"Cyclops" Dung Beetles Created By Switching Off Gene That Manufactures Their Horn

The heads of horned (left) and cyclopic (right) dung beetles. All that's needed to create the latter is switching off one specific gene. Credit: Eduardo Zattara

Genes are strange, and science has barely scratched the surface when it comes to determining which genes are responsible for what. Many are responsible for multiple characteristics, and some can switch roles depending on the situation. A pair of curious new studies give a rather weird example of this – by switching off a certain gene in horned dung beetles, their central horn turns into a compound eye instead, effectively turning them into cyclops beetles.

The first study, published in the Proceedings of the Royal Society B, found that the orthodenticle genes in horned beetles of the genus Onthophagus completely changed their head structure, with the replacement of their combat-ready horns being particularly strange. Weirder still, the physical consequences of this gene knockout were specific to this genus. When the same technique was applied to the hornless flour beetles (genus: Tribolium), nothing of the sort happened.

“We were amazed that shutting down a gene could not only turn off development of horns and major regions of the head, but also turn on the development of very complex structures such as compound eyes in a new location,” lead author Eduardo Zattara, a postdoctoral researcher at Indiana University Bloomington (IUB), said in statement.

“The fact that this doesn’t happen in Tribolium is equally significant, as it suggests that orthodenticle genes have acquired a new function: to direct head and horn formation only in the highly modified head of horned beetles.”

At this point, it isn’t clear why this change does occur when these genes are knocked out, which is where the second study, published in the Journal of Experimental Zoology, comes into play. Instead of focusing on dung beetles’ adult lives, the team of researchers focused on their development as larvae.

A close-up of the strange compound eyes in the center of the head. Indiana University Bloomington

Generally speaking, beetles have four life stages in what is known as “complete metamorphosis”. The first form is the egg, which hatches into a larva about a week or so later. They then spend several months eating and growing in size. When it is satiated and sizeable enough, they mostly stop eating and enter the third stage, the pupa. Within its casing, it rearranges its innards for another week before it emerges as a fully-formed beetle.

Many genes vital for plotting out the biological “plan” of the head of larvae have been known to science for some time, but it’s unclear what happens to these genes when the pupa is turning into the adult beetle – are they also used to plot out the adult head too, or do they become redundant?

When they switched off the orthodenticle genes in larvae, these genes appeared to take on a new function in adults: namely, they were involved in reorganizing the head, shrinking or removing the horns, and helping spur the development of unusual, central compound eyes.

It seems that these specific genes that linger throughout most of the life cycle of dung beetles can be “recruited” to help spur on very different morphological features. Importantly, this means that the development of new genetic sequences isn’t required, and thus certain beetles can effectively take a genetic “shortcut” to suddenly develop new features if need be throughout their lives.

As the researchers point out, a hammer is originally meant for hammering nails, but you could use the same hammer as a nutcracker. Similarly, the orthodenticle gene is adaptable in very much the same way in dung beetles, able to switch roles if evolutionary pressure demands it.

A dung beetle doing its thing. efendy/Shutterstock

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