Treehoppers display an endless diversity of forms, most of which are conveyed by a bizzare structure called the helmet, an novel homologue to wings no longer involved in flight.
Credit: Nicolas Gompel, Nature
Credit: Nicolas Gompel, Nature
Credit: Nicolas Gompel, Nature
Credit: Nicolas Gompel, Nature
PARIS: The extravagant headgear of small bugs called treehoppers are in fact wing-like appendages that grew back 200 million years after evolution had supposedly cast them aside, according to a new study.
That's probably shocking news if you are an entomologist, and challenges some very basic ideas about what makes an insect an insect, the researchers said, publishing in this week's Nature.
"Primitive insects 350 million years ago had wings on all of their body segments," said lead author Benjamin Prud'homme, a researcher at the Development Biology Institute of Marseille-Luminy in France.
"We don't know if they were all for flight, but we do know - from fossil records - that these wing-like structures were present on each and every body segment."
Non functional flappers in the head
The thorax of all insects is by definition divided into three segments, each with a pair of legs. In most orders, there are also two pairs of wings, one on the middle segment of the thorax and another at the rear.
Other orders such as flies and mosquitoes have only one set of wings, at the rear, and a few - most ants, for example - have no wings at all.
But no insects today have functional flappers in the first segment next to the head. Their forebear, however, did.
Losing wings and gaining them
For 100 million years following the first primitive insects, Prud'homme explained, wings on the first segment of the thorax and the abdomen dropped away entirely.
But then, some 50 million years ago, something strange happened to the cicada-like treehoppers: they once again sprouted wing-like structures from the top of the first segment of the thorax.
Some of these wildly divergent extrusions resemble thorns, others look like antlers, and still others like aggressive ants or animal droppings, creating one of Nature's most exotic menageries.
Experts had long assumed that these so-called 'helmets' were armour-like expansions of the insects' exoskeletons.
Full-circle evolution
But by carefully observing the treehopper's development into adulthood, Prud'homme and colleagues showed that this headgear began as a pair of buds - attached at the sides, and articulated like wings - that fused together as they grew.
Evolution is usually described as linear, but these modified wings suggested the process had come full circle. "This is the only known example of a modern insect that has grown a third pair of wings," Prud'homme said by phone. "It is a modification of the basic body plan of insects."
