Quantification of supercolonial traits in the yellow crazy ant, Anoplolepis gracilipes.

Benjamin D Hoffmann

doi:10.1093/jis/14.1.25

Abstract

Supercoloniality is a social structure displayed by many invasive ant species, but there has been surprisingly little research quantifying the extent to which individual species display traits underlying such social organisation. This study quantifies three traits for the yellow crazy ant, Anoplolepis gracilipes Smith (Hymenoptera: Formicidae): little or no aggression between workers from different nests; the exchange of workers among nests; and resource exchange among nests, as well as supercolony structure arising from patterns of distribution and density of detections. Supercolonies displayed a structural continuum from being small ( < 10 ha) and “aggregated” with great continuity among detections through to being large (>10,000 ha) and “diffuse” with little continuity among detections. Smaller supercolonies had greater ant densities than larger supercolonies. In laboratory trials, no aggression was observed between workers from different nests sourced from different supercolonies, and paired nests merged within 24 hours. Workers lacked nest fidelity by rapidly populating artificial nests containing alien queens. The daily worker turnover rate per nest was estimated to be below 20%. Resources were readily moved among nests, with a resource being detected up to 13 m away from a source within 24 hours, and as far as 32 m after four days. The rate and distance of resource movement increased with increasing worker and nest density. This research has demonstrated that A. gracilipes displays supercoloniality equivalent to that of the well-studied Argentine ant Linepithema humile . Quantification of these traits is required for other supercolonial species to improve our understanding of this social strategy, especially for invasive ants to aid in understanding factors that promote invasion success and to improve management.

Highlights

The study of supercoloniality in ants is of great research importance not just for our understanding of eusociality, but because the extreme forms of supercoloniality are disproportionally displayed by invasive ants (Chapman and Bourke 2001; Holway et al 2002; Krushelnycky et al 2010)
The absence of A. gracilipes between disparate detections at supercolony 13 was confirmed by pitfall traps in both assessment plots throughout four years of sampling
In one trial, merging occurred within 12 minutes, and all others merged within 24 hours, confirming that the lack of workerlevel aggression quantified in prior work corresponded with a lack of colony-level aggression

Summary

Introduction

The study of supercoloniality (large-scale polygyny-polydomy) in ants is of great research importance not just for our understanding of eusociality, but because the extreme forms of supercoloniality are disproportionally displayed by invasive ants (Chapman and Bourke 2001; Holway et al 2002; Krushelnycky et al 2010). In the case studies presented here, a supercolony is explicitly referred to as an individual population that is geographically, and reproductively, isolated from others (sensu Hoffmann et al 1999; Krushelnycky et al 2005; Hoffmann and Saul 2010; Thomas et al 2010). Multiple discrete populations within the study region that are genetically indistinct and do not display aggression when experimentally brought into contact (Gruber et al 2012) are not referred to as being one supercolony (sensu Buczkowski et al 2004; Jaquiéry et al 2005; Suhr et al 2009)

Methods

Results

Discussion

Conclusion