Mechanisms behind the death feigning behaviour in Tetramorium quadrispinosum in the Cape Floristic Region, Western Cape, South Africa
Date
2021-12
Authors
Journal Title
Journal ISSN
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Publisher
Stellenbosch : Stellenbosch University
Abstract
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.
AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar.
Description
Thesis (MSc)--Stellenbosch University, 2021.
Keywords
Tetramorium quadrispinosum -- Habits and behavior, Ant communities, Tetramorium -- Western Cape (South Africa) -- Cape Floristic Region, UCTD