a vegetarian in 40 years is too flexible and stretched, right? Can they still be so calm when they get to the place where the meat dishes slap their faces?
Some researchers have begun to wonder how to get these little guys to “break” and start eating meat again. Their results once again left the researchers jaw-dropping.
In 2010, researcher Bart Vervust and colleagues at the University of Antwerp in Belgium published a series of experiments they did. For 15 weeks, they fed arthropods, such as insects, to Pod-Makalu Italian wall lizards to see if their bodies changed. Except for “meat”, these wall lizards cannot eat any vegetarian food.
As a result, the guts of these lizards became shorter, and the ileocecal valve even disappeared. It turns out that for the Italian wall lizard, this blind valve can be switched on and off at will.
In fact, the “summoning” of the ileocecal valve may just be a trivial skill for Italian wall lizards. Their extreme adaptability has long been studied in various ways. Italian wall lizards, for example, come from the dry and hot Mediterranean region, but they are able to adapt to -20 degrees Celsius winters on Long Island, New York, and have spread to many parts of North America.
This is because they can perform an advanced version of hibernation: let the water in the body directly enter a supercooled (below freezing point) state without freezing, and sleep directly through the winter through this “whole machine protection mode”. They are also good at learning. A study published in Biology Letters in 2018 found that they could not only apply the experience of the same lizard, but even learn from lizards of different species, find the plastic box with the food hidden and open the lid Take out food.
In this way, Pang Dajun, who has forgotten the taste of meat and can only eat bamboo poles, has to work hard. Vegetarian animals have round heads and round stomachs and have high body temperature. It seems that vegetarians can’t lose weight!