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

sarily the path of nitrogen contained in urates. In subsequent
work, however, Mullins et al. (1992) demonstrated
that, third, 15 N from uric acid fed to females did find its
way into the nitrogen pool of oothecae, and was incorporated
into four different amino acids. The question
nonetheless remains as to whether the uric acid derived
from a particular male ends up in the offspring that he
sires (Vahed, 1998). Female B. germanica expel the empty
spermatophore with the adhering urates about 24 hr after
mating, then consume them between 4 and 18 days
later, depending on her nutritional status (Mullins and
Keil, 1980). Females typically transfer 90% of the food reserves
accumulated during the pre-oviposition period
into the next ootheca (Kunkel, 1966). It seems reasonable
to assume, then, that the majority of the uric acid transferred
during a given copulation is incorporated into the
eggs of the next reproductive bout, particularly in unsated
females. Young females rarely mate more than once
prior to their first ootheca (Cochran, 1979b), so during
the first oviposition period a male can be reasonably certain
that his nuptial gift will benefit his own offspring. Females
may, however, mate between ovipositions. Paternity
of subsequent oothecae is variable, but there is a
tendency for first-male precedence (Fig. 6.6). The nuptial
gifts of male consorts following the first male, then, may
benefit some nymphs fathered by other males.
Gwynne (1984) argued that uric acid donation should
not be classified as paternal investment, because, as a
waste product, uric acid is likely to be low in cost. Vahed
(1998) countered that it is likely to be a true parental investment
precisely because of the low cost. If a gift is
cheap, just a small resultant benefit to offspring will
maintain selection for the investment. Neither author appreciated
the fact that males deplete their uricose glands
with each copulation, and actively forage for uric acid by
seeking it out in bird and reptile droppings. The degree to
which this foraging activity entails a cost in predation risk
and energetic expense is an additional consideration.
Although a demonstration that male-derived nutrients
are incorporated into eggs supports the paternal investment
hypothesis, it does not necessarily rule out the
mating effort hypothesis (Vahed, 1998). Because female
cockroaches feed on male-provided urates after spermatophore
transfer, the nuptial gift cannot influence
overt mate choice. The possibility remains that after copulation,
females may bias sperm use based on the size or
quality of the urate gift. In many species, females preferentially
use the sperm of males that provide the largest
nuptial gifts (reviewed by Sakaluk, 2000). With four separate
chambers for sperm storage (discussed below), female
B. germanica certainly have potential for exercising
choice. The existence of substantial variation in sperm
precedence suggests that she may be doing so.
MALE GENITALIA
The genitalia of most male cockroaches are ornate,
strongly asymmetrical, and differ, at times dramatically,
among species. Because they are among the primary
characters used in cockroach taxonomy, some beautifully
detailed drawings are available, but we have little understanding
as to the functional significance of most components.
The genital sclerites are usually divided into the
left, right, and median (also called ventral) phallomeres.
These can be relatively simple and widely separated, or
form groups of convoluted, well-muscled structures elaborately
subdivided into movable rods, hooks, knobs,
spines, lobes, brushes, flagellae, and other sclerotized
processes (Fig. 6.11).
Several male genital sclerites are associated with the
process of intromission and insemination; these include
“tools” for holding the female, positioning her, and orienting
her genitalia to best achieve spermatophore transfer.
In Blatta orientalis, for example, all five lobes of the
left phallomere, together with the ventral phallomere,
serve to stabilize the ovipositor valves of the female, while
a sclerite of the right phallomere spreads the valves from
the center so that the spermatophore can be inserted
(Bao and Robinson, 1990). Nonetheless, phallomeres are
nearly absent in some blaberids, suggesting that elaborate
hardware is not always a requisite for successful copulation.
Mate-Holding Devices
Some male genital structures function as mate-holding
devices, allowing him to stay physically attached to the female
during copulation. If the female mounts the male
prior to genitalic connection (type I mating behavior),
the male has a greatly extensible, sclerotized hook (“titillator”),
used to seize and pull down her crescentic sclerite
and to maintain his grasp on her when she rotates off his
back into the opposed position. After the pair is end to
end the male inserts the genital phallomeres. In B. germanica
a pair of lateral sclerites, the paraprocts, grip the
ovipositor valves from each side, and parts of the right
phallomere (cleft sclerite) hold the valves from the ventral
side (Fig. 6.12). The location of the genital hook in
cockroach males varies, and distinguishes the Pseudophyllodromiinae
(hook on right—Fig. 6.11A) from the
Blattellinae (hook on left—Fig. 6.11C). The hook is always
on the right in the Blaberidae (Fig. 6.11D) (Roth,
2003c).
Besides maintaining his grasp during positional
changes, there are two basic reasons why a male needs a
secure connection to the female during copulation: male
competition and female mobility. In several species of
MATING STRATEGIES 101