Spatial organization in a dimorphic ant: caste specificity of clustering patterns and area marking

Living in groups constitutes the root of social organization in animals. Likewise, the spatial aggregation between members of insects societies plays a crucial role in social cohesion and division of labor, namely, in polymorphic ant species. In the present paper, we show caste-specific aggregation patterns in the strictly dimorphic Pheidole pallidula ant species. We investigate the influence on the clustering of ants exerted by direct contacts between nest mates as well as by indirect cues through chemical marking. In a homogeneous environment deprived of chemical cues, majors show a higher aggregation level than minors and a centripetal behavior. By contrast, minors are more scattered in the experimental arena and display a centrifugal behavior. In addition, area marking laid by minors enhances their own aggregative behavior while contributing to the localization of the spontaneously aggregating majors. Such differences in aggregative patterns as well as their adaptive value have to be coupled with the mobility level and the task performance efficiency of each worker caste. Contrary to majors that are likely to aggregate, highly mobile minors, scattered inside and outside the nest colony, can detect colony needs and can carry out most of the daily tasks for which they are more efficient than majors.