Below-ground ants follow pheromones more quickly under dark conditions, but pheromones do not affect decision accuracy nor aggression

Communication allows organisms to quickly convey information vital for survival or fitness. Chemical communication and speed-accuracy trade-offs are ubiquitous in animal decision making. Most studies have used species which forage mainly above-ground species, tested in an epigean setting, but it remains unclear whether below-ground species behave similarly. Here, we use the below-ground ant Tetramorium alpestre to assess the efficacy of above- vs. below-ground mazes, the accuracy of decisions when using natural vs. artificial pheromones, the presence of a speed-accuracy trade-off, and the pheromones effect on aggression. Ants decided more quickly under below-ground than above-ground conditions, indicating they may be distracted by above-ground stimuli. Ants followed both natural and artificial trails but in direct competition preferred artificial trails, likely due to a higher pheromone concentration. Surprisingly, no speed-accuracy trade off was observed during path decision-making. Lastly, population origin but not pheromones affected if and how aggression occurred in presence of trail and home-range marking pheromones. We argue that the design of behavioural tests should match the lifestyle of the focal organism. We further speculate that speed-accuracy trade-offs likely are highly species- and context-specific and other factors besides chemicals seem important to trigger aggression, at least in this species.