Structural complexity of chemical recognition cues affects the perception of group membership in the ants Linephithema humile and Aphaenogaster cockerelli

Abstract

SUMMARY Hydrocarbon profiles on the cuticle of social insects act as multi-component recognition cues used to identify membership in a species, a colony or, within colonies, cues about its reproductive status or task group. To examine the role of structural complexity in ant hydrocarbon recognition cues, we studied the species recognition response of two ant species, Linepithema humile and Aphaenogaster cockerelli, and the recognition of conspecifics by L. humile. The cuticular hydrocarbons of ants are composed of molecules of varying chain lengths from three structural classes, n-alkanes, methyl-branched alkanes and n-alkenes. We employed species recognition bioassays that measured the aggressive response of both species of ants to mixtures of hydrocarbon classes, single structural classes of hydrocarbons (n-alkanes,methyl-branched alkanes and n-alkenes), and controls. The results showed that a combination of at least two hydrocarbon structural classes was necessary to elicit an aggressive species recognition response. Moreover, no single class of hydrocarbons was more important than the others in eliciting a response. Similarly, in the recognition of conspecifics, Linepithema humile did not respond to a mixture of n-alkane cuticular hydrocarbons presented alone, but supplementation of nestmate hydrocarbon profiles with the n-alkanes did elicit high levels of aggression. Thus both L. humile and A. cockerelli required mixtures of hydrocarbons of different structural classes to recognize species and colony membership. It appears that information on species and colony membership is not in isolated components of the profile, but instead in the mixture of structural classes found in cuticular hydrocarbon profiles.

Colony Fusion in Argentine Ants is Guided by Worker and Queen Cuticular Hydrocarbon Profile Similarity

“…In this study, we found that quantitative differences of worker and queen CHC profiles reflect colony identity, and that a statistically derived subset of compounds may mediate colony discrimination. Worker CHC supplementation studies (Greene and Gordon 2007;Torres et al 2007) suggest that a mixture of CHC of different structural classes, with varying ratios across colonies rather than a few compounds from a single structural class, may be used as nestmate recognition cues in L. humile. Our findings support this view and, in addition, suggest that alkenes and monomethylalkanes may be important in queen discrimination, while dimethyl-and trimethylalkanes and other unidentified long-chain CHC may be important in worker recognition.…”

“…This is in line with studies showing that aggression levels between colonies, or populations, of social insects are based on similarity of genetically-based CHC profiles (Dronnet et al 2006). In L. humile, intraspecific aggression is based on levels of genetic similarity (Tsutsui et al 2000), and is also guided by worker and queen hydrocarbons (Greene and Gordon 2007;Torres et al 2007;. However, the roles of chemical and genetic factors in regulating behavioral interactions among conspecifics have not been tested simultaneously.…”

“…In the unicolonial, polygynous, and widespread invasive Argentine ant, Linepithema humile, CHC play a central role in nestmate recognition (Liang and Silverman 2000;Greene and Gordon 2007;Torres et al 2007). An inverse relationship between intraspecific aggression and genetic similarity between nests in both native and introduced populations suggests that recognition cues are heritable (Tsutsui et al 2000).…”

A conserved fertility signal despite population variation in the cuticular chemical phenotype of the trap-jaw antOdontomachus brunneus

“…Recent experimental work on cuticular hydrocarbons and nestmate recognition has shown that changes in specific subsets of the overall chemical profile are primarily responsible for distinguishing non-nestmates from nestmates (Greene and Gordon, 2007;Martin et al, 2008a;Martin et al, 2008c;Brandt et al, 2009;Guerrieri et al, 2009;van Wilgenburg et al, 2010). Aggression seems to be triggered by recognizing cuticular profiles as being unfamiliar, and the degree of difference from the colony's template correlates with aggression (Suarez et al, 2002;Ozaki et al, 2005;Guerrieri et al, 2009;Martin et al, 2012;Sturgis and Gordon, 2012).…”

A statistical approach to identify candidate cues for nestmate recognition

“…These cuticular lipids, synthesized by the animals themselves (Howard and Blomquist, 2005;, and partly obtained from environmental sources (Obin and Vander Meer, 1988;Woodrow et al, 2000;Buczkowski et al, 2005), are typically mixed throughout the colony by means of liquid food transfer, grooming, and exchange through nest material (Soroker et al, 1995;d'Ettorre et al, 2006;Couvillon et al, 2007;Bos et al, 2011). Direct evidence for the use of hydrocarbons in nestmate recognition has been obtained in several ant and bee species, by testing the level of aggression toward NMs supplemented with synthetic hydrocarbons (Lahav et al, 1999;Dani et al, 2005;Ozaki et al, 2005;Martin et al, 2008b;Guerrieri et al, 2009), or to inert materials treated with either the hydrocarbon profile of fellow workers or synthetic mixtures of hydrocarbons (Wagner et al, 2000;Akino et al, 2004;Greene and Gordon, 2007;Martin et al, 2008b). The use of these manipulative experiments has allowed researchers to provide not only direct evidence about the involvement of cuticular hydrocarbons (CHCs) in nestmate recognition, but also information about which compounds constitute the nestmate recognition signal in specific species.…”