Weak patriline effects are present in the cuticular hydrocarbon profiles of isolated Formica exsecta ants but they disappear in the colony environment

Chemical recognition cues are used to discriminate among species, con‐specifics, and potentially between patrilines in social insect colonies. There is an ongoing debate about the possible persistence of patriline cues despite evidence for the mixing of colony odors via a “gestalt” mechanism in social insects, because patriline recognition could lead to nepotism. We analyzed the variation in recognition cues (cuticular hydrocarbons) with different mating frequencies or queen numbers in 688 Formica exsecta ants from 76 colonies. We found no increase in the profile variance as genetic diversity increased, indicating that patriline effects were absent or possibly obscured by a gestalt mechanism. We then demonstrated that an isolated individual's profile changed considerably relative to their colony profile, before stabilizing after 5 days. We used these isolated individuals to eliminate the masking effects of the gestalt mechanism, and we detected a weak but statistically significant patriline effect in isolated adult workers and also in newly emerged callow workers. Thus, our evidence suggests that genetic variation in the cuticular hydrocarbon profile of F. exsecta ants (n‐alkanes and alkenes) resulted in differences among patrilines, but they were obscured in the colony environment, thereby avoiding costly nepotistic behaviors.     

Ontogenesis of visual and olfactory kin recognition,in the ant Myrmica sabuleti (Hymenoptera: Formicidae)

In the present work, firstly, ant emergence was observed: it is a long, stereotyped, precarious event which may require the help of congeners. Then, our experiments on Myrmica sabuleti Meinert 1861 callow ants emerging apart from or inside their colony showed the following points. 1. Newly emerged workers, even if having never olfactorily perceived nestmates, are attracted by congeners’ odor. They can distinguish such an odor from that of another species of Myrmica as well as somewhat from that of alien workers of the same species. So, they might have acquired, at least partly, the knowledge of their congeners’ odor during their larval life. 2. Callow ants having visually perceived congeners at their emergence move towards a presented congener’s washed corpse. Callow ants having emerged without seeing any congeners do not move towards such a corpse. Callow ants having emerged beside a piece of thyme moved towards a non-odorous (solvent-washed) piece of thyme. So, ants may acquire, at least partly, the knowledge of the visual aspect of their species just at their emergence, probably by imprinting. 3. Very young workers confronted with their congeners’ odor on one hand and their congeners’ visual aspect on the other hand, somewhat prefer the odor, even if these young ants belong to a species which exclusively uses its vision for navigating. So, for very young ants, whatever the species, odors are more important and better known than visual characters.     

Functional morphology of the postpharyngeal gland of queens and workers of the ant Monomorium pharaonis (L.)

Eelen D., Børgesen L.W. and Billen J. 2006. Functional morphology of the postpharyngeal gland of queens and workers of the ant Monomorium pharaonis (L.). —Acta Zoologica (Stockholm) 87 : 101–111 The postpharyngeal gland (PPG) is unique to ants and is the largest exocrine gland in their head. In queens of the pharaoh's ant, Monomorium pharaonis, the gland contains approximately 15 finger‐like epithelial extensions on each side and opens dorsolaterally in the posterior pharynx. In these ants the PPG morphology varies considerably according to age and mating status. The epithelial thickness increases with age and reaches a maximum at 3 weeks in both virgin and mated queens. A considerable expansion of the lumen diameter occurs in both groups between 4 and 7 days. Virgin queens release their secretion into the gland lumen from an age of 7 days, whereas mated queens accumulate large amounts of secretion in their epithelium. The increasing epithelial thickness, together with the increasing lumen diameter, the presence of numerous inclusions in the epithelium and the release of secretion, are indicative for increasing gland activity. The gland ultrastructure indicates involvement in lipid metabolism and de novo synthesis of lipids. The PPG of workers consists of 12 finger‐like tubes at each side. There is a significant difference in epithelial thickness between nurses and repletes and between nurses and foragers. We suggest the PPG serves different purposes in pharaoh's ants: it is likely that the PPG of workers and virgin queens is used to feed larvae. In mated queens the gland probably plays a role in providing the queen with nutritious oils for egg production. The PPG may also function in signalling species nestmate and caste identity, as well as in the reproductive capacity of the queens.     

Interindividual distances in mixed-species groups of ants: an estimation of cohesion in social groups

Spatial organization was estimated in mixed-species groups of ants with interindividual distance measures as a function of: (1) the age of the workers when associated; and (2) the presence of the brood. Workers ofManica rubida (Myrmicinae) andFormica selysi (Formicinae) were reared in single-species groups (control) or in artificial, mixed-species groups, created 5 h, 12 h or 22 h after emergence, with or without brood. By recording the location of each individual in the nest during the 10 days following the creation of the groups, we evaluated the spatial organization and the interindividual distances between homocolonial or allospecific workers, and between workers and homocolonial or allospecific brood. The cohesion of the group, depend on the age of the workers when associated: the younger the individuals are when the groups are created, the smaller are the interindividual distances. Moreover, homocolonial individuals aggregated with brood, when present, which improves the overall cohesion of the group. However, in mixed groups, both species associated preferentially with members of their own species. This suggests that newly-emerged ants do not depend totally on the odors of their nestmates to construct their recognition template and that they also possess an innate, specific template.     

PARTIAL INCOMPATIBILITY BETWEEN ANTS AND SYMBIOTIC FUNGI IN TWO SYMPATRIC SPECIES OF ACROMYRMEX LEAF-CUTTING ANTS

Abstract We investigate the nature and duration of incompatibility between certain combinations of Acromyrmex leaf‐cutting ants and symbiotic fungi, taken from sympatric colonies of the same or a related species. Ant‐fungus incompatibility appeared to be largely independent of the ant species involved, but could be explained partly by genetic differences among the fungus cultivars. Following current theoretical considerations, we develop a hypothesis, originally proposed by S. A. Frank, that the observed incompatibilities are ultimately due to competitive interactions between genetically different fungal lineages, and we predict that the ants should have evolved mechanisms to prevent such competition between cultivars within a single garden. This requires that the ants are able to recognize unfamiliar fungi, and we show that this is indeed the case. Amplified fragment length polymorphism genotyping further shows that the two sympatric Acromyrmex species share each other's major lineages of cultivar, confirming that horizontal transfer does occasionally take place. We argue and provide some evidence that chemical substances produced by the fungus garden may mediate recognition of alien fungi by the ants. We show that incompatibility between ants and transplanted, genetically different cultivars is indeed due to active killing of the novel cultivar by the ants. This incompatibility disappears when ants are force‐fed the novel cultivar for about a week, a result that is consistent with our hypothesis of recognition induced by the resident fungus and eventual replacement of incompatibility compounds during force‐feeding.     

Selective Acceptance of Alien Host Species Pupae by Slaves of the Dulotic Ant,Harpagoxenus sublaevis (Hymenoptera,Formicidae, Myrmicinae)

The European slave-making ant, Harpagoxenus sublaevis, has up to three host species which occasionally are found all together in one colony. Colonies with only Leptothorax acervorum slaves, or with both L. acervorum and L. muscorum, are frequent, whereas colonies with only L. muscorum slaves are rare, although young H. sublaevis queens found their colonies about equally frequently with either of the two main host species. We demonstrate here, that the two host species exhibit an asymmetric acceptance behavior towards each other's pupae: L. muscorum workers accept L. acervorum pupae, both in non-enslaved colonies and as slaves in H. sublaevis nests, whereas L. acervorum never accepted L. muscorum pupae. Origin and meaning of this behavioral difference are unknown. The findings, however, might be very important with respect to host specificity and host-parasite interactions also in other slave-making ants.     

Worker brain development and colony organization in ants: Does division of labor influence neuroplasticity?

Brain compartment size allometries may adaptively reflect cognitive needs associated with behavioral development and ecology. Ants provide an informative system to study the relationship of neural architecture and development because worker tasks and sensory inputs may change with age. Additionally, tasks may be divided among morphologically and behaviorally differentiated worker groups (subcastes), reducing repertoire size through specialization and aligning brain structure with task‐specific cognitive requirements. We hypothesized that division of labor may decrease developmental neuroplasticity in workers due to the apparently limited behavioral flexibility associated with task specialization. To test this hypothesis, we compared macroscopic and cellular neuroanatomy in two ant sister clades with striking contrasts in worker morphological differentiation and colony‐level social organization: Oecophylla smaragdina , a socially complex species with large colonies and behaviorally distinct dimorphic workers, and Formica subsericea , a socially basic species with small colonies containing monomorphic workers. We quantified volumes of functionally distinct brain compartments in newly eclosed and mature workers and measured the effects of visual experience on synaptic complex (microglomeruli) organization in the mushroom bodies—regions of higher‐order sensory integration—to determine the extent of experience‐dependent neuroplasticity. We demonstrate that, contrary to our hypothesis, O. smaragdina workers have significant age‐related volume increases and synaptic reorganization in the mushroom bodies, whereas F. subsericea workers have reduced age‐related neuroplasticity. We also found no visual experience‐dependent synaptic reorganization in either species. Our findings thus suggest that changes in the mushroom body with age are associated with division of labor, and therefore social complexity, in ants. © 2017 Wiley Periodicals, Inc. Develop Neurobiol 77: 1072–1085, 2017     

Role of Early Experience in Mixed-colony Odor Recognition in the Ants Manica rubida and Formica selysi

An experimental model of mixed societies of ants was used to test the effect of early conditioning to a mixed colony odor on interspecific recognition after various periods of separation, with Manica rubida (Myrmicinae) and Formica selysi (Formicinae). Recognition was evaluated by recording the behaviour of individuals interacting after they had been grouped in mixed societies. The observed frequency and nature of these interactions depended on the way the societies were made up (whether with the same or different species, and with or without previous exposure to that species). The recognition displayed by the workers was much more altered in interspecific than in intraspecific groupings, which is evidence of the existence of some species recognition. In addition, the adult is capable of recognizing the olfactory characteristics of its group, the group odor would be a mixture of individual odors.     

Unadapted behaviour of native,dominant ant species during the colonization of an aggressive,invasive ant

Among the factors driving the invasive success of non-indigenous species, the “escape opportunity” or “enemy release” hypothesis argues that an invader’s success may result partly from less resistance from the new competitors found in its introduced range. In this study, we examined competitive interactions between the little fire ant Wasmannia auropunctata (Roger) and ant species of the genus Pheidole in places where both are native (French Guiana) and in places where only species of Pheidole are native (New Caledonia). The experimental introduction of W. auropunctata at food resources monopolized by the Pheidole species induced the recruitment of major workers only for the Guianian Pheidole species, which were very effective at killing Wasmannia competitors. In contrast, an overall decrease in the number of Pheidole workers and no recruitment of major workers were observed for the New Caledonian species, although the latter were the only ones able to kill the Wasmannia workers. These results emphasize the inappropriate response of native dominant New Caledonian species to W. auropunctata and, thus, the importance of enemy recognition and specification in the organization of ant communities. This factor could explain how invasive animal species, particularly ants, may be able to successfully invade species-rich communities.     

Information use by an Invading Species: Do Invaders Respond More to Alarm Odors than Native Species?

Two species of crayfish were tested in the laboratory to evaluate the hypothesis that successful invaders use a broader range of chemical information than do displaced native species. The invasive species Orconectes rusticus reduced responses to food odors just as strongly when heterospecific (O. propinquus, O. virilis) alarm odors were introduced with food odors as they did when conspecific alarm odors were introduced at the same time as food odors. Individuals of the displaced native species, O. propinquus, did not reduce feeding responses as strongly when O. virilis alarm odor was introduced as with conspecific alarm odor or O. rusticus alarm odor. These results are consistent with the hypothesis that successful invaders use a wider range of information about their environment than do displaced native species.     

Trail‐sharing among tropical ants: interspecific use of trail pheromones?

1. Trail‐sharing between different ant species is rare and restricted to a small number of species pairs. Its underlying mechanisms are largely unknown. For trail‐sharing to occur, two factors are required: (i) one or both species must recognise the other species or its pheromone trails and (ii) both species must tolerate each other to a certain extent to allow joint use of the trail. A species that follows another's trails can efficiently exploit the other's information on food sources contained in the pheromone trails. Hence, food competition and thus aggressive interactions between a species following another's trail and the species being followed, seem likely. 2. In the present study, we investigated interspecific trail following and interspecific aggression in trail sharing associations (i) among Polyrhachis ypsilon, Camponotus saundersi, and Dolichoderus cuspidatus, and (ii) among Camponotus rufifemur and Crematogaster modiglianii. We tested whether trail‐sharing species follow each other's pheromone trails, and whether the ants tolerated or attacked their trail‐sharing partners. In both associations, we confronted workers with pheromone trails of their associated species, and, for the former association, measured interspecific aggression among the trail‐sharing species. 3. In our assays, D. cuspidatus and C. rufifemur regularly followed heterospecific pheromone trails of P. ypsilon and C. modiglianii, respectively. However, only few workers of the remaining species followed heterospecific pheromone trails. Thus, shared trails of P. ypsilon and C. saundersi cannot be explained by interspecific trail‐following. 4. Interspecific aggression among P. ypsilon, C. saundersi, and D. cuspidatus was strongly asymmetric, C. saundersi being submissive to the other two. All three species differentiated between heterospecific workers from the same or another site, suggesting habituation to the respective trail‐sharing partners. We therefore hypothesise that differential tolerance by dominant ant species may be mediated by selective habituation towards submissive species and this way determines the assembly of trail‐sharing associations.     

Interactions between ants attendingAphis fabae ssp.cirsiiacanthoidis on thistles and foraging parasitoid wasps

We describe the behavioral interactions between honeydew-collecting workers of the ants Lasius nigerand Myrmica ruginodisand females of three species of aphidiid wasps (Lysiphlebus cardui, Lysiphlebus testaceipes, Trioxys angelicae)foraging for their aphid host, Aphis fabaessp. cirsiiacanthoidis,on thistles. Using field and laboratory experiments, we show that the ant-parasitoid interactions are species specific. Workers of both ant species generally attacked and killed females of T. angelicae,but they ignored those of L. cardui.This pattern was not altered when we anesthetized the wasps slightly with carbon dioxide to reduce their mobility. Prior contacts between L. carduiand either conspecific L. nigerfrom a different nest or workers of a different ant species (M. ruginodis)did not influence L. niger'snonaggressive behavior. The number of aphids parasitized by L. testaceipeswas significantly reduced in aphid colonies attended by L. niger,although this parasitoid was rarely attacked by ants. In encounters between these species of ants and wasps, ant aggression is consistent with differences in wasp behavior. We suggest that, in addition, chemical cues located in the cuticula may enable L. carduito avoid detection by honeydew-collecting ants.     

Visual prey discrimination of queen and worker ants by a generalist lizard

Laboratory experiments were conducted to test the hypothesis that widelyforaging generalist lizard,Eumeces okadae, visually discriminates palatable queen ants from unpalatable worker ants. The workers ofCamponotus japonicus andLasius niger were rejected on sight, while the queens of both species were eaten with little prior chemical examination by tongue flicks or licks. Comparison of the lizards' responses towards the workers and wingless queens of similar size indicated that neither body size nor presence or absence of wings accounted for difference in responses toward the 2 ant castes. The lizards probably discriminated different ant castes by body proportions.     

Convergent evolution of the Dufour’s gland secretion as a propaganda substance in the slave-making ant genera Protomognathus and Harpagoxenus

Slave-making ants are social parasites which exploit the workforce of heterospecific slaves for their own reproduction, and to this end they have developed a variety of morphological and behavioural adaptations. Furthermore, social parasites utilize the chemical communication system of their hosts by breaking their nestmate recognition code, and some slave-maker species additionally employ semiochemicals as weapons during colony foundation and slaveraiding. Here, we demonstrate the use of such a ‘propaganda allomone’ by the North American myrmicine slave-maker Protomognathus americanus. This substance is produced in the Dufour’s gland and may be employed during slave raids to elicit panic among defending host workers. Slave-maker Dufour’s gland secretions evoked agitation and heightened levels of activity among host workers when applied directly on a host nest, and strong aggressive responses of nestmates when applied onto a host worker. Although the hosts own Dufour’s gland secretion also elicits intra-colonial fights, no support for the hypothesis was found that the slave-maker propaganda substance mimics a fertility signal of the host, as the chemical profile of the gland secretions is highly divergent between the two species. Preliminary results on the chemical composition of the secretion obtained by gas chromatography indicate that the propaganda substance of P. americanus differs from that of the related European slavemaker Harpagoxenus sublaevis, and is thus likely to represent an independent evolutionary development. Received 24 February 2005; revised 28 July 2005 and 2 March 2006; accepted 6 March 2006.     

Unexpected,well-developed nestmate recognition in laboratory colonies of polygyne imported fire ants (Hymenoptera: Formicidae)

Aggression bioassays were used to investigate nestmate recognition in polygyne laboratory colonies of the imported fire ant, Solenopsis invictaBuren. Unlike workers from polygyne field colonies, laboratory-maintained (>10 weeks) workers exhibited well-developed nestmate recognition. As in monogyne colonies of this species, both heritable and environmentally acquired (diet) odors provided recognition cues and were roughly additive in their effect. Within diet treatments, polygyne colonies responded in a graded fashion to polygyne conspecifics, monogyne conspecifics, and heterospecifics (S. richteri Forel),thus suggesting incipient genetic divergence between the two S. invictasocial forms. Hypotheses to account for the acute intraspecific discrimination observed in the laboratory are presented. Empirical testing of these hypotheses will illuminate ecological constraints and proximate mechanisms underlying the reduced intercolony discrimination associated with natural polygyne colonies of this and other ant species.     

Early learning of volatile chemical cues leads to interspecific recognition between two ant species

Nestmate recognition in social insects generally involves matching a label to the template that is acquired through the early learning of non-volatile cuticular hydrocarbon cues. However, a possible role of the volatile chemical cues that exist in the nest, and which may also affect template formation, has not been studied. We investigated this possibility using experimental mixedspecies groups composed of the two ant species Manica rubida and Formica selysi. The experimental set-up either allowed full contact between workers of the two species or interspecific contact was hindered or prohibited by a single or a double mesh. After three months, workers of M. rubida ants were selected as focal ants for aggression tests including the following target ants: F. selysi workers from the same mixed-species group (for each of the three rearing conditions) or from a single-species group (control). Workers of M. rubida were always amicable towards their group-mates, irrespective of the experimental group (contact, single or double mesh). However, M. rubida that were not imprinted on F. selysi, expressed high levels of aggression towards the non-familiar F. selysi workers. The finding that F. selysi workers in the mixed-species groups appeared familiar to their M. rubida group-mates even without physical contact between them, suggests that the volatile cues produced by F. selysi affected nestmate recognition in M. rubida. In an attempt to identify these volatile cues we performed SPME analysis of the head space over groups of F. selysi workers. The findings revealed that F. selysi Dufour’s gland constituents, with undecane as the major product, are released into the head space, rendering them likely candidates to affect template formation in M. rubida. Analysis of Dufour’s gland secretion of F. selysi revealed a series of volatile alkanes, including undecane as a major product. These alkanes were not present in the glandular secretion of M. rubida, whose secretion was mainly composed of isomers of farnesene. We therefore hypothesize that callow M. rubida workers in the mixed-species groups had become imprinted by the above alkanes (in particular undecane, being the major heterospecific volatile in the head space) and incorporated them into their own template. Received 18 October 2007; revised 2 January 2008; accepted 7 January 2008.     

Opportunist slave-making ants Myrmoxenus ravouxi discriminate different host species from a non-host species

Slave-making ants exploit the worker force of host colonies permanently and have to make recurrent raids in order to replenish the slave’s stock. Some of these parasite species exploit different host species and few studies so far have been devoted to host species recognition mechanisms. Here, we tried to determine if opportunist slave-making ants using different host species rely on innate or experience-induced preferences to discriminate host from non-host species. We show that Myrmoxenus ravouxi slave-making workers are not only more aggressive toward heterocolonial host and potential host species workers when compared with non-host species workers, but also toward heterocolonial host workers than toward heterocolonial conspecifics. Moreover, M. ravouxi workers display more antennations and contacts toward the heterocolonial host species when compared with the non-host species. We also show that they do not discriminate between homocolonial and heterocolonial conspecifics. Together, our results suggest that this opportunistic slave-making ant species may have a complex social recognition template based on both innate and experience-based mechanisms.     

Recognition of Individuals from Mixed Colony by Formica sanguinea and Formica polyctena Ants

It was examined whether Formica polyctena and F. sanguinea ants from a mixed colony elicit higher levels of aggression of conspecific ants in comparison to ants from homospecific colonies. Individuals were confronted in an experimental arena and their behavior was recorded. It was found that F. polyctena workers behaved more aggressively toward ants from a mixed colony. This pattern, however, was not confirmed in F. sanguinea. Moreover, both species clearly discriminated between conspecific and allospecific ants from a mixed colony. It seems that as a result of social interactions both species exchanged cuticular hydrocarbons, which caused their recognition labels to adjust to some extent. Results of the present study support the idea that that F. sanguinea is able to form mixed colonies in which species-specific recognition cues are probably still retained.     

Selective isolation of dematiaceous fungi from the workers of <Emphasis Type="Italic">Atta laevigata</Emphasis> (Formicidae: Attini)

Leaf-cutting ants (Formicidae: Attini) are considered pests in agriculture for their impact in human crops, as they utilize leaf fragments to raise their fungal mutualist (Agaricales: Lepiotaceae). Basically, the basidiomycetous fungus is cultivated to supply food to adult workers and broads; in return, the ants protect it against natural enemies. However, recent studies have claimed that other microorganisms are associated to ant nests where a wide range of interactions may take place. To investigate the occurrence of dematiaceous fungi on the cuticle of Atta laevigata ants, 30 workers were sampled from an adult nest located in the surroundings of the Center for the Studies of Social Insects, UNESP-Rio Claro, SP, Brazil. The use of selective techniques to avoid high-sporulation fungi has been recommended and was tested in this study. To favor the isolation of the desired fungi, heads and cuticle scrapings of ant bodies were inoculated on Mycosel agar and incubated for 3 weeks at 35°C. Morphological and molecular methods were used to identify the filamentous fungi recovered. From 56 isolates, 19 were hyaline filamentous species, and among the remaining 37, some are mentioned as phyto-associated fungi like Alternaria arborescens, Bipolaris sorokiniana, Bipolaris eleusines, Bipolaris zeae, Curvularia trifolii, and Paraphaeosphaeria michotii. These species are reported from A. laevigata bodies for the first time. None of the isolation trials revealed the presence of the parasite Escovopsis or entomopathogenic fungi. The possible spread of the fungi in nature by the ants is discussed.     

Elevated dominance of extrafloral nectary-bearing plants is associated with increased abundances of an invasive ant and reduced native ant richness

Aim Invasive ants can have substantial and detrimental effects on co‐occurring community members, especially other ants. However, the ecological factors that promote both their population growth and their negative influences remain elusive. Opportunistic associations between invasive ants and extrafloral nectary (EFN)‐bearing plants are common and may fuel population expansion and subsequent impacts of invasive ants on native communities. We examined three predictions of this hypothesis, compared ant assemblages between invaded and uninvaded sites and assessed the extent of this species in Samoa. Location The Samoan Archipelago (six islands and 35 sites). Methods We surveyed abundances of the invasive ant Anoplolepis gracilipes, other ant species and EFN‐bearing plants. Results Anoplolepis gracilipes was significantly more widely distributed in 2006 than in 1962, suggesting that the invasion of A. gracilipes in Samoa has progressed. Furthermore, (non‐A. gracilipes) ant assemblages differed significantly between invaded and uninvaded sites. Anoplolepis gracilipes workers were found more frequently at nectaries than other plant parts, suggesting that nectar resources were important to this species. There was a strong, positive relationship between the dominance of EFN‐bearing plants in the community and A. gracilipes abundance on plants, a relationship that co‐occurring ants did not display. High abundances of A. gracilipes at sites dominated by EFN‐bearing plants were associated with low species richness of native plant‐visiting ant species. Anoplolepis gracilipes did not display any significant relationships with the diversity of other non‐native ants. Main conclusions Together, these data suggest that EFN‐bearing plants may promote negative impacts of A. gracilipes on co‐occurring ants across broad spatial scales. This study underscores the potential importance of positive interactions in the dynamics of species invasions. Furthermore, they suggest that conservation managers may benefit from explicit considerations of potential positive interactions in predicting the identities of problematic invaders or the outcomes of species invasions.