Differential skeletal development in relation to embryo size. A Deme-wise GLM-predicted notochord lengths (± 95% confidence bounds) at 50% probability for reaching certain stages in nine skeletal development traits (see Additional file 2). Cold deme larvae are larger in most of the skeletal traits. Skeletal traits are: Anal-fin pterygiophores initiated; Cleithrum ossified; Dentary ossified; Dorsal vertebral spines initiated; Dorsal-fin pterygiophores initiated; Hypurals>5; Operculum ossification initiated; Oral teeth present; Ventral vertebral spines initiated. B. Cleared-and-stained caudal areas from 14.9 mm cold-deme larva (upper photo) and 15.0 mm warm-deme larva (lower photo) illustrating the relatively delayed skeletal development of the cold deme larvae. Lower arrow points to forming anal spines and upper arrow points to anterior dorsal vertebral spines, neither of which are present in the cold-deme larvae.