Nestmate discrimination in the queenless ponerine ant Diacamma sp. from Japan

We examined the nestmate discrimination ability of Diacamma sp., an ant that reproduces by colony budding. We also tested for a relationship between internest distance and hostility. Hostility toward non‐nestmates was significantly stronger than that toward nestmates, suggesting that Diacamma sp. discriminates between nestmates and non‐nestmates. There was no significant correlation between internest hostility and internest distance, which indicates the absence of a “dear enemy” phenomenon in this species.     

Hydrocarbon distribution and colony odour homogenisation in <Emphasis Type="Italic">Pachycondyla apicalis</Emphasis>

Summary Within and between individuals hydrocarbon (HC)-circulation was studied in Pachycondyla apicalis workers, using radioactive labeling. Newly synthesized HCs occurred both in the PPG and on the epicuticle in appreciable amounts, lesser quantities were found in the crop. The front basitarsal brush contained a greater amount of radiolabeled HCs than could be predicted from its surface area, suggesting preferential secretion to these organs. We propose that the newly synthesized HCs are secreted primarily to the front basitarsal brushes and are thereafter either distributed throughout the body surface, or cleared via the PPG and the alimentary canal.Using labeled HCs as a model, we tracked the time-dependent dispersion of cuticular lipids among 11 workers, one of which was prelabeled for 24 hours. Distribution among the recipients became progressively uniform, reaching near homogenization between 5–10 days. The mean HCs transfer of P. apicalis to the PPG was substantially lower compared to that of Camponotus fellah or Aphaenogaster senilis. In contrast, transfer to the cuticle in this species was superior. We attribute the low transfer to the PPG to the inefficacy of passive body contact characteristic of P. apicalis, as opposed to trophallaxis and/or allogrooming that typify the other two species. The higher occurrence of radiolabeled HCs in P. apicalis cuticle can be attributed to their accumulation in the basitarsal brushes. The impact of cuticular lipid transfer and formation of uniform colony odour, as opposed to the maintenance of an idiosyncratic caste-specific composition, are discussed.Received 5 September 2002; revised 17 January 2003; accepted 10 February 2003.     

Contact between supercolonies elevates aggression in Argentine ants

Complex recognition systems underlie the social organization of many organisms. In social insects the acceptance of other individuals as nestmates can involve a variety of different cues, but the relative importance of these cues can change in relation to the fitness costs of accepting or rejecting other individuals. In this study we investigate the mechanisms that underlie recognition behaviour in Argentine ants (Linepithema humile). Introduced populations of Argentine ants are characterized by a social structure known as unicoloniality where intraspecific aggression is absent over large distances resulting in the formation of expansive supercolonies. Recent research has identified sites where multiple, mutually aggressive supercolonies co-occur allowing an examination of Argentine ant behaviour at territorial boundaries. We found that workers from different supercolonies always interact aggressively with one another, but that neighbours from different colonies (i.e., workers from nests located in the immediate vicinity of territory borders) consistently exhibited higher levels of aggression compared to those displayed by non-neighbours from different colonies (i.e., workers from nests located far enough away from a territory border so that interactions are unlikely). This difference in the level of aggression displayed between neighbours and between non-neighbours from different supercolonies cannot be explained by differences in relatedness or genetic similarity. Instead our findings suggest that direct contact between mutually antagonistic colonies is sufficient to elevate aggression. A laboratory experiment in which we manipulated the extent to which colonies with no prior history of contact could interact with one another, revealed that aggression increased after colonies were permitted to interact, but dropped after connections between colonies were severed. Moreover, the mere presence of an aggressive supercolony was sufficient to elicit elevated aggression. Overall these patterns are opposite to the “dear enemy” phenomenon and could be the result of the intense territorial aggression exhibited by established supercolonies of this species. Received 8 January 2007; revised 27 March 2007; accepted 28 March 2007.     

Macro- and microgeographic genetic structure in an ant species with alternative reproductive tactics in sexuals

The genetic structure of social insect populations is influenced by their social organization and dispersal modes. The ant Hypoponera opacior shows diverse reproductive behaviours with regular cycles of outbreeding via winged sexuals and inbreeding via within-nest mating wingless sexuals that reproduce by budding. This unusual life cycle should be reflected in the genetic population structure, and we studied this on different scales using microsatellites. On a macrogeographic scale, populations were considerably structured and migration rates within the Chiricahuas were higher than those in between mountain ranges. On a local scale, our analyses revealed population viscosity through dependent colony foundation and a high genetic diversity with a multicolonial structure. The latter was also evident from recognition trials revealing consistent aggression between non-nestmates. Within-nest matings led to high inbreeding coefficients. Finally, the observed seasonal changes in relatedness can be explained by variation in queen number and differential dispersal of the two reproductive morphs.     

Cuticular hydrocarbons in a termite: phenotypes and a neighbour–stranger effect

Abstract The composition of cuticular hydrocarbons of different colonies of the fungus-growing termite Macrotermes falciger shows considerable intercolonial variation. Ordination, as well as cluster analyses, separate profiles into three distinct chemical phenotypes. Behavioural tests with major workers reveal no alarm behaviour or mortality in pairings of workers from the same colony but a full range from no alarm to overt aggression, with associated death, when individuals were paired from different colonies. The level of mortality increases with differences in the composition of cuticular hydrocarbons between colonies. However, no mortality occurs in pairings of individuals from neighbouring colonies belonging to different phenotypes. The data thus provide evidence for a 'neighbour–stranger' effect (so-called 'dear-enemy' phenomenon) in termites.     

Unicoloniality, recognition and genetic differentiation in a native Formica ant

Some ants have an extraordinary form of social organization, called unicoloniality, whereby individuals mix freely among physically separated nests. This mode of social organization has been primarily studied in introduced and invasive ant species, so that the recognition ability and genetic structure of ants forming unicolonial populations in their native range remain poorly known. We investigated the pattern of aggression and the genetic structure of six unicolonial populations of the ant Formica paralugubris at four hierarchical levels: within nests, among nests within the same population, among nests of populations within the Alps or Jura Mountains and among nests of the two mountain ranges. Ants within populations showed no aggressive behaviour, but recognized nonnestmates as shown by longer antennation bouts. Overall, the level of aggression increased with geographic and genetic distance but was always considerably lower than between species. No distinct behavioural supercolony boundaries were found. Our study provides evidence that unicoloniality can be maintained in noninvasive ants despite significant genetic differentiation and the ability to discriminate between nestmates and nonnestmates.     

Species and Colony Components in the Recognition Odor of Young Social Wasps: Their Expression and Learning (Polistes biglumis and P. atrimandibularis; Hymenoptera: Vespidae)

In Polistes, nestmate recognition relies on the learning of recognition cues from the nest. When wasps recognize nestmates, they match the template learned with the odor of the encountered wasp. The social wasp Polistes biglumis use the homogeneous odor of their colony to recognize nestmates. When these colonies become host colonies of the social parasite P. atrimandibularis, colony odor is no longer homogeneous, as the parasite offspring have an odor that differs from that of their hosts. In trying to understand how the mechanism of nestmate recognition works in parasitized colonies and why parasite offspring are accepted by hosts, we tested the responses of resident Polistes biglumis wasps from parasitized and unparasitized colonies to newly emerged parasites and to nestmate and non-nestmate conspecifics. The experiments indicate that immediately upon eclosion both young parasites and young hosts lack a colony odor and that colony odor can be soon acquired from the accepting colony. In addition, while residents of nonparasitized colonies recognize only the odor of their species, resident hosts of parasitized colonies have learned a template that fits the odors of two species.