Insects’ Exuberant Helmet Is Actually an Extra Set of Wings

In 250 million years of insect evolution, the appearance of new wings is unprecedented. Transformations and losses of wings, yes, but additions, never. A team from the Institut de Biologie du Développement de Marseille-Luminy (CNRS/Université Aix-Marseille 2) has shattered this belief by providing proof that the exuberant helmet of Membracidae, a group of insects related to cicadas, is in fact a third pair of profoundly modified wings.

Membracidae, or treehoppers, are a family of insects, related to cicadas, whose various species vie with each other as regards the originality of their shapes, textures and colors. This diversity is to a large extent conferred by a rather surprising structure covering a large part of their bodies: a ‘helmet’. This sometimes resembles an ant in attack position, sometimes a bird dropping, a dead leaf, a thorn, etc. Before the team headed by Nicolas Gompel and Benjamin Prud’homme, both CNRS researchers, studied them with an electronic microscope, the evolutionary origin of this structure was still much debated.

Unlike the horn of the rhinoceros beetle, the helmet of Membracidae is not a simple outgrowth of the cuticle, but a dorsal appendage attached to each side of the thorax by an articulation, with muscles and a flexible membrane that allow it to move. These anatomical observations have been confirmed by the team of researchers at the genetic level: the same genes are involved in the development of the helmet and the wings. Membracidae could thus be insects with three pairs of wings, one of which is heavily modified and unrecognizable.

This discovery is the first example of a change in the body plan of insects by the addition of an evolutionary innovation. This plan is defined by a body divided into three parts (head, thorax and abdomen), a pair of antennas, three pairs of legs and, most frequently, two pairs of wings, always present on the second and third segment of the thorax. However, variations in this general plan exist. In Diptera, such as houseflies or mosquitoes,” for example, the hind wings are reduced to small round appendages known as balancers. In Coleoptera (ladybugs, beetles, maybugs, etc.), the first pair is transformed into elytra, hard and often colored “wings” that protect the hind wings. In certain insects, the wings have even totally disappeared. This is the case with fleas and lice, which have a parasitic lifestyle, or red bugs, commonly known as Fire Bugs.

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One Response to Insects’ Exuberant Helmet Is Actually an Extra Set of Wings

  1. alfy says:

    Oh dear. Here we go again. This discovery is NOT “the first example of a change in the body plan of insects by the addition of an evolutionary innovation.” Each thoracic segment genetically has the potential to produce wings. For the most part, three pairs of wings is a bit excessive and natural selection has ruled it out.
    In the case of the Membracidae they have realised the potential wings on every segment, albeit that the prothoracic wings are modified to a totally different use, as is described for other thoracic wing pairs in other insect orders.

    This is not the origin of something completely new from an evolutionary point of view, it is the exact opposite, i.e. the re-emergence of an ancient trait. Don’t they teach comparative anatomy to biology students and their lecturers anymore? If they did, perhaps we would not see so many of these gaffes.

    Let’s take an easy example. Primitive vertebrates were segmental. Each segment had a a set of muscles, a pair of nerves to work them,and a set of bones as a skeleton. There were other things, but let’s keep it simple. In the modern human body this basic pattern is retained but it has been subject to some telescoping during the course of evolution.

    The spinal nerves are still basically segmental as a glance at any textbook of anatomy would show you. In the head this is still true of the twelve pairs of cranial nerves underneath the brain.
    Human musculature is still segmental too. However, in the head region the muscles do quite unusual jobs. For example, each eyeball is moved by eight muscles. Two muscle pairs are controlled by pair A of cranial nerves, two muscle pairs are controlled by pair B cranial nerves, and the third and last muscle pair is controlled by pair C of cranial nerves.
    Why so complicated? Because evolution was working with the segmented material to hand and not designing something from scratch as we do nowadays.

    Originally, in vertebrates, every segment would have a pair of bony ribs. In fish like herrings this is still the case. In snakes this is also true. You may have noticed that this is not the case in mammals. Although each segment probably has the potential to develop a rib, they are limited to fourteen pairs in the thoracic or chest region.

    Suppose a group of mammals suddenly developed two extra pairs of ribs. Would this be an evolutionary innovation? Yes, but only up to a point. Can you see that this is a partial reversion to a more ancient form? The genetic potentiality for ribs was always there but suppressed or undeveloped. The interesting question is why that potentiality suddenly became active again.

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