A blog post highlighting the article by in Insectes Sociaux
By Vicki Simkovic
If you want to discover the secrets of life as a subterranean termite, you (literally) have to dig beneath the surface. Hidden from view, termite colony members (namely workers) are busy excavating and connecting networks of foraging tunnels to various food and nest sites. Each termite worker is small, delicate and soft-bodied, yet is formidable and impressive as part of its larger colony. A colony containing thousands to millions of termites – made up of workers, soldiers and reproductives – can build hundreds of intersecting tunnels within an hour and in urban centers a single colony can stretch across several city blocks. How they determine who belongs to which colony, however, is not as clear as you might expect.
One integral aspect of social living is maintaining well-defined colony boundaries through the defense of nest territory, keeping colony members safe in the colony and defending the colony from intruders. Among termites, both workers and soldiers participate in defensive behaviors, which can be both active (i.e. biting, lunging, stinging) and passive (social avoidance or blocking tunnel entrances) (Šobotník et al., 2010; Prestwich 1984). However, in some cases, colonies may take on a more diffuse form with no obvious inter-colony aggression or nestmate recognition. Why some colonies are well defined (‘closed’) while others are diffuse (‘open’) is not well understood.
To find out more, we studied Canadian populations of the Eastern subterranean termite (Reticulitermes flavipes), as they provide an interesting case study in nestmate recognition and territorial defense. Colonies of R. flavipes are found in isolated pockets in Ontario, having been introduced to the province on at least three separate occasions (Scaduto et al. 2012). Populations show a mixture of open versus closed societies, they may vary in their propensity for inter-colony aggression or resource defensiveness, and their differing backgrounds provide a potential source of genetically variable recognition cues (Scaduto et al. 2012). In the City of Toronto, termite colonies show low levels of genetic diversity, low inter-colony aggression (Grace 1996), and are more typical of invasive ‘open societies’. In contrast, termites in the Pelee region form discrete colonies that are genetically well differentiated from each other (Raffoul et al. 2011). The Pelee termites live independently of any human habitation, are potentially native to the area (Kirby 1965) and are effectively ‘closed’ societies.
Finding out about the cryptic world beneath our feet is not always easy. As termite behaviour occurs underground, we need to collect a sub-sample of live individuals and study their interactions in artificial lab-designed arenas or assays to evaluate their behaviour. However, designing an assay that truly reflects field conditions can be challenging. One method common method in termite and ant aggression studies is using a Petri dish lined with moist filter paper. Although convenient and easy to replicate, this artificial situation may not reflect ecological context, particularly for termite species, which are soft-bodied and desiccate quickly in open air. In previous studies using Petri dishes, R. flavipes showed no evidence of aggression towards non-nestmates (either intra or interspecific) and possibly a lack of nestmate recognition (Polizzi and Forschler 1998; 1999; Bulmer and Traniello 2002a, b; Fisher and Gold 2003; Perdereau et al. 2011).
We paired Ontario populations (Toronto and Pelee colonies) of R. flavipes of varying geographic distance in both short-term (5-minute) Petri dish and longer-term (2- and 7- day) shared-resource assays, in order to test for evidence of aggression or nestmate recognition. The resource-design assay was meant to be more reflective of field conditions and introduce the soil interface, simulating two colonies meeting and foraging at a central food resource. In Petri dish trials, we found no evidence of aggression or nestmate recognition. However, in shared-resource assays we observed very little inter-colony mixing and high mortality in non-nestmate pairings, indicating that R. flavipes can sort and potentially compete on the basis of nest origin, and that this recognition is influenced by ecological context. In our study, the soil interface was essential as aggressive encounters occurred while the termites were foraging for new resources. This behavior would not be evident from Petri-dish style assays, which lack the soil interface and may explain why prior studies of nestmate recognition have had mixed results. These results therefore highlight the importance of designing an assay that accurately reflects the ecological context of a species.
Šobotník J, Jirošová A, Hanus R (2010) Chemical warfare in termites. J Insect Physiol 56:1012–1021
Preswitch GD (1984) Defense mechanisms of termites. Ann Rev Entomol 29:201–232
Scaduto DA, Garner SR, Leach EL, Thompson GJ (2012) Genetic evidence for multiple invasions of the Eastern subterranean termite into Canada. Environ Entomol 41:1680–1686
Grace JK (1996) Absence of overt agonistic behavior in a northern population of Reticulitermes flavipes (Isoptera, Rhinotermitidae). Sociobiology 28:103–110
Raffoul M, Hecnar SJ, Prezioso S, Hecnar DR, Thompson GJ (2011) Trap response and genetic structure of Eastern subterranean termites (Isoptera, Rhinotermitidae) in Point Pelee National Park, Ontario, Canada. Can Entomol 143:263–271
Kirby CS (1965) The distribution of termites in Ontario after 25 years. Can Entomol 97:310–314
Bulmer MS, Traniello JFA (2002a) Foraging range expansion and colony genetic organization in the subterranean termite Reticulitermes flavipes (Isoptera: Rhinotermitidae). Environ Entomol 31:293–298
Bulmer MS, Traniello JFA (2002b) Lack of aggression and spatial association of colony members in Reticulitermes flavipes. J Ins Behav 15:121–126
Fisher ML, Gold RE (2003) Intercolony aggression in Reticulitermes flavipes (Isoptera: Rhinotermitidae). Sociobiology 42:651–661
Perdereau E, Dedeine F, Christides JP, Dupont S, Bagnères AG (2011) Competition between invasive and indigenous species: an insular case study of subterranean termites. Biol Invasions 13:1457–1470