Evolutionary biology of learning in insects: the search for food
Despite the intuitive idea of what learning means, there is still debate on a clear-cut defi nition of learning (Shettleworth, 1999). The most commonly used defi nition is that learning is a modifi cation of behaviour as a result of experience (Dukas, 1998; Papaj and Prokopy, 1989; Shettleworth, 1999). This defi nition, however, may include other phenomena which cannot be associated with learning. For example, when animals have been starved (experience) they are more likely to eat when given food but this change in behaviour cannot be attributed to learning. To occur, learning
requires that animals possess neuronal plasticity and that neuronal organisation is modifi ed by integration of information. In honeybees, functional calcium imaging has shown that odour representations in the primary chemosensory centre of the honeybee, the antennal lobe, are modifi ed after associative learning (Faber et al., 1999). These results indicate that neural representations of the environment may be modifi ed through associative learning. It is then important to see whether these neuronal modifi cations translate into behavioural changes. Experimental demonstration of learning would then consist of observing whether the behaviour of an individual subjected to this information differs from control individuals. These experiments require extensive controls as behaviours can be affected by many factors (for example, motivation, stress, circadian rhythms and age; Cahill et al., 2001).