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

maximum rate of yolk deposition (Roth, 1964a, 1964b).
Mating is necessary for initiation of yolk deposition in D.
punctata (Engelmann, 1960; Roth and Stay, 1961), but has
no effect on yolk deposition in Byr. fumigata, Pyc. indicus,
or B. germanica (Roth and Stay, 1962a). Stimuli from
feeding, drinking, mating, and social contact are required
for the highest rates of yolk deposition in P. americana. A
graded series of “sexually suppressed”females can be produced
by withholding one or more of these stimuli
(Weaver, 1984; Pipa, 1985).
EGG NUMBER AND SIZE
Comparisons of reproductive investment within a taxon
require the resolution of differences attributable to body
size. Although little information on the subject has been
compiled for cockroaches, we do know that the body
length of adults in the smallest species can be 3% the
length of the largest (Chapter 1), making them good
candidates for investigations on the allometry of reproduction.
At the species level there appears to be little
relationship between the size of the mother and the
packaging of the reproductive product. In the oviparous
cockroaches, 18 mm long Cartoblatta pulchra females
place about 95 eggs into an ootheca, more than any other
species of Blattidae (Roth, 2003b). Ovoviviparous cockroaches
average about 30 eggs per ootheca, but the relatively
small Panchlora produces broods larger than a
Blaberus 10 times its size and mass. Panchlora nivea is 2.5
cm long and internally incubates 60 or more eggs per
clutch. The egg case is distorted into a semicircular or J-
shape so that it may be internally accommodated (Roth
and Willis, 1958b). The record, however, probably belongs
to African Gyna henrardi, which somehow puts up
to 243 eggs into a z-shaped ootheca that she stuffs into her
brood sac (Grandcolas and Deleporte, 1998). Hatch must
resemble the endless supply of clowns exiting a miniature
car at the circus.
We know little regarding relative egg sizes among cockroaches.
Two species with large post-ovulation investment
are known to lay small eggs. In C. punctulatus eggs
are only 44% of expected size for an oviparous cockroach
of its dimensions (Nalepa, 1987). Most resources are
channeled into an extensive period of post-hatch parental
care and into the maintenance of the long-lived adults
(Nalepa and Mullins, 1992). At hatch neonates in this
species are tiny, blind, dependent, and fragile (Nalepa and
Bell, 1997). Viviparous D. punctata also produces small
eggs, with yolk insufficient to complete development
(Roth, 1967d). As with all viviparous animals, supplying
embryos with gestational nutrients places less reliance on
producing large yolky oocytes. Neonates emerge at the
precocial extreme of the developmental spectrum, with
the largest relative size and shortest postembryonic development
known among cockroaches.
EVOLUTION OF REPRODUCTIVE MODE
Of the two major divisions of the cockroaches, the superfamilies
Blattoidea and Blaberoidea (McKittrick, 1964),
most evolutionary drama with regard to reproductive
mode is in the latter. It includes the Blattellidae, in which
some species retain the egg case externally for the entire
period of gestation, and where ovoviviparity arose independently
in two different subfamilies. It also includes the
Blaberidae, all of which incubate egg cases internally, suggesting
that they have radiated since an ancestor acquired
the trait. The sole viviparous genus, as well as the group
that lost the oothecal covering, are in the Blaberidae. Of
course, critical analysis of the pattern of reproductive
evolution is dependent on the availability of robust phylogenies
for the groups under study, but, as with most aspects
of cockroach systematics, the relationships among
several subgroups of the Blaberoidea are unsettled. In all
phylogenetic hypotheses proposed so far, however, Blaberidae
is most closely related to Blattellidae (Roth,
2003c), and some studies (Klass, 1997, 2001) suggest that
blaberids are a subgroup of the Blattellidae.
The evolution of reproductive mode in cockroaches
can be described with some confidence as a unidirectional
trend from oviparity to viviparity, without character
reversals. Reproduction is an extraordinarily complex
process, with morphology, physiology, and behavior integrated
and coordinated by neural and endocrine mechanisms.
Transitions therefore tend to be irreversible due to
genetic or physiological architecture, or because strong
selection on offspring prevents them (Tinkle and Gibbons,
1977; Crespi and Semeniuk, 2004). An initial step in
the evolution of ovoviviparity in cockroaches was likely
to be facultative transport of the egg case, as in the
oviparous type A species that retain oothecae until a suitable
microhabitat is found. Ectobius pallidus, for example,
typically deposits its egg case in one or two days, but has
been reported to carry it 16 days or longer (Roth and
Willis, 1958a). Therea petiveriana deposits the ootheca
within a day of extrusion, but may retain it for as long as
90 hr if a suitably moist substrate is not available (Livingstone
and Ramani, 1978). From this flexible starting
point, the trend toward ovoviviparity would be exemplified
by cockroaches that retain the egg case for the entire
period of embryogenesis, but provide no materials
additional to those originally in the egg case. Currently,
there are no records of extant cockroaches that exhibit
this pattern; the only oviparous type B species that has
been studied, B. germanica, provides water and soluble
materials to embryos. Obligate egg retention evolves
REPRODUCTION 123