Fig. 5: Theoretical workflow for categorizing the ancestral plastic response of a given gene to increased urban temperatures as adaptive or maladaptive.

First, the direction of gene expression correlation (measured from a panel of 130 lizards) was used to identify a given gene as a positive regulator (positively correlated with heat tolerance, CT_MAX) or a negative regulator (negatively correlated with CT_MAX). Next, the gene was categorized as upregulated (increasing in expression) or downregulated (decreasing in expression) in forest lineages born and raised in common conditions (a proxy for the ancestral condition) in response to increased temperature (25 °C–32 °C). Theoretical dots and bars represent mean ± 1 SE. Positive regulators displaying increased expression at high temperature and negative regulators displaying decreased expression at high temperature in common garden lizards were categorized as displaying adaptive plasticity. Decreased expression of positive regulators at high temperature and increased expression of negative regulators at high temperature in common garden individuals were deemed maladaptive plasticity.