Developmental lines of least resistance predict standing genetic covariation but do not constrain plasticity or rapid evolution.

Some phenotypic dimensions are more developmentally variable than others. Such developmental variability (or bias) is common and uncontroversial. However, how and at what time scales these biases constrain or facilitate the emergence of standing genetic variation, plastic responses, as well as adaptation remains contentious. To investigate the extent to which developmental variability shapes genetic variation, plasticity and evolution, we first quantify developmental variability in the shape of the dung beetle foreleg-a functional trait critical for the excavation of breeding tunnels. We do so by testing how random developmental perturbations, manifesting themselves in fluctuating asymmetry, shape standing genetic variation within populations. Next, we investigate whether such developmental variability is aligned with thermal plasticity and recently evolved latitudinal variation. We find that, while developmental variability is a strong predictor of standing genetic (co)variance (i.e. the G-matrix), latitudinal population differentiation and thermal plasticity were unrelated to developmental variability. This suggests that, while developmental variability may shape standing genetic variation, it does not seem to constrain the evolution of putatively adaptive population differentiation and plastic responses. At least in this system, developmental biases do not seem to constrain morphological differentiation on ecological time scales.