Stephan Halloy was conducting plant and wildlife surveys on the high plateau around San Miguel de Tucumán in northwestern Argentina in the 1970s when he first encountered the Lizard Popsicles.
The mountains around the Argentine city climb rapidly at altitudes of 13,000 to 16,400 meters, packing a warm ecological host into a relatively small area. The plateau at the top can be hot in the afternoon, but it quickly freezes down overnight – not exactly the kind of place you would expect to find a lizard.
However, Dr. Halloy, now a senior adviser at the New Zealand Ministry of Primary Industries, grabbed some and put them in a box outside his tent overnight. “When I opened the box in the morning, they were as hard as wood ̵1; you could not bend them,” Dr. recalled recently. HALLOY. “They looked absolutely dead.”
But as soon as the sun appeared, the lizards began to scorch and very quickly were spinning in the box just like normal.
“Of course 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 he has since studied the lizard Popsicles. Lizards belong to the genus Liolaemus, and research by Dr. Espinoza and his colleagues has revealed that lizards are arguably the coldest on the planet. While tropical lizards like iguanas fall from trees when it gets cold, Liolaemus can supercool their bodies, tolerate freezing, and live further south and at higher altitudes than any other known lizard species.
“They are real record holders,” said Dr. Espinoza.
Liolaemus species have been found on the island of Tierra del Fuego, in the southern tip of America, and one researcher has even heard their story walking on Perito Moreno, a glacier in Patagonia. Most of Liolaemus are found in Argentina and Chile, although some have been 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 species of lizard.
Dr. Espinosa is still investigating how these lizards survive such cold climates. In one experiment, his team placed models of lizards, made of hollow copper, with temperature cuts, and placed them in an area at 13,369 meters in Salta Province. The models recorded temperatures as low as minus 11.2 degrees Fahrenheit on the surface and 15.8 Fahrenheit underground. (Lizards usually spend the night in burrows.)
The team then tested the cold adaptations of six species from different heights. They found that some could survive the cold as low as 21.2 degrees Fahrenheit, although Drs. Espinosa suspects that wild lizards can withstand colder temperatures. Liolaemus huasihuasicus, the species that Dr. Halloy first encountered, lives on a mountain about 1,640 feet higher than the tallest species Dr. Dr Espinoza observed – a seemingly colder area.
Dr. Halloy noted in a 1989 edition that Liolaemus huasihuasicus could survive freezing to 14 degrees Fahrenheit, but only when at an altitude of 13,944 feet; the lizards died when they cooled to 26.6 degrees Fahrenheit in tests done at 1,476 feet.
Dr. Espinoza and his co-authors discovered that Liolaemus lizards have adapted their ability to deal with the cold through three mechanisms. Some lizards avoid extreme cold by going underground. Others use a supercooling process; by standing fully, they can allow their body to fall below freezing without actually solid freezing. Finally, some may also tolerate complete freezing of the body for short periods of time. Dr. Espinoza said some Liolaemus species have certainly used more than one mechanism, depending on the conditions.
The full-body freezing strategy is likely to be similar to that seen in North American wood frogs, which stay frozen during the winter thanks to a glucose-like antifreeze solution that protects cells; Dr. Espinoza still needs to investigate this hypothesis to be sure. The southernmost joy in the world, Darwin’s marked gecko, another Argentine lizard studied by Dr. Espinoza, most likely adopts the strategy of supercooling.
Lizards of many colors
The reason Liolaemus lizards can withstand such cold temperatures and high altitudes may also explain why there are so many lizards. While there were only about 50 described for science when Dr. Halloy worked on them in the late 1970s, now there are 272 species.
Dr. Espinoza and others have discovered a number of 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 his close cousin, the genus Phymaturus. On one occasion, Dr. Lobo discovered a species under his tent, in cloudy, frozen weather in the Argentine province of Santa Cruz near the Chilean border.
“They did not look like any of the others,” said Dr. Lobo. “We suspected they were a teenager. We’ve had that excitement dozens of times in those 25 years.”
At the current rate of discovery, Liolaemus is likely to become the most numerous genus of living mammals, reptiles and birds in the coming years.
‘A species pump’
The large number of Liolaemus species may be related to the mountainous region where they live, said Dr. Espinoza. The Andes are relatively young – with the same evolutionary era as lizards. He believes that as the Andes were pushed out of the Earth’s crust, the genus spread into ecological niches that eventually took on new species.
“Andes are just a kind of pump species that creates all these new types,” said Dr. Espinoza.
Most lizards are of similar size, but they vary greatly in color and even in diets and birth strategies. Dr. Lobo told a story about an expedition to Argentina’s Jujuy Province. During their work, a local woman appeared from a small village of sheep and herb-llama in the mountains.
“She told us very clearly what that species was with their Indian names and said ‘He lays eggs and she gives birth,'” said Dr. Lobo.
Dr. Espinoza said half of the lizards are born young, probably because laying eggs at cold temperatures is unlikely to be a recipe for success for some species. In 2016 he also described a new species, Liolaemus parthenos, in which females reproduce through virgin birth, without fertilization by a male.
Melisa Olave, a researcher at Argentina’s National Council for Scientific and Technical Research, who heard about lizards on Perito Moreno, conducted a recent study showing that the rise of the Andes may not be the only factor driving Liolaemus evolution and diversity. . Liolaemus species have very low extinction rates compared to other lizards. Their change in habitat use, generalist approach to diet – some species are herbivorous, while others are ubiquitous or carnivorous – and various forms of reproduction may be critical to explaining the richness and survival of Liolaemus species. She said being a generalist is usually considered beneficial because it is easier to find suitable habitats in the very diverse landscapes of South America’s southern cone.
In other words, Liolaemus high diversity may be more a product of low extinction rate than of habitat fragmentation.
Dr. Espinoza agreed that species persistence over time may be a contributing factor to species richness, but he also believes it alone cannot explain diversity.
In any case, Dr. Olave shares the general meaning of the wonder that infects many of the researchers who have worked with these lizards.
“Liolaemus species have an extraordinary ability to survive over time,” she said.
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