The evolution of animal “intelligence”: Among-individual differences and the heritable basis of cognitive and personality (co)variation in the Trinidadian guppy (Poecilia reticulata)

Abstract

Among-individual variation in cognition is common within populations, and has been demonstrated across a range of animal taxa. From an evolutionary perspective, this variation is a pre-requisite for natural selection and genetic variation – both of which are required for adaptive evolution to occur. Selection has been hypothesised to favour high cognitive performance, however directional selection would be expected to erode genetic (and among-individual) variation over time. Furthermore, as selection does not act on traits in isolation, understanding the extent to which cognitive traits covary with other aspects of phenotype (e.g. personality traits) is an important factor. The question of how among-individual variation is maintained is therefore central to our understanding of the adaptive evolution of cognition in the context of the wider phenotype. The overall aim of my PhD thesis was to study the evolutionary biology of among-individual variation in cognitive and personality traits, and to explore the relationship between them in the Trinidadian guppy (Poecilia reticulata). I aimed to characterise among-individual differences in cognitive performance and personality, and investigate the extent to which genetic variation contributes to these, and to relationships between them. Each chapter was intended to obtain novel insights into the mechanisms explaining the existence and maintenance of these two important facets of behaviour across multiple hierarchical levels. I advocate the use of quantitative genetic style modelling approaches throughout, and seek to highlight the value of multivariate approaches to investigating animal cognition and associated behavioural traits. Firstly, relationships between cognition and personality were explored at the among-individual level, using a measure of cognitive performance in a spatial learning task and a stress-related behavioural trait. Secondly, to further scrutinise links between cognition and personality, the multivariate structure of among-individual variation in cognitive performance across different domains was investigated in addition to variation in personality trait ‘boldness’. Next, among-individual and genetic variation in phenotypic ‘predictability’ (within-individual variation) of a stress-related behavioural trait was analysed using a novel form of ‘double hierarchical’ model. I then explored whether genetic variation contributes to among-individual differences in cognitive performance in a detour reaching task, and further investigated whether an interplay by genotype-by-environment interactions contributed to this variation. And finally, I discuss these results and how they contribute to our understanding of the causes of among-individual variation in cognitive performance, in addition to their evolutionary implications and ideas for future work.