There are more than 20.000 bee species worldwide, but ot all bees respond equally to environmental pressures. Indeed, while some bees are drastically declining, some species can thrive in human modified ecosystems. Is the brain size playing a key role in these adaptation differences?

A research team at the Doñana Biological Station (EBD-CSIC) and the Centre for Research on Ecology and Forestry Applications (CREAF) has investigated if the different bee species with larger brains also have better learning abilities. "Surviving in cities may require to learn complex and rapidly changing landscapes in order to locate flower patches and nesting sites. Hence, understanding if bee species with larger brains, and more abilities to learn can better adapt to chaning conditions would be a huge advance", explains Ignasi Bartomeus, researcher at Doñana Biological Station – CSIC and author of the study. 

When it comes to the brain, bigger is generally considered better in terms of cognitive performance. While this notion is supported by studies of birds and primates showing that larger brains improve learning capacity, similar evidence is surprisingly lacking for invertebrates. Although the brain of invertebrates is smaller and simpler than that of vertebrates, recent work in insects has revealed enormous variation in size across species.

The research team conducted an experiment in which field-collected bee individuals had to associate a reward (sucrose) with a arbitrary stimulus (coloured strip). Every experiment consisted of the presentation of yellow and blue carboard small trips easily distinguishable by bees' vision. One of the coloured strips was dipped in sucrose and the other one in water. The experiment was repeated seven times to allow individuals to associate the stimuli (colour) with the reward (food) through associative learning, switching the strip's position to prevent bees learning to obtain the reward by using spatial information instead of colour cues.

Most bees learned to associate a colour with a food reward and researchers found evidences that bees with bigger brains were more likely to learn. "Our study is important because it puts forward the importance of cognitive processes in insects. This kind of relationships between brain structures and learning has been found in mammals and birds, but rarely investigated in insects, with exception of the honeybee", explains Ignasi Bartomeus.

Insects also face some of the same challenges than require a fast learning. Investing in brain tissue is costly and it make sense to do it only when it provides a benefit. Species requiring higher cognitive demands, -for example, bee specialists who need to locate particular flower resources- has evolved to have larger brains. "There is still much to learn. We are just starting to understand the huge capacity of bee's miniature brains", concludes the researcher.

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Reference:

Collado MÁ, Montaner CM, Molina FP, Sol D, Bartomeus I. 2021 Brain size predicts learning abilities in bees. R. Soc. Open Sci. 8: 201940. https://doi.org/10.1098/rsos.201940