Social buffering in a eusocial invertebrate: termite soldiers reduce the lethal impact of competitor cues on workers

Abstract

While the impact of predator-induced stress on prey has received considerable attention, there has been far less research into the effect of competitors. Cues from aggressive competitors should be particularly likely to evoke behavioral and/or physiological responses, since they may be indicative of both direct (interference) and indirect (exploitative) threats. The danger posed by such competitors, and the "fear" they evoke, should be reduced at lower competitor densities and by the presence of individual conspecifics specialized for defense. We assessed how Reticulitermes flavipes termite workers and soldiers were affected by cues from conspecific nestmates, conspecific non-nestmates, and the heterospecific competitor R. virginicus. Competitor cues altered flavipes worker and soldier behavior, decreasing worker growth and increasing their mortality. The presence of flavipes soldiers largely ameliorated these negative impacts: adding even a single soldier (5% of flavipes individuals) decreased worker mortality by 50-80%. Although worker mortality increased with competitor density, increased soldier densities did not increase the benefit to workers. The small number of soldiers required to substantially alter cue-mediated interactions suggests that this caste, in addition to providing direct defense, also occupies a "keystone role" by providing homeostatic feedback to workers functioning in stressful environments.

Abnormal energy metabolism can alter foraging behavior in termites in different social contexts

“…The foraging success of dsIDH-injected workers significantly increased (Fig 3E and F), while it decreased sharply when predator ants were present without nestmate soldiers (Treatments 8 in Table 1), indicating that predator ants seriously affect foraging behavior and that the absence of nestmate soldiers means that foraging workers face a greater risk of predation if worker termites forage for a long time and feed on a large amount of food when the energy supply is lacking [2]. Although energy deficiency caused the foraging workers to significantly reduce the cumulative duration of visits in food zones, the increasing number of soldiers enhanced the frequency in food zones appropriately (Treatment 9 in Table 1), illustrating that soldiers can provide social buffering to cover the damage caused by the increase in ants during foraging [24,32,70]. However, the foraging trajectory of worker termites with normal energy metabolism became complex when ants were present (Treatments 3 and 6 in Table 1), indicating that the increase in ants led to more purposeless walking, which is energetically demanding [19,22].…”

“…In addition, the walking activity and foraging success of the worker termites showed no significant changes as the number of soldiers was increased together with the number of ants (Treatments 1, 2 and 3 in Table 1). Therefore, the presence of nestmate soldiers is crucial to reduce the purposeless walking of foraging workers and relieve the predation pressure from ants to help foragers to accurately find food sites [24]. Even though the increase in nestmate soldiers could decrease the purposeless walking caused by a small number of ants, foraging success still decreased when the number of soldiers increased (Treatment 5 in Table 1).…”

“…Considerable research has shown that predation risk seriously affects animal activity and foraging behavior [18][19][20][21][22]. Biological individuals may make collective decisions in intricate social contexts [23] and then respond to the presence of predators by showing a range of behavioral and physiological changes to reduce the likelihood of injury or death [24].…”

“…Social buffering is involved in the ability of neighboring individuals in a colony to reduce the negative impact of stressors on other individuals in a wide range of vertebrates [32]. For example, in the termite Reticulitermes flavipes, the presence of nestmate soldiers can change the ability of workers to cope with the competition risk imposed by conspecific non-nestmates [24]. However, the changes in behavioral characteristics are unclear when nestmate soldiers provide social buffering to foraging termites with different energy levels in the presence of predator ants.…”

Social information use in threat perception: Social buffering, contagion and facilitation of alarm responses

“…Similarly, mothers separated from their infants did not increase their cortisol levels if placed in their social groups after infant separation 4 . Many experiments have corroborated these findings and added knowledge regarding the behavioral and physiological effects of social buffering across different species, including non-human primates, 5 rodents, 6 birds, 7 fish 8 and invertebrates, 9 suggesting that social buffering is an evolutionary conserved process among social animals (for a review see ref. 10).…”