Oothecal Rotation

The position of the ootheca while it is carried prior to deposition is taxonomically significant and important in understanding the evolution of reproductive mode in cockroaches (Roth, 1967a).All ofthe Blattoidea and some of the Blaberoidea carry the ootheca with the keel dorsally oriented. However, in some Blattellidae and in all of the Blaberidae, the female rotates the ootheca 90 degrees so that the keel faces laterad at the time it is either deposited on a substrate, carried externally for the entire period of embryogenesis, or retracted into the brood sac. Within the Blattellidae, rotation of the ootheca has been used as a taxonomic character to separate the non-rotators (Ana-plectinae and Pseudophyllodromiinae) from the rotators (Blattellinae, Ectobiinae, and Nyctoborinae) (McKittrick, 1964). Most studies (McKittrick 1964; Roth, 1967a;Bohn, 1987; Klass, 2001) indicate that ootheca rotation evolved just once, and the recent phylogenetic tree of Klass and Meier (2006) (see Fig. P.1 in Preface) supports this view. One must be careful in determining oothecal rotation in museum specimens, as females may have been preserved while in the process of oothecal formation, prior to rotation. LMR found females with rotated oothecae from groups that do not normally exhibit this character; a museum worker had glued the oothecae to the females in an "incorrect" orientation. Some Polyphagidae exhibit a "primitive" or "false" type of rotation in which the ootheca is rotated and held by a "handle" or flange at the female's posterior end (Roth, 1967a). This type of rotation may have evolved as a way to prevent oothecae from being pulled off females as they move through sand (Fig. 2.6). The oothecae itself does not contact the female's vestibular tissues and ovoviviparity did not evolve in this group.

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