Biology subjects

Czaczkes, T. J.

Publications and source records attributed to Czaczkes, T. J..

3 recordsLinked to original sources

bioRxiv2018

Relative value perception in an insect: positive and negative incentive contrasts in ants

Humans tend to value things not on their absolute values, but relative to reference points such as former experience or expectations. People rate the quality of a new salary relative to their previous salary and the salaries of their peers, instead of appreciating its absolute value. Here, we demonstrate a similar effect in an insect: ants, which had previously experienced a low quality food source, showed higher acceptance of medium quality food (e.g. 0.1M then 0.5M; positive contrast) than if they had received the medium food all along (e.g. 0.5M then 0.5M; control), and vice versa for high expectations. Further experiments demonstrate that these contrast effects arise from cognitive rather than mere sensory or pre-cognitive perceptual causes. Pheromone deposition also correlates with perceived reward value, and ants showed successive contrasts in their pheromone deposition. Relative value perception can therefore be expected to have strong effects not only on individual behaviour, but also on collective decision-making. Contrast effects were also social: the quality of food received from other ants affected the perceived value of food found later. Value judgement is a key element in decision making, and thus relative value perception will strongly influence how animals interact with their environment.

animal behavior and cognition↗

bioRxiv2018

Small differences in learning speed for different food qualities can drive efficient collective foraging in ant colonies

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.\n\nWe 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.\n\nTo 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.\n\nAs 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.\n\nFitting 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.\n\nSignificance statementCollective decisions of insects are often achieved via communication and/or other interactions between individuals. However, animals can also make collective decisions in the absence of communication.\n\nWe show that foraging motivation and food quality can affect both route memory and the likelihood to return to the food source and thus mediate selective food exploitation. An agent-based model, implemented with our empirical findings, demonstrates that, at the collective level, even small differences in learning lead to ecologically sensible behaviour: mildly starved colonies are selective for high quality food while highly starved colonies exploit all food sources equally.\n\nWe therefore suggest that non-interactive factors such as individual learning and the foraging motivation of a colony can mediate or even drive group level behaviour. Instead of accounting collective behaviour exclusively to social interactions, possible contributing individual processes should also be considered.

animal behavior and cognition↗

bioRxiv2018

Information synergy: adding unambiguous quality information rescues social information use in ants

Animals have access to many alternative information sources when making decisions, such as private information (e.g. memory) and social information. Social insects make extensive use of social information. However, when intentional social information (e.g. pheromone trails in ants) conflicts with private information (e.g. route memories), insects often follow their private information. Why is this? We propose that an asymmetry in the type of information provided by these two information sources drives the neglect of social information: In ants, workers with certain information about the quality of a food source (memory) ignore valuable social information (pheromone trails) because the pheromone trails encode only a very ambiguous measure of food quality. This leads to a testable hypothesis: the addition of unambiguous quality information should rescue social information following. To test this, we trained ants to a poor quality (0.25M sucrose) food source, and then provided an alternative path along with either 1) no information, 2) a pheromone trail, 3) a 0.2l 1.5M sucrose droplet, providing unambiguous quality information, or 4) both a trail and a droplet. When either no or only one information source was provided (1-3), most ants (60-75%) continued following their own memory. However, the addition of unambiguous quality information (4) rescued trail following: when both a trail and a droplet were provided, 75% of ants followed the trail. In further experiments, we show that quality information gleaned from direct contact with fed nestmates produced similar effects. Using florescence microscopy, we demonstrate that food (and information) flows from fed workers to outgoing foragers, explaining the frequent contacts on trails. We propose that the type of information an information source can convey, and its ambiguity, is a strong driver of which source of information is attended to.

animal behavior and cognition↗