The main aim of this research is to investigate the evolutionary benefit of early life play experience using the domestic pig (Sus scrofa) as a model species. While play is a highly studied, although typically controversial, area of animal behaviour, little experimental evidence exploring the effect of early life social play on later life behaviour has been presented. Furthermore, play-related studies typically rely upon natural variation in play experience, or induced variation via means of social isolation. To the best of my knowledge, no attempts to increase the levels of social play experienced have been made. Here I investigate the influence of early life socialisation on social play, cognition, and aggression in the domestic pig (Sus scrofa). In Study 1 I find that while socialisation does not increase play fighting or additional piglet directed play experience, socialised individuals direct approximately one third of these behaviours towards non-related individuals. Furthermore, socialisation is observed to decrease attack latency in the performance of a ResidentIntruder (RI) test, suggesting an enhanced decisiveness when presented with an unfamiliar social situation. Male and female pigs are also observed to perform preweaning play behaviours and post-weaning aggression coincident with the sexual dimorphism observed in their later life social environments. In Study 2 I provide evidence to suggest that early life play experience can influence contest outcome and contest behaviour during later life agonistic encounters. Additionally, play fighting experience is found to be an indicator of resource-holding potential (RHP), revealing the use of a novel form of mutual assessment in dyads containing socialised pigs, and opponent-only assessment in dyads containing control individuals. This difference in assessment strategy suggests variation in cognitive ability. Subsequently in Study 3 use a range of cognitive tests to explore the effect of early life socialisation on postweaning cognition. However, limited evidence to suggest socialisation influences cognitive development is reported. In line with the findings of Study 1, socialised individuals demonstrate a reduced neophobia to the presentation of unfamiliar individuals. Furthermore, sex difference in spatial cognition are also observed. Lastly, Study 4 was designed to further explore the role of play fighting experience during agonistic encounters by investigating its effect on assessment strategy. Dyads containing individuals that experienced high levels of social play fighting preweaning were observed to rely upon a pure-self assessment strategy, while dyads containing individuals that experienced low levels appeared to perform a novel form of self-assessment consistent with the desperado effect. This thesis provided an original contribution to the study of play by providing experimental evidence to support the social skills hypothesis. Early life play experience is found to influence both the performance of contest behaviours and the outcome of later life agonistic encounters, as well as the assessment strategies used by contestants. Early life social play and its influence on cognition and aggression is also observed to be sexually dimorphic. These findings are consistent with the sexual dimorphism observed in the later life social environments of male and female freeranging pigs, providing further support for the social skills hypothesis. Additionally, this research expands upon the welfare benefits of pre-weaning socialisation in the domestic pig. Pre-weaning socialisation is observed to reduce the novelty of postweaning encounters with unfamiliar pigs and subsequently improve decisiveness when individuals are presented with a novel social situation. Consequently, the early life socialisation of domestic pigs may play a crucial role in the minimisation of postweaning mixing aggression, leading to a substantial welfare improvement.
| Date of Award | Dec 2019 |
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| Original language | English |
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| Awarding Institution | - Queen's University Belfast
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| Sponsors | Northern Ireland Department for the Economy |
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| Supervisor | Gareth Arnott (Supervisor) |
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The Influence of Early Life Socialisation on Social Play, Cognition, and Aggression in the Domestic Pig (Sus scrofa)
Weller , J. E. (Author). Dec 2019
Student thesis: Doctoral Thesis › Doctor of Philosophy