Nestmate Discrimination Research Articles

Geographical variation in Argentine ant aggression behaviour mediated by environmentally derived nestmate recognition cues

Social insects use a complex of recognition cues when discriminating nestmates from non-nestmate conspecifics. In the Argentine ant, Linepithema humile, recognition cues can be derived from exogenous sources, and L. humile acquires prey-derived hydrocarbons that are used in nestmate discrimination. We studied Argentine ant population-level distinctions in response to external recognition cues. Ants belonging to a California population were strongly affected by the imposition of prey-derived hydrocarbons, with spatially isolated colony fragments that had been fed different cockroach prey (Blattella germanica or Supella longipalpa) showing high and injurious intracolony aggression when reunited. In contrast, colonies of Argentine ants from the southeastern U.S. showed only moderate and noninjurious aggression when subjected to the same treatment. Field-collected colonies of L. humile had hydrocarbons in the range of those provided by S. longipalpa, and colonies from the southeastern U.S. had significantly higher initial levels of Supella-shared hydrocarbons. When fed cockroaches, Argentine ants from both regions acquired additional amounts of Supella- and Blattella-specific hydrocarbons, with a significant increase in levels of Blattella-specific hydrocarbons. Therefore, diet partitioning produced a greater change in the proportion of prey hydrocarbons in the California than in the southeastern U.S. populations, which may be responsible for the altered behaviour observed in the California population. Identifying factors underlying geographical variation in cue expression and/or perception may bring us closer to elucidating the selective forces driving nestmate recognition systems.

Renewal process of nestmate recognition template in European honeybee Apis mellifera L. (Hymenoptera: Apidae)

To investigate the process of template renewal in the European honeybee, we collected workers showing nestmate discrimination ability and exposed them to unfamiliar colony environments by keeping them with non-nestmates in a small box or by fostering them in an unrelated colony. Bees exposed to non-nestmates for 25 min showed more tolerance, than bees not exposed, to members of the colony to which they had been exposed, but were still aggressive to bees from other colonies. However, this treatment did not affect their response to nestmates. In the fostering experiment, although fostered bees became significantly more tolerant to bees from the fostering colony after 24 h, their response to former nestmates changed little until 96 h after fostering started. These results suggest that European honeybees change their template rapidly by referring to the inner-colony environment but retain the old template temporally in the early phase of template renewal. This is probably appropriate for accepting nestmates who have not yet acquired the new recognition cue when the colony odor changes.

Role of early experience in ant enslavement: a comparative analysis of a host and a non-host species.

BackgroundAnts use the odour of the colony to discriminate nestmates. In some species, this odour is learned during the first days following emergence, and thus early experience has a strong influence on nestmate discrimination. Slave-making ants are social parasites that capture brood of other ant species to increase the worker force of their colony. After emerging in the slave-maker nest, slave workers work as if they were in their own colony. We tested the hypothesis that early experience allows the deception of commonly enslaved species, while non-host species use a different mechanism, which does not involve learning.ResultsPupae of a host species, Temnothorax unifasciatus, and a non-host species, T. parvulus, were allowed to emerge in the presence of workers of one of two slave-maker species, Chalepoxenus muellerianus or Myrmoxenus ravouxi. When T. unifasciatus was exposed to slave-makers for 10 days following emergence, they were more aggressive towards their own sisters and groomed the slave-maker more. T. parvulus gave a less clear result: while workers behaved more aggressively towards their sisters when exposed early to C. muellerianus workers, this was not the case when exposed early to M. ravouxi workers. Moreover, T. parvulus workers allogroomed conspecific nestmates less than T. unifasciatus. Allogrooming activity might be very important for the slave-makers because they are tended by their slaves.ConclusionOur findings show that early experience influences nestmate discrimination in the ant T. unifasciatus and can account for the successful enslavement of this species. However, the non-host species T. parvulus is less influenced by the early environment. This might help to explain why this species is never used by social parasites.

Sensing Friend or Foe

Ants secrete and recognize specific blends of hydrocarbons in the cuticle, which enables them to display aggressive behavior toward non-nestmates. This identification process is thought to occur at a higher neural level. Ozaki et al. have found chemosensory sensilla in the ant antenna that respond to cuticle hydrocarbon blends from non-nestmates and have identified a protein that may carry the compounds to sensory receptors in the sensilla. This finding suggests that chemical information is also processed peripherally. M. Ozaki, A. Wada-Katsumata, K. Fujikawa, M. Iwasaki, F. Yokohari, Y. Satoji, T. Nisimura, R. Yamaoka, Ant nestmate and non-nestmate discrimination by a chemosensory sensillum. Science 309 , 311-314 (2005). [Abstract] [Full Text]

Ant Nestmate and Non-Nestmate Discrimination by a Chemosensory Sensillum

In animal societies, chemical communication plays an important role in conflict and cooperation. For ants, cuticular hydrocarbon (CHC) blends produced by non-nestmates elicit overt aggression. We describe a sensory sensillum on the antennae of the carpenter ant Camponotus japonicus that functions in nestmate discrimination. This sensillum is multiporous and responds only to non-nestmate CHC blends. This suggests a role for a peripheral recognition mechanism in detecting colony-specific chemical signals.

Nest Hydrocarbons as Cues for Philopatry in a Paper Wasp

AbstractPhilopatric behavior has been demonstrated in a wide taxonomic spread of animals. In temperate environments, overwintered Polistes wasp foundresses often return to their natal nest prior to initiating colony construction. Previous research has shown that these spring foundresses can identify the natal nest in the absence of landmark and gross morphological cues. Hydrocarbons are essential recognition cues for Polistes nest and nestmate discrimination, but cuticular hydrocarbon profiles can become homogenized when foundresses overwinter in mixed colony groups. We examined the hydrocarbon profiles of Polistes dominulus foundresses and nests before and after an overwintering period, and found that the hydrocarbon profiles of nests remain unique over time and that this uniqueness is influenced by the original foundresses. Our data raise the possibility that in returning to the natal nest, foundresses reacquire their colony‐specific signature, which may play a role in the formation of cooperative associations.

Context-dependent nestmate discrimination and the effect of action thresholds on exogenous cue recognition in the Argentine ant

The optimal acceptance threshold model predicts that kin/nestmate discrimination is context dependent and that, in a fluctuating environment, the action component of nestmate discrimination is plastic, rather than static. We examined changes in intraspecific aggression among colonies of Argentine ants, Linepithema humile , in various discrimination contexts, and found that aggression occurred at higher rates when either nestmates or familiar territory indicated nest proximity, but not when social context was absent, thereby providing additional support for the optimal acceptance threshold model. Context-dependent aggression in the Argentine ant appears to result from a shift in acceptance threshold in response to fitness costs associated with accepting nonkin. The change in the action component of Argentine ant nestmate discrimination was explained to some degree by the hypothesis that the presence of nestmates indicates nest proximity and denotes a fitness payoff for active defence (nest indicator hypothesis) and by the hypothesis that nestmates share the cost of nest defence in groups, but not singly (cost minimizer hypothesis). Isolated nest referents (familiar territory, conspecific brood, or single familiar nestmates), however, had no effect on aggression thresholds. We provide mixed support for the hypothesis that workers from genetically less diverse colonies attack workers from more diverse colonies. We found that, in the context of nest defence, genetically more diverse colonies initiated attacks on colonies with lower genetic diversity. Therefore, the role of asymmetrical aggression in reducing genetic diversity within introduced populations of L. humile remains unknown and other extrinsic factors such as nest status and/or colony size may affect the outcome of aggressive interactions in the field. Finally, our finding that colonies reared under uniform conditions showed diminished intraspecific aggression only when assayed in a social and/or ecological context underscores the importance of using appropriate aggression assays for testing patterns of intercolony aggression in L. humile , and that the use of different rearing regimes, source colonies and collection times may produce contradictory results.

Intraspecific competition influences the symmetry and intensity of aggression in the Argentine ant

Cooperative social groups rely on the ability to distinguish members from nonmembers. Accordingly, social insects have evolved a variety of systems that allow discrimination of nest mates from non‐nest mates. In this study, we show that experience can modify patterns of intraspecific aggression in Argentine ants (Linepithema humile). In laboratory experiments, we found that aggression between colonies was often asymmetrical, but in all five cases, this asymmetry shifted to symmetrical aggression after contact with a hostile colony. Moreover, in the field, aggression between workers collected from colony borders was symmetrical, whereas polarized aggression occurred between workers collected 500 m away from colony borders. Coinciding with this shift in aggression symmetry, we also observed an increase in both the overall level of aggression and the frequency of aggression in both the field and laboratory bioassays. We found little evidence for colony-level competitive asymmetries stemming from polarities in aggression at the worker level, either in the laboratory or in the field. These results illustrate that recognition systems in Argentine ants are surprisingly dynamic and provide experimental evidence for how recognition can be adjusted in response to specific circumstances—in this case the presence of intraspecific competitors. Key words: aggression symmetry, intraspecific competition, invasive species, nest-mate recognition, unicoloniality. [Behav Ecol]

Epicuticular lipids and fertility in primitively social wasps (Hymenoptera Stenogastrinae)

Abstract. Lipid cuticular profiles of females of four species belonging to three different genera of stenogastrine wasps are examined in connection with reproductive potential (relative ovarian development). Cuticular lipids may not only represent the cues for nestmate discrimination (already behaviourally ascertained in three of the same species), but also allow discrimination of fertile and non fertile individuals. Comparisons with more socially evolved insects are reported and discussed.

Cuticular hydrocarbon dynamics in young adult Polistes dominulus (Hymenoptera: Vespidae) and the role of linear hydrocarbons in nestmate recognition systems

In social insects, cuticular hydrocarbons (CHCs) play an important role in nestmate discrimination processes, but young individuals are usually not discriminated. We studied CHC changes in young workers of the social wasp Polistes dominulus. A quantitative estimation demonstrated that total quantities of CHCs increased after emergence, with branched alkanes increasing drastically when compared with other classes of hydrocarbons. The relative quantity of longer-chain compounds increased with respect to shorter ones; unsaturated compounds decreased. These changes might reduce the capacity of the cuticle to acquire compounds of environmental origin. We then tested whether individuals acquire hydrocarbons from the environment, and whether this capability equally characterises newly emerged and mature wasps. We exposed wasps of two age classes (adults younger or older than 24h) to four linear hydrocarbons in turn, and observed how nestmates reacted to their re-introduction into the natal colony. Exposed young wasps elicited significantly more aggressive responses than control sisters; but treated wasps older than 24h were generally accepted by nestmates. Chemical assays showed that exposed young wasps readily absorbed hydrocarbons; older ones did not incorporate hydrocarbons, suggesting that the chemical profiles of mature wasps are less prone to chemical shifts than those of newly emerged wasps.

Nestmate discrimination in the harvester termite Hodotermes mossambicus

Nestmate discrimination was studied in the African harvester termite Hodotermes mossambicus in trophallactic feeding experiments. The results show that Hodotermes mossambicus is able to discriminate nestmates from non-nestmates, feeding nestmates significantly more than non-nestmates. Experiments in which termites were treated with the antibiotic tetracycline for 48 hours and then used either as donors or as recipients in the trophallactic assay indicate that the degree of similarity in the intestinal flora strongly affects nestmate discrimination. Antibiotic-treated termites were fed more frequently by treated non-nestmates than by untreated nestmates. Pairs of non-nestmates, which were both treated with the antibiotic, exchange food as frequently as untreated nestmates. Pairs of nestmates, on the other hand, out of which only one animal was treated, exhibit nearly as little trophallactic contacts as the non-nestmate controls. The results parallel similar recent results in Reticulitermes speratus and indicate that termites can make use of recognition cues which are quite different from those of social hymenopterans, cues that are produced by intestinal symbionts.

Nestmate discrimination in ants: effect of bioassay on aggressive behavior

Aggression assays are commonly used to study nestmate recognition in social insects. Methods range from detailed behavioral observations on small numbers of insects to counts of individuals fighting in group interactions. These assays vary in the equipment used and the intensity and duration of observations. We used the Argentine ant, Linepithema humile, to compare four aggression bioassays for consistency between replicates, similarity between assays, and ability to predict whole colony interactions. The assays included were 1 live – 1 dead ant interactions, live 1-1 battles, live 5-5 battles, and 1 ant introduced to a foreign colony. We tested six ant colonies in all pairwise combinations using four different assays and two to three scoring methods per assay. We also conducted a colony merging experiment to see which assays were capable of predicting this ecologically important event. We found that scoring methods within assays yielded very similar results, giving us no reason to favor observationally intense procedures, such as continuous scanning, over less observationally intense systems, such as snapshot surveys. Assays differed greatly in their consistency between replicates. No two replicates of the 1 live – 1 dead assay were significantly correlated. The live 5-5 and the colony introduction assays were the most consistent across replicates. The mean scores of the live 1-1, live 5-5 and colony introduction assays were all significantly correlated with each other; only the live 5-5 assay was significantly correlated with the 1 live – 1 dead assay. Assays that utilized the greatest number of live ants were the most likely to reveal high levels of aggression. The aggression scores of all but the 1 live – 1 dead assay were positively correlated with the number of ants that died during whole colony encounters and negatively associated with colony merging. We conclude that all live ant assays tested are useful tools for analyzing aggressive interactions between colonies, but that the pairing of a live and dead ant produced inconsistent results and generally lower levels of aggression. We found relatively low consistency between trials using the live 1-1 assay, but found that with sufficient replication its results were highly correlated with the assays using more interacting ants. We suggest that isolated aggressive acts in assays do not necessarily predict whole colony interactions : some colonies that fought in bioassays merged when the entire colonies were allowed to interact.

Spatiotemporal patterns of intraspecific aggression in the invasive Argentine ant

The Argentine ant, Linepithema humile, is a widespread invasive species characterized by reduced intraspecific aggression within introduced populations. To illuminate the mechanisms underlying nestmate recognition in Argentine ants, we studied the spatial and temporal fidelity of intraspecific aggression in an introduced population of Argentine ants within which intraspecific aggression does occur. We quantified variation in the presence or absence of intraspecific aggression among nests over time both in the field and under controlled laboratory conditions to gain insight into the role of environmental factors as determinants of nestmate discriminatory ability. In addition, we compared levels of intraspecific aggression between nest pairs to the similarity of their cuticular hydrocarbons to determine the potential role of these compounds as labels for nestmate discrimination. In both field and laboratory comparisons, nest pairs behaved in a consistent manner throughout the course of the experiment: pairs that fought did so for an entire year, and pairs that did not fight remained nonaggressive. Moreover, we found a negative relationship between cuticular hydrocarbon similarity and the degree of aggression between nests, suggesting that these hydrocarbons play a role in nestmate discriminatory ability. In contrast to the prevailing pattern, ants from one site showed a marked change in behaviour during the course of this study. A concomitant change was also seen in the cuticular hydrocarbon profiles of ants from this site. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Chemical nestmate recognition in a stenogastrine wasp, Liostenogaster flavolineata (Hymenoptera Vespidae)

We investigated the chemical basis of nestmate recognition in the clusternesting stenogastrine wasp, Liostenogaster flavolineata. We conducted both behavioural experiments and chemical analysis of the cuticular lipids. As controls, colonies were presented with dead nestmate or non-nestmate conspecific females. The importance of cuticular lipids was tested by (i) presenting nestmates and non-nestmates deprived of their cuticular lipids; (ii) presenting specimens deprived of their own cuticular lipids and then re-treated with the cuticle extracts of nestmate or alien females. We also performed bioassays to test the involvement of the Dufour's gland secretion in the recognition process. The behavioural reactions of the colonies indicate that chemical cues on the body surface are necessary for nestmate discrimination. The chemical composition of the cuticular lipids of nestmates was found to be more similar than that of nonnestmates, suggesting the possible involvement of these compounds in the recognition process. We suggest two hypothesis to explain the common recognition errors observed during our bioassays.

Short Communication: Lack of Aggression and Spatial Association of Colony Members in Reticulitermes flavipes

INTRODUCTIONThe concept of kin selection and the evolution of altruistic behavior, whichis fundamental to the evolution of eusociality, predicts that either relativescan recognize one another and discriminate against strangers or the popu-lation structure naturally keeps nonrelatives separate (Carlin, 1989). SinceHamilton (1964a,b) formulated the kin selection theory, numerous socialinsects have been found to possess the ability to distinguish between kinand nonkin (Fletcher and Michener, 1987). Many investigations of nestmatediscrimination in social insects have revealed some degree of hostility be-tween conspecifics from different colonies (Carlin, 1989), including studiesof nestmate discrimination in termites (Thorne and Haverty, 1991).A large number of termite species are subterranean and there are noobvious physical structures associated with individual colonies that might re-veal their spatial distribution. Behavioral assays have been successfully em-ployed to investigate spatial aspects of termite colony organization (Levingsand Adams, 1984; Adams and Levings, 1987; Binder, 1988; Husseneder

Nestmate discrimination and cuticular profiles of a temporary parasitic ant Lasius sp. and its host L. fuliginosus (Hymenoptera, Formicidae)

Workers of the temporary parasitic ant Lasius sp. were perfectly compatible with their hosts Lasius fuliginosus. Aggression was never seen between allospecific nestmates in either field or laboratory. In the laboratory, trophallaxis and allogrooming between allospecific nestmates were statistically more frequent than that between conspecifics. These ants were highly aggressive toward individuals of either species from another mixed colony located 1 km away, indicating that they discriminated nestmates and nonnestmates regardless of the species to which they belonged. No aggressive actions, however, were observed between two neighboring mixed nests located 5 m apart. We have not considered, however, the relationship of the two neighboring nests: the two nests may have been two subunits of the same family or sister colonies, or may have been different colonies but discriminated from distant aliens. Gas chromatography analysis on the total cuticular extracts showed that Lasius sp. and L. fuliginosus possess distinct cuticular profiles, even though they were collected from the same mixed colony.

Nestmate recognition in the absence of a pheromone

Individual recognition cues were manipulated to elucidate the system of nestmate recognition employed by the introduced European paper wasp, Polistes dominulus. Tests involved exposing P. dominulus individuals to their natal nest material, to which we added a novel hydrocarbon, pentacosanoic acid methyl ester, or exposing them to the artificial odor alone. Results show that P. dominulus (1) performs nestmate discrimination, (2) can use artificial exogenous chemicals as recognition odors, and (3) can distinguish single differences in hydrocarbon profiles. Taken individually, these experiments provide evidence revealing the nature of the production and action components of recognition. Taken together, these results establish that recognition takes place outside the classical definition of a pheromone-based system.

An Improved and Quantified Technique for Marking Individual Fire Ants (Hymenoptera: Formicidae)

Individual fire ants, Solenopsis invicta Buren, were marked with dots of Markal brand Ball Point Paint Markers. Marked ants were returned to the colony while the paint was still wet. The marks were slowly lost over a 100-day period, with one mark lasting 119 days. No mortality could be attributed to the paint. The proportion of ants retaining marks over time can be expressed as a simple exponential decay model: proportion with marks = 0.7665 * exp (-0.0175 * time in days). The technique will be useful in assessing basic behavioral characteristics, such as polygyne versus monogyne interactions, nestmate discrimination, foraging profiles, and in assessing impact of candidate biological control organisms on behavior and survivorship of fire ants.

Thief workers and variation in nestmate recognition behavior in a ponerine ant, Ectatomma ruidum

Our findings give new insight into the relationship between nestmate recognition and cleptobiosis, intraspecific thievery of newly collected food items, in a neotropical ponerine ant, Ectatomma ruidum. The expression of discrimination of nestmates from non-nestmates varied among local aggregations of E. ruidum in a population at Barro Colorado Island, Panama. This result is due to differences in the behavior of the guard ants among aggregations, rather than differences in the expression of recognition cues by ants. Baiting experiments show that E. ruidum colonies in Panama have a greater tendency to have overlapping home ranges than a similar population in Costa Rica. The pattern of cleptobiosis, however, is strikingly similar between the Panamanian and Costa Rican populations.

Neurochemicals aid bee nestmate recognition

The theory of kin selection1, which revolutionized the study of social behaviour, requires the discrimination of relatives from non-relatives. Many animals possess this ability, but the underlying neurobiological mechanisms have not been studied. Here we provide evidence for the neurochemical modulation of nestmate recognition: treatment with octopamine agonists improves the discrimination of related nestmates from unrelated non-nestmates in honeybees.