Hard limits to cognitive flexibility: ants can learn to ignore but not avoid pheromone trails

Abstract

Learning allows animals to respond to changes in their environment within their lifespan. However, many responses to the environment are innate, and need not be learned. Depending on the level of cognitive flexibility an animal shows, such responses can either be modified by learning or not. Many ants deposit pheromone trails to resources, and innately follow such trails. Here, we investigated cognitive flexibility in the ant Lasius niger by asking whether ants can overcome their innate tendency and learn to avoid conspecific pheromone trails when these predict a negative stimulus. Ants were allowed to repeatedly visit a Y-maze, one arm of which was marked with a strong but realistic pheromone trail and led to a punishment (electroshock and/or quinine solution), and the other arm of which was unmarked and led to a 1 M sucrose reward. After circa 10 trials ants stopped relying on the pheromone trail, but even after 25 exposures they failed to improve beyond chance levels. However, the ants did not choose randomly: rather, most ants begun to favour just one side of the Y-maze, a strategy which resulted in more efficient food retrieval over time, when compared to the first visits. Even when trained in a go/no-go paradigm which precludes side bias development, ants failed to learn to avoid a pheromone trail. These results show rapid learning flexibility towards an innate social signal, but also demonstrate a rarely seen hard limit to this flexibility.

A systematic examination of learning in the invasive antLinepithema humilereveals very rapid development of short and long-term memory

“…While some studies report ants ( Camponotus fellah ) failing to form a negative association to a scent (Josens et al 2009), studies on Las. niger ants and honeybees do (Avarguès-Weber et al 2010; Wenig et al 2021). Also remarkable is that L. humile is able to form an association with a food source given only one cue: a food flavour or a runway odour.…”

Appetitive olfactory learning suffers in ants when octopamine or dopamine receptors are blocked

“…This species has previously been shown to rapidly associate floral odours with sucrose rewards (Czaczkes and Kumar, 2020) and to acquire a preference for food of certain odours (Beckers et al, 1994). It can even be taught to ignore its own trail pheromones through differential conditioning (Wenig et al, 2021). First, we established an assay for training the ants to associate a mixture of linear hydrocarbons with a sugar reward.…”

Conflict interference in an insect.

“…Second, in Lasius niger , trail pheromone is not subjected to negative associative learning: Wenig et al (2021) demonstrate that although ants can learn to ignore pheromone information, they cannot learn to avoid it, even after extensive punishment with quinine or electric shocks. This again implies that responses to pheromone trails are not well-explained by a purely associative account.…”

“…In this respect, it is in practical terms more like the traditional Stroop task than fully training-based animal analogs (Haddon et al, 2008), as the subjects (both ants and humans) enter the experiment with a strong response preference and have spent all their mature life making one particular response. However, it is important to note that although pheromone-following in ants can be subjected to learning (Wenig et al, 2021), it is an innate response, not an overlearned response as is word reading in the traditional Stroop task.…”