Dimorphism

In addition to dimorphism in the presence of wings (Chapter 2) and overall body size (discussed below), male and female cockroaches may differ in the color and shape of the body or in the size, color, and shape of specific body parts. The general shape of the male, particularly the abdomen, is often more attenuated than that of the female. Several sex-specific morphological differences suggest that the demands of finding and winning a mate are highly influential in cockroach morphological evolution. Dimorphism is most pronounced in species where males are active, aerial insects, but the females have reduced wings or are apterous. These males may have large, bulging, nearly contiguous eyes while those of the more sedentary female are flattened and farther apart, for example, several species of Laxta and Neolaxta (Mackerras, 1968b; Roth, 1987a, 1992) and Colapteroblatta compsa (Roth, 1998a). Male morphology in the blattellid genera Escala and Robshelfordia is completely different from that of the opposite sex (Roth, 1991b). Such strong sexual dimorphism makes associating the sexes difficult, particularly when related species are sympatric (Roth, 1992); as a result, conspecific males and females are sometimes described as separate species. Additional sexual dimor phisms include the presence of tergal glands on males of many species, and the size and shape of the pronotum.

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