Wing reduction influences male mating success but not female fitness in cockroaches.

Although cockroaches (Blattodea s. str.) exhibit high proportion of species with reduced wings, the underlying evolutionary forces remain unclear. Wing reduction in insects is generally considered advantageous for females and a trade-off between investment into the flying apparatus and reproduction is predicted to explain its evolution. However, what if the wing maintenance is an important issue for males' fitness? Males raise wings during the ritualized courtship which is viewed as an unavoidable movement unveiling the tergal glands for female access. We, however, propose a novel male mating success hypothesis suggesting that male wings are essential for their successful mating. We tested these two competing, but not mutually exclusive hypotheses in the cockroach Eublaberus distanti. We found no effect of female wing loss on any of the measured fecundity characteristics despite that alatectomized females histolyzed flight muscles. On the contrary, alatectomized males did not histolyze wing muscles, but experienced a markedly decreased mating success. Our findings, therefore, provide the first evidence on the crucial mechanical role of wings on male mating success. Consequently, selection for the retention of wings in males rather than for their reduction in females can explain the evolution of sexual wing dimorphism in cockroaches and other insects.