Transition to Live Bearing

Oothecal rotation is a key character when comparing the cockroach lineages that evolved ovoviviparity. Only one of the two subfamilies of Blattellidae exhibiting this reproductive mode rotates its egg case, but rotation occurs in all Blaberidae. Within the Blattellinae, the oviparous type B species, as exemplified by B. germanica, rotate the ootheca 90 degrees once it is formed and females carry it that way throughout gestation (Fig. 7.6). The ootheca is thus reoriented from its initial vertical position to one in which the long axes of the oocytes lay in the plane of the female's width. When first formed the egg cases are much

Fig. 7.6 Blattella germanica female carrying a fully formed ootheca (scale = mm). Photo courtesy of Donald Mullins.

taller than they are wide, like a package of frankfurters standing on end. Rotation likely evolved to prevent dis-lodgment of these egg cases as the morphologically flattened females scurried through crevices (Roth, 1968a, 1989a). Females of B. germanica that carry a rotated ootheca are able to crawl into spaces narrower than females carrying them in the vertical position (Wille, 1920). A gravid female one day before oviposition needs a space of 4.5 mm. A female with the ootheca carried in the vertical position requires 3.3 mm, and after the egg case is rotated the female can move into a space 2.9 mm high. Ovo-viviparous cockroaches in the same subfamily as Blattella (e.g., Stayella) carry within their brood sac a rotated ootheca virtually identical to the externally carried, rotated egg case of B. germanica (Roth, 1984).

In the second blattellid subfamily with oviparous type B reproduction (Pseudophyllodromiinae),two species of Lophoblatta maintain the original vertical position of the ootheca while carrying it externally throughout gestation. These oothecae, however, are distinctly wider than high (Roth, 1968b). Ovoviviparous females in this subfamily (e.g., Sliferia) have similarly squat oothecae, and retract them while they are vertically oriented, without rotation. The two blattellid subfamilies, then, employ different but equivalent mechanisms for achieving the same end. An ootheca of dimensions appropriate for a crevice-

Fig. 7.7 Diagram of presumed sequence of stages in the evolution of ovoviviparity from oviparity in two subfamilies of Blattellidae. Note the difference in the orientation of the ootheca between the two subfamilies. Current evidence suggests that the oothecal rotation exhibited by the Blattellinae and by the ovoviviparous Blaberidae originated in a common ancestor.

Fig. 7.7 Diagram of presumed sequence of stages in the evolution of ovoviviparity from oviparity in two subfamilies of Blattellidae. Note the difference in the orientation of the ootheca between the two subfamilies. Current evidence suggests that the oothecal rotation exhibited by the Blattellinae and by the ovoviviparous Blaberidae originated in a common ancestor.

dwelling insect to carry or internalize must be either squashed dorsoventrally or rotated so that it is as flat as the female (Fig. 7.7). Intermediate stages in parity mode are conspicuous in the Pseudophyllodromiinae. Sliferia is considered ovoviviparous; nonetheless the egg case is partially exposed while it is carried. Initially it was thought that these females were collected while still forming the ootheca. Now this condition is considered the norm, and points up the continuum of reproductive modes in this subfamily (Roth, 2003b).

All species in the ovoviviparous family Blaberidae carry a rotated egg case in their brood sac and are thought to have evolved from a Blattella-like ancestor (Roth and Willis, 1955c; Roth, 1967a; Mullins et al., 2002). Except for retraction of the egg case into the body, B. germanica exhibits all characteristics of an ovoviviparous cockroach (Roth and Willis, 1958a; Roth, 1970a). The oothecal case is thinner and less darkly colored than in other oviparous cockroaches,there is flow of water and other materials between mother and unhatched offspring, and oogenesis is suspended while females are carrying egg cases. The evolution of ovoviviparity would require only a minor tran sition from that starting point. Ovoviviparity evolved independently two or three times in cockroaches, but only in the blattellid/blaberid lineage (Roth, 1970a, 1989a): once in the Pseudophyllodromiinae, and once or twice in the clade that includes Blattellinae and Blaberidae. Viviparity evolved once, in D. punctata of the monogeneric subfamily Diplopterinae. Some authors also include Calo-lampra or Phoetalia in this subfamily (Roth, 2003c), so these genera may be logical targets for comparative study. Worldwide, Blattellidae is the largest cockroach family with about 1740 described species; there are approximately 1020 species of Blaberidae. The oviposition behavior is known in relatively few genera and species of these two families (Roth, 1982a).

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