Figure 8

Illustration of latitudinal and ontogenetic trends in genetic variation in the height (a) and slope (b) of thermal reaction norms of larval size in damselflies sampled from 18 populations across Europe. Thin gray lines connect the Bayesian point estimates of genetic variances at days 42, 84 and 126 in each latitudinal population for illustrating the ontogenetic trend. Each ontogenetic trend is centered along the x-axis at the latitudinal position of the sampled population. For readability, error bars are not shown but span approximately 2 units on the scale of the y-axis. Each thick black line represents the predicted ontogenetic trend at a given latitude, based on mixed models where the posterior mode of V_A height and V_A slope were modeled as a function of age, latitude, latitude² and latitude³, an interaction between age × latitude and a random population effect (see the Methods section and Table 1). Areas shaded gray represents the 95% prediction interval accounting for uncertainty in both fixed and random effects. In a, note that the northern population of C. puella (the uppermost data series at ~58°N) was considered as outlier when fitting the mixed model as it harbored considerably more variation than any other population. The dashed gray line in each panel represents the approximate latitude where a shift occurs from a 1-year to a 2-year life cycle. Note that the ontogenetic trend tends to be more positive in populations above 58°N in a and b, coinciding with the shift in generation length.