Ants resort to heuristics when facing relational-learning tasks they cannot solve.

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.

Private information conflict: Lasius niger ants prefer olfactory cues to route memory.

Foraging animals use a variety of information sources to navigate, such as memorised views or odours associated with a goal. Animals frequently use different information sources concurrently, to increase navigation accuracy or reliability. While much research has focussed on conflicts between individually learned (private) information and social information, conflicts between private information sources have been less broadly studied. Here, we investigate such a conflict by pitting route memory against associative odour cue learning in the ant Lasius niger. Ants were alternatingly trained to find a high-quality scented food source on one arm of a Y-maze, and a differently scented low-quality food source on the opposite arm. After training, ants were presented with a Y-maze in which the high- and low-quality-associated scents were presented on opposite arms than during training. The ants showed an extremely strong preferential reliance on the odour cues, with 100% of ants following the high-quality odour and thus moving towards the side associated with low-quality food. Further experiments demonstrated that ants also learn odour associations more rapidly, requiring only one visit to each odour-quality combination to form a reliable association. Side associations in the absence of odours, by contrast, required at least two visits to each side for reliable learning. While much attention has been focussed on visual route learning in insect navigation and decision-making, our results highlight the overwhelming importance of odour cues in insect path choice.

Tasting the unexpected: disconfirmation of expectations leads to lower perceived food value in an invertebrate.

To make sensible decisions, both humans and other animals must compare the available options against a reference point-either other options or previous experience. Options of higher quality than the reference are considered good value. However, many perceptible attributes of options are value-neutral, such as flower scent. Nonetheless, such value-neutral differences may be part of an expectation. Can a mismatch between the expectation and experience of value-neutral attributes affect perceived value? Consumer psychology theory and results suggest it can. To test this in a non-human animal, we manipulated a value-neutral aspect of a food source-its taste-while keeping its absolute value-its sweetness-the same. Individual ants (Lasius niger) were allowed to drink either lemon- or rosemary-flavoured 1 M sucrose. After three successive visits to the food, we switched the taste in the last, fourth, visit to induce a disconfirmation of expectations. In control trials, ants received the same taste on all four visits. Disconfirmed ants showed lower food acceptance and laid less pheromone on the way back to the nest, even though the molarity of the food was unchanged. As ants recruit nest-mates via pheromone depositions, fewer depositions indicate that the ants valued the food less. Thus, an expectation of value-neutral attributes can influence the perceived value of a resource. Such influences of value-neutral variables on value perception may affect how animals interact with and exploit their environment, and may contribute to phenomena such as flower constancy.