Collective movement increases initial accuracy and path efficiency in talitrid amphipod orientation

Talitrid amphipods are an extensively studied system for navigation due to their robust ability to navigate back to the optimal burrowing zone after foraging and could be a model system in which to study the impacts of collective behaviour on short-distance navigation and orientation. We investigated whether talitrid amphipods (Megalorchestia pugettensis) differ in their orientation abilities when released individually versus in a group. When released individually, the amphipods took longer to start moving (p < 0.001), travelled longer paths (p = 0.003), moved faster (p = 0.016), had a different initial bearing (p = 0.003) and exhibited more spread in their initial bearing (p = 0.009) than when released in groups. There was no difference between individuals and groups in terms of their trial time nor in the direction or spread of their final orientation. This study introduces a tractable, invertebrate species in which to study the impacts of collective movement and reveals previously unexamined differences in orientation abilities for talitrid amphipods released independently versus in a group that have implications for experimental design in this system.