Age-based soldier polyethism: old termite soldiers take more risks than young soldiers

Abstract

Who should take on risky tasks in an age-heterogeneous society? Life-history theory predicts that, in social insects, riskier tasks should be undertaken by sterile individuals with a shorter life expectancy. The loss of individuals with shorter life expectancy is less costly for colony reproductive success than the loss of individuals with longer life expectancy. Termite colonies have a sterile soldier caste, specialized defenders engaged in the most risky tasks. Here we show that termite soldiers exhibit age-dependent polyethism, as old soldiers are engaged in front-line defence more than young soldiers. Our nest defence experiment showed that old soldiers went to the front line and blocked the nest opening against approaching predatory ants more often than young soldiers. We also found that young soldiers were more biased toward choosing central nest defence as royal guards than old soldiers. These results demonstrate that termite soldiers have age-based task allocation, by which ageing predisposes soldiers to switch to more dangerous tasks. This age-dependent soldier task allocation increases the life expectancy of soldiers, allowing them to promote their lifetime contribution to colony reproductive success.

Ant‐termite interactions: an important but under‐explored ecological linkage

“…These adaptations have been shown to be extremely effective against ant invaders (Seid, Scheffrahn & Niven, ). Older soldiers tend to engage in such risky tasks more often than young soldiers, which are involved more in defence inside the nest (Yanagihara et al ., ). In some termite species (e.g.…”

Soldier neural architecture is temporarily modality-specialized but poorly predicted by repertoire size in the stingless bee Tetragonisca angustula

“…Soldier temporal polyethism across distinct defense tasks has only been demonstrated in two eusocial species previously [14,26] and is still largely unstudied. To our knowledge, this is the first study to investigate the potential rapid neural investment transitions that underlie age-related shifts in in discrete defense tasks.…”

A Review of Termite Pheromones: Multifaceted, Context-Dependent, and Rational Chemical Communications

“…In termites, colony defense is performed by soldiers and workers (Roisin et al, 1990;Reinhard and Clement, 2002;Šobotník et al, 2010;Ishikawa and Miura, 2012;Yanagihara et al, 2018). Alarm pheromones elicit alarm behaviors including orientation to the pheromone source, nestmate recruitment, and attack on enemies in termite soldiers and workers (or pseudergates), although the details of the behavioral sequences are different among species.…”

“…The nests of R. speratus are divided into chambers connected by small openings; the royal chamber (i.e., location of reproductive castes) is located deep inside the nest wood. In this species, younger soldiers gather around the royal chamber to protect kings and queens, while older soldiers are distributed in the periphery of the nest wood to defend the nest entrances (Yanagihara et al, 2018). When workers decide whether to move among chambers, they examine the amount of soldier pheromone held by the soldier standing guard at the chamber entrance; they do not move to the next chamber if the amount of soldier pheromone is very small (that is, if the soldier is very young) .…”