Fine Individual Specialization and Elitism among Workers of the Ant Ectatomma tuberculatum for a Highly Specific Task: Intruder Removal

Abstract

Insect societies are characterized by a relatively sophisticated division of labor; they form tightly knit groups that must effectively exclude non-members from the colony. However, the Neotropical predatory ant Ectatomma tuberculatum can harbor several specific myrmecophiles and, in particular, various eucharitid parasitoid wasp species. Adult wasps eclose in the host nests and are removed by worker ants without harm. Previous observations suggest that only a few workers perform this task. To test this hypothesis, we introduced different types of intruders, live and dead, pentane-washed broad-nosed grain weevil individuals (Caulophilus oryzae) and dead, pentane-washed eucharitids (Dilocantha lachaudii), into laboratory colonies containing individually marked workers. We recorded all encounters and behaviors until the intruders were removed. Certain workers removed intruders more frequently than expected by chance. The number of encounters with an intruder was positively correlated with the number of removals performed by the workers. For each nest, a small group of workers was identified as specialized in intruder removal. A subset of very committed workers in the specialists group that performed up to 57% of removals qualified as hyperspecialists or elite workers. The behavioral sequences differed based on the type and condition of the intruder: the sequence was more complex and included numerous aggressive behaviors (mandibular strikes and attempts at stinging) when workers encountered a live weevil. In contrast, the behavioral sequences with dead, pentane-washed insects were characterized by numerous detections through contact that did not lead to rejection and by the intruders simply being seized and removed from the nest. Overall, the data show that the ants discriminated between live and pentane-washed intruders and adjusted their behavior accordingly. This is the first demonstration in ants of both behavioral specialization and hyperspecialization in intruder removal.

Fine-tuned intruder discrimination favors ant parasitoidism

“…Laboratory tests were conducted using artificially reduced colonies, homogeneous in size with one queen, 50 workers chosen at random from the initial colony (from both the nest and the foraging arena), and the brood. Reduction in colony size does not affect colony functioning [30]. Ant behavior against alien organisms or items inside their nests (hereafter intruders, Table 1) was studied by experimentally placing an intruder in the middle of the nest box.…”

“…oryzae (Coleoptera: Curculionidae) are currently reared in our laboratory. The hard cuticle of weevil adults might prevent ant attack; furthermore, they are similar in size to eucharitids [30]. Alcohol preserved adult eucharitid wasps ( D .…”

“…However, how social insects, and in particular ants, combat macro-parasites (arthropods) that threaten their colony resources or their brood has not been fully addressed. It has been suggested that once an alien is inside the nest or emerges within the nest, colony-level prophylactic and hygienic behavioral responses such as active removal of intruders are probably the most general and flexible forms of defense to eliminate them [15,30]. Paradoxically, this general response (removal), well suited to cope with disease [29], might have created a window of evolutionary opportunity for ant parasitoids and might have driven the evolution of ant-parasitoid interactions.…”

Ectaheteromorph ants also host highly diverse parasitic communities: a review of parasitoids of the Neotropical genus Ectatomma

“…They are transported unharmed (Lachaud et al 1998;Howard et al 2001;Rocha et al 2014) outside the host nest where mating takes place (Clausen 1941). Eight associations involving eight species of eucharitine wasps and three Ectatomma species (E. brunneum, E. ruidum, E. tuberculatum) have been documented ( Table 2).…”

Ant workers exhibit specialization and memory during raft formation

“…The Communicated by: Sven Thatje specialization of individuals in performing particular tasks or roles tends to increase group efficiency (Beshers and Fewell 2001;Oster and Wilson 1978). In social insects, workers can display a wide array of specific tasks in colony defence, foraging or brood care (Rocha et al 2014;Wilson 1980). Factors determining task specialization are numerous and include worker morphology, age, previous experience or genetic background (reviewed in Duarte et al 2011).…”