Cockroache; Ecology, behavior & history - W.J. Bell

when maternal tissues became responsive to the attached
egg case; this recognition then induces further modifications
of maternal function (Guillette, 1989).
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 of the 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 (Anaplectinae
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.
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 dislodgment
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. Ovoviviparous
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-
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