Cuticular hydrocarbons as queen adoption cues in the invasive Argentine ant

Abstract

SUMMARYIn social insects, individuals typically recognize and behave aggressively towards alien conspecifics, thereby maintaining colony integrity. This is presumably achieved via a nestmate recognition system in which cuticular compounds, usually cuticular hydrocarbons (CHC), of genetic and/or environmental origin serve as recognition cues. Most invasive populations of the Argentine ant, Linepithema humile (Mayr), display minimal nestmate-non-nestmate discrimination, resulting in low levels of intraspecific aggression allowing free movement of workers and queens among nests. However, invasive L. humile in the southeastern United States show relatively high levels of intraspecific aggression, and selectively adopt non-nestmate queens. Using behavioral assays and gas chromatography, we found an association between non-nestmate queen adoption and similarity of the CHC profiles of adopted and host colony queens. Also, nestmate and non-nestmate queen CHC profiles became more similar after adoption by queenless colonies. Furthermore, queens treated with non-nestmate queen CHC had distinct CHC profiles and were generally attacked by nestmate workers. We suggest that in L. humile, CHC are used as queen recognition cues, and that queen recognition errors are more likely to occur when the CHC profiles of non-nestmate and host colony queens are similar. Our findings provide further evidence for the complex and dynamic nature of L. humile nestmate discrimination, which may in part underlie the success of introduced populations of this invasive ant.

Nestmate Recognition and the Role of Cuticular Hydrocarbons in the African Termite Raiding Ant Pachycondyla analis

“…2 Total ion chromatograms for the cuticular hydrocarbons of Pachycondyla ants from the colonies studied. Colony 1=CHC extracts from colony 1 ants, Colony 2=CHC extracts from colony 2 ants, Colony 3=CHC extracts from colony 3 ants (see Table 1 for the list of identified compounds) are in agreement with those previously reported for the invasive Argentine ant (Linepithema humile) workers by Vásquez et al (2008), where they showed evidence that CHCs are used in queen adoption, confirming that the MOR is a sensitive assay that can be used effectively to determine recognition or aggression thresholds in ants. Recognition thresholds usually are based on a template odor that is characteristic of a given colony, with ants deciding to accept or reject an individual when it smells greater than a minimum similarity threshold or below a dissimilarity threshold (Reeve 1989).…”

“…Aggression towards nestmates of similar CHC profiles could be due to errors arising while reacting to recognition cues, as shown by Vásquez et al (2008) in L. humile, or due to a lower threshold to avoid false-positive identification. In the present study, the MOR bioassay was used successfully to measure inter-colony aggression at the individual and colony levels in P. analis.…”

“…Intruders or encroachers are usually killed upon encounter (AAY personal observation). By contrast the invasive Argentine ant displays minimal nestmate discrimination and individual non-nestmates are often integrated into an alien colony (Vásquez et al 2008).…”

Aggression in imported fire ants: an explanation for shifts in their spatial distributions in Southern United States?

“…Several studies have suggested the involvement of cuticular hydrocarbons in nestmate recognition in ants (Provost et al , 1994; Lenoir et al , 1999). This proposition is supported by a growing number of studies which showed direct evidence for cuticular hydrocarbons as nestmate recognition cues in many ant species (Lahav et al , 1999; Liang & Silverman, 2000; Wagner et al , 2000; Akino et al , 2004; Ozaki et al , 2005; Vasquez et al , 2008). In contrast, Obin (1986) reported that the cuticular hydrocarbon profile was a poor predictor of aggressive behaviour in a laboratory colony of red imported fire ants.…”

The underdog invader: Breeding system and colony genetic structure of the dark rover ant (Brachymyrmex patagonicus Mayr)

“…The founder effect during an invasion could have reduced the genetic diversity at the loci influencing the cuticular hydrocarbons used to discriminate non-nestmates (Beye, Hasselmann, Fondrk, Page, & Omholt, 2003;Lockey, 1991;Pirk, Neumann, Moritz, & Pamilo, 2001;Reeve, 1989;Tsutsui et al, 2000). This results in homogenized colony templates, leading to a worker's inability to discriminate between nestmates and non-nestmates (Tsutsui, Suarez, & Grosberg, 2003;Tsutsui et al, 2000;Vásquez, Schal, & Silverman, 2008).…”