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Lateral lizards in most of the Mojave Desert have brown and brown markings that blend well into their desert environment. On the Pisgah lava flow, however, there is a very different population of side-lizard lizards, as black as the rocks on which they live.
How do animals invade new environments different from those for which evolution equipped them with precise adaptations? Light-colored lizards on a lava flow should be easy to pick for predators, so how did they survive long enough to develop a darker color?
One of the explanations is that many of the characteristics of an animal are not fixed, but can change during one's life. This "phenotypic plasticity" allows individual animals to change their appearance or behavior to survive in a new environment. In the long term, new adaptations that promote survival occur in the population through genetic changes and natural selection, which affect the population over generations. This is what is called the "Baldwin Effect" after the psychologist James Mark Baldwin, who presented the idea in a reference document published in 1896.
Scientists studying side-lizard lizards on the Pisgah lava flow have now documented this process in a meticulous way. They showed how individual lizards can change color in a new environment to become darker on the lava; they identified genes that regulate staining and differ between populations on and off the lava; and they found that genetic changes in the population suitable for lava flow make these lizards darker than others. Their conclusions, published on 6 September in Current Biology, can be the most detailed example of the Baldwin effect occurring in a wild population.
"This is an old and very powerful idea, and we now have genetic evidence of how this occurs in nature," said co-author Barry Sinervo, professor of ecology and evolutionary biology at the Santa Cruz University.
Sinervo has been studying California side lizards for over 30 years. First Author Ammon Corl, who earned his Ph.D. in Sinervo's lab, is now at the Museum of Vertebrate Zoology at UC Berkeley. Corl said he first learned about the Pisgah lizard population from an unpublished doctorate. co-author Claudia Luke's thesis, now at Sonoma State University.
"Claudia understood how plastic their coloring is, and I tested for genetic changes that affected staining in the Pisgah population," said Corl. "Baldwin predicted that plasticity allows organisms to colonize new environments and then develop new adaptations through natural selection. Until now, however, we lacked genetic tools to show that this was happening on the ground.
When researchers move lizards laterally from one background to another (eg, sand to lava rock), color changes begin to appear within a week and gradual changes in coloring continue for months. "It seems that there is a slow and gradual accumulation of dark melanin pigment," said Corl.
The lizard populations on and off the lava flow have this plasticity allowing them to change color when they are moved into a new environment. But both populations also have inherited differences in pigmentation. The genetic analysis revealed differences between the two populations in two genes involved in the regulation of melanin production.
The researchers crossed lizards from both populations, reared offspring in a common environment, and measured offspring coloration. These experiments showed that variations in melanin-related genes correlated with the darkness of lizard skins.
Genetic sampling of side-lizard lizards surrounding the lava flow has shown that the genetic variants found in the lava population are limited to this population, suggesting that the variants result from mutations occurring in lizards living in the lava flow. washed. Demographic modeling studies have suggested that the new mutations occurred thousands of years after the lava flow about 22,000 years ago.
"We've been studying side-lizard lizards everywhere, even in another lava flow, and these genetic variants are only found in Pisgah, so we know where they appeared," Sinervo said. "These are the genes that govern staining by controlling the production pathway of melanin, but in a complex way. Pisgah lizards are best suited to the color of the lava of all populations, but they can still return to the sand and adapt to a completely different environment. "
The range of coloration possible for an individual lizard is remarkable. "In some ways, it is amazing that natural selection continues to act in the presence of so much plasticity. All it takes is a bit of lag and it can mean the difference between life and death, "said Corl. "There are still variations within the population, so we were faced with natural selection by acting on these genes. We can now conduct further field and laboratory studies to better understand how the evolution of highly plastic characters is shaped by evolution.
In addition to Corl, Luke and Sinervo, co-authors of the article are Rasmus Nielsen, Ke Bi, Akshara Sree Challa and Aaron James Stern at UC Berkeley. This work was funded by the University of California and the National Science Foundation.
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