Age-based spatial distribution of workers is resilient to worker loss in a subterranean termite

Abstract

Elaborate task allocation is key to the ecological success of eusocial insects. Termite colonies are known for exhibiting age polyethism, with older instars more likely to depart the reproductive center to access food. However, it remains unknown how termites retain this spatial structure against external disturbances. Here we show that a subterranean termite Coptotermes formosanus Shiraki combines age polyethism and behavioral flexibility to maintain a constant worker proportion at the food area. Since this termite inhabits multiple wood pieces by connecting them through underground tunnels, disastrous colony splitting events can result in the loss of colony members. We simulated this via weekly removal of all individuals at the food area. Our results showed that termites maintained a worker proportion of ~ 20% at the food area regardless of changes in total colony size and demographic composition, where younger workers replaced food acquisition functions to maintain a constant worker proportion at the food area. Food consumption analysis revealed that the per-capita food consumption rate decreased with younger workers, but the colony did not compensate for the deficiency by increasing the proportion of workers at the feeding site. These results suggest that termite colonies prioritize risk management of colony fragmentation while maintaining suitable food acquisition efficiency with the next available workers in the colony, highlighting the importance of task allocation for colony resiliency under fluctuating environments.

Context‐dependent expression of variation in defensive behaviour in the lower termite Zootermopsis nevadensis

“…The previous study has demonstrated that the old‐age soldiers frequently protected the nest compared to young‐age soldiers under the artificial experiments in the termite Reticulitermes speratus (Yanagihara et al, 2018). It should also be noted that the age‐related task allocation could contribute to the colony maintenance under variable environments in the termite Coptotermes formosanus (Lee et al, 2022). Each individual experiences different tasks in the process of ageing, and the individual behavioural differences and resulting task allocation could be determined through individual experiences in some ants (Stroeymeyt et al, 2011; Tanaka et al, 2022).…”

“…There were no relationships between aggressive response, and body size and sexes in either soldiers or pseudergates in our study (Figures S1-S4 et al, 2018). It should also be noted that the age-related task allocation could contribute to the colony maintenance under variable environments in the termite Coptotermes formosanus (Lee et al, 2022).…”

“…One possible explanation is that defensive decision‐making may be determined by sex and/or size differences between intracolonial members. Other intrinsic factors are thought to be the individual ages and experiences in some ants and termite (Lee et al, 2022; Stroeymeyt et al, 2011; Tanaka et al, 2022; Yanagihara et al, 2018). In contrast, the encounter has the advantage of colony defence from intruders at the narrow entrance in lower termites (Yanagihara et al, 2018).…”

Life and Death of Termite Colonies, a Decades-Long Age Demography Perspective

“…It was also shown that foraging termites display degrees of age polyethism, as older workers tend to forage further away from the central part of the nest than younger workers (Du et al, 2017;Su et al, 2017;Lee et al, 2021). It therefore explains why the demographic profile of a colony may vary among traps on any given sampling date, as the age cohort of foragers are not homogeneously distributed throughout the colony foraging territory (Lee et al, 2022). For a given colony with multiple monitored foraging sites, it can therefore be inferred that a trap with a majority of old workers is located further away from the central part of the nest than a trap with a majority of relatively young workers (Shimizu, 1962;Su et al, 2017;Lee et al, 2022).…”

“…It therefore explains why the demographic profile of a colony may vary among traps on any given sampling date, as the age cohort of foragers are not homogeneously distributed throughout the colony foraging territory (Lee et al, 2022). For a given colony with multiple monitored foraging sites, it can therefore be inferred that a trap with a majority of old workers is located further away from the central part of the nest than a trap with a majority of relatively young workers (Shimizu, 1962;Su et al, 2017;Lee et al, 2022). In mature colonies of C. formosanus, soldiers (S) are produced from various worker pathways through a presoldier stage (PS), which depends on the availability of workers at the time they initiate differentiation into soldiers: W 1 → PS 2 → S 2 , W 2 → PS 3 → S 3 , and W 3 → PS 4 → S 4 .…”