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 non-enslaved 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.