Insect wings originally formed out of lobes used to glide to the ground from tall vegetation, not from ancestral gills as once thought, according to a recent study published by a Wayne State University researcher.

Aleksandar Popadiæ, Ph.D., associate professor of biological sciences in WSU’s College of Liberal Arts and Sciences, was published in a recent issue of Developmental Biology for a study that characterizes the role of the hox gene Scr in the body plan of the cockroach, or Periplaneta americana. The findings, which include the location of an ancestral third pair of wings, provide support to one side of a decades-long debate on the origin of insect wings.

The work builds off a study that made the cover of the May 1, 2009 issue of Developmental Biology, in which Popadiæ’s lab presented evidence connecting Scr with development of the T1 body segment, including suppression of a third pair of wings that were present on many ancestral insects.

In the current study, the authors investigated where the ectopic T1 wings would form if Scr expression were turned off. Using a technique known as RNA interference (RNAi), the Scr gene was effectively “knocked out.” The results showed that in the absence of the gene, rudimentary wings appeared on the upper side of the prothorax in adult cockroaches.

These findings support the Paranotal Theory of wing evolution, which states that wings originally arose as an extension of the side of the prothorax, providing a softer landing to insects falling or jumping from vegetation. Opposing this is the Exite Theory, which states that wings were dorsal appendages formed out of ancestral gills on the upper part of T1 legs – legs closest to the head. Although no living insect possesses such multibranched appendages, the presence of these structures in crustaceans are frequently cited as evidence for the Exite Theory.

Although the results support the Paranotal Theory, they do not close the book on the debate completely. “Because this study unambiguously showed that ectopic wings arose from the dorsal lateral region of the prothorax, it is tempting to postulate that Paranotal Theory is correct,” Popadiæ said. “However, the origin of this wing tissue is still unknown, and further studies are needed.”

Aside from providing support for a theory of evolution, the study has other, more practical applications as well. Among these is the potential for scientists to use their growing knowledge of the genes behind insect wing formation to better manage certain insect populations. One example would be utilizing RNAi to induce less-functional wings in the locust, the detrimental “pest” insect. By disabling locusts’ ability to fly, the damage of any single-crop swarm would be dramatically reduced.

“This application is not yet a reality,” Popadiæ said. “It goes to show, however, that increasing our understanding of insect genetics not only satisfies scientific curiosity of evolution, but offers the potential to better manage insects that are beneficial as well as detrimental to human life.”

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