New research led by China’s Southern Medical University suggests that bumblebees are only able to make use of ordinal ranking memories to guide foraging choices outside their original learning contexts.
Bumblebees don’t seem to keep memories for how sweet a flower was, but instead only remember if it was sweeter than another flower. Image credit: Annette Meyer.
“What do animals remember about items out of context? For example, suppose we learn that different options (e.g. coffee shops) result in different reward outcomes (e.g. waiting time and quality), and later we are presented with a choice between two previously encountered options which we have never experienced side-by-side,” said Southern Medical University’s Professor Fei Peng and colleagues.
“What types of values do we remember for those options now presented in a novel context?”
“Do our memories of the subjective values for each option contain absolute information (e.g. delay to reward), remembered ranking (how they compared to previous alternatives), or a weighted combination of both?”
“In typical studies exploring the economic choices of animals including humans, subjects do not have to use distant memories of the options; they are presented with choices where the objective values (e.g. amount, cost, and status) are concurrently visible and can be directly compared.”
“Only more recently have investigations of absolute and relative information traversed into the realm of reinforcement learning, where value must be inferred from memories.”
“Studies on starlings and humans demonstrated that both absolute memories and remembered ranking are combined in particular ways to give rise to these animals’ preferences.”
“So far, however, no other species have been investigated for the roles played by absolute memories and remembered ranking in learned preferences.”
In their study, the authors focused on buff-tailed bumblebees (Bombus terrestris), an invertebrate and a key model for examining the economy of decision-making outside of humans.
The insects were first trained on two flowers, learning that one flower was sweeter than a second flower.
Later, they learned that a third flower was sweeter than a fourth flower.
Then bumblebees were given the choice between two of the flowers they hadn’t seen together before, for example the second and third or the first and third.
Over a series of experiments, bumblebees’ preferences during the tests indicated that they could only retain very basic ranking memories for the flowers for very long.
The bumblebees could only remember that a flower had been better or worse during training phase.
They couldn’t seem to remember for more than a few minutes how sweet or rewarding the flowers were on their own or even how much sweeter they were compared to other flowers.
“Our results reveal an intriguing divergent mechanism for how bumblebees retain and use information about options, compared to humans and birds,” said Yonghe Zhou, a Ph.D. student at Queen Mary University of London.
“It may be that the different strategies used by bumblebees and humans may have evolved because of their different diets,” Professor Peng said.
“Maybe because bumblebees evolved to mostly only eat flower nectar, they never needed to remember the details and could survive and thrive simply using simple comparisons.”
“Despite what may seem to be a poor memory strategy, bumblebees do very well in finding the most profitable flowers,” Zhou added.
“It’s fascinating to consider how different animals, in their own ecological niche, can be similarly successful using such different strategies.”
The study was published in the journal eLife.
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Cwyn Solvi et al. Bumblebees retrieve only the ordinal ranking of foraging options when comparing memories obtained in distinct settings. eLife, published online September 27, 2022; doi: 10.7554/eLife.78525
