Wasps that learn quickly have larger brains than members of their species that learn more slowly. But this fast learning has a price: smarter wasps have shorter lives. This discovery was made by wasp trainer Dr. Michaël van den Berg of Wageningen University.
Van den Berg recently defended his doctoral thesis on the memory formation of wasps. Parasitic wasps of the species Cotesia glomerata have the natural ability to learn quickly. They only require a single learning experience to store something in their long-term memory. But not every C. glomerata is the same. Some of them learn slightly faster than others. Van den Berg used this natural variation to breed two lines of wasps: faster learners and slower learners. 'Within a few generations, you could already see a significant difference in learning capacity', he explains enthusiastically. And that difference is easy to see. The faster-learning wasps have more brain mass. But not only that: they also don't live as long. This is an excellent example of a trade-off: a shift in the investment of energy. Fester-learning wasps have to use more energy to maintain their brains. This additional energy requirement shortens their lifespan.
Brussels sprout leaves
Despite the additional energy costs, the populations of smarter wasps do not die out. According to Van den Berg, this is completely logical and explainable in terms of evolution. The C. glomerata lays its eggs in the caterpillars of the Cabbage White (Pieris brassicae). These caterpillars are usually found very close to each other on the leaves of the Brussels sprout plant. The wasp is attracted by the odour of the damaged leaves. This odour is the learning stimulus for successful egg laying. The wasp immediately stores this experience in its memory. And that is good, explains Van den Berg. 'The odour of the plant has a great predictive value for encountering caterpillars to lay eggs in.' Fast learning is therefore beneficial. This concerns a 'customised memory'. Fast learning is not inherently better than slow learning. It is an adaptation to the ecological niche in which the animal lives.
Memory formation
But the wasp trainer went even further. He also believes he is on the track of the molecular basis for memory formation. This is because the formation of long-term memory depends on protein synthesis. The so-called CREB protein plays a key role in this process. This is not only the case with wasps and other insects, but also in the entire animal kingdom. Different forms of this protein promote or retard the expression of genes that play a role in memory formation. The proportion of the different isoforms is the switch. In any case, that is the hypothesis. But until now, no one has been able to prove it. Van den Berg is also cautious about drawing conclusions. But he has demonstrated that his wasps have a different proportion of CREB proteins after training than untrained wasps. 'With the fast-learning line of wasps, the proportion changes due to learning. This indicates that the hypothesis could be true. But it is not yet 100% certain. The statistical proof was not solid enough due to an insufficient number of successful repetitions. However, additional research is now being conducted on this topic in entomology.' For that matter, the confirmation of this hypothesis would only be one piece of the memory puzzle. For example, the activation mechanism for the switch remains unknown. / Roelof Kleis