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  • Dr. Rosenblum weighing lizards at White Sands

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White Sands, New Mexico

It’s Not Only the Gene That Counts, But How You Use It

The lizards must have felt like they were in that dream where the guest speaker arrives at the podium only to be laughed off stage for forgetting to put on pants.

About 7,000 years ago, a large region of New Mexico swiftly changed from brown to white due to gypsum sand from evaporating lakes forming large dunes. Suddenly, the lizards’ brown backs were not very good at hiding them from aerial predators.

Since then, every species living in the White Sands region has adapted to their new environment by evolving a white appearance.

Erica Bree Rosenblum, assistant professor of biology, was curious about whether or not different species used the same gene to change colors. She discovered that not only do some use the same gene, but how they use it can have important consequences.

The findings were published in December in a paper titled, “Molecular and functional basis of phenotypic convergence in white lizards at White Sands,” in the online early edition of the Proceedings of the National Academy of Science (PNAS).

“It’s cool that really different species solve the same problem in a similar way,” says Rosenblum. “But what’s even cooler is that a very slight difference actually has a big effect on the lizards.”

Two of the three species she studied – the fence lizard and the whiptail lizard – used the same gene that controls the production of melanin; the same substance that controls the color of human hair.

But Rosenblum took her research deeper. She discovered that the lizards use the gene in different ways, which affects whether a white back is a dominant or recessive trait, and thus the rate of adaptation.

“It shows a difference in the function of a single gene can actually matter,” she says.

The gene in question creates receptors that sit in the membranes of cells that make melanin and transmits a signal that controls melanin production. In fence lizards, the gene mutated so that the receptors no longer sit correctly into the membranes of the melanin cells. In whiptail lizards, the mutation affects how well the receptor transmitted the “on" and "off” signal to make melanin.

What’s more, Rosenblum found the mutation causing the misfit receptors is a dominant trait while the mutation that messes up the signal transmission is recessive. This means fence lizards using the first mutation only need one copy of the mutated gene to be white, while whiptail lizards need two.

“What seems like a nitpicky technical detail about how the receptor is compromised actually affects the natural population of lizards,” says Rosenblum. “It changes how fast the white phenotypes spread in the population and whether migrants from one population moving to another can survive. It’s really fascinating.”

Scientists discover not only that different species can use the same gene to adapt to a new environment, but slight differences in its use can have important consequences.