They carry antennas, horns and spikes on its back: in the insect world treehoppers are among the most visually spectacular animals. So far, researchers said to understand the origin of the strange shapes - but now a study turns this assumption on its head.
They are best known for their enlarged and ornate pronotum, which most often resembles thorns, apparently to aid camouflage. But in some species, the pronotum grows to a horn-like extension, and even more bizarre and hard-to-describe shapes are also found.
When on host plants, they blend in the plant to protect themselves from its predators. The thorn on the thornbug discourages other predators from eating it, often confusing them with a thorn.
It is sometimes called thornbug as well as treehopper. This insect can fly, but part of its defense from predators is that it looks like a thorn on a tree limb which may prevent birds or other predators from eating it.
Darth Vader of the Insect World
"Nature has made a joke when designing the treehoppers", is supposed to be a statement made by one of the first explorer of the creatures, John Henry Comstock. Entomologists still laugh at the joke. The strange shapes on the insect's backs seem to be so out of this world that researchers like to joke around and say the excesses are antennas, which let the insects communicate with their home planet.
Until now, insects, researchers believe that these structures, also called back shields, were outgrowths of the exoskeleton, like the horn of the rhinoceros beetle. Although entomologists suggested in 1953 the strange shapes could be a kind of limb, but the idea did not catch on, and disappeared soon after again.
In their study evolutionary biologists around Benjamin Prud'homme in the Center for Developmental Biology in Marseille made a surprising discovery. The study was published in the scientific journal Nature and showed that the structures were once wings.
Treehoppers are common, but mostly they live in the tropics. Just a few of the 3,000 known species are known to exist in Europe. Most striking about them are the eponymous hunches: various, sometimes bizarre shapes on the back, reminiscent of modern art. Meanwhile, the function remains still unclear. Whether it is a kind of camouflage or "jewelry", is solved except for a few species.
Prud'homme and his colleagues used modern techniques to confirm their theory of the origin of the bizarre excesses.
In some cases the back plate of some species of the treehoppers eased because they were soft and not hard in contrast to the rigid horns known among some beetles. The biologists believed this flexibility to be a kind of joint that keeps the spine label - a reference to a structure like a limb. In the electron microscope, they looked more closely at the animals and indeed found two tiny joints, left and right of the forward part of the upper body. Even this number said that the formations are reshaped rear limbs. Like humans, insects form their limbs balanced, otherwise a double anchoring of the single back plate wouldn't be absolutely necessary.
But these considerations were not enough to clarify the origin of the hump clearly enough. So the biologists studied the evolution of insects and observed that the early stages of the precursors from the back plate were comparable with wings. In these regions of the insects there were also active genes normally only to be found in wings or limbs.
The researchers finally have been proved that the back plate was created of wings - and eventually provided an evolutionary explanation. Admittedly, most insects have three pairs of legs and two pairs of wings. But evolutionary biologists assume that ancient insects had more limbs - such as centipedes. There were also wings as well, where now the joints of the
carapace at treehoppers are situated. To this day these are also created in the body plan, but certain genes normally prevent their growth.
The biologists in Benjamin Prud'homme's team suspect that this mechanism no longer works at treehoppers. The ancestors of today's humpback crickets had a third pair of wings that was not used for flying. Evolution had its own plans: Freed from the compulsion of having to function as a wing, it has become today's antennas, antlers and other bizarre shapes.
In a relatively short period of 40 million years the process of using a useless single pair of wings in such a way is interpreted as an impressive testament to the power of evolution by the researchers.