Jiminy's wings turned out as fine as his conscience

Kyoto, Japan -- "A bird does not fly because it has wings; it has wings because it flies,” said American playwright Robert Ardrey. The same might apply to crickets.

A team led by Kyoto University could be one step closer to solving the mystery surrounding the evolution of flying insects' wings. The study on Gryllus bimaculatus has revealed evidence that the wings on crickets originate from the lateral tergum, or upper back, of their wingless ancestors. 

The approach to investigating where the wing formed involved reverse engineering. Using gene knockouts and a microsurgery experiment, the team found that the cells on the tergum and not the pleura, or sides, are key to wing formation. 

Lead author Takahiro Ohde elaborates, "A removal of lateral tergal cells at a juvenile stage resulted in an almost complete loss of the adult wing." 

Microsurgery was also used to test the development of cricket legs and wings on flies. But when it was discovered that these were regenerated during the juvenile stage, the consequences of partially removing crickets' lateral tergum came as a surprise.

"We didn't expect to see such a clear difference among cell types and species."

As for how wings developed, Ohde's team investigated genes showing high expression in lateral tergal cells and identified highly expressed components of three intercellular signaling pathways. Then, the scientists deduced the contribution of these pathways by repressing the genes, resulting in small-winged crickets. 

"So why don't we see a diversity of flying spiders instead?" Ohde asks, addressing the question of the lack of wings on what considers the single most successful terrestrial arthropod.

Recent developmental studies in crustaceans have revealed that the lateral tergum in today's insects emerged from the fusion of ancestral appendages. 

Without the evolutionary formation of the tergum, Ohde adds, "the wingless ancestor of insects may have given us flightless descendants instead."