Recruiter or recruit: who boosts the recruitment in starved nests in mass foraging ants?

In social insects, each behavioural group holds information that may be crucial for the colony's functioning and regulation. We investigated which behavioural group plays the key role in the regulation of recruitment and how it manages to tune the foraging effort according to the level of starvation in the colony. We focused on recruiters and recruits: Recruiters hold information concerning the characteristics of the food source whereas domestics and potential recruits may be better informed about the colony's needs because of the constant contact that they have with their recruits and/or larvae. We imposed different starvation levels on nest-workers and recruiters and observed their interactions. The level of starvation did not alter the behaviour of the recruiters. However, we observed a change in the recruits' response to the recruiter's signal if the starvation level increased. This induced more recruits and thus more workers foraging in starved colonies. In nonstarved colonies, recruits did not respond to the recruitment signal and no recruitment occurred. Our results suggest that the recruits' response is the major key to the regulation of the recruitment process. This study has deciphered how individuals assess the colony's needs and integrate all the information to build up an optimal food exploitation strategy adjusted to starvation. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.