Planet Earth Online

Bumblebees gain fitness through learning

18 December 2008

Many people are confused when I tell them I study learning in bees. I can see them asking if animals as simple as bees learn. They are in good company. Karl von Frisch, joint winner of the 1973 Nobel Prize in Physiology for his work on honeybee behaviour, also expressed his doubts, saying, 'The brain of a bee is the size of a grass seed and is not made for thinking. The actions of bees are mainly governed by instinct.'

Bees do have small brains, but far from being little pre-programmed automata, they can achieve amazing feats of learning and memory. They can learn the colour, shape and scent of flowers, the location of landmarks to find their way around, and even how to recognise human faces. In fact, the ability to learn is not restricted to animals as 'complex' as bees - simple learning has even been found in single-celled protozoans.

The costs of learning

Learning, or the adaptive modification of behaviour based on experience, affects almost every aspect of animal behaviour. It lets animals respond to the changing world in which they live. If learning is so useful why do we see such variation among animal species, or individuals within a species, in their learning capabilities? From a human perspective, we spend lots of time and effort learning, so we can appreciate that there are significant costs as well as benefits associated with it.

If cognitive abilities are selected in the same way as other biological traits, it is easy to assume that differences in learning performance between animals occur because of differences in the particular natural environments in which they live. We know a lot about how animals learn, but very little about how variation in learning ability might be adapted to real ecological conditions. This is where our research on bees comes in.

Bees forage in a complex pollination market typically containing dozens of flower species, which provide different amounts of nectar and pollen and vary in how easy these rewards are to collect. Depending on patterns of reward production, and how many other ollinators are active, the average rewards in a flower species may change quickly during the course of the day. So a bee can't simply pick one flower type and visit it all day. Instead, each bee must solve a complex problem every day to keep track of the most rewarding flower types.

To do this they use a variety of cues, including floral colour, pattern and scent, to discriminate between flowers and learn which to visit, and when. As social bees, bumblebee workers forego their own ability to reproduce and instead forage to provide their colony with food. The more food they collect, the greater the energy budget available for the colony to raise more new queens and males which will form the basis for the next generation. Lars Chittka and I were interested to see if differences in a colony's learning ability are linked to its foraging performance, and ultimately its reproductive success.

We conducted laboratory learning trials, in which bees from 12 colonies each foraged on an array of blue and yellow artificial flowers. Blue flowers contained no reward while yellow flowers contained nectar. The bees' challenge was to overcome their natural preference for blue and learn that only yellow flowers were rewarding.

Bright bees benefit

Ecologically, this is equivalent to a situation in which rewards in the blue species dry up
and the bees switch to visiting the yellow species to continue collecting nectar. The same colonies were then taken into the field so that we could assess their performance collecting nectar from real flowers.

We found that colonies that learned the new colour quickly were more successful foragers. The colonies' learning speeds varied by almost a factor of five. Those colonies which learnt to associate yellow flowers with rewards fastest in the laboratory went on to harvest 66 per cent more nectar from real flowers in the wild than the slowest-learning colonies. This impressive difference in foraging success would lead to big differences among colonies in the amount of resources available to invest in reproductive offspring.

Such a big survival advantage suggests evolution would select strongly for the fast-learning trait over long periods. We think that quickly learning floral cues, such as colour, helps bees to track changes in the rewards on offer, so they can preferentially visit the type of flower that is currently the most profitable. Bees that learn new colours rapidly might also be fast learners in other tasks - for example learning floral scents.

So what can we learn from bees? Rather like us, some bees learn from their mistakes more quickly than others. These faster-learning bees collect more nectar from flowers, which ultimately means their colony will be more successful. We hope this study will be the first of many to go out and test the assumption that the cognitive abilities of animals are adapted to the environments in which they live.

Keywords: Biodiversity, Europe,

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