Repeatability and heritability of social reaction norms in a wild agamid lizard

In the evolutionary transition from solitary to group living, it should be
adaptive for animals to respond to the environment and choose when to
socialise to reduce conflict and maximise access to resources. Due to the
associated proximate mechanisms (e.g. neural network, endocrine system),
it is likely that this behaviour varies between individuals according to
genetic and non-genetic factors. We used long-term behavioural and genetic
data from a population of eastern water dragons (Intellagama lesueurii) to
explore variation in plasticity of social behaviour, in response to sex
ratio and density. To do so, we modelled individual variation in social
reaction norms, which describe individuals’ mean behaviour and behavioural
responses to changes in their environment, and partitioned variance into
genetic and non-genetic components. We found that reaction norms were
repeatable over multiple years, suggesting that individuals consistently
differed in their behavioural responses to changes in the social
environment. Despite high repeatability of reaction norm components, trait
heritability was below our limit of detection based on power analyses (h2
< 0.12), leading to very little power to detect heritability of
plasticity. This was in contrast to a relatively greater amount of
variance associated with environmental effects. This could suggest that
mechanisms such as social learning and frequency-dependence may shape
variance in reaction norms, which will be testable as the dataset grows.
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