Figure 4

Latitudinal trends in the age-corrected height (a) and age-specific slope (b) of thermal reaction norms across 18 latitudinal populations in six species of damselflies. In a, age-corrected TRN height represents the predicted value at 21 °C based on ordinary least-squares (OLS) regressions between log(head width) and log(temperature) fitted for each combination of latitudinal population and age, corrected for differences in mean size across all populations at each age. The dashed and solid black lines represent the second-order polynomial for regression with (solid) or without (dashed) the observation of C. johanssoni (cluster of observation in the lower right hand corner). In b, data points correspond to the slope coefficient from the same OLS regressions. The vertical, dashed gray line in each panel represents the approximate latitudinal position where a shift occurs from a 1-year to a 2-year or longer life cycle.