Evolution of Flightlessness

Macropterism is clearly the primitive condition in cockroaches (Rehn, 1932b). Because no fossil cockroaches are known with abbreviated organs of flight (R.J. Tillyard, in Shaw, 1918), it is assumed that Paleozoic cockroaches were swift-flying and diurnal (Brodsky, 1994). Flight may have been advantageous in Carboniferous swamps, as it would allow movement between patches of habitat surrounded by water. On the other hand, the possession of wings does not assure the ability to fly, and apterous and brachypterous cockroaches are less likely to leave fossil evidence than their more volant relatives. There are indications of wing sexual dimorphism in the fossil record. Schneider (1977,1978) concluded that the wings of Carboniferous females were broader than those of males, and Laurentiaux (1963) demonstrated that there were intersexual differences in both the length and the shape of wings.

It is possible to induce alary reduction experimentally in a normally winged species (e.g., Blab. craniifer),but attempts to produce fully developed wings in an apterous cockroach have been unsuccessful; Lefeuvre (1971) therefore concluded that the evolutionary loss of wings is irreversible. On the other hand, Masaki and Shimizu (1995) suggested that wing reduction is possible without elimination of the genetic background for macropterous development, and potential evolutionary reversal of wing loss has been demonstrated in the Hemiptera-Heter-

optera (Anderson, 1997) and in the Phasmatodea (Whiting et al., 2003). As robust phylogenetic trees become available for varying cockroach taxa, the possibility of the re-evolution of wings in the Blattaria can be put to the test.

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