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

Many behaviors shared by termites and young cockroaches
relate to food intake. Termites also resemble
cockroach juveniles in aspects of digestive physiology and
dietary requirements (Nalepa and Bandi, 2000). More so
than older stages, early instars of cockroaches rely on
conspecific food and ingested microbial protein to fuel
growth, and are dependent on the metabolic contributions
of microbial symbionts in both the gut and fat body
for normal development. As termites evolved, they elaborated
on this food-sharing, microbe-dependent mode
instead of shifting to a more adult nutritional physiology
during ontogenetic growth.
Caste control in termites also may be rooted in the developmental
physiology of young cockroaches (Nalepa
and Bandi, 2000). It is the early cockroach instars that are
most susceptible to developmental perturbations related
to nutrition, injury, and group effects (Woodruff, 1938;
Seamans and Woodruff, 1939; Holbrook and Schal,
1998). Moreover, these stimuli are extrinsically controllable
and may allow for manipulation of individual development
by fellow colony members (Nalepa and Bandi,
2000).
In sum, a large number of the juvenile characters of
their cockroach ancestors were co-opted by termites in
the course of their evolution, and these were integral in
the cascade of adaptations and co-adaptations that resulted
in the highly derived, eusocial taxon it is today.
Heterochrony is known to provide a basis for rapid divergence
and speciation, because integrated character sets
are typically under a system of hierarchical control
(Gould, 1977; Futuyma, 1986). Simple changes in regulatory
genes, then, can result in rapid, drastic phenotypic
changes (Futuyma, 1986; Stanley, 1998).
WOOD DIET, TROPHALLAXIS,
AND SYMBIONTS
That the character and direction of Isopteran
evolution as a whole has been in the main determined
by their peculiar food is obvious.
—Wheeler, The Social Insects
There are distinct advantages to living within your
food source. Logs offer mechanical protection and refuge
from a number of predators and parasites, with an interior
temperature and humidity generally more moderate
than that of the external environment. Abundant if lowquality
food is always close at hand. One disadvantage is
that when on this fixed diet, a wood-feeding dictyopteran
would forfeit the opportunity to move within the habitat
seeking specific nutrients and nitrogenous bonanzas
(e.g., bird droppings) as its developmental and reproductive
needs change. Reliance on slowly accumulated reserves
and the use of food originating from conspecific
sources, then, would become considerably more important,
particularly in those stages with a high nitrogen
demand—reproducing females and young nymphs (Nalepa,
1994).
Termites inherited from cockroaches a suite of interindividual
behaviors that allow for nitrogen conservation
at the colony level and provide a means of circulating
it among individuals within the social group (Table
4.6). These include cannibalism, necrophagy, feeding on
exuviae, and coprophagy. Two behaviors of particular
note are allogrooming and trophallaxis, first, because
they supply the organizational glue that keeps termite
colonies cohesive and functional, and second, because
among cockroaches these behaviors are only known from
wood-feeding species. Allogrooming has been noted in
Panesthia (M. Slaytor, pers. comm. to CAN) and Cryptocercus,
and in the latter it occurs exactly as described in
termites by Howse (1968). The groomer grazes on the
body of a conspecific, and the insect being groomed responds
by rotating its body or appendages into more accessible
positions (Fig. 5.5B).As with termites, the nymph
being tended may enter a trance-like state and afterward
remain immobile for a short period of time before resuming
activity (Nalepa and Bandi, 2000).
Trophallaxis is the circulatory system of a termite
colony. It is the chief mechanism of disseminating water,
nutrients, hormones, dead and live symbionts, and the
metabolic products and by-products of the host and all
its gut symbionts. Stomodeal trophallaxis (by mouth) occurs
in all termite families, and proctodeal trophallaxis
(by anus) occurs in all but the derived family Termitidae
(McMahan, 1969; Breznak, 1975, 1982). Both types of
trophallaxis occur in wood-feeding cockroaches, and in
these taxa the behaviors occur in the context of parental
care. Salganea taiwanensis feeds its young on oral secretions
(T. Matsumoto, pers. comm. to CAN; Fig. 8.3B), and
Cryptocercus adults feed young nymphs on hindgut fluids
(Seelinger and Seelinger, 1983; Nalepa, 1984; Park et al.,
2002).
Hindgut Protozoa
Digestion in Cryptocercus is comparable to that of lower
termites in all respects. The hindgut is a fermentation
chamber filled to capacity with a community of interacting
symbionts, including flagellates, spirochetes, and bacteria
that are free in the digestive tract, attached to the gut
wall, and symbiotic with resident protozoans. Included
are uricolytic bacteria, cellulolytic bacteria, methano-
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