Dottorato in BIOLOGIA AMBIENTALE ED EVOLUZIONISTICA

Titolo della tesi: Technical intelligence in captive capuchin monkeys (Sapajus spp.)

Humans show a great inter-individual variability resulting in cognitive and behavioural differences in many skills. Behavioural variation has been demonstrated also in other primate and non-primate species, both across and within groups. Since individuals of the same group can be exposed to a different set of experiences during their lifespan, a growing body of studies focus on the factors at the basis of the within-group cognitive variation. In general, researchers interested in animal cognition investigate inter-individuals differences in performances by using problem-solving tasks. In my thesis, I investigated factors affecting inter-individual behavioural differences by testing captive capuchin monkeys (Sapajus spp.) in an unconstrained social context, where all individuals in a group were able to access the testing area on a voluntary basis. In particular, I carried out two experimental studies. I experimentally tested whether a behavioural trait likely linked to tool use innovation - i.e., reaction to novelty (Study 1) - and innovation in a tool use task (Study 2) were influenced by the individual characteristics and previous experiences in related domains accumulated over the lifespan of each individual. In Study 1, I provided familiar and novel food to 23 subjects belonging to four social groups differing in previous experience with novel food; in Study 2, I presented 14 subjects belonging to two social groups with a novel tool using problem-solving based on Aesop's fable task. The task required the insertion of provided tools into a vertical tube containing a reward floating on some water, so as to increase the water level and reach the reward (functional tube). The task also comprised a second, non-functional tube containing the same reward resting on sand (non-functional tube). My main prediction was that individuals who were more exposed to novel stimuli would be less fearful towards novel foods (i.e., less neophobic) and that those that accumulated more experience in tool use would perform better in a novel tool use task. I also hypothesised an effect of the presence of conspecifics on food choice (Study 1) and performance (Study 2). In particular, I predicted that lower-ranking individuals would prefer familiar food over novel food in the absence of higher-ranking individuals, but would modify their preference in favour of novel food in the presence of higher-ranking individuals (Study 1), and that lower ranking individuals would show a worse performance (i.e., interact less with the functional part of the apparatus and insert tools less often in the functional part) when higher ranking individuals are present than when there are no higher ranking individuals close-by. Although my main prediction was not supported by results from Study 1 (i.e., no significant effect of previous experience with novel stimuli on capuchins’ neophobia), I found a weak signal of the effect of previous experience with tool use tasks on the experimental performance (Study 2). This represents an encouraging result, suggesting that with a larger sample, this result would support the role of lifelong background in shaping individuals’ performance in innovation tasks. My results showed no effect of the presence of higher ranking individuals on the behaviour (i.e., food choice and task performance) of lower ranking individuals. However, as demonstrated in Study 1the presence of higher-ranking individuals might have affected the participation in the task rather than the behaviour. Overall, my results represent a prompt to enhance the investigation on the role of previous experience in determining inter-individual variation, involving a larger sample size and increasing the differences among individuals.