| Summary: | Individual variation can be seen in many aspects of an organism, from its physical structure to its behaviour. Contributing factors to variation in behaviour may includes, age, genetic differences and even size. The response to new objects and environments is a varying behavioural trait found in a wide range of species. The aim of this thesis was to investigate the causes of variation in response to novel stimuli in the common marmoset, Callithrix jacchus. The investigation focused on the effects of sex, age, genetic differences and size. Variation in response was tested by a simple novel stimulus presentation test paradigm. Sixty eight animals were each individually presented with nine novel stimuli in home cage tests. Five measures of response were recorded: latency to approach and contact, duration of proximity and contact, and visual attendance. Responses were analysed and stimuli were categorised as: mirror, food related stimuli, unattractive stimuli and novel stimuli. Response across the nine stimuli was investigated for variation due to sex, age or weight of the subjects. Across the analysis, limited significant sex differences were seen in response to food related stimuli, with males being more responsive. To investigate whether general measures of response could be derived from the individual behaviours recorded, principal component analysis was carried out on the response data, which was split into the four stimulus groups. Simple response continua were successfully derived from components from analysis of mean stimulus group scores. The mirror and food stimulus groups each had two continua, one reflecting latency to response, and one reflecting the duration of time spent near the stimulus. The responses to the unattractive stimulus group and novel stimulus group could each be described by one response continuum. In order to assess whether genetic variation contributed to response, heritability analyses were carried out on both the derived continua and the five response measures, separated by stimulus group. No significant heritabilities were found after correction for multiple comparisons. This study thus demonstrates that sex is a more important determinant of response that individual genetic differences, age or weight in the common marmoset.
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