X‐ray computed tomography reveals that intraspecific competition promotes soldier differentiation in a one‐piece nesting termite

Abstract

Investment in soldier production in eusocial lineages involves a trade‐off between maintenance costs and defense benefits. Termites are eusocial insects that live in colonies organized into three castes: primary reproductives, soldiers, and workers or pseudergates. Neotermes chilensis (Blanchard) (Isoptera: Kalotermitidae) is a one‐piece nesting termite that nests and forages in a single piece of wood. Two scenarios may be of importance in a defense context of one‐piece nesting termites: during swarms, when colonies may be invaded by winged termites (alates) in search of a place to found a new colony, and when colonies of conspecifics are present within the same substrate. It was hypothesized that the ratio of soldiers to non‐soldiers would be higher at the onset of the swarming period and in substrates bearing more than one termite colony. A method based on X‐ray computed tomography (CT) was developed to study gallery connectivity in colonies of N. chilensis and caste composition within colonies. Computed tomography allowed the digital reconstruction of the galleries within the substrate, even when they belonged to different colonies, and was effective in distinguishing termites from substrate, and soldiers from reproductives and pseudergates. Using CT, the ratio of soldiers to non‐soldiers was shown to be highest in colonies within multicolonial scapes (i.e., neighboring colonies were present in the same substrate) during the swarming season, thus supporting our initial hypotheses. These results constitute a unique example of induced defenses arising from intraspecific interactions in termites.

Exploring nest structures of acorn dwelling ants with X-ray microtomography and surface-based three-dimensional visibility graph analysis

“…X-ray imaging is a powerful tool to visualize structure and discover novel biological function in diverse systems ranging from the rhythmic pulsations of insect tracheal systems [52] to the four-dimensional morphology of large vertebrates in locomotion [53]. As a tool for non-destructive morphology, X-ray microtomography has helped to identify and classify a number of ant species, including some preserved within amber [54,55], as well as visualize the natural cavities inhabited by small insects [56,57]. Indeed X-ray imaging of artificial ant nest enclosures in the laboratory has been used to study social insect digging and building behaviours; however, using X-rays to examine these behaviours and the 3D spatial nest organization in natural conditions is technically challenging [28].…”

Geometric morphometrics in entomology: Basics and applications

“…This approach also displays its usefulness and further progress in the field of entomology (Friedrich et al ). The use of non‐destructive inspection of materials was implemented, for instance, for the identification of different social castes in nests (Aguilera‐Olivares et al ) and for tracking the movement of insects inside nests (Johnson et al ; Jennings & Austin ).…”

Body Size and Symmetry Properties of Termite Soldiers Under Two Intraspecific Competition Scenarios

“…zoellneri [ex P. berteroniana- Zizka et al (2013)] and P. chilensis (Molina, 1782) among its hosts (Aguilera-Olivares et al, 2015). In previous work at the same study site (Aguilera-Olivares et al, 2017), we reported that about half of the scapes were occupied by a single colony (unicolonial substrates) and the other half contained between 2 and 9 colonies (multicolonial substrates). Additionally, we observed galleries interconnecting two colonies within a scape which had been blocked with sawdust, probably following an agonistic interaction.…”

“…), temperature and seasonality significantly affect hormone and gene expressions (Scharf et al, 2007;Miura and Scharf, 2011) which trigger the differentiation from pseudergate to presoldier instar. This process may also be enhanced by ecological factors such as inter and/or intraspecific competition as a form of induced defense at the colony level (Passera et al, 1996;Aguilera-Olivares et al, 2017).…”