Miniaturisation decreases visual navigational competence in ants.

Evolution of a smaller body size in a given lineage, called miniaturisation, is commonly observed in many animals including ants. It affects various morphological features and is hypothesised to result in inferior behavioural capabilities, possibly owing to smaller sensory organs. To test this hypothesis, we studied whether reduced spatial resolution of compound eyes influences obstacle detection or obstacle avoidance in five different species of ants. We trained all ant species to travel to a sugar feeder. During their return journeys, we placed an obstacle close to the nest entrance. We found that ants with higher spatial resolution exited the corridor - the area between the two ends of the obstacle - on average 10 cm earlier, suggesting they detected the obstacle earlier in their path. Ants with the lowest spatial resolution changed their viewing directions only when they were close to the obstacle. We discuss the effects of miniaturisation on visual navigational competence in ants.