We often think of evolutionary processes as a painfully long ordeal (at least in terms of our measly human lifespan). Then again, evolution has no fixed schedule. A notable change might take millions of years to occur, or it might take a few years. As these lizards show, it can sometimes take just a couple of months to give an evolutionary process a massive kickstart.
Side-blotched lizards are speckled with sandy brown markings to help them blend in with the surrounding dusty Mojave Desert terrain. A small number of these lizards living on the desert’s Pisgah Lava Flow, however, are black, just like their environment.
This sparked the curiosity of a team of researchers at the University of California – Santa Cruz. A light-colored lizard on a black rock is easy pickings for predators. So, how did they survive long enough to evolve darker coloration? It turns out, the lizards can adapt to their new environment freakishly quickly. Take a look at the lizard in the image above – that's the same lizard just four months after moving to a black lava field from a sand-colored environment.
Importantly, the different colored lizards also have heritable differences in pigmentation. A lizard might be born brown, but if it moves to the lava fields, it can adapt to its surroundings, in this case become darker, and this learned behavior is passed on to its offspring, which are born darker. This means they can influence new adaptations that go on to be selected through natural selection.
This is an evolutionary theory put forward a hundred years ago, called the Baldwin effect. As reported in the journal Current Biology, researchers have documented the Baldwin effect in amazing detail outside of the lab for the first time.
"It's an old and very powerful idea, and now we have genetic evidence of how it happens in the wild," co-author Barry Sinervo, professor of ecology and evolutionary biology at UC Santa Cruz, said in a statement.
The Baldwin Effect occurs thanks to “phenotypic plasticity,” the ability of one genotype to express itself in more than one way when exposed to different environments. The lizards have two certain genes that code for their coloration by controlling melanin production. Interestingly, they can code for different levels of melanin in response to a new environment. This plasticity helps the darker lizards survive, and natural selection refines the phenotype as it's passed on.
To test out this idea out in the field, the researchers gathered side-blotched lizards from within the lava field and outside the lava field. They then swapped their environments. Within one week, they noticed a slow, gradual change in pigmentation.
A genetic analysis of lizards surrounding the lava flow also highlighted that the gene variants were restricted to the lizards living within the lava field area. This suggests the variants arose through mutations that occurred in lizards living on the lava and spread within that population.
"Baldwin predicted that plasticity allows organisms to colonize new environments, and they then develop new adaptations through natural selection," said first author Ammon Corl.
"In some ways, it's amazing that natural selection still acts in the presence of so much plasticity. All it takes is a bit of a mismatch and that can make the difference between life and death."