Revisiting stigmergy in light of multi-functional, biogenic, termite structures as communication channel

Abstract

Termite mounds are fascinating because of their intriguing composition of numerous geometric shapes and materials. However, little is known about these structures, or of their functionalities. Most research has been on the basic composition of mounds compared with surrounding soils. There has been some targeted research on the thermoregulation and ventilation of the mounds of a few species of fungi-growing termites, which has generated considerable interest from human architecture. Otherwise, research on termite mounds has been scattered, with little work on their explicit properties. This review is focused on how termites design and build functional structures as nest, nursery and food storage; for thermoregulation and climatisation; as defence, shelter and refuge; as a foraging tool or building material; and for colony communication, either as in indirect communication (stigmergy) or as an information channel essential for direct communication through vibrations (biotremology). Our analysis shows that systematic research is required to study the properties of these structures such as porosity and material composition. High resolution computer tomography in combination with nonlinear dynamics and methods from computational intelligence may provide breakthroughs in unveiling the secrets of termite behaviour and their mounds. In particular, the examination of dynamic and wave propagation properties of termite-built structures in combination with a detailed signal analysis of termite activities is required to better understand the interplay between termites and their nest as superorganism. How termite structures serve as defence in the form of disguising acoustic and vibration signals from detection by predators, and what role local and global vibration synchronisation plays for building are open questions that need to be addressed to provide insights into how termites utilise materials to thrive in a world of predators and competitors.

Submillimetre mechanistic designs of termite-built structures

“…[61] has been shown to play a key role in construction and other properties of termite nests. Similar to the inner scaffolding, curvature may play a central role with regards to stability, wave propagation and other functions [1]. While we did not study curvature in this present study, it seems plausible that species' functional characteristics are directly moulded into geometric features of different termite nests [1,12,22] and self-organized biotectonics should be studied using network quantification, graph theory, multi-agent systems and complex nonlinear times series/ dynamics approaches [1,12,22,62,63].…”

“…Our results for N. exitiosus (Isoptera) are the first to exemplify univocally submillimetre details related to the finer mechanistic structures of termite mound components. Knowing these finer structural details is required for a better … materials, a topic of significant interest in general, as also … required for the understanding of multifunctionality in biogenic materials as also previously raised by Perna & Theraulaz [12], Singh et al [7] or more recently by Oberst et al [1].…”

“…Our measurements were based on high-resolution μCT imaging (which is about one order of magnitude more accurate than commonly employed medical CT). We used Taud's method to calculate porosity and we provided an estimate of the fractal dimension using volumetric data, instead of images photogrammetric surface models and 2D crosssectional images which allow us to quantify the complexity of the internal nest structure more accurately on a smaller scale [1,17,44,45,49]. Our estimates of macro-and microporosity for a sample of two colonies of N. exitiosus ranged between 32.19% to 31.71%, and 34.1% to 32.8%, with an estimated total porosity of 66.29% and 64.51% when compared with about 58% to 59% [34] (for Microceratermes nervosus, Macrognathotermes sunteri and Tumulitermes pastinator).…”

“…The morphology of termite mounds (termitaria) and other build structures (e.g. foraging galleries) is diverse and can be linked to different trophic categories, such as soil and soil/wood interface feeding, wood and litter foraging or specialized and incidental feeding, evolved over more than 181 Ma as a consequence of changed habitat, predation and tightly linked to sociality and brood care [1][2][3][4]. Termitaria are classified into hypogeal (subterranean), epigeal (above ground, usually called 'mounds') and arboreal (within or attached to tree) nests, for details cf.…”

“…Termitaria are classified into hypogeal (subterranean), epigeal (above ground, usually called 'mounds') and arboreal (within or attached to tree) nests, for details cf. [1]. Even though living in complete darkness, termites have evolved the ability to allocate their tasks efficiently among up to several million nest-mates [5,6].…”