Snakes do it faster, better: How a group of scaly, legless lizards hit the evolutionary jackpot

Then, with a burst of innovation in form and function, snake ancestors developed legless bodies that could slither along the ground, highly sophisticated chemical detection systems to locate and locate prey. , and flexible skulls that enabled them to swallow large animals.

These changes set the stage for the spectacular diversification of snakes over the past 66 million years, allowing them to quickly take advantage of the new opportunities that came after an asteroid impact wiped out nearly three-quarters of the planet’s plant and animal species. have emerged after

But what triggered the evolutionary explosion of snake diversity — a phenomenon known as adaptive radiation — that gave rise to nearly 4,000 living species and made snakes the greatest evolutionary achievement? Made one of the stories?

A major new genetic and dietary study of snakes by an international team led by University of Michigan biologists suggests that speed is the answer. According to the study, scheduled for publication online Feb. 22 in the journal Science, snakes evolved three times faster than lizards, with massive changes in traits related to feeding, locomotion and sensory processing.

“Fundamentally, this study is about what makes an evolutionary winner. We found that in some important ways snakes are evolving faster than lizards, and this speed of evolution allowed them to take advantage of new opportunities. that other lizards cannot,” said the university. Michigan evolutionary biologist Daniel Rabosky, senior author of the forthcoming Science paper.

“Snakes evolve faster and — dare we say it — better than some other groups. They’re versatile and flexible and able to master prey that other groups can’t,” Rabowski said. Said, curator of the UM Museum of Zoology and a professor in the Department of Ecology and Evolutionary Biology.

For the study, the researchers created the largest, most comprehensive evolutionary tree of snakes and lizards by sequencing partial genomes for nearly 1,000 species. In addition, they compiled a large dataset on lizard and snake diets, examining stomach contents records from thousands of preserved museum specimens.

To analyze the evolutionary history of snakes and lizards through geologic time and to study how various traits, such as limb size, evolved, they applied this mountain of data to sophisticated mathematical tools. and fed into statistical models, supported by large amounts of computer power.

This multifaceted approach revealed that while other reptiles have evolved many snake-like traits — 25 different groups of lizards have lost their limbs, for example — only snakes have. Experience this level of explosive diversity.

Take the Australian legless gecko, for example.

Like snakes, this lizard lost its legs and developed a flexible skull. Yet creatures have barely diversified over millions of years. No evolutionary explosion — only a few species are dying out in the Australian outback.

So, it seems that there is something special about snakes that enabled them to hit the evolutionary jackpot. Maybe there is something in their genes that makes them evolutionarily flexible while other groups of organisms are much more constrained.

“One striking aspect of snakes is how ecologically diverse they are: burrowing underground, living in freshwater, living in almost every imaginable habitat in the ocean and on land,” said Alexander Pirone, study co-author and professor at George Washington University. said an associate professor of biology. “While some lizards do some of these things — and there are far more lizards than snakes — in most places there are many more snakes in these habitats.”

The ultimate causes, or triggers, of adaptive radiations are one of the great mysteries of biology. In the case of snakes, there are likely to be many contributing factors, and it may never be possible to tease them out.

The authors of the upcoming Science study refer to this one-time event in evolutionary history as a macroevolutionary singularity with “unknown and probably unknowable” causes.

A major evolutionary singularity can be seen as a sudden shift into a higher evolutionary gear, and biologists suspect that these explosions have occurred repeatedly throughout the history of life on Earth. The sudden emergence and subsequent dominance of flowering plants is another example.

In the case of snakes, homogeneity began almost simultaneously (from an evolutionary perspective) with the acquisition of long-limbed bodies, advanced chemical detection systems, and flexible skulls.

These important changes allowed snakes, as a group, to pursue a wide variety of prey, while simultaneously enabling individual species to develop highly specialized diets.

Today, cobras with deadly venom attack, giant pythons that limit their prey, shovel-nosed granivores that prey on desert scorpions, slender tree snakes called “goo-eaters” that scurry off the ground. Preys the eggs of higher snails and frogs. Tailed sea snakes that probe rock crevices for fish eggs and eels, and more.

“One of our key findings is that snakes have had a very varied feeding ecology that completely separates them from other reptiles,” Rabosky said. “If there is an animal that can be eaten, it is likely that a snake, somewhere, has developed the ability to eat it.”

For the study, researchers got an inside look at snake food preferences by reviewing field observations and stomach contents records for more than 60,000 snake and lizard specimens, mostly from natural history museums. Contributing museums include the University of Michigan Museum of Zoology, home to the world’s largest research collection of snake specimens;

“Museum specimens give us an incredible window into how animals live in the wild. For cryptic animals like snakes, it’s nearly impossible to get this kind of data any other way because so much of their behavior is directly related.” It is difficult to observe,” the study said. Co-lead author Pascal Titel of Stony Brook University, who completed his doctorate at UM in 2018.

The study’s 20 authors are from universities and museums in the United States, the United Kingdom, Australia, Brazil and Finland.

“What I love about this study is how it integrates hard-earned field and museum data with new genomic and analytical methods to reveal a fundamental biological truth: snakes are modest and clearly quite cool,” said co-lead author Sonal Singhal of California State. University, Dominguez Hills, who began work on the project as a UM postdoctoral scholar.