At the University of Indiana, three-eyed dung beetles are teaching researchers something unexpected about evolution of facial features.
Insects like beetles hatch as larvae and then transition into full-grown bugs. Like all other life forms, its DNA has a working plan for the maturation of the dung beetle.
Team leader Eduardo Zattara and his researchers already knew that certain genes were responsible for forming the heads but were surprised at what happened when they deactivated the orthodenticle gene: To their amazement, the subjects turned out to have no horn but instead had developed a third compound eye where the horn should have been.
Since the orthodenticle gene controls the growth of the head in most creatures, getting a third eye was unexpected.
As it turns out, in beetle embryos, the orthodenticle gene is needed to develop heads, but when the larvae metamorphosizes into an adult beetle, the gene restructures the growth of the head and adds in the normal horn a dung beetle expects.
When researchers tried to replicate the experiment in flour beetles, it failed, suggesting that this function is unique to horned beetles.
The study showed that when the orthodenticle gene, which is supposed to turn on when the beetle metamorphosizes but is delayed, presents opportunities for genetic mutations.
In this study, it allowed a complex structure like the eye to emerge; in a previous mutation it may have allowed the horn itself to arise.
The research, funded by the National Science Foundation, was published by the Proceedings of the Royal Society B in July.