‘Cyclops’ beetles hint at solution to ‘chicken-and-egg’ problem in novel trait evolution

From Indiana University:

IMAGE: Heads of horned and cyclopic beetles of the genus Onthophagus are shown. After knocking out the gene otd1, the cyclopic beetle (right) lost the horn but gained a pair of… view more

Credit: Indiana University

BLOOMINGTON, Ind. — Beetles with cyclops eyes have given Indiana University scientists insight into how new traits may evolve through the recruitment of existing genes — even if these genes are already carrying out critical functions.

The study, reported in the Proceedings of the Royal Society B, was led by Eduardo Zattara, a postdoctoral researcher in the IU Bloomington College of Arts and Sciences’ Department of Biology. It was published in tandem with another study led by Hannah Busey, an undergraduate student researcher at IU Bloomington and 2016 Goldwater fellow, which appeared in the Journal of Experimental Zoology.

The discovery was made after switching off orthodenticle genes in horned beetles of the genus Onthophagus, also known as dung beetles. Knocking out these genes caused drastic changes in the insects’ head structure, including the loss of horns — a recently evolved structure used for male combat over access to females — as well as the growth of compound eyes in a completely unexpected place: the top center of the head.

The results were specific to Onthophagus; the same changes did not produce the same effects in Tribolium, or flour beetles, which do not have horns.

“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,” Zattara said. “The fact that this doesn’t happen in Tribolium is equally significant, as it suggests that orthodenticle genes have acquired a new function: to …

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