Ants appear to be optimistic when making decisions based on ambiguous information, even more so if they have just had a sweet reward.
This could be a sign that these animals experience something like our emotions, says at the University of Regensburg in Germany. “There is no good reason to rule out emotions in invertebrates, and indeed good reasons to think carefully about this,” he says.
An earlier study found that bumblebees show “emotion-like state changes” in certain laboratory tests, so Czaczkes and his team wanted to see whether the same was true of black garden ants (Lasius niger).
Advertisement
First they trained the ants to associate two distinct odours with a positive outcome – access to a sugar solution – or a negative one – getting a bitter quinine solution or an electric shock. Then the ants were placed in a maze where they had a choice of two paths: one with a mixture of the two odours and one with no scent.
Around two-thirds of the ants chose an equal parts mixture of the two odours over the odourless option. “In an ambiguous situation, the ant acted as if it expected a reward,” says Czaczkes. “Does this mean it experiences a subjective hopeful feeling?”
When the ants were given a sugar solution at the start of the maze, they were even more likely to choose the mixed odour. “This could be the ants becoming even more optimistic, possibly because they are happy,” says Czaczkes.
However, we can’t tell what the ants are really feeling – they might behave this way because they have simply updated their estimate of the probability of finding food, he says.
This study is exciting because it shows us that the origins of mental states such as optimism might be simple circuits, says at the University of Sussex in the UK. “It’s nice that you can demonstrate that the changing balance of basic memories can lead to sophisticated decision making which could be described as optimism,” he says.
This study adds to a growing body of evidence that insects conduct more sophisticated cognition than once thought. “Invertebrates experience the world in ways which are often very similar to how we experience it,” says Czaczkes.
Graham, however, is wary of drawing comparisons with humans. “We have a much more complex set of memories active across all realms of our lives over much longer time,” he says. “It’s orders of magnitude more complex.”
Reference: bioRxiv, DOI:
