Polynesians shorten the wings of a New Zealand insect

Polynesians shorten the wings of a New Zealand insect
Polynesians shorten the wings of a New Zealand insect
Anonim

The incident confirmed the long-standing hypothesis of Charles Darwin that the loss of wings - for all their apparent usefulness - for insects has significant evolutionary meaning.

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Scientists from New Zealand studied the frequency of occurrence of flying and flightless forms of the local insect species Zelandoperla fenestrata (pictured). Populations of this species have different wing lengths: the shortest-winged ones cannot fly, the longer-winged ones can. The authors of the work studied data for five regions where this unique species is found (it is nowhere to be found outside the southern island of New Zealand). In three places of the forest, they disappeared after the colonization of the Maori island (it began in the XIII century), and in two forests did not interrupt their existence in the last thousand years.

As expected, the percentage of short-winged individuals unable to fly depended on the height of the mountain slopes at which they were collected. At altitudes of about 600 meters, all individuals of this species were able to fly. At altitudes closer to a thousand meters, the situation was the opposite: almost no one could fly. A similar picture is observed with different species of insects around the world: the higher up the mountains, the less often local insects are able to fly.

However, in the case of Zelandoperla fenestrata, the situation was more complicated. Where forests have survived (two locations), a much larger percentage of individuals had the ability to fly even with an increase in height. Where there were no forests, the inability to fly became widespread even at medium altitudes, long up to a thousand meters.

Researchers do not go into detail on the specific reasons why the presence of forests in the habitats of these insects reduces their risk of losing their propensity to fly. However, the likely mechanisms are fairly obvious. First, the forest somewhat neutralizes the direct effect of the wind on flying insects, slowing down the air flow in the surface layers. Secondly, even if a strong gust of wind picks up an insect, it always has a chance to run into a tree and catch on to it, waiting for the wind. In places where there are no forests, neither one nor the other is impossible - and the wind can carry an insect with wings to the place where it dies or does not leave offspring, that is, beyond the biogeocenoses suitable for it.

The authors of the work conclude that the reason for the loss of the ability to fly should be considered a strong wind in the absence of factors that reduce its effect on flying insects. This confirms the long-standing theory of Charles Darwin about the reasons why insects lose their ability to fly. The rejection of functional wings does not seem very logical: due to them, insects can quickly move over great distances. For example, the red-headed vagrant, one of the species of dragonflies, rises to an altitude of 6200 meters and migrates for many thousands of kilometers (it can fly over the Pacific Ocean). High mobility makes it easier to find food and a sexual partner. Why, in a number of ecosystems, do insects massively abandon it?

This question arose before biologists back in the 19th century, when it turned out that on the islands between Australia and Antarctica, almost all insects were devoid of wings. This is strange: to get here, they obviously had to use wings, since the native species are old, and they clearly arrived here before humans. Darwin suggested that individuals capable of flying are often carried away by the wind into the sea, where they die. As a result, natural selection contributes to the survival of those unable to fly. At that time, his hypothesis was severely criticized. However, the new work of New Zealand scientists points to the correctness of the researcher.

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The authors of the work note that human impact on forests, thus, is capable of pushing individual populations of insects to abandon flight.This is potentially a problem: if some populations do not fly, they will not be able to exchange genes with others, which will reduce their local genetic diversity.

At the same time, deforestation is unlikely to pose a threat to the existence of the species Zelandoperla fenestrata. The fact is that modern New Zealanders do not cut forests: this was done by the Polynesian Maori tribes, who arrived on the island no later than the 13th century. By the beginning of the 19th century, there were at least one hundred thousand of them, but by the end of the century their number had dropped many times. For European agricultural methods, mountain slopes are poorly suited, so now there is practically no anthropogenic economic impact on mountain forests. If over the hundreds of years that have passed since the burning of the Maori forests, the refusal to fly did not lead to the loss of the Zelandoperla fenestrata range, then this is hardly possible in our days, when there are no burns anymore.

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