Competition induced stress and soldier caste-dependent stress resistance in a termite

Many animals suffer chronic stress under extended exposure to predation /competition risk. In social mammals, predator/competitor induced stress can be attenuated when threatened animals are accompanied by social partners. However, it remains unknown if strategies against chronic stress evolves in social invertebrates. Termite colonies produce a distinct soldier caste, who performs nest defense while suppressing nest mate’s defensive response to intruders.  In the current study we examined if chronic exposure to competition risk can cause chronic stress in termites, and if the soldier caste serves to attenuate competition risk induced chronic stress on nest mate workers.  The eastern subterranean termites, Reticulitermes flavipes were chronically exposed to competitor cue in laboratory experiments. Survival, body weight, food consumption and behavior of the worker caste were measured.  A 15-day exposure to competitor cue resulted in significant mortality, reduction of body weight and decrease in food consumption rate. Workers markedly increased time spent in defensive display and reduced time spent in feeding during a 24-hour exposure to competition risk. Workers accompanied by a soldier exhibited higher survival rate, lost less weight and retain higher food consumption rate under competition risk, than did workers without the soldier companion. The results suggest that extended competition risk can induce chronic stress in termites.  Nevertheless, the soldier caste can enhance workers’ fitness under competition risk, possibly by alleviating their stress response to competitor cue.