Fine-tuned intruder discrimination favors ant parasitoidism.

Gabriela Pérez-Lachaud,Franklin H Rocha,Jean-Paul Lachaud,Javier Valle-Mora,Yann Hénaut

doi:10.1371/journal.pone.0210739

Abstract

A diversity of arthropods (myrmecophiles) thrives within ant nests, many of them unmolested though some, such as the specialized Eucharitidae parasitoids, may cause direct damage to their hosts. Ants are known to discriminate between nestmates and non-nestmates, but whether they recognize the strength of a threat and their capacity to adjust their behavior accordingly have not been fully explored. We aimed to determine whether Ectatomma tuberculatum ants exhibited specific behavioral responses to potential or actual intruders posing different threats to the host colony and to contribute to an understanding of complex ant-eucharitid interactions. Behavioral responses differed significantly according to intruder type. Ants evicted intruders that represented a threat to the colony’s health (dead ants) or were not suitable as prey items (filter paper, eucharitid parasitoid wasps, non myrmecophilous adult weevils), but killed potential prey (weevil larvae, termites). The timing of detection was in accordance with the nature and size of the intruder: corpses (a potential source of contamination) were detected faster than any other intruder and transported to the refuse piles within 15 min. The structure and complexity of behavioral sequences differed among those intruders that were discarded. Workers not only recognized and discriminated between several distinct intruders but also adjusted their behavior to the type of intruder encountered. Our results confirm the previously documented recognition capabilities of E. tuberculatum workers and reveal a very fine-tuned intruder discrimination response. Colony-level prophylactic and hygienic behavioral responses through effective removal of inedible intruders appears to be the most general and flexible form of defense in ants against a diverse array of intruders. However, this generalized response to both potentially lethal and harmless intruders might have driven the evolution of ant-eucharitid interactions, opening a window for parasitoid attack and allowing adult parasitoid wasps to quickly leave the natal nest unharmed.

Highlights

Ants are among the most diverse and abundant organisms on earth
Ants detected the intruder in all 353 remaining observations; of these the intruder was ignored in 35 trials (9.9%), predominantly those with filter paper balls (18 cases) and pentane washed eucharitids (11 cases; Fig 1)
In this study we experimentally demonstrated that E. tuberculatum workers were, in addition, able to recognize and discriminate among several distinct potential or actual intruders and that they further adjusted their behavior to the type of intruder encountered in the nest

Summary

Introduction

Ants are among the most diverse and abundant organisms on earth. Their complex nests and colonies provide both rich, homeostatic microhabitats and available resources that are exploited by other organisms [1,2,3]. An efficient system to discriminate between nestmates and non-nestmates is essential to maintain the integrity, cohesion and functioning of social insect societies [2], and to detect intruders and effectively defend the colony [14,15]. Ants are known to effectively discriminate between nestmates and non-nestmates, but their capabilities to detect a threat and adjust their behavioral responses to its intensity have only been addressed recently [16,17,18]

Objectives

Results

Conclusion