The evolutionary origin of group recruitment in acorn ants.

The communication systems used by different species vary greatly in their complexity. Understanding the traits that promote evolutionary transitions to more sophisticated communication systems, such as human language, is a major research goal of evolutionary biology. Acorn ants (genera Temnothorax and Leptothorax), which utilize a communication method known as tandem running, are uniquely valuable as a model clade for studying the evolution of animal communication. Tandem running involves a leader ant directing a follower ant to either a food source or a potential nest site. This communication system relies on bidirectional feedback between leaders and followers, is mediated through physical contact, and can vary in complexity as followers can occasionally form groups of several interacting individuals that pursue the leader. In the current study, we observed recruitment behavior across 31 different acorn ant species and obtained high resolution trajectory data from tandem run participants. Using this trajectory data, we quantified information flow between leaders and followers and assessed the interaction patterns within tandem groups. We show that acorn ant species exhibit interspecific differences in their tandem running traits, and we assess if species that exhibit more complex tandem interaction rules exhibit faster rates of evolution in their communication traits.