From “scared to death” to “peace of mind”: The functionality of soldiers

Predation and competition stress can exert deleterious impacts on fitness of an organism. Strategies for stress tolerance may evolve to minimize fitness loss under the stressful environment. To date, our knowledge of predation and competition stress, and adaptive response to the stress are primarily known from solitary organisms. In the case of social insects, in which survival and reproductive effort is based on division of labor, stress tolerance would be achieved by communications among functional castes. We tested the hypothesis by experimentally exposing workers of a subterranean termite, Reticulitermes flavipes, to competitor cues from a congeneric species R.virginicus. Exposure to competitor cues resulted in high worker mortality. However, worker mortality was significantly lower in groups containing the soldier caste in comparison to the soldier-less groups. This suggested that competition stress might affect colony fitness by reducing survivorship of the worker caste.  It also suggested that termite soldiers might serve to increase tolerance of nestmates to competition stress to ensure normal function of a colony under competitive environment.  Therefore, the study illustrates a unique, caste-dependent strategy of social insects to cope with competition stress.