View print quality image The creation of three-eyed beetles through a new technique developed at IU provides scientists a new way to investigate the genetic mechanisms responsible for the evolutionary emergence of new physical traits. Photo by Eduardo Zattara

On "Game of Thrones," a three-eyed raven holds the secrets of the past, present and future in a vast fantasy kingdom. But for real-world biologists, a "three-eyed beetle" may offer a true glimpse into the future of studying evolutionary development. Using a simple genetic tool, IU scientists have intentionally grown a fully functional extra eye in the center of the forehead of the common beetle. Unraveling the biological mechanisms behind this occurrence could help researchers understand how evolution draws upon pre-existing developmental and genetic building blocks to create new complex traits -- or "old" traits, such as an eye, in new places. The study's results appear in the journal of the Proceedings of the National Academy of Sciences. The work also provides deeper insights into an earlier experiment that accidentally produced an extra eye as part of a study to understand how the insect head develops. "Developmental biology is beautifully complex in part because there's no single gene for an eye, a brain, a butterfly's wing or a turtle's shell," said Armin P. Moczek, a professor in the IU Bloomington College of Arts and Sciences' Department of Biology. "Instead, thousands of individual genes and dozens of developmental processes come together to enable the formation of each of these traits. "We've also learned that evolving a novel physical trait is much like building a novel structure out of Legos, by re-using and recombining 'old' genes and developmental processes within new contexts." As a consequence, the evolution of novel features often requires many fewer genetic changes than biologists originally thought. But unlike rearranging and combining toy plastic bricks to form a new structure, Moczek said it's unclear what biological mechanisms guide the construction of new physical traits under some circumstances but not others.

View print quality image Armin Moczek. Photo by Marc Lebryk

"You can make new things over and over or in new places using the same old set of 'bricks,'" he said. "But in Legos, we know the rules of assembly: which pieces go together and which things don't. In biology, we still struggle to understand the respective counterparts." One of the ways that scientists have sought to get a clearer view of this process is by coaxing the growth of "ectopic" organs – or organs that form on the wrong part of the body. Early work in the field has focused on the formation of fruit fly eyes in the wrong place, such as on the wing or leg. However, these experiments required activating major regulatory genes in the new location, a method that is limited to only a few study organisms. The resulting "eyes" were also never fully functional. By contrast, the new IU-led study reports on the formation of an extra functional eye -- technically, a "fusion" of two sets of extra eyes -- following the knockdown of a single gene, a method widely available to scientists in most organisms. The unexpected formation of a complex, functional eye in a novel location in the process is "a remarkable example of the ability of developmental systems to channel massive perturbations toward orderly and functional outcomes," Moczek said. To create a fully functional eye in the center of a beetle's head, Moczek's team deactivated a single gene called orthodenticle, or odt, which their research has previously shown to play a role in instructing the formation of the head during development. "This study experimentally disrupts the function of a single, major gene," Moczek said. "And, in response to this disruption, the remainder of head development reorganizes itself to produce a highly complex trait in a new place: a compound eye in the middle of the head. "Moreover, the darn thing actually works!"

View print quality image Eduardo Zattara. Photo by Eric Rudd, IU Communications