Neural crest cell biology shapes lizard skull evolution across evolutionary time scales

The vertebrate skull originates from two embryonic lineages, the mesoderm and the neural crest, offering a unique framework to study how developmental mechanisms connect phenotypic variation and evolutionary diversification. Using 3D geometric morphometrics, we analysed skull shape variation in lacertid lizards. Mesoderm- and neural crest-derived bones formed two distinct, conserved modules at both micro- and macroevolutionary scales. In the common wall lizard (Podarcis muralis), rapid evolution of skull shape under sexual selection was primarily driven by neural crest-derived bones. While the primary axis of shape divergence in P. muralis aligned with a major axis of variation across lacertids, neural crest-derived bones exhibited overall slower evolutionary rates and lower morphological disparity than mesodermal-derived bones. We propose that this discrepancy between the role of the neural crest for skull evolution on micro- and macroevolution reflects developmental bias imposed by neural crest cell biology. By enabling developmental coupling of skull shape, body colouration and behaviour, the neural crest cells can facilitate rapid, correlated responses under sexual selection but may limit long-term evolvability in the skull.