Even Desert Lizards Are Feeling the Heat Due to Climate Change

For many plants and animals, the Sonoran Desert would be an inhospitable place. But for the flat-tail horned lizard, it’s home. Before the sun gets too high in the sky, the small lizards, just a few inches in length, can be spotted feeding on native ants in sparsely vegetated areas near Yuma, Arizona, and around the Salton Sea in nearby California.

Their homes are “almost like a lunarscape,” says Dan Mulcahy, a herpetologist at the Smithsonian National Museum of Natural History. “They need places to hide,” he says. Otherwise, “they would be toast by noon.”

The lizards, however, may have bigger worries than a scorching noonday sun. The accidental creation of the Salton Sea in the early 20th century cut off one population in California’s Coachella Valley, and roads separate others. Suburbs, agricultural fields and other bits of modern life, such as army facilities and an off-roading park, have encroached onto prime lizard territory. Invasive Argentine ants are crowding out the lizards’ food source in some spots. And climate change is another concern.

If the flat-tail horned lizard is to survive these threats, scientists will need to know more about its genes, says Mulcahy. So he and Andrew Gottscho, a postdoctoral fellow at NMNH, will soon do just that, taking advantage of the museum’s state-of-the-art biotechnology facility to map out the species’ genetic diversity.

Mulcahy has studied the genes of the flat-tail horned lizard before. In 2006, while at Utah State University, he led a study that surveyed the mitochondrial DNA of the flat-tail horned lizard and the desert horned lizard, a more common species that overlaps in range. The team collected lizard toe and tail tips—as well as some whole lizards—in Arizona and California and sequenced their mitochondrial DNA. This is the DNA found in cells’ energy-producing organelles, and it’s only passed from mother to child.

Scientists use mitochondrial DNA “kind of how you could track your ancestor through your surname, because it’s only handed down through the paternal side,” Mulcahy says. Though it is “a limited source,” mitochondrial DNA can be a good tool for studying the geographic relationships of individuals and populations, he says.

The mitochondrial DNA indicated that the flat-tail horned lizards near Yuma belonged to an ancestral population, with more genetic diversity than the populations found to the east. The eastern lizards tended to be genetically similar, even when the populations were cut off from each other. Sometime in the past, Mulcahy’s team thought, individuals of the species expanded their range from Arizona into California. Later, the populations became separated by natural geographical features as well as human-made ones.

But to get a really good look at gene flow between the populations, scientists will need deeper information from the lizards’ nuclear DNA, Mulcahy says. That’s the genetic material that is found within the nucleus of an organism and is a combination of the DNA from both parents. There’s a lot more nuclear DNA than mitochondrial DNA, and ten years ago, it just wasn’t feasible to sequence nuclear DNA in a study like Mulcahy’s.

“But now we have the technology to rapidly sequence a lot of DNA,” he says. “With the next-generation sequencing, we can capture big pieces of the genome very quickly and efficiently.”

Mulcahy and Gottscho won’t be sequencing the entire genomes of lizards; they’ll look for single nucleotide polymorphisms (SNPs). These are DNA sequences in which a single nucleotide differs from one individual to the next. That will let the pair investigate genetic variation between populations and see how genes have flowed through them. Because nuclear DNA has genetic material from both parents, the study may come up with different results from the earlier analysis that used only DNA passed from mom.

Such data may help researchers determine whether there are certain populations that are more valuable to the species. For the lizards, “things are constantly changing, whether its disease or climate” or something else, says Mulcahy. Genetic diversity can help a species weather such changes, he says.

And big changes, like global warming, are already happening, he notes. Scientists worry that a warming climate may be especially dangerous for lizards, which aren’t able to regulate their own temperatures. The flat-tail horned lizards deal with heat by reatreating to a cool burrow. But if they have to hide earlier in the day, that will leave less time for obtaining the resources necessary for mating and producing more lizards.

The lizards “may need to become nocturnal if they want to survive,” Mulcahy says, “and their genes may not let them do it that quickly.”

Editor's Note: This story has been updated to give the correct name of the postdoctoral fellow  involved in the project, Andrew Gottscho.

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Sarah Zielinski is an award-winning science writer and editor. She is a contributing writer in science for Smithsonian.com and blogs at Wild Things, which appears on Science News.