The interplay between maze complexity, colony size, learning and memory in ants while solving a maze: A test at the colony level

Abstract

Central-place foragers need to explore their immediate habitat in order to reach food. We let colonies of the individually foraging desert ant Cataglyphis niger search for a food reward in a maze. We did so for three tests per day over two successive days and an additional test after a time interval of 4-20 days (seven tests in total). We examined whether the colonies reached the food reward faster, consumed more food and changed the number of workers searching over time, within and between days. Colonies' food-discovery time shortened within and between days, indicating that some workers learnt and became more efficient in moving through the maze. Such workers, however, also forgot and deteriorated in their food-discovery time, leveling off back to initial performance after about two weeks. We used mazes of increasing complexity levels, differing in the potential number of wrong turns. The number of workers searching increased with colony size. Food-discovery time also increased with colony size in complex mazes but not in simple ones, perhaps due to the more frequent interactions among workers in large colonies having to move through narrow routes. Finally, the motivation to solve the maze was probably not only the food reward, because food consumption did not change over time.

Fig 1

Illustration of a nest and a maze of complexity levels (a) 0, (b) 1, (c) 2 and (d) 3. Each circle represents a passage and a decision to make (light gray ones are correct decision, leading to the food reward, and dark grey ones are wrong decisions). The larger circle on the right upper (a, c) side or right lower side (b, d) represents the food reward (honey). The correct number of decisions, including the decision to enter the maze are 1, 2, 3, and 4 for complexity levels 0 to 3, respectively. The total number of decisions are 1, 3, 7, and 15 for the same complexity levels. Mazes included either right or left turns as the correct ones, which were randomly applied per colony.

Fig 2

(a) The interaction between colony size and maze complexity in their effect on food-discovery time on the first test; (b) the decrease in food-discovery time with successive tests performed on the same day. Letters denote significant differences according to a post-hoc comparison.

Fig 3

(a) The decrease in food-discovery time between the first tests on two successive days; (b) the positive correlation between colony size and the number of workers searching (mean values for the first tests on the two successive days are presented). The asterisk indicates a significant difference.

Fig 4. The effect of the time interval (in days, horizontal axis) between tests on the difference between food-discovery time before and after this interval (Δ discovery time, vertical axis).

Values above zero indicate that colonies reached the food reward faster after the time interval than before it, while values below zero indicate that colonies reached the food reward faster before the time interval. As intervals become large, food-discovery time returns to the basic initial levels (around zero), which takes place according to this model after ~16 days.