Trail Pheromone Does Not Modulate Subjective Reward Evaluation in Lasius niger Ants

Abstract

Comparing the value of options is at the heart of economic decision-making. While an option may have an absolute quality (e.g. a food source has a fixed energy content), the perceived value of the option may be malleable. The factors affecting the perceived value of an option may thus strongly influence which option is ultimately chosen. Expectations have been shown to be a strong driver of perceived value in both humans and social insects, causing an undervaluation of a given option if a better option was expected, and an overvaluation if a poorer one was expected. In humans, perceived value can be strongly affected by social information. Value perception in some insects has also been shown to be affected by social information, showing conformism as in humans and other animals. Here, over a series of experiments, we tested whether pheromone trail presence, a social information source, influenced the perceived value of a food source in the ant Lasius niger. We found that the presence of pheromone trails leading to a sucrose solution does not influence food acceptance, pheromone deposition when returning from a food source, drinking time, or frequency of U-turns on return from the food. Two further assays for measuring changes in food acceptance, designed to increase sensitivity by avoiding ceiling effects, also showed no effect of pheromone presence on food acceptance. In a separate study, L. niger have also been found to show no preference for, or avoidance of, odors associated with foods found in the presence of pheromone. We are thus confident that trail pheromone presence does not affect the perceived value of a food source in these ants.

Trail-pheromone modulates subjective reward evaluation in Argentine ants

“…In a study conducted in parallel to our work (Oberhauser et al, 2020), the presence of pheromone trails leading to a sucrose solution did not influence food acceptance or feeding behavior of Lasius niger ants, a result that, in principle, contradicts our findings. These ants had to run once on a 20-cm channel covered with filter paper, onto which different amounts of trail pheromone were applied.…”

“…Important differences between this work and ours are the duration and method chosen for pheromone exposure. Whereas in our work, Argentine ants were pre-exposed for 20 min in an enclosure before they departed to the food source, in Oberhauser et al (2020), L. niger ants were not pre-exposed to the pheromone, but exposed during a single short run in the channel. This means that their experience with the pheromone was significantly shorter than that of the Argentine ants in our work.…”

Ants prefer the option they are trained to first

“…Unlike the serial position, pheromone did not significantly affect the choices of ants in our study. This suggests that the presence of pheromone does not alter learning in a systematic way, which is in accordance with other studies which found no effect of pheromone on learning in Linepithema humile ( Rossi et al, 2020 ) or Lasius niger ( Oberhauser et al, 2020b ; Czaczkes et al, 2016 , but see Czaczkes et al, 2013a ). At a collective level, such independent evaluation of a food source by multiple ants (conditioned amplification: Feinerman and Korman, 2017 ) is crucial for keeping positive feedback in check and preventing collective biases during decision making.…”

“…In honeybees, geraniol, an attractive pheromone, improved olfactory associative learning, while 2-heptanone, an aversive pheromone, impaired learning ( Baracchi et al, 2020 ). Evidence for the effect of trail pheromones on ant learning is, however, mixed ( Czaczkes et al, 2016 , 2013a ), and their impact on foraging ants might be species specific ( Oberhauser et al, 2020b ; Rossi et al, 2020 ).…”

Formic acid modulates latency and accuracy of nestmate recognition in carpenter ants

“…Pheromones do more than conveying specific messages to members of the same species. In insects, for instance, they can modulate in the long term responsiveness to relevant stimuli (appetitive, aversive) in contexts that differ from the one for which the pheromone is used as a messenger (Baracchi et al 2017;Rossi et al 2018;Hostachy et al 2019;Rossi et al 2019;Baracchi et al 2020;Murmu et al 2020;Oberhauser et al 2020;Rossi et al 2020). Further studies are needed to clarify these novel functions of pheromones as neuromodulators and to understand their implications for the functioning of recognition systems in general.…”