Flight or protection: the genes Ultrabithorax and apterous in the determination of membranous and sclerotized wings in insects

Present-day pterygote insects have two pairs of wings, one in the mesothorax (T2), the other in the metathorax (T3), and both have diverged in structure and function in different groups. Studies in endopterygote and paraneopteran species have shown that the gene Ultrabithorax (Ubx) specifies the identity and wing structure in T3, whereas the gene apterous (ap) significantly contributes to forming modified T2 wings. We wondered whether these Ubx and ap mechanisms operate in the lineage of polyneopterans. To explore this possibility, we used the cockroach Blattella germanica (Polyneoptera and Blattodea), in which the T2 wings are sclerotized (tegmina), whereas those of the T3 are membranous. We found that Ubx determines the structure of T3 and the membranous wing, while ap significantly contributes to form the sclerotized T2 tegmina. These results along with the studies carried out on the beetle Tribolium castaneum by Tomoyasu and collaborators suggest that ap plays an important role in the sclerotization and melanization of the T2 wings in neopteran groups that have sclerotized forewings. In turn, the sclerotizing properties of ap demonstrated in beetles and cockroaches suggest that the origin of this function goes back to the emergence of Neoptera, in the mid Devonian.The work was supported by the Spanish Agencia Estatal de Investigación (grant nos. PID2019-104483GB-I00/AEI/10.13039/501100011033; CGL2015-64727-P and CGL2012-36251), the Catalan Government (grant no. 2017 SGR 1030), and European Fund for Economic and Regional Development (FEDER funds). M.E.-N. was awarded with a post-doctoral fellowship by the Fundação de Amparo à Pesquisa do Estado de São Paulo, Brazil (grant no. FAPESP 2012/15397-0) to work in Xavier Belles laboratory in Barcelona