Fig. 2

a The position of the 16 landmarks used. LM1: Anterior tip of the upper lip, LM2: Posterior extent of supraoccipital, LM3: Anterior insertion of first dorsal spine, LM4: Anterior insertion of second dorsal spine, LM5: Anterior insertion of dorsal fin on the dorsal midline (DML), LM6: Posterior insertion of dorsal fin on DML, LM7: Origin of the caudal fin membrane on DML, LM8: Posterior extent of caudal peduncle on lateral midline, LM9: Origin of the caudal fin membrane on ventral midline (VML), LM10: Posterior insertion of anal fin, LM11: Anterior insertion of anal fin, LM12: Caudal tip of the posterior process of the pelvic girdle on the VML, LM13: Posterior tip of the ectocoracoid, LM14: Anterior tip of the ectocoracoid, LM15: Posterior edge of the angular, LM16: Anterior tip of the upper lip (placed same place as LM1). b PCA scatter plot of the first and second, first and third, and second and third principal components that account for most of the variation in body shape. Marine individuals (Nor, red, plus sign), the downstream group (OddM, blue, empty squares) and the upstream group (OddU, pink, full squares) are shown in convex hulls. c Thin-plate spline transformation grid showing the body shape changes between the mean shapes of Nor to OddM (top), mean shapes of Nor to OddU (middle), and means shapes of OddM to OddU (bottom). The colored grids show the color-coded Jacobian expansion factors which measure the degree of local expansion or contraction of the grid: yellow to red for factors >1, indicating expansion; light to dark blue for factors between 0 and 1 indicating contraction