Which types of bees have a lot of brains?

What are the characteristics of the brain sizes in the various bee species? (Image: ConstantinCornel / iStock)

From honey bees to bumblebees to solitary species: One might think that among the numerous representatives of the bee family, the socially living species have particularly large brains. But as a study now shows, there is apparently no such link. How many species of bees have in their heads, however, depends on the diet. According to this, species of bees that specialize in certain flowers have larger brains compared to generalists. As the researchers explain, the different ways of life could be associated with special demands on the cognitive abilities from which the different brain sizes result.

For a long time they were considered to be simple beings – but in recent years this image of insects has changed significantly. Numerous studies have made it clear what complex cognitive performance some representatives of this group of animals are capable of: They can learn to grasp connections and adapt their behavior in a complex way to experience. These abilities are based on the performance of brains, which comprise units comparable to the higher brain regions of mammals and birds. However, there are still many unanswered questions about the characteristics of the “thinking organs” of insects.

For example, it is unclear to what extent certain rules also apply to the insect brains that are emerging in vertebrates. It is assumed, for example, that a social way of life is usually associated with the development of large brains. The prime example is humans. Likewise, in our lifestyle and that of other vertebrates, further cognitive requirements seem to be linked to relatively large brains. It is becoming apparent that species with a wide range of food tend to have more in their heads than those that only specialize in certain resources. One reason for this may be the greater challenges that arise when dealing with different food sources.

Bee brains in comparison

Against this background, the researchers led by Ferran Sayol from the University of Gothenburg have now looked at the relationships between brain sizes and lifestyles in a prominent family of insects: the bees (Apiformes). The interesting thing is that among the thousands of species worldwide there are social bees such as honeybees and bumblebees, but also many solitary species. In addition, this group of insects includes both generalists and specialists: some only visit the flowers of certain plant species, while others are not fussy. As part of their study, the scientists have now systematically recorded the brain sizes as well as the body characteristics and lifestyles of 93 bee species. They then combined this data to uncover possible principles behind the variance in brain sizes.

As they report, a fundamental commonality with vertebrates first became clear: larger species also have larger brains. What is important is evidently the relationship with bees too. So the researchers calculated this factor out of the data. Then the differences in the relative brain size between the examined species became apparent. The comparisons with the ways of life of the different species then showed: Obviously, life in the social group of bees is not associated with a particularly large brain. Even the generalists among these insects do not have a lot in their heads. However, it became apparent that solitary species that specialize in certain food sources have comparatively large relative brain masses.

Special backgrounds with bees

The exact background of these relationships remains unclear so far, but according to the researchers there are quite plausible explanations for the initially surprising result. An important aspect is that the social way of life in bees and also the nutritional strategy as pollen and nectar collectors cannot necessarily be compared with the conditions in vertebrates. Accordingly, it is possible that the division of labor in the insect communities even results in comparatively low cognitive demands on individual animals. Perhaps this aspect outweighs the capacities necessary for social interactions, which means that, in the case of socially living bee species, no expansion of the nerve organ was necessary.

But why did the specialists of all bees produce comparatively large brains? This could have to do with increased cognitive challenges they face while foraging, the scientists explain. The bees, which specialize in a few species, may have to memorize placemarks more intensively in order to find their way to “their” food plants. Put simply, generalists, on the other hand, can simply buzz from flower to flower when searching for food. In the case of vertebrates, on the other hand, fundamentally different framework conditions usually apply, the researchers emphasize: Typical generalists use different seeds, fruits or prey animals, which require very different handling challenges and thus increased cognitive capacities. This distinguishes them from the bee generalists. “It may be that the theory that generalists need larger brains is not relevant in bees, in contrast to vertebrates,” the scientists write.

Ultimately, the publication by Sayol and his colleagues shows that there is still some research to be done on the characteristics of the insect brains. Perhaps further studies can soon provide more insights into which evolutionary drivers have shaped the development of the different brain sizes in bees and also in other groups of insects.

Source: Proceedings of the Royal Society B: Biological Sciences, doi: 10.1098 / rspb.2020.0762

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