Professor Mizuki Tsuji of the University of the Ryukyus and his team, in collaboration with Chiba University and others, have elucidated the mechanism by which ants perceive the size of their colony. The research team also includes Kyoto Institute of Technology, Toyama University, the University of Reading in the UK, Shimadzu Corporation, and Tohoku Gakuin University.
Ants and termites live underground in pitch black, but they seem to be aware of the size of their colony (the number of nestmates). However, the mechanism by which they do this was largely unknown. The research team conducted an experiment on the giant ant, a species of ant that lives in Okinawa, whose ecology is well known.
All worker ants are female and capable of laying eggs, but egg-laying behavior is usually suppressed by the action of the queen pheromone secreted by the queen. In this species, the queen periodically walks around the nest, making contact with worker ants and transmitting the queen pheromone, a "patrol behavior." The larger the colony, the more time the queen spends patrolling, but the smaller the colony, the less time she spends on patrolling. This study focused on the queen's reaction.
When queen pheromone transmission is cut off, worker ants develop ovaries. In this experiment, it was found that queens can identify worker ants with developed ovaries, and increase their patrols when they encounter such workers. Furthermore, it was found for the first time that the queen pheromone of this species is a non-volatile cuticular hydrocarbon. When the queen encounters worker ants that have entered the "physiological state for laying eggs," she increases her patrol time, which leads to her perception of the colony size.
The research team has now presented the world's first convincing evidence of a mechanism by which social insects indirectly "perceive" colony size. However, it is unclear whether this mechanism is common among social insects, and future comparative studies using other species are needed.
Paper information:[Biology Letters] Testing the negative feedback hypothesis of colony-size sensing in social insects
