CARBON NITROGEN-BALANCE AND TERMITE ECOLOGY

Termites, feeding on dead plant matter with a carbon to nitrogen ratio much higher than their own tissues, have to balance their C and N inputs. Two classes of C-N balancing mechanisms are possible: adding N to inputs, or selectively eliminating C. Termites achieve both of these mechanisms with the aid of microorganisms (symbionts). We first show that a termite can utilize food resources, thus attain productivity, only to the extent that the C-N balance capabilities of the termite-symbionts system allow. Two hypotheses follow: (i) 'one-piece' termites (species nesting in and consuming wood) tend not to possess C-eliminating symbionts, whereas 'separate' termites (species foraging outside their nests' tend to have a full range of C-N balance symbionts; this advantage for separate termites results in their observed greater productivity and colony size; and (ii) only separate termites have a sterile worker caste because their ability to utilize resources, which is conferred by their C-N balancing symbionts, makes the increase in a true (sterile) worker's contribution to the reproductives' fitness, combined with their higher nest stability, great enough to exceed the threshold for the evolution from false to true workers.