Stephan Halloy was conducting surveys on plants and wildlife in the highlands around San Miguel de Tucumán, in northwestern Argentina, in the 1970s, when he first met the lizard.
The mountains around the Argentine city rise rapidly to elevations of 13,000 to 16,400 feet, packing multitudes of ecological niches into a relatively small area. The plateaus at the top can be hot in the afternoon, but they quickly fall below freezing at night, not exactly the kind of place you would expect to find a lizard.
However, Dr Halloy, now a senior adviser to the New Zealand Ministry of Primary Industries, caught a few of them and placed them overnight in a box outside his tent. “When I opened the box the next morning they were hard as wood; you couldn̵7;t bend them,” Dr. Halloy recently recalled. “They looked absolutely dead.”
But once the sun came up, the lizards began to thaw and soon ran out into the box of the same.
“Obviously I found it very surprising,” Dr. Halloy said.
In the 1990s, Robert Espinoza, a biologist at California State University, Northridge, heard this story from Dr. Halloy, and has since studied lizard popsicles. Lizards belong to the genus Liolaemus, and research by Dr. Espinoza and his collaborators has revealed that lizards are arguably the coolest on the planet. While tropical lizards such as iguanas fall from trees when it is cold, Liolaemus can overwinter their bodies, tolerate freezing, and live further south and at higher elevations than any other known lizard species.
“They’re real record holders,” Dr. Espinoza said.
Liolaemus species have been found on the island of Tierra del Fuego, in the far south of the Americas, and a researcher has even heard stories about them walking through Perito Moreno, a Patagonian glacier. Most Liolaemus are found in Argentina and Chile, although some are found as far north as Peru. Containing more than 272 documented species, Liolaemus is the second largest genus among all mammals, birds and reptiles, after only anoles, another type of lizard.
Dr. Espinoza continues to investigate how these lizards survive such cold climates. In one experiment, his team assembled models of lizards, hollow copper, with temperature records, and placed them in an area at 13,369 feet in the province of Salta. The models recorded temperatures as low as less than 11.2 degrees Fahrenheit on the surface and 15.8 degrees Fahrenheit underground. (Lizards usually spend the night on terraces.)
The team then tested the cold adaptations of six species at different heights. They found that some could survive by cooling to 21.2 degrees Fahrenheit, although Dr. Espinoza suspects that wild lizards can withstand colder temperatures. Liolaemus huasihuasicus, the species Dr. Halloy initially found, lives on a mountain about 1,640 feet higher than Dr. Espinoza looked at, presumably a colder area.
Dr. Halloy noted in a 1989 publication that Liolaemus huasihuasicus could survive freezing at 14 degrees Fahrenheit, but only when it was at 13,944 feet; the lizards died as they cooled to 26.6 degrees Fahrenheit in tests conducted at 1,476 feet.
Dr. Espinoza and his co-authors found that Liolaemus lizards have adapted abilities to cope with the cold through three mechanisms. Some lizards avoid extreme cold by passing on the ground. Others use an overlay process; by staying completely still, they can allow your body to fall below freezing without freezing really solid. Finally, some may also tolerate whole-body freezing for short periods of time. Dr. Espinoza said some Liolaemus species probably used more than one mechanism, depending on the conditions.
The freezing strategy of the whole body is probably similar to that observed in American wooden frogs, which remain frozen during the winter thanks to an antifreeze-like glucose solution that protects the cells; Dr. Espinoza still needs to investigate this hypothesis to be sure. The southernmost gecko in the world, the marked gecko of Darwin, another Argentine lizard that Dr. Espinoza has studied, most likely adopts the supercool strategy.
Lizards of many colors
The reason Liolaemus lizards can withstand such cold temperatures and high elevations may also explain why there are so many lizards. While there were only about 50 described in 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 its 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 under his tent, in cloudy and icy weather, in the Argentine province of Santa Cruz, near the Chilean border.
“He didn’t look like any of the others,” Dr. Lobo said. “We suspected they were a new one. We’ve had this illusion dozens of times in these 25 years.”
At the current rate of discovery, Liolaemus will become the most numerous genus of living mammals, reptiles and birds in the coming years.
“A kind of bomb”
The large number of Liolaemus species may be related to the mountainous region where they live, Dr. Espinoza said. The Andes are relatively young, about the same evolutionary age as the lizards. He believes that as the Andes moved away from the Earth’s crust, the genus separated into countless ecological niches that gave rise to new species.
“The Andes are just a kind of bomb that creates all these new types,” Dr. Espinoza said.
Most lizards are similar in size, but differ greatly in color and even in diet and birth strategies. Dr. Lobo told a story about an expedition to the Argentine province of Jujuy. During her work, a local woman appeared on the mountain of a small sheep and llama village.
“She explained to us very clearly what the species was with its Indian name, and she said that‘ it lays eggs and gives birth, ’” Dr. Lobo said.
Dr. Espinoza said half of the lizards give birth to young, perhaps because laying eggs at cold temperatures is probably not a successful recipe for some species. In 2016 he also described a new species, Liolaemus Parthenos, in which the females reproduce through the virgin part, without fertilization of a male.
Melisa Olave, a researcher at the National Council for Scientific and Technical Research in Argentina, who spoke about lizards to Perito Moreno, conducted a recent study showing that the rise of the Andes may not be the only factor driving the evolution and diversity of Liolaemus. Liolaemus species have very low extinction rates compared to other lizards. Their variation in habitat use, the general approach to diet — some species are herbivorous while others are omnivorous or carnivorous — and different forms of reproduction can be crucial in explaining the richness and survival of the species Liolaemus. He said being a generalist is generally considered advantageous, as it is easier to find suitable habitats in the very varied landscapes of the southern South American cone.
In other words, the high diversity of Liolaemus may be more a product of low extinction rate than of habitat division.
Dr. Espinoza agreed that the persistence of species over time could be a contributing factor in species richness, but he also believes that diversity alone cannot be explained.
In any case, Dr. Olave shares the general feeling of wonder that infects many of the researchers who have worked with these lizards.
“Liolaemus species have an extraordinary ability to survive through time,” he said.
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