Distinct types of foragers in the ant Ectatomma ruidum: typical foragers and furtive thieves

Abstract

Available online MS. number: A15-00300R Keywords: ant colony defence conspecific thievery Ectatomma ruidum food pilferage foraging kleptoparasitism nestmate recognition social livingA principal benefit of social living is the communal defence of resources. However, in the ant Ectatomma ruidum, specialized thieves often circumvent detection by conspecific non-nestmates, and those detected are peacefully expelled. Colonies can gather food through typical foraging (opportunistically tracking prey or nutrients in the home range) or by robbing (entering a conspecific nest, waiting for, and then removing a newly arrived food item carried in by a forager). Here, we conducted behavioural assays to determine whether robbers (or 'thieves'), carrying purloined food, manifest behaviours that minimize the probability of detection relative to nonthieving individuals. We found several lines of evidence that individuals carrying stolen food behave distinctly from normal nonthieving foragers. When returning to their home nest with a stolen food item, thieves had fewer encounters with conspecifics, were more likely to pause during movement, and were more likely to release food when grasped. Thieves walked faster while travelling in the victim's home range, compared to their own home range. When experimentally perturbed, thieves were more likely to reverse their direction of movement, while normal foragers continued moving in the same direction. Because the carbon and nitrogen stable isotope composition, as well as the C:N ratio, was the same for both thieves and nonthieves, we conclude that both groups were accessing the same food sources, using different behaviours to repartition a common resource. We conclude that, although thieves are morphologically indistinguishable from nonthieving foragers, their food retrieval behaviours are distinct in a manner that reduces the probability of detection and aggressive interactions with other conspecifics. We propose that thieves are a distinct caste of forager in E. ruidum.

Insect societies fight back: the evolution of defensive traits against social parasites

“…social parasites. Many social parasites are social themselves, such as the slavemaking ants [12], cleptoparasitic ants and bees [13][14][15] or ants, wasps and bees that sneak into other nests to reproduce [16][17][18], while others have social ancestors, such as many workerless ant inquilines [19]. We will restrict our discussion to these cases.…”

“…Social parasites are often closely related to their hosts (referred to as 'Emery's rule') [64,65], which distinguishes these host-parasite interactions from those of microbial or viral parasites and their multicellular hosts. In cases of intraspecific parasitism, colonies are parasitized by workers or queens of the same species [14,16,18,28,51,52,66,67] or sub-species [17,29] that attempt to raid resources or reproduce. Even in interspecific relationships, such as in the workerless ant inquilines (table 1), they are often their hosts' sister species [19,30].…”

Caught red-handed: behaviour of brood thieves in an Indian ant

“…When the thieves were able to steal successfully during a visit, the latency for revisiting the victim nest was significantly reduced. Absence of lethal levels of aggression against thieves may influence the behaviour of thieves and the success of theft, and is also suggested in the case of food thieves of the ant E. ruidum (McGlynn et al, 2015).…”

“…The ant Ectatomma ruidum has specialized food thieves, which sneak in and wait inside a conspecific nest to steal food from returning foragers when they enter the nest. The thieves also modify their behaviour to avoid capture while returning to their own nesttaking a roundabout path through dense leaf litter, walking slowly and vigilantlypresumably to avoid encountering conspecifics (McGlynn et al, 2015;Jandt et al, 2015). Ants are a suitable system to study theft as the behaviour is particularly prevalent in these social insects.…”

Ecologia comportamental e de interações entre <i>Pseudomyrmex concolor</i> Smith (Hymenoptera, Formicidae, Pseudomyrmecinae) e sua planta hospedeira <i>Tachigali myrmecophila</i> Ducke (Fabaceae: Caesalpinioideae) na Amazônia amapaense

“…Esses inimigos naturais, em especial outras formigas predadoras ou parasitas sociais (Buschinger, 2009;Lachaud et al, 2012), podem invadir uma colônia para roubar alimento armazenado (Adams, et al, 2000;Dijkstra & Boomsma, 2003;Adams et al, 2015;McGlynn et al, 2015), crias para suprir suas necessidades alimentares (Breed et al, 1990;Adams & Longino, 2007) e sociais (e.g. operárias como força 84 de trabalho) (Lenoir et al, 2001) ou explorar recursos territoriais (Powell et al, 2014) e do ambiente intracolonial (Akino, 2002).…”