Heterogeneous selection on a heritable temperament trait in a variable environment

P> Temperament traits increasingly provide a focus for investigating the evolutionary ecology of behavioural variation. Here, we examine the underlying causes and selective consequences of individual variation in the temperament trait 'exploration behaviour in a novel environment' (EB, based on an 8-min assay) in a free-ranging population of a passerine bird, the great tit Parus major. First, we conducted a quantitative genetic analysis on EB using a restricted maximum likelihood-based animal model with a long-term pedigree. Although repeatability was relatively high, EB was only moderately heritable and permanent environment (V-PE) effects contributed as much to phenotypic variance as additive genetic effects. We then asked whether heterogeneous selection acted on EB at various temporal and spatial scales. Using estimates of lifetime reproductive success, we found evidence of weak negative directional selection acting on EB amongst females which was driven by selection through recruitment, but not fecundity, in one of the four breeding years. There was no evidence of any selection on EB through survival. Heterogeneous selection on EB within seasons was also observed amongst males through fecundity along two fine-scale environmental gradients - local breeding density and habitat quality; we are unaware of any previous equivalent demonstrations. All of these analyses were repeated on a second measure of exploration behaviour (EB2, measured during a 2-min assay) to facilitate comparison with other studies. EB and EB2 were strongly correlated to one another at the genetic level, but were only moderately correlated at the phenotypic level and V-PE was undetected in EB2. Selection on EB2 was similar to that on EB; we conclude that both traits are broadly equivalent from an evolutionary perspective. Our analyses suggest that to the extent that the temperament trait 'exploration behaviour' is subject to natural selection in this population, this selection is highly context dependent and most evident along two environmental gradients. Furthermore, the strong V-PE effect detected suggests that understanding the causes and consequences of variation in this trait will require studies firmly embedded in an environmental context.