Working with Prof. Patrizia D'Ettorre from the University of Copenhagen, biologist Prof. Giovanni Galizia from the University of Constance has achieved some completely new and fascinating insights into the communication behaviour of ants.
An ant colony can house several million ants and survives only if it is well protected. Predatory foes (non-nest mates) are the greatest danger for the colony. These ants can quickly attack a colony and forage the stores. Therefore, it is vital for ants to be able to discriminate friends (nest mates) from foes (non-nest mates). Scent plays an important role in the ants' ability to discriminate non-nest mates from their colony mates; scent is like a passport that is presented to the guards at the entrance to the colony. The guards make quick work of enemies from other colonies that have a different odour, attacking them en masse. Professor Giovanni Galizia is investigating the mechanisms with which insects recognise olfactory cues and he is also hoping to find out what happens in their brain when information about odour is stored.
Working with Prof. Patrizia D’Ettorre from the University of Copenhagen, Galizia has obtained completely new and fascinating insights into ants and their clever door-opening system. The scientists used carpenter ants (Camponotus herculeanus) for their laboratory studies. The research results have just been published in the renowned journal ‘Proceedings of the Royal Society’ published by the Royal Society.
“People have to carry and present passports when crossing national boundaries. And it is more or less the same case with ants. Ants must have a particular odour in order to enter their own colony,” said Galizia summarizing his findings. Olfactory cues are vital factors in the complex communication system of ants. Ants perceive olfactory cues with their antennae. A complicated gland system produces a broad range of odours. The importance of olfactory cues in the communication system of ants has been an important research topic for many years. But how exactly does the ants’ odour-based communication system work?
“When we started our experiments there were a number of different ways in which the communication system could have been explained,” said the biologist. One option focused on the similarity of odours. Galizia explains what this means: “The guard ant checks how similar or dissimilar the odour of the ant seeking to enter its hive is to its own.” Another possibility the researchers checked was whether the overall odour of an ant had characteristic cues to which the ants would respond. This might for example be the wax on the ants’ body surface. The third option was that ants actually actively recognise their enemies bearing odour cues that are novel to their own odour profile, but do not specifically recognise their own nest mates.
The experiments carried out by Galizia and his team of researchers show that option three is the correct one. Ants only recognise their non-nest mates, but not their nest mates. This means that their friends do not need a passport, only their foes! “We have been able to show this by removing individual substances from the ants’ body odour and adding others. We found that the presence of an additional component is necessary for the ants to be able to recognise another ant as a non-nest mate,” said the biologist explaining the complicated mechanism. If one component is missing, then the ants react aggressively.
The experiments have also shown that the discrimination of friends and foes depends very much on the individual substances in the odour cocktail. Not all substances tested produced a result. It appears that the odour cocktail is precisely defined and does not tolerate even the smallest variations. The ants react specifically to certain substances, and do not react at all to others. “The ants have a pre-conditioned system of odours that is used to recognise non-nest mates. We were able to substantiate this with substance tests in the laboratory,” said Galizia.
The particular odour of the ants develops for the most part through the food they consume. But this process happens very slowly. The consumption of food has an important function in the development of a single odour that is common to an ant colony. “The ants that consume the same type of food, will all develop the same odour. The mutual exchange of food even promotes the shared odour,” said Galizia explaining the relationship between social behaviour, odour and communication.
The scientists tested three substances: one long unbranched, one mono-methylated and one dimethylated hydrocarbon (alkane). Only the dimethylated alkane was effective in eliciting aggression. “These substances potentially give the ants a greater variety of own odour signatures,” said Galizia. In order to exclude the possibility that the ants’ movements or other optical factors affected the discrimination between friend and foe, the scientists presented the ants of a particular experimental series with synthetic hydrocarbons and tested whether they became aggressive or whether they remained completely relaxed.
Galizia and D’Ettorre’s research on the role of odours in the recognition of friend and foes among ants has provided the researchers with basic information on their communication behaviour. “This is both a big and a tiny step. Many more experiments have to be carried out before we will be able to gain a comprehensive understanding of the communication of these fascinating animals,” summarised Galizia.
"Ants recognize foes and not friends"
Fernando J. Guerrieri, Volker Nehring, Charlotte G. Jørgensen, John Nielsen, C. Giovanni Galizia, and Patrizia d'Ettorre
Proc R Soc B published 1 April 2009, 10.1098/rspb.2008.1860