• The study of the evolution of insects makes it possible to understand the establishment of their "megadiversity" and their predator avoidance strategies, according to our partner The Conversation.
  • Thus, fossils attest that "mimetic" grasshoppers were already trying, more than 260 million years ago, to escape their predators by taking the appearance of leaves.
  • This analysis was conducted by Romain Garrouste, researcher at the Institute of Systematics, Evolution, Biodiversity of the National Museum of Natural History.

For more than 260 million years, insects have been practicing mimicry, through which they pose as other animals or plants.

Understanding the origin and evolution of insects means understanding our planet in order to anticipate its future and those of the ecosystems that compose it, where insects must be able to continue to evolve.

Even if some insects, especially invasive species, can disturb or disgust us, they participate in the functioning of ecosystems by taking part in the food chains of the territories they invest. To understand these mysterious insects, the establishment of their "megadiversity" and their predator avoidance strategies, we look at their evolution.

In France, north of Nice, thick red rocks form a set of spectacular mountains and gorges: the Cians and Daluis gorges. These compact, sandstone rocks date from the "Permian", an era that welcomed large amphibians and large reptiles, some ancestors of dinosaurs ... as well as many insects, already with multiple lineages.

In 1963, Jean Vernet, tireless alpine geologist and great mountaineer, evaluated for the CEA the uranium potential of this massif near the winter sports resort of Valberg, in the adhesion area of the Mercantour National Park. Indeed, Permian France rocks are often dotted with uranium deposits and have been intensively studied for this. In doing so, he discovered a fossil insect wing in this Permian basin south of the Alps, where no one had yet seen the shadow of a fossil.

Giant dragonflies and grasshoppers

This fossil insect wing then represented the first insect of the French Permian, and remained for a long time the only fossil of the regional Permian.

Even today, the only witnesses of life in the "Colorado Nice" at this time are insect fossils. One of them is a "small" giant dragonfly (less than 20 centimeters wingspan for Arctotypus verneti, while some reach 70 centimeters wingspan), which attracted generations of geologists in its footsteps after its discovery in the 1950s.

It was not until 2017 that a second fossil, Permotettigonia, was found, which is exceptional for several reasons.

It took us a little while to conclude on the relationship of this fossil with modern grasshoppers. This was highlighted by studying the current grasshoppers (Orthoptera Ensiferous) and their morphological similarities... with plants.

Resembling plants, a power that helps to adapt

A simple wing print of a medium-sized insect, this wing fossil alone carries the information needed to recognize one of the oldest representatives of Orthoptera – crickets and grasshoppers. But above all, it bears a resemblance to the mimetic orthoptera of plants such as grasshoppers that we know today, which imitate in great detail the living (green) or dead leaves of plants.

These mimetic grasshoppers were already trying, more than 260 million years ago, to escape their predators by taking the appearance of leaves. Predators could be gliding reptiles known at the same time in different deposits (Madagascar, Germany) or "giant" dragonflies (Meganeurides).

The fact that insects were already imitating plants at the time, which is a valuable indication of the ecosystems of this period, because mimicry is the manifestation of a "selection pressure": it is likely that predators must have already been numerous and effective enough for insects to go unnoticed.

Thus, this fossil wing, by testifying to the antiquity of these relationships between plants and insects (biological interaction), has made it possible to postpone by nearly 80 million years the proven cases of mimicry.

Adventurous paleontologists

The red "pelites" of the Permian are often fossiliferous, but are not easy to study: they are often solidified sediments that resist erosion, which complicates excavation operations. Raised by the alpine folding in the Miocene (around 10 million years ago), they are found here in the mountains, where steep slopes complicate progression and prospecting. Mountaineering techniques are convenient to reach complicated sites.

Among these, canyoning methods make it possible to descend into the streams that have carved deep canyons and make it possible to examine eroded surfaces, to look for areas favorable to fossilization. The paleontologist must be a little adventurous to flush out unpublished fossils.

Our ancestors used these methods of mountaineering in this massif to find minerals such as native copper since antiquity and the Middle Ages. Today, these ancient mines are only accessible with alpine techniques (such as rappelling for example) in the cliffs of the Daluis gorges.

OUR "INSECTS" FILE

The massif of the Dome of Barrot, remarkable and wild, has not revealed all these secrets and we continue the exploration, under the gaze of the wolves who also roam these territories. Other scientific treasures await us.

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This article is produced by The Conversation and hosted by 20 Minutes.

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