Figure 2: The phenotypically derived species has higher endogenous levels of Wnt signalling during craniofacial development.

(a) The phenotypically intermediate species, MZ, exhibits a gradual response to increasing concentrations of LiCl with respect to craniofacial shape (n=264, error bars are s.e.). This species also shows relatively low levels of Wnt signalling in the preorbital region of the skull at stage 17 (b) just before outgrowth of the preorbital (po) region of the skull, and stage 18 (c) just after outgrowth has commenced. (d) Alternatively, the phenotypically novel species, LF, exhibits a far more pronounced and erratic response to increasing concentrations of LiCl with respect to craniofacial shape (n=230, error bars indicate s.e.). LF also exhibits relatively higher levels of Wnt signalling in the preorbital region of the skull at stages 17 (e) and 18 (f). For both species, the response of craniofacial shape to LiCl treatment was measured as procrustes distance (PD) from the mean shape of MZ control fish (g). The phenotypically novel species, LF, also exhibits a far more pronounced response to low concentrations of LiCl with respect to the development of a lethal, lock-jaw, phenotype (h). In particular, approximately half of LF larvae develop locked jaws with 2 mM of LiCl, whereas 8 mM of LiCl is required to elicit a similar frequency of lock-jaw larvae in MZ. Collectively, these experiments suggest that LF larvae possess higher levels of Wnt signalling during craniofacial development compared to MZ. Scale bars, 200 μm.