New Zealand’s South Island was once covered in dense forest, the trees breaking like a dark green tide around the grassy mountain tops. After the arrival of the Māori settlers about 750 years ago, some hills were cleared from their trees by people with fire and the foliage has not returned. For the organisms living in these forests, their habitat changed from protected forests to exposed, windy meadows almost overnight.
Since the forests burned, small winged insects called stone flies have changed too, researchers have found. Over the course of just a few centuries, the stoneflies that live above the tree line have lost the ability to fly, suggesting that man-made changes to an ecosystem, such as deforestation, are affecting the bodies of. radically transform its residents. The discovery was published in the journal Biology Letters on Wednesday.
Charles Darwin noted that insects on islands have a strange tendency to be incapable of flight, perhaps because flying is dangerous when you are small and the wind is strong. In New Zealand, scientists found flightless stone flies on many different mountains, said Jon Waters, professor at the University of Otago in New Zealand and author of the new paper. At first it was not clear why – whether something at high altitude favored a flightless form or whether something else was going on.
To answer the question, he and his colleagues collected stoneflies in five places and hiked through the woods to the bare mountain ridges. They caught insects as they went up the slopes and recorded their locations. Looking at all of the data, they were surprised to find a very clear trend.
“We found that there was this amazing transition from winged populations to flightless populations when you go up,” said Dr. Waters. “Wherever we looked, that correlation was related to where the trees ended, not to a certain height.”
Since the change took place at the tree line instead of at a certain height, this indicates that the exposed location above the trees favored flightlessness in stone flies. Perhaps the wind on the heights, like Darwin’s island insects, makes flying a nuisance.
It is possible that in some places, even before the forests burned, there were flightless stoneflies that simply expanded their territory after the fires. A genetic analysis of the stoneflies showed that three of the five populations the researchers studied were very different from their winged lowland brethren, suggesting that they may have evolved on their own for some time.
However, the other two had minor differences, suggesting the change was recent – new enough to have been since humans first arrived on the island.
The apparent rapidity of change is reminiscent of the case of the peppered moth, whose color shifted from light to dark when air pollution from the industrial revolution in England darkened the trees it lived on – light-colored moths were naturally altered for predators in theirs Vicinity. It does not take millennia for animal populations to change through natural selection, as these cases show.
“You go into the trees and suddenly find yourself in a different population. It is almost like magic that in some of these cases and in a short time frame, evolution seems to be working so clearly and effectively over a short distance, ”said Dr. Waters.
Now the researchers are studying the stonefly genetics to understand what changes when the insects lose their ability to fly. The details can reveal whether the stoneflies’ apparent flexibility is due to new mutations or whether their inability to fly is due to variations that already existed in their ancestral populations and were just waiting for the right moment to take them over.