Biology subjects

Czaczkes, T. J.

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

24 records · Page 2Linked to original sources

bioRxiv2019

Labelling effect in insects: cue associations influence perceived food value in ants

Humans usually assess things not in terms of absolute value, but relative to reference points. The framing of alternatives can strongly affect human decision-making, leading to different choices depending on the context within which options are presented. Similar reference-point effects have been recently reported in ants, in which foragers show a contrast effect: ants overvalue a medium-quality food source if they were expecting a poor one, and vice versa for expectations of good food. However, studies of human consumer psychology have demonstrated that expectations, for example from product labels, can drive value perception in the other direction via assimilation. For example, an expensive bottle of wine is perceived as more enjoyable compared to a cheaper bottle, even if the wine is the same. In this study, we demonstrate a similar labelling-association effect in an insect: ants showed assimilation effects by spending twice as long drinking at a medium quality food source if it was scented with an odour previously associated with high quality than if it was scented with a poor-quality label. The presence of odour cues in the food during consumption and evaluation is critical, as without them, odour-driven expectations of quality result in contrast, not assimilation effects. The addition of a quality label in the food thus reverses contrast effects and causes value to be aligned with expectations, rather than being contrasted against them. As value judgement is a key element in decision-making, relative value perception strongly influences which option is chosen, and ultimately how choices are made.

animal behavior and cognition↗

bioRxiv2019

Irrational risk aversion in ants is driven by perceptual mechanisms

Animals must often decide between exploiting safe options or risky options with a chance for large gains. While traditional optimal foraging theories assume rational energy maximisation, they fail to fully describe animal behaviour. A logarithmic rather than linear perception of stimuli may shape preference, causing animals to make suboptimal choices. Budget-based rules have also been used to explain risk-preference, and the relative importance of these theories is debated. Eusocial insects represent a special case of risk sensitivity, as they must often make collective decisions based on resource evaluations from many individuals. Previously, colonies of the ant Lasius niger were found to be risk-neutral, but the risk preference of individual foragers was unknown. Here, we tested individual L. niger in a risk sensitivity paradigm. Ants were trained to associate a scent with 0.55M sucrose solution and another scent with an equal chance of either 0.1 and 1.0M sucrose. Preference was tested in a Y-maze. Ants were extremely risk averse, with 91% choosing the safe option. Even when the risky option offered on average more sucrose (0.8M) than the fixed option, 75% preferred the latter. Based on the psychophysical Weber-Fechner law, we predicted that logarithmically balanced alternatives (0.3M vs 0.1M/0.9M) would be perceived as having equal value. Our prediction was supported, with ants having no preference for either feeder (53% chose the fixed option). Our results thus strongly support perceptual mechanisms driving risk-aversion in ants, and demonstrate that the behaviour of individual foragers can be a very poor predictor of colony-level behaviour.

animal behavior and cognition↗

bioRxiv2018

Copy when uncertain: Lower light levels result in higher trail pheromone deposition and stronger reliance on pheromone trails in the ant Lasius niger

Animals may gather information from multiple sources, and these information sources may conflict. Theory predicts that, all else being equal, reliance on a particular information source will depend on its information content relative to other sources. Information conflicts are a good area in which to test such predictions. Social insects, such as ants, make extensive use of both private information (e.g. visual route memories) and social information (e.g. pheromone trails) when attempting to locate a food source. Importantly, eusocial insects collaborate on food retrieval, so both information use and information provision may be expected to vary with the information content of alternative information sources. Many ants, such as Lasius niger, are active both day and night. Variation in light levels represents an ecologically important change in the information content of visually-acquired route information. Here, we examine information use and information provision under high light levels (3200 lux), moderate light levels simulating dusk (10 lux) and darkness (0.007 lux). Ants fail to learn the location of a food source in darkness. As light levels decrease, ants show decreasing reliance on private visual information, and increasing pheromone trail following, consistent with a copy when uncertain strategy. In moderate light levels and darkness, pheromone deposition increases, presumably to compensate for the low information content of visual information. Varying light levels for cathemeral animals provides a powerful and ecologically meaningful method for examining information use and provision under varying levels of information content.

animal behavior and cognition↗

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↗