There is nothing like experience, even for ants

(NC&T/CNRS) This is what the researchers of the Laboratoire d'éthologie expérimentale et comparée (CNRS/Université Paris 13) have shown.

Experience plays a major part in the development of individual behavior. Everyone agrees with this as far as humans are concerned, but the same is not true of animals. Up to now, many specialists thought that the role of experience was more important for those animal species considered to be closer to humans, that is, with a complex brain. But what about social insects? This is what the researchers of the Laboratoire d'éthologie expérimentale et comparée wanted to investigate by considering the case of ants.

In ants, four factors usually determine the division of labor for individuals in the colony. First of all there is genetics: workers from different parents are not equivalent from this point of view. Depending on their genetic lineage, some workers are more predisposed to perform a certain task. Then there is morphology: for example, small workers will look after the young, whereas the much bigger soldiers will defend the colony. Age is also a determining factor: in general, the young stay in the nest, doing maintenance and nursery jobs, while the older ants go out foraging or fighting. Lastly, there are dominant relationships, because in some species, workers fight for the right to reproduce. In that case the dominant ants stay in the nest to lay eggs and the dominated ones have to stick to foraging.

In order to study the role of individual experience acquired by each individual in the division of labor, those four known factors had to be ruled out. The researchers found the ideal species for this: Cerapachys biroi. This is an ant that comes from the Ryukyus, in Japan, and from Taiwan. It reproduces by parthenogenesis, that is, asexually. The individuals are all clones of each other, which eliminates the genetic variable and morphology as factors of division of labor. Moreover, with no queen and no hierarchy, dominance is not an issue. Lastly, the ants have a two-phase reproductive cycle, synchronized on the development of the brood (a term covering the eggs, larvae and pupae). During the first phase, known as the foraging phase, the ants look for food for the larvae. When the larvae mature, they change into pupae, which signals the start of the second phase, known as the stationary phase. During this period, the workers assemble inside the nest to lay eggs. On the day that the eggs hatch into larvae, and the pupae "emerge", the foraging phase begins again. So it is easy to make up groups of individuals of the same age, which eliminated the last known factor of division of labor. The researchers reconstituted groups of young individuals of the same age, size and genotype in the laboratory.

The researchers studied the effects of experience on ant specialization by marking them with paint to distinguish individuals. During one whole foraging phase, when the workers left the nest, the ethologists put half the individuals (always the marked ones) in an area with their prey, and the other half were placed in an area with no prey. During the next foraging phase, a month later, the first half of the group had become specialized in looking for food. On the other hand, the ants which had had no success in looking for food had turned to raising young inside the nest. Conclusion: in this case, experience alone orientates an individual to a particular social task.

These ants from the Ryukyus (Japan (Photo: © F. Ravary – CNRS 2007)
People had suspected it was true for a long time, and today it is proven: individual history plays a role in organizing insect societies. Life experience appears to be a fundamental variable of behavioral development.

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