Genetic variance for behavioural ‘predictability’ of stress response

Genetic factors underpinning phenotypic variation are required if natural
selection is to result in adaptive evolution. However, evolutionary and
behavioural ecologists typically focus on variation among individuals in
their average trait values, and seek to characterise genetic contributions
to this. As a result, less attention has been paid to if and how genes
could contribute towards within-individual variance, or trait
“predictability”. In fact, phenotypic ‘predictability’ can vary among
individuals, and emerging evidence from livestock genetics suggests this
can be due to genetic factors. Here we test this empirically using
repeated measures of a behavioural stress response trait in a pedigreed
population of wild-type guppies. We ask (1) whether individuals differ in
behavioural predictability, and (2) whether this variation is heritable
and so evolvable under selection. Using statistical methodology from the
field of quantitative genetics, we find support for both hypotheses and
also show evidence of a genetic correlation structure between the
behavioural trait mean and individual predictability. We show that
investigating sources of variability in trait predictability is
statistically tractable, and can yield useful biological interpretation.
We conclude that, if widespread, genetic variance for ‘predictability’
will have major implications for the evolutionary causes and consequences
of phenotypic variation.