Adaptable lizards illustrate key evolutionary process proposed a century ago

Date:  September 6, 2018

Source:  University of California - Santa Cruz

Side-blotched lizards in most of the Mojave Desert have tan and brown markings that blend in well with their desert surroundings. On the Pisgah Lava Flow, however, one finds a very different population of side-blotched lizards, as black as the rocks they live on.

How do animals invade new environments different from the ones for which evolution has equipped them with finely tuned adaptations? Light-colored lizards on a lava flow should be easy picking for predators, so how did they survive long enough to evolve darker coloration?

One explanation has been that many of an animal's traits are not fixed, but can change during its lifetime. This "phenotypic plasticity" enables individual animals to alter their appearance or behavior enough to survive in a new environment. Eventually, new adaptations promoting survival arise in the population through genetic changes and natural selection, which acts on the population over generations. This is known as the "Baldwin effect" after the psychologist James Mark Baldwin, who presented the idea in a landmark paper published in 1896.

Scientists studying the side-blotched lizards on the Pisgah Lava Flow have now documented this process in meticulous detail. They showed how individual lizards can change colors in a new environment to become darker on lava; they identified genes that regulate coloration and that differ between populations on and off the lava; and they found that the genetic changes in the population adapted to the lava flow make those lizards darker than others. Their findings, published September 6 in Current Biology, may be the most detailed example of the Baldwin effect occurring in a wild population.

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