Abstract
Intra-species cognitive variation is commonly observed, but explanations for why individuals within a species differ in cognition are still understudied and not yet clear. Cognitive processes are likely influenced by genetic differences, with genes in the monoaminergic systems predicted to be important. To explore the potential role of these genes in association with individual variation in cognition, we exposed red junglefowl (Gallus gallus) chicks to behavioural assays measuring variation in learning (discriminative learning, reversal learning, and cognitive flexibility) and optimism (measured in a cognitive judgement bias test). Following this, we analysed prefrontal cortex gene expression of several dopaminergic and serotonergic genes in these chicks. Of our explored genes, serotonin receptor genes 5HT2A and 5HT2B, and dopaminergic receptor gene DRD1 were associated with measured behaviour. Chicks that had higher 5HT2A were less flexible in the reversal learning task, and chicks with higher 5HT2B also tended to be less cognitively flexible. Additionally, chicks with higher DRD1 were more optimistic, whilst chicks with higher 5HT2A tended to be less optimistic. These results suggest that the serotonergic and dopaminergic systems are linked to observed cognitive variation, and, thus, individual differences in cognition can be partially explained by variation in brain gene expression.
Highlights
Intra-species variation in animal cognition is commonly observed (Dukas 2004; Thornton and Lukas 2012) and can have fitness consequences (Dukas 2004; Shaw et al 2019)
Of the genes we examined, genes of both the dopamine (DRD1) and serotonin (5HT2A and 5HT2B) systems correlated with our cognitive measures
We here explored the relationship between within-species variation in aspects of cognition in red junglefowl chicks, focusing on two aspects of learning, cognitive flexibility, optimism, and brain gene expression of genes from two monoaminergic systems
Summary
Intra-species variation in animal cognition (i.e., how animals perceive, process, retain, and act on cues from their environment, Shettleworth 2010) is commonly observed (Dukas 2004; Thornton and Lukas 2012) and can have fitness consequences (Dukas 2004; Shaw et al 2019). Cognitive flexibility can be measured through associative learning tasks, for example, in reversal learning, where animals need to learn new information, whilst retaining or forgetting older information (e.g., Strang and Sherry 2014; Shettleworth 2010). This flexibility is evolutionarily important, as it enables animals to respond to ever-changing environments and situations, allowing them to adapt to and overcome challenges as they arise (MorandFerron 2017). Despite the importance of such behavioural and cognitive flexibility, within-species variation still occurs
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