When faced with multiple competing goals, individuals must decide which goal to attend to. Voluntary task switching is an important paradigm for testing cognitive flexibility and spontaneous decision-making when competing tasks are present. Of particular importance is the study of how reward affects task switching, as reward is perhaps the most commonly used tool for shaping both human and animal behavior. Recently, Fröber and Dreisbach (2016) demonstrated that it is not reward level per se, but reward change, which most strongly affects switching behavior in humans: Task switching was lowest when reward remained high and highest when reward is changed (increase or decrease), while the repetition of low reward showed intermediate switching levels. Here we replicate their experiment on individual foragers of the ant species Lasius niger. Using an adapted spontaneous alternation task, we find that ants' switching response in light of their immediate reward history is qualitatively identical to that of humans. In a second experiment, we show that some of this behavior can be explained by the cue change, rather than the rewards. However, patterns exist in the data which cue change cannot explain. The striking parallel in behavior between humans and insects raises questions about how reward shapes behavioral flexibility and stability in humans. (PsycINFO Database Record

We humans sort the world around us into conceptual groups, such as ‘the same' or ‘different', which facilitates many cognitive tasks. Applying such abstract concepts can improve problem-solving success and is therefore worth the cognitive investment. In this study, we investigated whether ants ( Lasius niger ) can learn the relational rule of ‘the same' or ‘different' by training them in an odour match-to-sample test over 48 visits. While ants in the ‘different' treatment improved significantly over time, reaching around 65% correct decisions, ants in the ‘same' treatment did not. Ants did not seem able to learn such abstract relational concepts, but instead created their own individual strategy to try to solve the problem: some ants decided to ‘always go left', others preferred a ‘go to the more salient cue' heuristic which systematically biased their decisions. These heuristics even occasionally lowered the success rate in the experiment below chance, indicating that following any rule may be more desirable then making truly random decisions. As the finding that ants resort to heuristics when facing hard-to-solve decisions was discovered post-hoc , we strongly encourage other researchers to ask whether employing heuristics in the face of challenging tasks is a widespread phenomenon in insects.

Social insects frequently make important collective decisions, such as selecting the best food sources. Many collective decisions are achieved via communication, for example by differential recruitment depending on resource quality. However, even species without recruitment can respond to a changing environment on collective level by tracking food source quality.We hypothesised that an apparent collective decision to focus on the highest quality food source can be explained by differential learning of food qualities. Ants may learn the location of higher quality food faster, with most ants finally congregating at the best food source.To test the effect of reward quality and motivation on learning in Lasius niger, we trained individual ants to find a reward of various sucrose molarities on one arm of a T-maze in spring and in autumn after one or four days of starvation.As hypothesised, ants learned fastest in spring and lowest in autumn, with reduced starvation leading to slower learning. Surprisingly, the effect of food quality and motivation on the learning speed of individuals which persisted in visiting the feeders was small. However, persistence rates varied dramatically: All ants in spring made all (6) return visits to all food qualities, in contrast to 33% of ants in autumn under low starvation.Fitting the empirical findings into an agent-based model revealed that even a tendency of ants to memorise routes to high quality food sources faster can result in ecologically sensible colony-level behaviour. Low motivation colonies are also choosier, due to increasing sensitivity to food quality.

9Social insects frequently make important collective decisions, such as selecting the best food 10 sources. Many collective decisions are achieved via communication, for example by 11 differential recruitment depending on resource quality. However, even species without 12 recruitment can respond to a changing environment on collective level by tracking food 13 source quality. 14 We hypothesised that an apparent collective decision to focus on the highest quality food 15 source can be explained by differential learning of food qualities. Ants may learn the location 16 of higher quality food faster, with most ants finally congregating at the best food source. 17To test the effect of reward quality and motivation on learning in Lasius niger, we trained 18 individual ants to find a reward of various sucrose molarities on one arm of a T-maze in 19 spring and in autumn after one or four days of starvation. 20As hypothesised, ants learned fastest in spring and lowest in autumn, with reduced starvation 21 leading to slower learning. Surprisingly, the effect of food quality and motivation on the 22 learning speed of individuals which persisted in visiting the feeders was small. However, 23 persistence rates varied dramatically: All ants in spring made all (6) return visits to all food 24 qualities, in contrast to 33% of ants in autumn under low starvation. 25Fitting the empirical findings into an agent-based model revealed that even a tendency of ants 26 to memorise routes to high quality food sources faster can result in ecologically sensible 27 colony-level behaviour. Low motivation colonies are also choosier, due to increasing 28 sensitivity to food quality. 29 30 Key words 31Lasius niger, differential learning, route memory, agent-based modelling, collective decision 32 making, annealing 33 Significance statement 34Collective decisions of insects are often achieved via communication and/or other interactions 35 between individuals. However, animals can also make collective decisions in the absence of 36 communication. 37We show that foraging motivation and food quality can affect both route memory and the 38 likelihood to return to the food source and thus mediate selective food exploitation. An agent-39 based model, implemented with our empirical findings, demonstrates that, at the collective 40 level, even small differences in learning lead to ecologically sensible behaviour: mildly 41 starved colonies are selective for high quality food while highly starved colonies exploit all 42 food sources equally. 43We therefore suggest that non-interactive factors such as individual learning and the foraging 44 motivation of a colony can mediate or even drive group level behaviour. Instead of accounting 45 collective behaviour exclusively to social interactions, possible contributing individual 46 processes should also be considered.

Tropical ants experience intense intra- and interspecific competition for food sources, which influences their activity pattern and foraging strategies. Even though different ant species can coexist through spatial and temporal niche partitioning, direct competition for food cannot be avoided. Recruitment communication is assumed to help colonies to monopolize and exploit food sources successfully, but this has rarely been tested under field conditions. We studied if recruitment communication helps colonies of the Neotropical ant Pachycondyla harpax to be more successful in a highly competitive tropical environment. Additionally, we explored if temporal and spatial niche differentiation helps focal colonies to avoid competition. Pachycondyla harpax competed with dozens of ant species for food. Mass-recruiting competitors were often successful in displacing P. harpax from food baits. However, when foragers of P. harpax were able to recruit nestmates they had a 4-times higher probability to keep access to the food baits. Colonies were unlikely to be displaced during our observations after a few ants arrived at the food source. Competition was more intense after sunset, but a disproportionate increase in activity after sunset allowed focal colonies to exploit food sources more successfully after sunset. Our results support the hypothesis that recruitment communication helps colonies to monopolize food sources by helping them to establish a critical mass of nestmates at large resources. This indicates that even species with a small colony size and a slow recruitment method, such as tandem running, benefit from recruitment communication in a competitive environment.