The aggression test as a taxonomic tool: Evaluation in sympatric and allopatric populations of wood-ant species

Ant-workers of Formica lugubris and F. rufa from colonies living sympatrically (from the same area) and allopatrically (from different areas) were tested in pairs using a laboratory aggression test. The aim was to verify whether sharing the same area of origin influences the relationships among heteroeolonials between and within these species which belong to the F. rufa group. The results suggest that a similar degree of agonistic behaviour (ritualised aggression) was shown in sympatric and allopatric conspecific dyads of both species studied. The interactions between F. lugubris and F. rufa were characterised by a low level of overt aggression both in sympatric and allopatric pairs, confirming the interspecific tolerance observed in our previous studies on these wood-ant species. This reduced aggressiveness between workers of F. lugubris and F. rufa coming from the same or a different area can be interpreted on the basis of their sharing common signals, such as odours and patterns of behaviour. Therefore, their mutual tolerance and acceptance can be indicative of a phylogenetic closeness between such species. We propose that an aggression test can be a valid tool for elucidating systematic problems in this taxonomically difficult group of ants. © 1993 Wiley-Liss, Inc.     

The aggression test as a possible taxonomic tool in the Formica rufa group

The intra- and interspecific aggressive behavior of Formica polyctena, a species of the Formica rufa group, was analyzed and quantified both in the laboratory and in the field. This behavior was used as a potential taxonomic tool for gaining a better understanding of the phyletic relationships among the species within the group. No overt aggression was recorded toward members of the same species. To examine interspecific relationships, F. polyctena was first confronted with F. cunicularia, to ascertain its aggressiveness toward a distantly related species. All such encounters led immediately to overt and prolonged attacks with virtually no initial mutual inspection. This suggests that recognition of strangeness of the unrelated species is almost immediate in F. polyctena, as previously observed in F. lugubris and F. rufa toward the same antagonist. Subsequently, F. polyctena was contrasted with F. lugubris and F. rufa (also belonging to the F. rufa group) in order to compare these related species. Fierce attacks accompanied by all the elements of conflict behavior were observed in all encounters. Moreover, the degree of aggression in the field was higher than in laboratory-paired ants, possibly because of a territorial effect. These data and our previous and similar research indicate that the relationships between F. lugubris and F. rufa are closer than between these two species and F. polyctena. In considering different viewpoints on this problem, the validity of the aggression test is discussed and the opportunity to compare levels of aggressiveness among strictly sympatric samples of red wood ant species gathered from the same ecological environment are considered.     

Laboratory and field observations of attack by the red wood ant Formica lugubris Zett. On Formica cunicularia Latr. (Hymenoptera: Formicidae)

Attack by red wood ants (Formica lugubris Zett.) on an “alien” species (Formica cunicularia Latr.) was analyzed both in the laboratory and in the field. Elements of such attack were recorded. Attack and conflict were observed in each encounter and follow immediately after the first contact. This overt attack was vigorous and generally led to the death of the alien. Laboratory data were confirmed by field observations, although under these conditions aggressiveness of F lugubris appeared increased possibly because of the animal's familiarity with its surroundings.     

Individual and collective problem-solving in a foraging context in the leaf-cutting ant Atta colombica

In this paper we investigate the flexibility of foraging behavior in the leaf-cutting ant Atta colombica, both at the individual and collective levels, following a change in the physical properties of their environment. We studied in laboratory conditions the changes occurring in foraging behavior when a height constraint was placed 1 cm above part of the trail linking the nest to the foraging area. We found that the size and shape of the fragments of foraging material brought back to the nest were significantly modified when the constraint was placed on the trail: independent of their size, forager ants cut smaller and rounder fragments in the presence of a height constraint than in its absence. This size adjustment does not require any direct sensory feedback because it occurred when the ants cut fragments in the foraging area; no further cutting was done when they encountered the constraint. This points to the existence of a template that ants store and use as a reference to adjust their reach while cutting. Remarkably, despite the decrease in the foraging material brought to the nest per capita the colony was still able to improve its foraging performance by doubling the number of transporters. This study illustrates the flexibility of foraging behavior exhibited by an ant colony. It provides a rare example of insects finding an intelligent solution to a problem occurring in a foraging context, at both the individual and collective levels.     

Aggression in wood ants (Formica polyctena Foerst., Hymenoptera,Formicidae)

The relationship between aggression and predation was surveyed in Red wood ants, in the field as well as under laboratory conditions. Aggression between wood ant nests is highest in early spring, and many wood ant wars break out then. The end of these wars coincides with a strong increase in prey density. Since the casualties are taken as food to the warring nests, a hypothesis is formulated that warfare between wood ant nests only occurs in periods when prey demand exceeds the supply. Protein-rich food in early spring is mainly for the benefit of the queens and the sexual larvae. Although the most obvious function of warfare is the defence of a foraging area, the main function may be the advancement of the mating flight dates of the queens in order to make the chance of propagating their genes greatest.