Do animal personality components independently evolve and develop in response to environmental complexity?

Widespread existence of consistent differences in behaviour among
individuals even within species and populations, i.e., animal personality,
has been established since the last decades in a wide array of taxa.
However, little is known about personality traits' ontogeny and
evolution. This study aimed at exploring eco-evolutionary mechanisms
driving the emergence and development of animal personality. Focusing on
boldness as a personality trait, we assessed how personality components
(mean, among- and within-individual variabilities, repeatability, and
plasticity in response to environmental complexity) develop at early age.
Investigating developmental trajectories of all personality components,
rather than averages only, offers a more exhaustive and comprehensive
picture of how personality emerges, develops, and evolves. We compared
personality components between juveniles of five morphs of Arctic charr
(Salvelinus alpinus) ranging along gradients of ecological and genetic
divergence from a common ancestor, raised from hatching in plain vs.
structurally complex treatments. On the one hand, we show that some of
these personality components evolve and develop independently from the
others: mean boldness, which increases with divergence from the ancestor,
was predominantly genotype-dependent and suspectedly a highly heritable
trait with strong and stable selective pressures acting on it in the wild,
while boldness repeatability might rather depend on the ecology of each
morph. These two components were not affected by environmental complexity.
On the other hand, variability-related components of personality,
including their plasticity in response to environmental complexity, were
rather dependent on genotype-by-environment effects and seemingly evolve
and develop jointly. Boldness tended to be more consistent within the
treatment mimicking the structural complexity of a given morph’s natural
habitat, hinting that personality emergence might be favoured for
individuals experiencing conditions to which they have been adapted. These
findings suggest mechanisms by which personality components could be
implicated in adaptability to environmental changes or even sympatric
diversification and biodiversity.