Abstract
Why individuals differ in behavioral responses has received intense research attention (particularly in the context of animal personality), and has typically focused on describing variation in boldness, activity, and exploration. Nevertheless, the mechanisms underlying this behavioral variation remain largely unknown. Variation in these behaviors is likely influenced by genetic differences between individuals, with genes in the monoaminergic systems commonly implicated. When examining the link between variation in boldness, activity and exploration and genes, studies have focused on different monoaminergic systems (mainly serotonergic and dopaminergic), and predominantly on mammals and passerine birds. Therefore, to replicate this general approach and examine if genes from these systems are linked to boldness, activity, and exploration, we exposed red junglefowl chicks (Gallus gallus) to behavioral assays (measuring boldness, activity, exploration) before analyzing prefrontal cortex gene expression of several dopaminergic (DRD1, DRD2) and serotonergic genes (TPH, 5HT2A, 5HT2B, 5HT2C, 5HT1B). We observed no relationships between our measured behaviors and gene expression. Together with previous studies, our results suggest that a clear link between boldness, activity and exploration and monoaminergic gene variation is lacking. We, therefore, suggest that this is due to differences among studies (e.g., methodological differences), or that the nature of the relationship between these behaviors and monoaminergic systems is more species-specific, and/or more complex than so far assumed.
Highlights
Individual variation in behavior, consistent between-individual differences in behavioral responses (a.k.a. animal personality, Dall et al, 2004; Réale et al, 2007), has attracted increased research focus and is well-established across all taxa (Carere & Maestripieri, 2013; Gosling, 2001)
Polymorphisms in SERT were associated with risk-taking in dunnocks (Prunella modularis, Holtmann et al, 2016) and novelty-seeking in great tits (Parus major, Riyahi et al, 2015), suggesting increased boldness and exploration explained by SERT polymorphisms
Very few studies have simultaneously investigated how several genes from the serotonergic and dopaminergic systems may link to variation in a range of behavior. To both replicate the generally expected associations between monoaminergic systems and variation in behavior, and expand upon previous work in terms of genes and by using a species outside the common model organisms used when studying the relationship between monoamines and behavior, we investigated associations between genes of the serotonergic system (TPH, 5HT1B, 5HT2A, 5HT2B, 5HT2C) and dopaminergic system (DRD1, DRD2) with variation in boldness, activity, and exploration, in the red junglefowl (Gallus gallus)
Summary
Individual variation in behavior, consistent between-individual differences in behavioral responses (a.k.a. animal personality, Dall et al, 2004; Réale et al, 2007), has attracted increased research focus and is well-established across all taxa (Carere & Maestripieri, 2013; Gosling, 2001). Unclear results are obtained when comparing behavioral variation and dopamine receptor genes Most studies exploring such links focus on the association between polymorphisms of dopaminergic D4 receptor genes (DRD4), and novelty seeking and exploration in passerine birds (great tits: Fidler et al, 2007; Korsten et al, 2010; Riyahi et al, 2015; van Oers & Müeller, 2010; dunnocks: Holtmann et al, 2016; but see Garamszegi et al, 2014 for links between DRD4 and other aspects of animal behavior in collared fly catchers, Ficedula albicollis; and Ebstein et al, 1997; Munafo et al, 2008; Schinka et al, 2002; for associations between DRD4 and human behavior). The relationship between D1 and D2 receptors and boldness, activity, and exploration is, as far as we find, not yet explored
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