What is the evidence that speciation occurs

The theory of "Darwin's butterflies" confirmed

Black moths are a classic example of the principles of evolution. Now researchers have confirmed that the wing coloration of these butterflies actually affects their survival. This is the first time they have provided experimental evidence for a long-postulated connection. According to this, natural selection was responsible for the fact that the butterflies in England during the industrial revolution suddenly got more and more dark wings. This enabled them to hide better from predators in the polluted environment.

Moths are the prime example of evolution based on the principle of natural selection. The nocturnal moths usually rest on the trunk of trees during the day, where they are barely noticeable due to their white color with dark spots and stripes. They remain invisible to predators, both on the bark of birch trees and on trunks of other species overgrown with light-colored lichens. Rare monochrome dark mutants, on the other hand, are less able to camouflage themselves.

At the beginning of the industrial revolution, however, these exotic species suddenly had an advantage: when factory chimneys began to shoot up everywhere in England, more and more soot was deposited on the bark of trees and many lichens also disappeared due to air pollution. As a result, the white moths were now targeted by hungry birds. The dark color increasingly prevailed - it dominated until the air became cleaner again.

Textbook example put to the test

"This so-called industrial melanism appears in almost every biology book as an example of the mechanisms of evolution according to Charles Darwin," says Martin Stevens of the University of Exeter. “Surprisingly, however, nobody has yet investigated in a controlled experiment how much the color actually affects the chances of survival of the moths.” This is exactly what the scientist and his colleagues have now made up for.

For their study, they first used computer simulations to test how well birds can recognize different colored moths on the bark of trees. It was confirmed: For birds' eyes, white and dark patterned butterflies look similar to bark overgrown with light lichen. Dark moths, on the other hand, come closer to darker bark without lichen growth.

Clear survival advantage

But what does that mean in concrete terms? To test this, the researchers started an experiment in the UK's forests, mainly in Cornwall - an area where healthy trees with lots of lichens grow. Stevens and his colleagues placed artificial butterflies on the bark of these trees, which they equipped with tasty treats as bait.

In fact, typical predators of the birch moths hunted these dummies - but much less often on individuals with black and white body markings. Their chance of "surviving" was 21 percent higher than that of the dark-colored test objects. “The light butterflies therefore have a strong survival advantage,” states Stevens colleague Olivia Walton.

Theory confirmed!

“Our results show that differences in coloring go hand in hand with differences in camouflage and hunting - and that the accumulation of dark markings during the industrial revolution arose as a reaction to environmental pollution. We are thus confirming one of the most famous examples of natural selection, ”concludes Stevens. (Current Biology, 2018; doi: 10.1038 / s42003-018-0126-3)

(University of Exeter, 08/20/2018 - DAL)

20th August 2018