The placid slavemaker: avoiding detection and conflict as an alternative, peaceful raiding strategy

Abstract

Host entry is a crucial step in a parasite's life cycle. When parasites manage to circumvent host detection, exploitation of host resources is facilitated, as host defenses have not to be counteracted. Social parasites exploit animal societies and, likewise, detection avoidance can be beneficial. Yet, due to strong selection pressures, hosts of socially parasitic slavemaking ants often recognize them as enemies, so that slavemakers use open force to raid host colonies. These fights, however, prohibit the enslavement of adult host workers (eudulosis), which cannot be manipulated to work for them. Instead, they steal brood during raids, and enslave those upon emergence. In contrast to the violent raids of most slavemakers, no aggression occurs during most of the raids of the newly described slavemaker Temnothorax pilagens. Thereby, T. pilagens regularly induces adult host workers to be part of their slave workforce. We demonstrate that nonenslaved colonies of its host species respond to this slavemaker with little aggression. We further investigate how the slavemaker circumvents recognition and show that chemical resemblance of host profiles might explain the low aggressive responses. But, which parameters determine whether slave raids escalate, resulting in carnage among defenders? Our experiments reveal that host aggression is counterproductive as aggressive host colonies suffer from more fatalities during raids, but cannot save more brood. The slavemaker, however, benefits from not eliciting fights, as it doubles its enslaved workforce by capturing brood plus adult host workers. Hence, undercutting recognition allows the slavemaker to avoid raid escalation with its associated fitness benefits.

An Alpine ant’s behavioural polymorphism: monogyny with and without internest aggression inTetramorium alpestre

“…Among the authors of recent behaviour studies, there were both observers blind (Jongepier et al 2015; Purcell et al 2016; Yagound et al 2016) and observers not blind about the origin of workers (Kleeberg & Foitzik 2016; Parmentier et al 2016; Ślipiński & Żmihorski 2016). The aggression indices AI and MMAI yielded different values (Figs 2A–B and 3).…”

The influence of slavemaking lifestyle, caste and sex on chemical profiles in Temnothorax ants: insights into the evolution of cuticular hydrocarbons

“…These ants have small colonies with a few dozen workers and inhabit cavities in acorns or small sticks on the forest floor. Slavemaker colonies contain on average only two to five slavemakers and 30 slaves and are, in contrast to their facultative polygynous hosts, invariably monogynous [41,48]. Each slavemaker parasitizes multiple hosts, but shows a clear preference for a single host species [37,45] (electronic supplementary material, S1 for community composition and slavemaker preference).…”

“…and T. americanus changed its genus name from Protomognathus [38]). All of them raid host colonies for slaves, but their fighting strategies differ [31,[39][40][41]. Temnothorax americanus, the oldest slavemaker in this clade, shows little evidence of chemical mimicry [30,41], but uses the Dufour's gland secretion to divert host aggression [42,43].…”

“…Hosts recognize these parasites as enemies [41,44] and their raids are openly aggressive, often resulting in casualties among attackers and defenders [31,45]. A third slavemaking species, Temnothorax pilagens can perform peaceful raids facilitating the enslavement of adult workers [41]. These slavemakers are often not recognized because they use chemical camouflage, but in the cases where they are, they respond to host aggression by stinging host workers.…”

“…Temnothorax duloticus on the contrary, efficiently uses its sting [39]. Hosts recognize these parasites as enemies [41,44] and their raids are openly aggressive, often resulting in casualties among attackers and defenders [31,45]. A third slavemaking species, Temnothorax pilagens can perform peaceful raids facilitating the enslavement of adult workers [41].…”