How superfast evolution helps lizards change colour to survive
IT IS an evolutionary problem which has puzzled scientists since Charles Darwin first proposed the idea of development by natural selection.
How do species stay alive while they are evolving to suit their environment?
While Darwin supposed the fittest in any generation survived, passing on favourable traits, the 19th century psychologist James Mark Baldwin argued that traits could change in one lifetime – known as the Baldwin Effect.
Now scientists have proven the Baldwin Effect, after showing that lizards can change colour within just a few days to blend into a new environment and avoid being eaten. Their offspring are then born with the genes which produce the helpful new colour.
“It’s an old and very powerful idea, and now we have genetic evidence of how it happens in the wild,” said Dr Barry Sinervo, professor of ecology and evolutionary biology at the University of California, Santa Cruz.
To find out whether the Baldwin Effect was true, researchers studied two populations of side-blotched lizards, one in the sandy Mohave Desert and another in the black rocks of the Pisgah Lava Flow in California.
The Mohave lizards have evolved tan and brown markings as camouflage, while the lava flow lizards are jet black.
The light-coloured lizards would be easy pickings for predators on the lava flow, so scientists wondered how they survived long enough to turn darker.
But when they swapped the lizards from one background to another, they found that they started to change colour within a week and completed the process in four months.
The researchers cross-bred lizards from the two populations, raised the offspring in a common environment and measured their colouration. They found that variations in genes which produce melanin, – the tanning pigment – correlated with the darkness of the lizards’ skins, showing that changes were happening at genetic level.
Genetic sampling of side-blotched lizards surrounding the lava flow also showed that the darker gene variants found in the lava population were restricted to that population, suggesting that the variants arose through mutations in lizards living on the lava and spread within that population.
The study’s first author, Dr Ammon Corl, of the University of California Berkeley’s Museum of Vertebrate Zoology, said: “Baldwin predicted that plasticity allows organisms to colonise new environments, and they then develop adaptations through natural selection.
“Until now, however, we have lacked the genetic tools to show this is going on in a field setting.”
The findings were published in the journal Current Biology.