Causes and Consequences of Impulsivity in Red Junglefowl

Sammanfattning: Throughout the animal kingdom, animals vary in cognition (i.e., how they acquire, process, store, and act on environmental information). Yet, the causes and consequences of this variation are currently unclear. Inhibitory control is one such aspect of cognition that typically varies between individuals within all species investigated. Variation in inhibitory control underlies variation in impulsivity (i.e., the tendency to act without planning or considering the consequences). The causes and consequences of variation in impulsivity are, themselves, rarely explored, despite that these may have important ecological and evolutionary implications. My thesis (spanning 5 papers), therefore, aimed to fill some of these gaps by taking a holistic approach and investigating causes and consequences of variation in impulsivity (specifically, impulsive action and persistence measured in a detour task) in red junglefowl (Gallus gallus) males and females, chicks and adults. The red junglefowl was an ideal species for this investigation. Firstly, they show individual variation in impulsivity throughout their lives. They are also typically food motivated, and easily habituated to handling and new situations, which means they commonly willingly participate in behavioural and cognitive tests. Furthermore, they are precocial, which means that they can be hatched and raised without mothers, thus reducing parental effects. Finally, the large, accumulated knowledge of red junglefowl behaviour and cognition aids interpretations regarding this. As differences in experience early in life have been found to affect impulsivity, papers I and II empirically explored whether variation in two previously uninvestigated experiences in early life (exposure to enrichment, and social group size, respectively) influenced impulsivity. The dopaminergic and serotonergic systems are important signalling systems in the brain, which have been found to link to impulsivity in other species. Therefore, in paper I, I also explored if variation in impulsive action and persistence was connected to variation in dopaminergic or serotonergic gene expression. As impulsivity links to inhibitory control, in looking at the effect of group size on impulsivity, paper II explored the hypotheses that social environment affects cognition (e.g., that social environments which are assumed to be more cognitively demanding will lead to better cognitive performance, a.k.a., the social intelligence hypothesis). To uncover potential mechanisms by which group size could affect impulsivity, besides from variation in cognitive demand, paper II also investigated if behaviours that could covary with group size linked to impulsivity. As emotional arousal has been linked to impulsivity, in another species, and impulsivity is implicated in welfare issues, paper III looked into how both positive and negative affective states (which can be used to measure welfare) related to impulsivity. Prior to my thesis, whether variation in impulsivity could potentially affect animal welfare was scarcely explored. To better understand the potential consequences of impulsivity, and, thus, how selection could act on impulsivity, papers IV and V looked at potential implications of variation in impulsivity for social status (paper IV and V), foraging efficiency, and risk taking (paper V). My results showed that impulsivity could be consistent over time periods of weeks (in chicks, paper II) to months (in adults, paper V). Thus, impulsivity describes a characteristic of the individual. However, individuals could still learn to become less impulsive (paper I). Exposure to enrichment in early life could affect how impulsively individuals behaved. Environmental enrichment increased impulsivity, as did cognitive enrichment to a greater degree (paper I). Impulsive action, and persistence, correlated somewhat with brain gene expression of dopaminergic and serotonergic genes (DRD1, TPH; paper I). The social group size individuals experimentally experienced in early life did not affect their impulsivity (paper II). However, variation in impulsivity was connected to variation in activity, boldness, neophobia, and stress (paper II). Further, more impulsive individuals had less negative, more positive, affective states, but only when they were young chicks, and not as older chicks or adults (paper VI). No links were found between impulsivity and social status (paper IV and V), foraging efficiency, or risk taking (paper V). Taken together, paper I suggests that underlying explanations to observed individual variation in impulsivity could include variation in early life experiences and in dopaminergic and serotonergic gene expression, while paper II suggests that impulsivity may not be influenced by social aspects early in life. Papers II and III demonstrate that variation in impulsivity can associate with variation in behaviours and affective states (though these associations may vary over ontogeny), with the latter finding implying that variation in impulsivity could have welfare implications. Papers IV and V indicate that variation in impulsivity may have limited consequences for individuals in contexts that could affect reproduction or survival. Thus, it may not necessarily be costly to individuals if they are more impulsive than others. This, in turn, could help explain why variation in inhibitory control exists, because limited consequences of variation could result in low selection against variation. Overall, through the investigations conducted in its 5 papers, my thesis improves our understanding the potential causes and consequences of variation in impulsivity. As impulsivity is underlain by an aspect of cognition (inhibitory control), in exploring the causes and consequences of variation in impulsivity, my thesis also provides knowledge on causes and consequences of individual variation in cognition.