Irrational risk aversion in an ant

Abstract

Animals must often decide between exploiting safe options or risky options with a chance for large gains. Both proximate theories based on perceptual mechanisms, and evolutionary ones based on fitness benefits, have been proposed to explain decisions under risk. 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 one scent with 0.55 M sucrose solution and another with an equal chance of either 0.1 or 1.0 M sucrose. Preference was tested in a Y-maze. Ants were extremely risk-averse, with 91% choosing the safe option. Based on the psychophysical Weber–Fechner law, we predicted that ants evaluate resources depending on their logarithmic difference. To test this hypothesis, we designed 4 more experiments by varying the relative differences between the alternatives, making the risky option less, equally or more valuable than the safe one. Our results support the logarithmic origin of risk aversion in ants, and demonstrate that the behaviour of individual foragers can be a very poor predictor of colony-level behaviour.

Bundling and segregation affects “liking”, but not “wanting”, in an insect

“…Examining the results of the aforementioned model, we discovered a possible contrast effect, as depending on the condition, the amount of pheromone deposited for the same treatment changed abruptly. It is indeed crucial to consider how the first experience of ants can have ripple effect on its subsequent decisions (De Agrò et al, 2021). To further examine this effect we remodeled the data including the first experienced treatment as a factor.…”

“…The “liking” vs “wanting” distinction however, especially given the results observed in this experiment, suggests that perception and memory can be segregated process. Most experiments recording both pheromone deposition and subsequent choice use food quality (from high concentration sucrose to distasteful solutions) as the measured unit (De Agrò et al, 2021; Oberhauser and Czaczkes, 2018; Wendt et al, 2019). Logarithmic perception of quality is probably the reason mismatch a mismatch between choice and instantaneous value perception has eluded discovery.…”

“…(2019) demonstrated a faster rise in food acceptance in the lower range of acceptance food qualities than in the higher range. Recently, De Agrò et al (2021) demonstrated that Lasius niger ants have a strong aversion to risky food sources (i.e. with fluctuating quality), which could be fully explained by logarithmic value perception, as predicted by Prospect Theory.…”

Bundling and segregation affect pheromone deposition, but not choice, in an ant

“…Examining the results of the aforementioned model, we discovered a possible contrast effect, as depending on the condition, the amount of pheromone deposited for the same treatment changed abruptly. It is indeed crucial to consider how the first experience of ants can have ripple effect on its subsequent decisions ( De Agrò et al, 2021 ). To further examine this effect we remodelled the data including the first experienced treatment as a factor.…”

“…from 0.5 to 1.5 molar). Recently, De Agrò et al, 2021 , demonstrated that Lasius niger ants have a strong aversion to risky food sources (i.e. with fluctuating quality), which could be fully explained by logarithmic value perception, as predicted by prospect theory.…”