Mechanisms behind the death feigning behaviour in Tetramorium quadrispinosum in the Cape Floristic Region, Western Cape, South Africa

Thesis (MSc)--Stellenbosch University, 2021.ENGLISH ABSTRACT: Death feigning is a defense strategy where a prey responds to threat by pretending to be dead. The animal resembles the dead by remaining immobile, sometimes emitting a repulsive smell and assuming an unusual posture; this protects the prey or threatened animal, and deters the attacker. Much of the research has largely focused on more charismatic vertebrates with model animals including the opossum and some snake species, with a paucity of studies on invertebrate species. Research on these charismatic animals investigated the adaptive nature of this defense mechanism, as well as the physiological costs of the behaviour. In insects, the few studies measured the drivers of this behaviour under various contexts such as mating and resource competition, as well as the impacts of group living and responding to threats. Based on anecdotal evidence, death feigning behaviour has been shown to exist in social insects, including ants. In this study we investigated the mechanisms driving death feigning behaviour in the ant Tetramorium quadrispinosum under contexts of competition with two dominant ant species, one native and one invasive. Tetramorium quadrispinosum has been observed to feign death when encountering the invasive Argentine ant, Linepithema humile, under resource competition in both field and laboratory studies. Using a quantitative cuticular hydrocarbon bioassay, we tested whether death feigning could be induced with increasing number of Argentine ant and native ant, A. custodiens. Tetramorium quadrispinosum largely avoided any interactions with both dominant ant species, and only showed a freezing response in less than 5% of all the interactions with the species despite increasing numbers. We further used a tactile method to induce death feigning to ascertain the variation in trigger time to and duration of death feigning behaviour in the native ant, T. quadrispinosum. Ants showed variation in the time taken to be triggered into either freezing or feigning, and the duration was longer for those ants that went into a death feigning state. Individuals who feigned for longer were often roused by their nestmates, and those who self-roused did so relatively quickly. The mechanisms of death feigning in social insects require further investigation, because the social structure of the colony does not normally call for individual behaviour such as feigning as it is a last resort normally used by a threatened solitary individual. Individual ants, therefore under certain contexts of threat, may benefit from this behaviour. More research is needed to understand the various contexts in which this behaviour is elicited, as well as the adaptive benefits it can offer the colony.AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.Master