Plasticity of olfactory orientation to foods in the snail Achatina fulica

Snails were tested in an olfactometer for their orientation to food odours. Measures of odour choice, latency to make a choice and percentage of upwind orientations were obtained after experimental manipulations of dietary experience and hunger motivation. Juvenile snails, given an exclusive diet of a certain food for 12 h or less, oriented preferentially toward the odour of that food when subsequently presented with a choice between it and a novel food odour (Fig. 2). A 48 h period of exposure to a food resulted in a 21 day retention of the odour preference (Fig. 3). There was no evidence for an especially sensitive period for conditioning during the first 50 days of age (Fig. 4); however, adult snails (minimum 1 year old) required longer periods of dietary exposure to establish equivalent food odour memories (Fig. 5). Measures of latency and percentage of upwind orientations confirmed the choice data in demonstrating an effect of dietary experiences on olfactory orientation. Hunger motivation increased the selection for familiar food odours, and reduced the latency (Fig. 6 and Tables 3 and 4). Sensory adaptation appears inadequate to explain the conditioning phenomenon since formation of the preferences was contingent upon ingestion of the foods; exposure to the food odours alone was insufficient (Table 2). The data suggest that orientation preferences derive from a learned association between the odour of a food and its nutritional value.