Stephan Halloy was conducting plant and wildlife surveys on the high plateaus around San Miguel de Tucumán in northwestern Argentina in the 1970s, when he first encountered lizard paddles.
The mountains around the Argentine city quickly climb to elevations of 13,000 to 16,400 feet, filling a multitude of ecological niches in a relatively small area. The plateaus at the top can be hot in the afternoon, but they drop quickly to freezing temperatures at night, not exactly the kind of place where you would expect to find a lizard.
However, Dr. Halloy, now senior advisor to the New Zealand Ministry of Primary Industries, caught some and placed them in a box outside his store overnight. “When I opened the box the next morning they were hard as wood, they couldn’t bend,” Dr. Halloy recently recalled. “They seemed absolutely dead.”
But once the sun came up, the lizards began to thaw and soon ran around the box as usual.
“Obviously I found it very surprising,” said Dr. Halloy.
In the 1990s, Robert Espinoza, a biologist at California State University, Northridge, heard this story from Dr. Halloy, and has been studying lizard paddles ever since. Lizards belong to the genus Liolaemus, and research by Dr. Espinoza and his colleagues has revealed that lizards are hands down the coolest on the planet. While tropical lizards like iguanas fall from trees in cold weather, Liolaemus can cool their bodies, tolerate freezing, and live farther south and at higher elevations than any other known lizard species.
“They are true record holders,” said Dr. Espinoza.
Liolaemus species have been found on the island of Tierra del Fuego, in the extreme south of the Americas, and a researcher has even heard stories of them walking on Perito Moreno, a glacier in Patagonia. Most Liolaemus are found in Argentina and Chile, although some are found as far north as Peru. With more than 272 documented species, Liolaemus is the second largest genus among all mammals, birds, and reptiles, after just the anolis, another type of lizard.
Super cool
Dr. Espinoza is still investigating how these lizards survive such cold climates. In one experiment, his team installed models of lizards, made of hollow copper, with temperature loggers and placed them in an area 13,369 feet in the province of Salta. Models recorded temperatures as low as minus 11.2 degrees Fahrenheit at the surface and 15.8 degrees Fahrenheit below ground. (Lizards often spend the night in burrows.)
The team then tested the cold adaptations of six species at different elevations. They found that some could survive cooling in temperatures as low as 21.2 degrees Fahrenheit, although Dr. Espinoza suspects that wild lizards can withstand cooler temperatures. Liolaemus huasihuasicus, the species that Dr. Halloy initially found, lives on a mountain about 1,640 feet higher than the tallest species that Dr. Espinoza observed, an area presumably colder.
Dr. Halloy noted in a 1989 publication that Liolaemus huasihuasicus could survive freezing at 14 degrees Fahrenheit, but only when found at a height of 13,944 feet; the lizards died when they cooled to 26.6 degrees Fahrenheit in tests conducted at 1,476 feet.
Dr. Espinoza and his co-authors discovered that Liolaemus lizards have adapted abilities to deal with the cold through three mechanisms. Some lizards avoid extreme cold by going underground. Others use a supercooling process; By staying completely still, they can allow their bodies to drop below freezing without actually freezing. Finally, some may also tolerate freezing of the entire body for short periods of time. Dr. Espinoza said that some Liolaemus species probably used more than one mechanism, depending on the conditions.
The whole-body freezing strategy is probably similar to that seen in North American wood frogs, which remain frozen through the winter thanks to an antifreeze glucose solution that protects cells; Dr. Espinoza still needs to investigate this hypothesis to be sure. The southernmost gecko in the world, Darwin’s tagged gecko, another Argentine lizard that Dr. Espinoza has studied, probably adopts the supercooling strategy.
Lizards of many colors
The reason why Liolaemus lizards can withstand such cold temperatures and high elevations may also explain why there are so many lizards. While only around 50 were described to science when Dr. Halloy worked on them in the late 1970s, there are now 272 species.
Dr. Espinoza and others have discovered several species, and his occasional co-author Fernando Lobo, a zoologist at the National University of Salta in Argentina, has discovered 30 or more species of Liolaemus and its close cousin, the genus Phymaturus.. In one case, Dr. Lobo discovered a species underneath his tent, in cloudy and icy weather in the Argentine province of Santa Cruz, near the Chilean border.
“They didn’t look like any of the others,” said Dr. Lobo. “We suspected that they were new. We’ve had that emotion dozens of times in these 25 years. “
At the current rate of discovery, Liolaemus is likely to become the largest genus of living mammal, reptile, and bird in the coming years.
‘A species bomb’
The large number of Liolaemus species may be related to the mountainous region where they live, said Dr. Espinoza. The Andes are relatively young, approximately the same evolutionary age as lizards. He believes that as the Andes emerged from the Earth’s crust, the genus divided into countless ecological niches that ultimately resulted in new species.
“The Andes are a kind of species bomb that creates all these new types,” said Dr. Espinoza.
Most lizards are similar in size, but differ greatly in color and even in diet and hatching strategies. Dr. Lobo told a story about an expedition in the Argentine province of Jujuy. During his work, a local woman appeared in a small llama and sheep herding town in the mountains.
“She told us very clearly what each species was with their Indian names, and said ‘That one lays eggs and that gives birth,'” said Dr. Lobo.
Dr. Espinoza said that half of alligators give birth to live young, perhaps because laying eggs at low temperatures is probably not a recipe for success for some species. In 2016 he also described a new species, Liolaemus parthenos, in which the females reproduce through the virgin birth, without the fertilization of a male.
Melisa Olave, a researcher at the Argentine National Council for Scientific and Technical Research, who heard about lizards in Perito Moreno, conducted a recent study showing that the emergence of the Andes may not be the only factor driving the evolution and diversity of the Liolaemus. Liolaemus species have very low extinction rates relative to other lizards. Their variation in habitat use, the general diet approach (some species are herbivorous while others are omnivorous or carnivorous) and the different forms of reproduction can be critical to explain the richness and survival of Liolaemus species. She said that being a generalist is generally considered advantageous, because it is easier to find suitable habitats in the highly varied landscapes of the southern cone of South America.
In other words, the high diversity of Liolaemus may be more a product of a low extinction rate than of habitat fragmentation.
Dr. Espinoza agreed that the persistence of species over time could be a contributing factor in species richness, but he also believes that it alone cannot explain diversity.
In any case, Dr. Olave shares the general feeling of awe that infects many of the researchers who have worked with these lizards.
“Liolaemus species have an extraordinary ability to survive over time,” he said.
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