Abstract
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.
Highlights
The development of wings and active flight is recognized as one of the most iconic evolutionary innovations in insects which enabled them to inhabit a plethora of habitats, and drive the diversification to a countless number of forms[1, 2]
The prevailing assumption is that insect wing reduction is driven by directional selection
We firstly determined whether alatectomy leads to wing muscle histolysis in cockroaches
Summary
The development of wings and active flight is recognized as one of the most iconic evolutionary innovations in insects which enabled them to inhabit a plethora of habitats, and drive the diversification to a countless number of forms[1, 2]. Str., excluding termites), are one of the most diversified polyneopteran group containing more than 4500 species[26] and exhibiting one of the highest occurrences of forms with reduced wings[3, 27,28,29] They have achieved practically all possible wing conditions ranging from fully developed wings (macropterous), through forms with variable degree of reduction (brachypterous and micropterous), to those with completely absent wings (apterous) in one or both sexes. The male mating success and related behavioural parameters were not influenced by the absence of tergal secretions Based on these facts and our preliminary observations on cockroach mating biology, we argue, it is rather the male wings that may help to manoeuvre the female into a position which enables the achievement of connection. We employ wing alatectomy to obtain brachypterous and apterous experimental groups from naturally macropterous individuals
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